eMedicine Specialties > Sports Medicine > Knee

Patellar Injury and Dislocation

Gerard A Malanga, MD, Founder and Director, New Jersey Sports Medicine Institute; Director of Pain Management, Overlook Hospital; Director of Sports Medicine, Sports Medicine Fellowship Director, Mountainside Hospital; Clinical Chief, Rehabilitation Medicine and Electrodiagnosis, St Michael's Medical Center; Medical Director, Consultant, Horizon Healthcare Worker's Compensation Services, Blue Cross and Blue Shield Worker's Compensation
Brian F White, DO, Staff Physician, Department of Physical Medicine and Rehabilitation, Kessler Institute for Rehabilitation, University of Medicine and Dentistry of New Jersey; Wah Sang Lee, DO, MS, Staff Physician, Department of Physical Medicine and Rehabilitation, New Jersey Medical School/Kessler Institute of Rehabilitation; Thomas Agesen, MD, Assistant Clinical Professor, Department of Physical Medicine and Rehabilitation, UMDNJ, New Jersey Medical School; Consulting Staff, Mountainside Hospital, Summit Overlook Hospital

Updated: Sep 8, 2008

Introduction

Background

Patellar pain is common in both athletic and nonathletic individuals. Among athletes, men tend to present with more patellofemoral injuries, including traumatic dislocations, than women. In the nonathletic population, women present more commonly with patellar disorders.

Patellofemoral problems are mainly diagnosed by obtaining a thorough history and performing a physical examination. Imaging studies help confirm the diagnosis. Plain radiography is not as sensitive as magnetic resonance imaging (MRI), but it is the least expensive and most readily available modality.

Patellofemoral syndromes are usually the result of biomechanical imbalances of the kinetic chain, with each individual having an optimal joint-loading limit that is dependent on his or her unique skeletal and muscular anatomy, combined with his or her unique neuromuscular patterning. As this limit is surpassed, the patient is at risk for either acute injury, such as patella dislocation, or chronic injury, such as patellofemoral pain syndrome. Therefore, the goal of a rehabilitative treatment program must be to guide the patient toward performing functional activities without surpassing his or her optimal joint-loading limit. Therapy techniques need to be designed around this principle. 

In general, surgery is more effective in preventing recurrences of dislocation because skeletal and muscular components of the patellofemoral joint and extensor mechanism are realigned; however, surgery also has risks. In a patient with normal anatomy, surgery should be considered an option after all conservative treatment modalities are unsuccessful. Patients with anatomic abnormalities may benefit from earlier surgical consideration.

Traditionally, several different systems have been used to classify patellofemoral dysfunction. Some were developed from a functional perspective, whereas others were developed from an anatomic viewpoint. This latter perspective was held by Insall and Merchant, who classified patellofemoral dysfunction according to anatomy.

In 1972, Insall proposed a method of classification based on cartilage damage. The 3 categories in his system are normal, damaged, and variably damaged cartilage. In 1986, Fulkerson and Schutzer developed a system based on measuring arthralgias against joint instability to determine the necessity for surgical intervention. In 1988, Merchant created a system of 5 categories for patellofemoral dysfunction, which included acute trauma, dysplasia, idiopathic chondromalacia, osteochondritis dissecans, and synovial plicae.

No standardized and widely accepted method of patellofemoral dysfunction classification applicable for all specialties has been developed. However, for the purposes of rehabilitation medicine, patellofemoral disorders may be loosely divided into 3 categories. These are soft-tissue abnormalities, patellar instability due to subluxation and dislocation, and patellofemoral arthritis.

Also, for excellent patient education resources, visit eMedicine's Foot, Ankle, Knee, and Hip Center and Breaks, Fractures, and Dislocations Center. Also, see eMedicine's patient education articles Knee Pain and Knee Injury.

Related eMedicine topics:
Joint Reduction, Patella Dislocation
Knee Dislocations
Patellar Tendon Rupture
Patellofemoral Arthritis
Patellofemoral Joint Syndromes

Related Medscape topics:
Resource Center Arthritis
Resource Center Exercise and Sports Medicine
Resource Center Joint Disorders
Specialty Site Orthopaedics
Knee Complaints Seen in General Practice: Active Sport Participants Versus Non-Sport Participants
Joint Loading in the Lower Extremities During Elliptical Exercise
Osteoarthritis: What We Have Been Missing in the Patellofemoral Joint

Frequency

United States

Pain of the patellofemoral joint secondary to patellofemoral dysfunction is the most common disorder of the knee. A 5-year study published in 1984 revealed that 25% of all knee issues in a sports injury clinic were of patellofemoral origin. Another study similarly revealed that 1 in 4 runners is afflicted by patellofemoral pain. Whether related to sports or not, 1 of every 4 painful knees has been reported to be the result of patellofemoral dysfunction.   

Patellar injury and dislocation are more prevalent in individuals who participate in certain sports and activities. Anterior knee pain is the most common initial manifestation. In order of descending prevalence, soccer players, weight lifters, runners, and shooters regularly report acute knee pain. In addition, studies show soccer players and weight lifters have the most potential for long-term knee pain.

One study reported 52% of 31 soccer players, 31% of 29 weightlifters, 21% of 28 long-distance runners, and 17% of 29 shooters reported knee pain at least once per month.¹ Thijs et al evaluated gait-related intrinsic risk factors for patellofemoral pain in 102 novice recreational runners.² The authors findings suggested an increased risk for patellofemoral pain may be due to excessive impact shock during heel strike and at the propulsion phase of running. In addition, Thijs et al believe their results do not support the theory that those at risk for this condition show an altered static foot posture relative to those who are unaffected.²

Swimming also places the athlete at risk for knee pain.³ On the other hand, sports such as tennis are not associated with knee pain. In summary, factors that cause knee pain include the type, amount, and duration of sports activity.

In addition to activity-specific variance, patellofemoral pain displays some variation between the sexes. A study revealed that in the general population, the female-to-male ratio for patellofemoral dysfunction is 2:1. However, in the athletic population, more men than women experience such syndromes. Further, the study revealed acute dislocation occurred more frequently in males and that recurrent dislocation may be more common in individuals whose initial dislocation occurred when they were younger than 15 years.

Patellofemoral disorders are more likely the result of inappropriate activity duration and type as opposed to genetic factors. Aoyagi et al examined the higher prevalence of joint pain of female Japanese individuals living in rural Japan versus female Americans of Japanese descent living in Hawaii.⁴ Despite the similar genetic stock, significant differences in prevalence of joint pain were noted. The researchers postulated that environmental factors influencing activity levels and types were responsible.

Similarly, Zhang et al found that Chinese women in Beijing have a higher prevalence of knee osteoarthritis versus American women in Framingham, Massachusetts.⁵ Again, this was thought to be the result of the lower activity levels of women living in the United States. In the same study, men from Beijing were found to have a similar incidence of knee osteoarthritis compared with their Framingham counterparts.

International

Nietosvaara et al studied the annual incidence of acute patellar dislocations in Finnish children younger than 16 years.⁶ They found an annual incidence of 43 cases per 100,000 children. Over a 2-year period, 72 children revealed patellar dislocations. Of these, 28 (39%) of the knees had associated osteochondral fractures. Of the 28 osteochondral fractures, 15 had capsular avulsions of the medial patellar margin, and another 15 had intra-articular fragments from the patella and/or lateral femoral condyle.⁶

Functional Anatomy

Soft-tissue elements that affect the patella are the stabilizing capsular and ligamentous structures within which the patella lies. Some ligaments of the knee are continuous with the fibrous capsule surrounding the patella. When injuries occur, all structures are simultaneously affected. These ligaments hold the patella in place during static and dynamic phases.

The synovial capsule, a separate structure, lies deep to the fibrous capsule and may often be damaged. 
 
The regional anatomy of the knee soft tissues is as follows: 

• Anteriorly: The synovial capsule forms attachments around the peripheral margins of the patella.
• Laterally: The lateral or fibular collateral ligament is a tough, round cord that attaches proximally at the lateral epicondyle of the femur and distally at the head of the fibula. This ligament transects the tendon of the biceps femoris, and the popliteus tendon runs medial to it. The biceps femoris tendon is very strong, rarely tears, and protects the joint against varus forces. If torn, the biceps femoris tendon usually tears at the distal end, and the peroneal nerve may be injured, resulting in foot drop. In such cases, the head of the fibula is often fractured because the ligament is stronger than the bone. Increased tension from these lateral structures predisposes individuals for lateral patellar tracking and dislocation.
• Medially
  • The medial or tibial collateral ligament is a flat band extending from the medial epicondyle of the femur to the medial condyle of the tibia. The medial collateral ligament is continuous with the medial meniscus and the capsule of the knee joint.
  • Three medial ligamentous structures provide static restraint to lateral movement of the patella. These were further defined by a cadaveric study conducted by Andrikoula et al.⁷ The medial patellofemoral ligament (MPFL) is a band of retinacular tissue that originates at the medial femoral condyle and attaches to the proximal two thirds of the medial border of the patella. This ligament is overlaid by the distal fibers of the vastus medialis obliquus (VMO) muscle, and the authors found that to a variable extent, its fibers merge into the deep aspect of this muscle.
  • The medial patellomeniscal ligament (MPML) attaches the anterior horn of the medial meniscus to the inferior border of the medial patella.
  • The medial patellotibial ligament (MPTL) connects the distal patella to the tibia.
  • The MPFL has been found to be the major medial soft-tissue restraint to patellar lateral displacement. Studies indicate that up to 97% of acute lateral patella dislocations result in disruption of the MPFL. In studies examining in vitro patella subluxation, an isolated release of the MPTL resulted in a 50% increase in lateral displacement.
  • Finally, the 2 more distal structures, the MPML and MPTL, provide important secondary restraints.
• Posteriorly: The oblique popliteal ligament is broad and strengthens the synovial capsule posteriorly. The oblique popliteal ligament originates inferiorly from the medial condyle of the tibia, and it inserts superiorly and laterally to the posterior aspect of the capsule. The posterior capsule is supplemented by the arcuate popliteal ligament, which stretches from the fibular head and splits. Some fibers run medially to insert into the tibial intercondylar area, and other fibers run superiorly and medially to the posterior lateral epicondyle of the femur.
• Superiorly: The knee joint capsule inserts into the femur proximal to the condylar margins anteriorly and intercondylar line posteriorly.
• Inferiorly: The knee joint capsule attaches to the articular margin of the tibia and to the fibular head. The capsule opening for the popliteus is located here. The capsule has openings to the bursae and to the popliteus muscle and tendon.

Pain may develop in these periarticular soft-tissue structures as a result of patellofemoral dysfunction, or vice versa. All these structures operate as a functional unit to optimize weight-bearing capacity. These structures decrease joint-reaction forces (JRFs) and form a base of support for the upper body. If one of these structures is altered, a greater risk of patellar injury and dislocation can develop.

The patellofemoral mechanism is very complicated. Patellofemoral malalignment, abnormal patellar configuration, and a previous history of instability increase the risk for anterior knee pain, patellar dislocation, and recurrent dislocations. The risk for symptoms increases when a combination of factors exists.

Sport-Specific Biomechanics

Excluding acute patellar trauma, patellar injury and dislocation are the end result of patellofemoral force imbalances. These force imbalances may also result in less dramatic presentations of patellofemoral pain. Deformities of cartilage resulting from arthritis; congenital variants of the patellofemoral joint; imbalances in lower extremity muscular strength and/or firing pattern; skeletal imbalances at the hip, knee, ankle, or foot; and changes of the patellar stabilizing capsular and ligamentous elements may also contribute to the development of patellofemoral pain and/or dislocations.

The patella is the largest sesamoid bone in the body, and it resides within the complex of the quadriceps and patellar tendons, superiorly and inferiorly, respectively. The patella assists in coordinating the forces of these tendons and functions as both a lever and a pulley. As a lever, the patella magnifies the force exerted by the quadriceps during knee extension. As a pulley, the patella redirects the quadriceps force as it undergoes normal lateral tracking during flexion.

The greater the anteroposterior length of the patella, the greater the angle between the quadriceps and patellar tendons, thus decreasing the force generation needed by the quadriceps to support the upper body at any particular angle of knee flexion. One study demonstrated that the patella most significantly increases the moment arm of the quadriceps at 20° of knee flexion. After patellectomy, the moment arm of the quadriceps is obliterated. After patellectomy, one study demonstrated the effectiveness of the quadriceps-patellar moment arm to be reduced by 31% at 0° of flexion, 22% at 30°, 13% at 60°, 12% at 90°, and 10% at 120°.

The quadriceps tendon and the patellar tendon are continuous with each other and work in cooperation. Muscular forces are transmitted in differing proportions to each tendon over the changing angle of the knee as it flexes and extends. At different angles of knee flexion, the quadriceps and the patellar tendons appear to alternate the role of being the primary force transmitter. From 0-20° of knee flexion, the consensus among researchers is that tension in the patellar tendon is greater than in the quadriceps tendon. From 20-50° of flexion, which tendon has more tension is controversial among research findings. From 50° to full flexion, tension in the quadriceps tendon is greater than in the patellar tendon. Theoretically, isolated development of either the quadriceps tendon or the patellar tendon is accomplished by appropriately limiting knee flexion in exercise programs.

The chondral surface of the patella has several divisions. The 3 transverse ridges create 3 roughly equal-sized upper, middle, and lower groups. Two vertical ridges are found on the chondral surface of the patella. The prominent median vertical ridge separates the medial and lateral facets. The facets are at an acute angle to each other, with the prominent ridge acting as their adjoining corner.

These structures form a V-shaped wedge along the transverse plane for the purpose of better insertion into the depression formed by the trochlear groove. The lateral facet is larger in most individuals. The medial facet is further separated into medial and lateral surfaces by a less prominent vertical ridge. The medial surface of the medial facet is sagittally oriented and only makes contact with the femur when the knee is flexed past 90°. Pain at this range of motion (ROM) that is associated with a compressive mechanism, such as increased JRFs, is suggestive of lesions on the chondral surface.

In full extension, the patella does not fit into the trochlear groove but lies over the smooth synovial tissue that overlies the supratrochlear tubercle. The lateral aspect of the tubercle has a smooth, continuous transition with the trochlear groove. The medial aspect of the tubercle is sharply elevated in regard to the trochlear groove. In normal motion, the patella moves superolaterally, riding the lateral aspect of the supratrochlear tubercle so that it makes a smooth translation from the groove to the tubercle.

The cartilage of the patella contacts the trochlear cartilage of the femur to reduce friction during motion of the patellofemoral joint. Gross normal joint motion is along a sagittal plane. This is why examination of the joint at the transverse plane reveals a congruent articulation, whereas the joint along the sagittal plane is incongruent. Good contact at the transverse plane promotes medial/lateral stability, whereas the incongruent sagittal articulation provides more free space for superior/inferior movement.

Compared with the femoral cartilage, the patellar cartilage is thicker, more pliant, and more permeable. In fact, the cartilage of the inner patella at the prominent median vertical ridge is normally the thickest cartilaginous structure in the body, suggesting its role in counteracting tremendous JRFs. These characteristics of the patellar cartilage allow it to sit deeper in the trochlear groove and conform to its shape, allowing for better articulation and distribution of JRFs. However, these actions place a burden on the collagen-proteoglycan matrix of the patellar cartilage and may be the reason for the higher prevalence of patellar cartilaginous lesions compared with femoral trochlear cartilaginous lesions.

JRFs at the patellofemoral joint are directly related to the contraction of the quadriceps.

The stress at the patellofemoral joint can be mathematically defined as the sum JRF divided over the surface area of force distribution. From 0-60°, the surface area of the patella contacting the femur enlarges with increased knee flexion. This provides a larger contact surface area over which to distribute the load as the load is increasing. Beyond 60° of flexion, anatomic studies regarding the contact area have been inconclusive.

The location of contact for the patella and femur vary with different degrees of flexion and joint load. At 0°, no contact occurs; in early flexion, the distal patella contacts the proximal trochlea; at 90° of flexion, the superior aspect of the patella contacts the femur; when flexion is greater than 90°, the contact area returns to the center of the patella; and when the knee is fully flexed, the inner border of the medial femoral condyle is in contact with the small vertical ridge of the medial facet.

Lateral tracking of the patella leads to decreased efficiency of the quadriceps extensor mechanism and increased patellofemoral joint stress. A lateral patellar subluxation of only a few millimeters results in a decreased contact surface area between the patellar and trochlear surfaces as the lateral facet moves closer to the lateral side of the trochlear groove and the distance between the medial facet and the medial side of the trochlear groove increases. The total JRF, initially distributed over both patellar facets, is now completely transmitted to the lateral patellar facet. This increases lateral facet stress and may result in pain, chondromalacia, and the development of arthritic changes.

A summary of forces on the patellofemoral joint follows. They maintain the physiologic positioning of the patella dynamically within the trochlea and extensor mechanism and provide for patella stability and proper tracking.

• Static stabilizers: These provide fixed inhibition to lateral translation of the patella and most notably include the MPFL but also include the MPML and MPTL. These 3 structures play a primary role in stabilization during the first 20-30° of knee flexion when the patella has not fully engaged the trochlea. At knee flexion greater than 30°, the geometry of the patella-trochlea interface combined with posteriorly directed force vectors provide most of the stabilization for the joint.
• Dynamic stabilizers: These are muscular structures and are primarily the quadriceps group.
  • The VMO muscle has been noted to provide a medially directed dynamic stabilizing force on the patella during knee extension. Andrikoula et al's cadaveric study demonstrated that the VMO fibers are at approximately a 40° medially directed angle to the rectus tendon.⁷
  • Weakness of the quadriceps in general, and specifically of the VMO, allows lateral tracking and deviation of the patella. With persistent lateral patellar deviation, lateral structures (eg, distal fibers of the iliotibial band) contract, resulting in further lateral deviation and greater lateral subluxation. Lateral deviation of the patella also results in altered VMO length and/or tension, which may diminish the medially directed force generation of the VMO muscle.
  • The adductor magnus should also be noted with this group because the distal fibers of the VMO often attach to the adductor magnus tendon and strengthening of the adductor group may contribute to the ability of the VMO to provide active, dynamic restraint.

A summary of risk factors for patella subluxation and dislocation is as follows:

• Disruption of either of the 2 groups of stabilizers noted above
• Patella alta: This is an abnormally high-riding patella and is associated with a long patella tendon. In a healthy knee, the patella is roughly equal in length to the patella tendon. In patella alta, the ratio of the tendon length to the patella body length is increased, placing the patella in an elevated position that delays patella engagement of the trochlea until an increased angle of flexion. This greatly increases the risk for dislocation. Several different methods can be used to measure patellar instability on a true lateral radiograph of the knee. One such method is the Insall-Salvati index. Patella alta is defined as a ratio of patella tendon length divided by the greatest diagonal length of the patella equal to greater than 1.2. Escala et al found 78% sensitivity and 68% specificity for objective patella instability (OPI) for this parameter.⁸
• Patella tilt: This parameter may be measured on various axial views of the knee. For patella tilt greater than 11°, Escala et al found 93% sensitivity and an odds ratio of 8.7 for OPI.⁸ They found this single parameter to be of the highest combined sensitivity and specificity for identifying patients with OPI.
• Hypoplastic trochlea: This may also be evaluated on a true lateral radiograph. A classification system was designed by Dejour et al and defined 4 grades of dysplasia.⁹ Dejour et al also suggested that the so-called crossing sign they introduced was present on 96% of their patients with patella instability. Using a measurement of trochlear groove depth at the Roman arch level, Escala et al found 85% sensitivity and an odds ratio of 7.7 for OPI.⁸
• Elevated Q-angle: This represents an estimate of potential lateralizing forces on the patella and is affected by several skeletal features. It is the intersection of 2 lines on the anterior aspect of the lower extremity of a standing patient. One line is from the anterior superior iliac spine to the middle of the patella, and the second line is from the tibial tubercle to the middle of the patella; the Q-angle is the angle between these lines. A Q-angle greater than 15° may predispose an individual to lateral patellar tracking and possible dislocations, although some authors report as high as 20° within a patient’s normal range. This topic is explored in more detail in Physical.
• Genu valgum: This medially directed knee joint may be the result of a valgus femur, valgus tibia, or intra-articular height loss within the lateral compartment of the knee. Genu valgum may be evaluated on an anteroposterior radiograph. Increased valgum increases the tendency for valgus motion of the knee joint with loading and, as such, increases the potential for lateral motion of the patella.
• Increased femoral anteversion: This increases the internal rotation of the femur and increases the lateral displacement force vector affecting the patella. According to Post et al, this factor is additive when associated with concurrent genu valgum.¹⁰ This factor may be clinically estimated by evaluating relative internal versus external rotation at the hip. However, accurate measurement is best obtained with computed tomography (CT) scanning of the hips.
• Coxa valga: This also increases the lateral displacement force vector acting on the patella. This skeletal factor increases valgus stress at the knee. 
• Foot pronation: When present, this contributes to the lateral forces on the patella. It can be easily managed with in-shoe orthotics.  
• Lateral tibial tubercle: This moves the pull of the extensor mechanism laterally and thus increases laterally directed forces on the patella. 
• External tibial torsion: This contributes to the lateral placement of the tibial tubercle, thus increasing the effective Q-angle and increasing the lateral displacement vector acting on the patella.
• Family history of dislocation: This is reported in the literature and may represent a correlation with an underlying biomechanical anomaly preserved among family members.
• Other: Escala et al identified other radiographic measurements that are indicators of OPI. These include short patella nose (<9 mm) and small morphology ratio (<1.2).⁸

Kinetic chain models

JRFs of the patellofemoral joint are different when studied under closed and open kinetic chain models. When the kinetic chain is closed (eg, leg press, squats), the JRF increases when the knee is flexed 0-90°. To counteract this load, a greater surface area of the patella comes into contact with the femur, effectively dissipating the forces. However, the contact area does not increase as much as the reaction force. Therefore, forces on the contact areas increase during flexion to 90°. Further flexion greater than 90° causes a leveling off or a decrease in the JRFs. After 90° of flexion, the contact of the quadriceps tendon with the trochlear groove further diffuses the load. Irrespective of the cause, JRFs decrease when the knee is flexed 90-120°.

The open-chain model encompasses lower extremity non – weight-bearing exercises such as leg curls and extensions. When the leg is at 0° flexion, the reaction forces of the patellofemoral joint are low because the patella does not contact the femur when the leg is in full extension. Studies have shown widely varying results from 5-25° of flexion. With the knee flexed to 90°, the JRFs increase and the contact area decreases, resulting in very high patellofemoral stress. A study of knee flexion-extension with a 0.9-kg ankle weight showed JRFs are greatest at 36° of flexion. JRFs are lowest at 90° of flexion.

Closed-chain exercises are most protective for the patellofemoral joint when performed at 0-45° of flexion. Open-chain exercises should be performed from 0-5° of flexion and from 90° to full flexion. JRFs should be limited as much as possible during repetitive motion to avoid chondrosis and chondromalacia. In strengthening or rehabilitative exercises for the quadriceps, programs should be designed with open and closed kinetic chain models in mind.

Anatomic variants

When evaluating patients with patellofemoral disorders, the physician needs to consider anatomic variants, which often manifest as bone deformities and would include bipartite patellae. Additionally, the knee joint may be affected by congenital anomalies. Many genetic syndromes involve the knee joint, including congenital patellar aplasia, nail patella syndrome, small patella syndrome, Meir-Gorlin syndrome, RAPADILINO syndrome (RA for radial, PA for absent/hypoplastic patellas and cleft/high-arched palate, DI for diarrhea/dislocated joints, LI for little size/limb malformations, NO for long, slender nose/normal intelligence), and genitopatellar syndrome. A 2005 article by Bongers et al reviews genetic anomalies in greater depth.¹¹

Clinical

History

Obtaining a thorough history of the patient's symptoms is important when establishing a diagnosis of patellar injury or dislocation.

• A common symptom of patellar injury and dislocation is acute pain after direct contact or sudden change of direction (ie, a cutting maneuver). With sudden changes in direction, the femur medially rotates over the ground-stabilized tibia. Under these conditions, athletes commonly feel the knee giving way, which is the result of quadriceps inhibition from pain, a physiologic protective mechanism. Rapid swelling, intense knee pain, and difficulty with any knee flexion usually occur. Other dysfunctions with similar presentations and mechanism of injury are meniscal and ligamentous injuries, particularly injuries of the anterior cruciate ligament.
• Symptoms may also manifest as a slowly progressive sensation of anterior knee pain with increased physical activity. Intense physical activity increases JRFs across the knee. Such activities include inclined ambulation, squatting, prolonged sitting, and going up and down stairs.¹² Anterior knee pain aggravated by activity is typical of chondral pathology. Knee pain that improves during physical activity but returns after activity suggests tendinitis.
• A common symptom in nontraumatic patellofemoral problems is crepitus of the patellofemoral joint.

Physical

• The physical examination in cases of suspected patellar injury and dislocation begins with inspection. 
• In general, patellofemoral pathology does not cause any significant knee effusion. Acute patellar dislocation is an exception because knee joint effusion is common with this condition.
• Other observations common in patellofemoral dysfunction include abnormal femoral anteversion, patella alta, tibial torsion, genu recurvatum, genu valgum, genu varum, pes planus, and ligamentous laxity. These factors often contribute to patellar injury and dislocation.
• Following inspection, the examiner must palpate the knee and surrounding structures. Evaluate the patella by applying pressure to the superior pole, inferior pole, and medial and lateral aspects of the patella. Feel for changes in the quality of movement. Applying pressure to the superior pole (delivering the patella) allows the examiner to palpate for tenderness along the inferior, medial, and lateral aspects of the patella. 
• An evaluation of patients with patellofemoral pain must include an assessment of medial and lateral patellar glide. As noted previously, relative weakness of the VMO and tightness of the lateral soft-tissue structures may result in lateral patellar tilt; this tightness may manifest as decreased medial patellar glide. 
• In patients with an acute dislocation, significant tenderness medially near the medial retinaculum suggests a torn structure, often the MPFL. Individuals with patellofemoral pathology often experience pain with medial palpation. Tenderness noted superolaterally suggests chondral injury after dislocation. In the event of traumatic dislocation, soft-tissue lesions of the knee are commonly associated with intra-articular fractures and chondral injuries. These concomitant injuries contribute to the patient’s acute pain.
• The examiner may also palpate the medial and lateral tissues of the distal quadriceps during initiation of terminal knee extension to appreciate a crude timing difference between the vastus lateralis (VL) and VMO. Some authors suggest that a delay in the contraction of the VMO plays a role in patellar maltracking. 
• Formal examination of vertical patellar positioning requires a radiographic evaluation. However, the examiner may make a gross estimate of the patella position, which may suggest either a superiorly positioned patella, patella alta, or an inferiorly positioned patella (ie, patella baja).
• Chondromalacia may be evident by the presence of crepitus, which is a palpable grinding that occurs with knee flexion and extension and occurs secondary to chondral injuries of the patella undersurface and/or the distal femur. In persons with this condition, a patellar grind test and palpation of the medial and lateral patellar facets elicit pain.
• Plicae can be palpated in many patients with patellar injury. Plicae are often tender.
• Additionally, assess for tightness of the hamstrings (popliteal angle), quadriceps (Ely tests), and iliotibial band (Ober test). Muscular tightness affects patellar motion and function.
• The apprehension test can be used to evaluate a patient for possible previous dislocation or subluxation and is performed as follows (see Image 1):
  • This test involves applying a laterally directed force to the medial patella with the knee flexed 30°.
  • In patients with a previous dislocation or subluxation, this is very distressing. Patients often resist this test and become very apprehensive. Many times, the patient grabs the examiner's hand to prevent further pain and relieve apprehension.
  • With no previous patellar dislocation, the apprehension test is tolerated well. 
• Assessing lateral patellar tracking with knee motion is an important part of the examination for patellofemoral dysfunction.
  • A positive J sign indicates lateral patellar tracking. A positive J sign is observed as the patella tracking laterally when the patient brings the knee from flexion to extension (ie, the patella moves notably laterally at terminal knee extension). This can be visualized well if the examiner places a digit on both the medial and lateral aspects of the superior patella.
  • A healthy patella moves mostly superiorly and slightly laterally at terminal knee extension.
• The Q-angle should be assessed in persons with patellar injury or dislocation.
  • The Q-angle is the intersection between 2 anatomic lines on the anterior thigh. The first line is drawn from the anterior superior iliac spine to the center of the patella. The second line is drawn from the center of the tibial tubercle to the center of the patella.
  • Foot position needs to be standardized in the evaluation of the Q-angle because tibial torsion and foot pronation/supination change the Q-angle. The Q-angle is also impacted by femoral anteversion.
  • Supine and standing measurements also yield different values. Therefore, the Q-angle must be measured in a consistent fashion. The knee must be exposed to all physiologic forces to improve accurate measurement.
  • Measuring a clinically significant Q-angle requires the patella to be centered in the trochlear groove. Some authors recommend measurement of the Q-angle at 30° of knee flexion to move the patella into the proximal portion of the trochlea. Patients with patellofemoral malalignment may have a laterally positioned patella in full knee extension; this position falsely decreases the measured Q-angle.
  • Authors disagree on the reference range values, with values from 10º to 20° being a commonly accepted range.
  • Traditional teaching holds that females have a larger Q-angle than males, secondary to a wider pelvic structure. A study by Grelsamer et al found the mean difference in Q-angles between men and women to be only 2.3°.¹³ The authors found that, on average, taller people had smaller Q-angles than shorter people, regardless of sex, and surmised that the differences between males and females was related to the longer femur in males.
  • Clinically, an increased Q-angle may alert the treating physician to a potential cause for a patient's knee pain. However, the clinical usefulness of the Q-angle is debated. In a review article, Post et al reported that data correlating Q-angle measurements with patients’ clinical symptoms do not exist.¹⁰ The authors noted that studies have shown that up to 60% of patients with patellofemoral symptoms have normal Q-angles. Post et al surmised that the Q-angle as a measurement of valgus force vectors across the anterior knee is not without value; rather, they suggest that its value as an isolated clinical tool is questionable.¹⁰ Interpretation of a patient’s Q-angle should be part of a multifactorial evaluation.
  • Other authors have noted that rehabilitation programs for individuals with Q-angles greater than 15° are as successful as those for individuals with Q-angles less than 15°.
  • The senior author of this article doubts the importance of measuring Q-angles because more pertinent information can be obtained by other physical examination assessments of flexibility, patellar positioning, and mobility. In addition, a Q-angle measurement is a static assessment of a dynamic problem and, therefore, is limited in providing information pertinent to developing a treatment plan. 
• The bipartite patella is not a rare patellar variant. Typically asymptomatic, the bipartite patella is difficult to identify during a physical examination. Suspicion should arise when anterior knee pain and swelling are present. A symptomatic bipartite patella is easily revealed through radiologic films and commonly manifests with displacement of a fragment.
• When assessing individuals in the pediatric population, patellofemoral pain may indicate growth center abnormalities affecting the tibial tubercle (eg, Osgood-Schlatter disease) or affecting the distal pole of the patella (eg, Sinding-Larsen-Johansson syndrome).

Differential Diagnoses

Anterior Cruciate Ligament Injury
Medial Collateral Knee Ligament Injury
Meniscus Injuries
Patellar Injury and Dislocation
Patellofemoral Joint Syndromes

Other Problems to Be Considered

Bipartite patella
Chondromalacia
Osteochondritis dissecans
Patella fracture
Patellofemoral arthritis
Soft tissue and capsular injury

Workup

Imaging Studies

• Plain radiography
  • Plain radiography is the most common diagnostic imaging study performed for patellofemoral dysfunction, and it is the least costly.
  • A standard radiographic protocol for the screening for patellar dislocation includes anteroposterior, true lateral, and axial or sunrise views.
  • Several variations of the axial view radiograph can be used, but the most widely accepted techniques are taken with the patient supine and the knee at 20-45° of flexion with and/or without external rotation of the tibia.
  • A true lateral view can be used to assess for several possible problems. First, with a vertical position of the knee, it can be used to evaluate for patella alta or baja. Second, it can be used for a measurement of patella tilt. Some authors find this view provides more sensitivity for patellofemoral pain and previous subluxation than a measurement of tilt on an axial view. Third, it can help evaluate trochlear depth. In this view, examination of the proximal portion of the trochlear groove for dysplasia is possible. This area is especially important in patella motion in early flexion; this evaluation is not possible on an axial view.
  • A Merchant view can be used to determine the severity of patellar subluxation and the presence of a maintained dislocation, although this second condition is not very common because most acute dislocations spontaneously reduce.
  • Plain radiography is also very effective for identifying patellar, tibial, and femoral fractures. In a study of 214 patients with acute knee trauma, a single lateral view radiograph had 100% sensitivity in detecting fractures.¹⁴ Overall, plain radiography is an effective and inexpensive screening tool that is particularly useful in diagnosing fractures. However, radiography has limited value in assessing soft-tissue structures.
• CT scanning
  • When CT scanning was tested against standard radiography for determining patellar subluxation, CT scanning was found to be significantly more sensitive.
  • Stanciu et al found that CT scanning was roughly 1.5 times more sensitive in detecting patellar tracking anomalies than standard radiography.¹⁵ In Shea and Fulkerson also found that CT scanning was highly effective for detecting patellar subluxation.¹⁶ Using CT scanning, the authors accurately determined the severity of patellar tilt versus subluxation. In addition, based on CT scan findings, Shea and Fulkerson selected the patients for lateral retinacular release procedures (ie, patients in whom conservative treatment was unsuccessful). Finally, based on CT scan findings, they predicted the prognosis for patients undergoing surgery.
  • CT scanning may also be performed as a dynamic study. This study is performed using a helical CT scanning process and a continuous 10-second exposure through the midtrochlea level; patellofemoral dynamics may be evaluated for their in vivo physiologic relationships.
  • CT scanning has advantages over plain radiography because it is capable of imaging patellar cartilage.
  • A disadvantage of CT scanning is that it is less sensitive than magnetic resonance imaging (MRI) in detecting lesions in cartilage. CT scanning often requires contrast medium for certain studies, and it also exposes patients to radiation.
• MRI
  • MRI is extremely sensitive for identifying soft-tissue anomalies of the knee. In one study, MRI helped physicians identify MPFL injuries occurring secondary to acute patellar dislocation. MRI can also be used to help determine if joint laxity is present in the absence of bony deformities. MRI can be very helpful in assessing the extensor mechanism and its relationship to the patellofemoral apparatus.¹⁷
  • Although far more expensive, MRI is more effective than CT scanning in determining if patellar chondral lesions are present and for determining cartilage thickness and volume. Assessment of patellar cartilage thickness and volume is important to evaluate for osteoarthritis, and it is useful to preoperatively calculate the effect of joint contact and load transmission after surgical procedures.
  • T1-weighted images are not as sensitive as T2-weighted images. However, T2 imaging yields a high number of false-positive results, which may be due to the detection of very early cartilaginous lesions. Further tests need to be performed.
  • The kinematic MRI method is quite suitable to determine patellar tracking and other functional aspects of the patellofemoral joint. Brossmann et al found kinematic MRI findings correlated well with arthroscopic findings in patellofemoral pathology.¹⁸ The clinical value of kinematic MRI is questionable for most patients, and these studies are not available at most centers.
  • Axial views on MRI or CT scans may be used to evaluate the trochlea-tubercle distance. This is the horizontal distance in a vertical plane between the intercondylar notch and the tibial tubercle. Similar to the Q-angle, this evaluates the potential laterally directed vectors on the patella. Some authors suggest that a distance of 2 cm is specific, but not sensitive, for maltracking.
• Ultrasonography
  • Ultrasonography is not typically used in the assessment of patellar injury and dislocation.
  • Ultrasonography is better than CT scanning for distinguishing between cysts, granulation tissue, metaplasia, mucinoid degeneration, and congenial defects of the patellar ligament. Knowing that ultrasonography is available to help determine the cause of anterior knee pain is important.

Treatment

Acute Phase

Rehabilitation Program

Physical Therapy

During the acute phase of a patellar injury or dislocation, the immediate goals are to reduce inflammation, relieve pain, and stop activities that place excessive loads on the patellofemoral joint. Patients with an acute patella dislocation typically have been evaluated in an emergency department, with radiographic evaluation, and have often had a consultation with an orthopedist to assess for intra-articular pathology. Acute phase management should apply the PRICE principle: protection of the injured joint, relative rest, ice, compression, and elevation to control inflammation.

A study by Mãenpãã and Lehto suggested that a period of immobilization may be beneficial. In their study of 100 acute dislocations, patients were divided into 3 treatment groups: plaster cast, posterior splint, and patellar bandage/brace.¹⁹ At long-term follow-up, fewer redislocations were noted in the posterior splint group and the cast group than in the patellar bandage group. The first 2 groups had a period of immobility, whereas the bandage group did not. The mechanism of benefit is thought to be the time to heal the disrupted medial structures. The best outcomes were noted in the group initially treated with a posterior splint. The plaster cast group had a longer period of immobilization, and the authors suggested limiting the period of immobilization to 3 weeks to avoid muscle atrophy, knee joint restrictions, and retropatellar crepitation.¹⁹

Quadriceps strengthening is initiated during the acute phase. In the event of acute patella dislocation, these should be static exercises initiated during the period of immobilization. Quadriceps electrical stimulation is an option for muscle reeducation if the patient has difficulty activating the muscle secondary to pain. Electrical stimulation may also play a role in the management of knee joint effusion. When dolor, calor, rubor, and edema resolve, the patient may progress to the recovery phase of rehabilitation.

Therapy should also include a protocol for hamstring muscle stretching. Tight hamstring muscles functionally counteract their agonist group, the quadriceps.

Surgical Intervention

In the acute phase, surgical interventions are reserved for complicated dislocations with associated fractures. The most common site of cartilage injury to the patella occurs as osteochondral fractures of the medial patellar facet or cracks in the central dome of the patella. Cartilaginous injuries are also frequently seen on the lateral femoral condyle. Arthroscopy can repair or remove fracture fragments. However, acute surgical interventions are unnecessary in most cases of patellofemoral syndromes.

Consultations

If conservative management is not effective and the patient still experiences symptoms, consult an orthopedic surgeon. Particular attention should be paid to symptoms of an intra-articular foreign body, such as clicking, locking, or persistent intra-articular knee pain. These may be signs of an occult loose body within the knee.

Other Treatment

• General considerations
  
  
  • In the acute phase, protecting the patellofemoral joint involves reducing loads by postural correction, activity modification, and shoe changes/orthotic management if pes planus is present.
  • Shoe wear and orthotics can prevent excessive hip internal rotation, knee valgus, and subtalar joint pronation, all of which promote lateral patellar tracking.
  • Inappropriate cartilage-wear disorders can also be resolved by these measures.
  • Proper foot support helps reduce patellofemoral pain. Proper foot alignment helps correct some biomechanical causative factors due to congenital deformities.
  • Conservative treatment of acute traumatic patellar dislocations in this fashion has shown good results.
• Patellar bracing
  
  
  • Some controversy exists regarding the effectiveness of knee braces with a patella buttress in the treatment of patellofemoral pain and redislocation. Some authors find bracing to be useful primarily for patient reassurance and believe the primary benefit is psychologic in nature. However, other authors support their use both as a pain reduction adjunct in a conservative rehabilitation program that includes quadriceps strengthening and as protection against redislocation and subluxation.
  • Study results on the efficacy of bracing for patellofemoral pain are highly variable. None of the studies reviewed controlled for the amount of pressure elicited by the brace on identified muscle groups. One study identified a significantly increased sulcus angle through the entire knee flexion range secondary to the brace use. However, the gross tracking pattern did not change, and minute differences in alignment may have influenced joint mechanics to improve patellofemoral pain. Another study found no benefits when braces were worn. Neptune et al found that increasing VMO strength produces more uniform results than those achieved with brace orthotics.²⁰
  • The goal of bracing is to restore proper alignment. This occurs either by mechanical inhibition of lateral patella motion with a patella buttress or, as in taping, by a change in neuromuscular recruitment secondary to muscular proprioception. A case study by Shellock et al that evaluated the use of loaded kinematic MRI to evaluate patellar positioning while the patient wore a patellar realignment brace demonstrated a reduction in lateral subluxation at 30° of flexion and a functional decrease in patient pain.²¹ Additionally, bracing unloads painful structures, keeps the joint warm, provides proprioceptive feedback, and may assist in improving knee extension neuromuscular patterning.
  • Care must be used in the acute phase, because bracing may aggravate the patient’s acute condition. However, a neoprene sleeve or other knee wrap that provides external compression helps control inflammation. Many braces have a patellar cutout and lateral buttresses to help prevent lateral patellar tracking. 
• Patellar taping (McConnell method)
  • The goals of McConnell taping are to restore proper alignment and control pain.
  • With proper alignment, VMO retraining is initiated. Once taped, patients should note decreased pain when performing painful activities such as stepping down from a stool. The goal of taping is to optimize patellar positioning and facilitate better activation of the medial patellar stabilizers, particularly the VMO. The technique can be taught to patients to perform themselves. Taping is continued until appropriate patellar positioning and tracking is achieved through the rehabilitation process, which includes appropriate activation of the VMO.
  • A study by Gilleard et al examined the timing of VMO and VL firing in patients with patellar pain while walking up and down stairs.²² The authors demonstrated that during step-up activities, the VMO in the taped knee fired earlier in the gait cycle, and the VL had no change in the cycle timing. During step-down activities, the VMO in the taped knee fired earlier and the VL fired later. The authors postulated that these timing changes very early in the gait cycle, when the knee is near full extension, may have a beneficial effect on patellofemoral mechanics and promote movement of the patella into the trochlea groove early in flexion.²²

Recovery Phase

Rehabilitation Program

Physical Therapy

Therapeutic theory goals of nonoperative management of patellar injury and dislocation are to improve patellar tracking. The VMO is an important medial stabilizer of the patella. Inappropriate synergy patterns between the VMO and the VL have been theorized for lateral patellar tracking. The VL is a much larger muscle than the VMO. By overpowering the VMO, the VL may contribute to lateral tracking.

The prevailing theory has been that lateral patellar tracking is associated with VMO weakness. However, research has been inconclusive for VMO weakness as a direct causative mechanism of lateral patellar tracking. A study by Mohr et al examined timing differences between the VMO and VL in patients both with and without patellofemoral pain.²³ The authors concluded that the timing differences noted and their relationship to the gait cycle suggest overall quadriceps weakness rather than specific, focal VMO weakness. As such, Mohr et al recommended overall quadriceps strengthening as the basis of rehabilitation strengthening programs. Other authors have also noted that general quadriceps strengthening has demonstrated reductions in lateral tracking irrespective of the mechanism.

The patient should be educated about correct posture and joint preservation at this time. Supportive adjuncts such as taping and bracing are common treatment modalities. Exercises to strengthen the quadriceps muscle (focusing on VMO activation) include quadriceps-setting exercises and straight-leg raises.

Quadriceps-setting exercises are performed with the patient in the supine position. The contralateral hip and knee are flexed to approximately 45° to protect the low back, and the ipsilateral leg is kept in extension. The quadriceps muscle in the extended leg is contracted, and the contraction is held for 5 seconds. The patient then relaxes the quadriceps and repeats the contraction. (Repetitions and sets are gradually increased.) The ankle of the exercising leg must be actively dorsiflexed during the contraction.

Straight-leg raises are performed with the patient in the supine position and the contralateral hip and knee flexed to approximately 45°. The extended leg (the leg to be strengthened) is raised 8-12 inches from the table and is held at that level for 10 seconds. (Repetitions and sets are gradually increased.)

Additional strengthening exercises must be performed for the hip adductors, hip abductors, and hip flexors. Hip adductors are strengthened with the patient lying on his or her side. The leg against the exercise mat is lifted away from the mat and is held for 10 seconds, followed by relaxation. Hip abductors are strengthened with the patient lying on his or her side. The leg away from the exercise mat is lifted away from the mat and is held for 10 seconds, followed by relaxation. Hip flexors are strengthened with the patient in a seated position. Both the knee and hip are held at 90° of flexion, and the leg to be exercised is lifted off the ground and is held for 10 seconds. (Repetitions and sets are gradually increased for all exercises.)

Any physical therapy program for patellofemoral problems must address tightness of the lower-extremity musculature. Reduced flexibility of the hamstrings, hip abductors, and iliotibial band all can increase patellofemoral pain. Additionally, tight gastrocnemius muscles can increase patellofemoral pain.

Medial patellar gliding exercises may loosen lateral retinacular tightness in this stage. Medial patellar gliding exercises are performed with the leg extended. The patient manually pushes the patella medially and holds for a count of 10 seconds.

An important concept in the rehabilitation of patellar dislocation and patellofemoral pain is knee flexion. Initially, any activity that requires greater than 40-45° of knee flexion causes symptoms. Initial rehabilitation programs start with the isometric open kinetic chain exercises described earlier. Early rehabilitation programs should limit all activities that require quadriceps firing with the knee flexed greater than 45°.

Once isometric open kinetic chain exercises are tolerated without discomfort, the rehabilitation program advances to closed kinetic chain exercises (eg, mini squats, lunges, stair climbing). The rectus femoris, VMO, and VL are all strengthened by the mini squats (repetitions and sets modified to the tolerance of the patient). Earl et al found that when isometric hip adduction is performed in conjunction with mini squats, the strength in these muscles increased significantly compared with the control group performing conventional squats.²⁴

Important goals are to restore ROM in the joint, mobilize soft tissues, and strengthen the surrounding musculature. Lunges and bike riding allow strengthening through a controlled ROM. The patient becomes more active in this phase, and the clinician must screen the patient for exacerbations of symptoms. If symptoms reemerge, the optimal loading zone of the knee and the activity level must be reevaluated. The patient learns activity limits in this phase. Once pain has resolved sufficiently to complete daily activity requirements without exacerbations, the patient can advance to the final phase of rehabilitation.

Advanced rehabilitation programs progress to jogging, running, plyometrics, and sport-specific exercises. Patients must be monitored and must always follow proper technique, as well as learn to properly fire the VMO.

Surgical Intervention

Surgical intervention may be appropriate in 2 different patient populations: (1) those with normal anatomy who experience recurrent dislocation or pain and (2) those with an anatomic abnormality who may benefit from surgical intervention either upon initial acute dislocation or later with recurrence of dislocation or subluxation. In general, following acute patella dislocation, patients with normal lower extremity anatomy and without radiographic indications of intra-articular injury are best served by conservative treatment.  

Buchner et al compared conservative treatment with surgical repair in patients with acute patella dislocation²⁵ ; patients with radiologic signs suggestive of a predisposition to redislocation were excluded from the study. Results indicated no significant difference between surgically treated and conservatively treated groups in terms of redislocation rate, reoperation rates, level of activity, or functional or subjective outcomes.

• Medial repair
  • This group includes 3 primary procedures, all of which attempt to recreate an appropriate physiologic mechanism at the knee joint by improving the integrity of the structures that provide medially directed forces on the patella. The techniques include (1) plication of the medial patellar retinaculum, (2) anatomic repair of the MPFL, and (3), plasty surgery of the VMO.
  • Anatomic and biomechanical studies have indicated that the MPFL and the VMO are the primary restraints to lateral patella translation, particularly early in flexion before full trochlear engagement.
  • An article by Arendt et al suggested that repair or reconstruction of the MPFL needs to be a component of any surgical intervention to control lateral translation of the patella in a knee with demonstrated lateral instability or dislocation.²⁶
  • 2 studies evaluated MPFL surgical reconstruction in patients with recurrent patellar dislocations.
    • Sillanpãã et al compared the results of MPFL reconstruction by adductor magnus tenodesis (18 knees) with distal patellar realignment (ie, Roux-Goldthwait procedure) (29 knees).²⁷ The authors also evaluated the development of patellofemoral osteoarthrosis for these 2 procedures at a median 10-year follow-up. The incidence of patellar redislocation after surgery was 7% in the adductor magnus group and 14% in the Roux-Goldthwait group. Patellofemoral articular cartilage lesions were found on MRI in 22 knees (73.3%) at follow-up, including 14 knees (46.6%) with full-thickness cartilage loss, whereas radiographs revealed patellofemoral osteoarthritis in 5 patients in the Roux-Goldthwait group but in none of the patients in the adductor magnus group. Based on their findings, Sillanpãã et al concluded that "adductor magnus tenodesis is a reliable method to treat recurrent patellar dislocation. The medial patellofemoral ligament reconstruction seems to reduce the risk of osteoarthrosis compared with distal realignment surgery."
    • Panagopoulos et al used a single hamstring tendon graft that was passed through the medial intermuscular septum at the adductor's magnus insertion and then fixed to the superomedial pole of the patella.²⁸
  • A study by Krause et al followed 28 patients for 5 years following a VMO plasty.²⁹ In this procedure, the VMO was detached from its insertion on the patella and reinserted 10-15 mm distally. Their 5-year follow-up results indicated a 7% redislocation rate. Also noted was that 83% of patients reported good or excellent satisfaction with the procedure, and 89% of the knees had little or no evidence of arthrosis.²⁹ These authors reported the results as better than those for other surgical repairs, and they attributed the positive results to the minimal interference with physiologic joint mechanics and restoration of the anatomic structure of the knee. 
• Lateral release: This procedure involves making an incision of the capsule of the lateral retinaculum to divide it. Lateral release may be performed as either an open or arthroscopic procedure, and it may also include release of the distal VL. 
  • Extending the release too far can cause medial subluxation of the patella; in fact, medial patella subluxation or dislocation is almost always iatrogenic, secondary to an overzealous lateral release. Instead, the goal of this procedure is to facilitate medial motion of the patella into the trochlear groove and/or to level a patella with a large degree of lateral patella tilt.
  • This procedure has come under extensive criticism, especially as a sole surgical procedure. Anatomic studies suggest that in addition to providing a laterally directed force on the patella, the lateral retinaculum also provides a posteriorly directed force, with the net force being posterolateral. This posterior force component may provide stability as the patella is directed into the trochlea early in flexion.
  • In a knee with soft-tissue laxity, a lateral release removes one of the forces directing the patella into the trochlea and further destabilizes the knee. Post et al suggested that this problem is accentuated in patients with a large Q-angle.¹⁰ In a cadaveric study by Christoforakis et al, the investigators demonstrated that a lateral retinacular release decreased the force needed to displace the patella laterally 10 mm by 16-19% at knee flexions of 0-20°.³⁰ This correlates exactly with the range of flexion in which the laterally unstable knee is most at risk for lateral dislocation.
  • Arendt et al suggested that a lateral release should only be performed if it facilitates the recentering of the patella by other procedures or when it is specifically performed to address objective lateral patella tilt.²⁶
• Combined proximal procedures
  • Multiple studies have examined surgical treatment that combines medial reconstruction and lateral retinaculum release.
  • Haspl et al reported a small study of 17 patients who were followed for up to 26 months following plication of the medial patellar retinaculum and release of the lateral patella retinaculum.³¹ The results were deemed good by the authors, and they reported no redislocations or subluxations in that period.
  • Nam and Karzel reported a study of 23 patients who were followed for an average of 4.4 years after undergoing a medial reefing and arthroscopic lateral release.³² The authors reported 1 dislocation, 1 subluxation, and good patient satisfaction. All the patients reported the procedure was worthwhile, with 26% rating the results as excellent and 65% rating the results as good.³²
  • Mãenpãã and Lehto treated 284 knees operatively with reefing of the medial capsule.³³ In 243 of the knees, the lateral patellar retinaculum was released. The patient population mostly consisted of soccer players, gymnasts, and ice hockey players. The authors noted that the prognosis for decreased redislocation rate and subjective improvement was better if the mechanism of injury was traumatic.

Distal procedures

• Tibial tubercle transfers
  • Tibial tubercle transfer was first described by Hauser in 1938 with a medial and distal transplantation of the tibial tuberosity. This procedure was associated with a high rate of arthrosis, reportedly up to 71% of patients, and had a relatively high redislocation rate, reportedly 17-20%. Consequently, medial and distal transplantation of the tibial tuberosity are no longer performed.
  • Initially, high rates of arthrosis were thought to be secondary to the posterior movement of the tubercle inherent in the original procedure. This realignment makes use of muscular pull to maintain the patella in a central position in the trochlea. In current practice, numerous variations of this procedure are in use, and they are typically performed in conjunction with the proximal procedures described above.
  • Tibial tubercle transfer procedures are often performed in an effort to correct for an abnormal Q-angle. However, a large variation in norms for the Q-angle is reported in the literature. Arendt et al noted that in many patients, an exaggerated Q-angle at full extension may correct to normal at 90° of flexion, and surgical correction of those knees would lead to overmedialization of the patella mechanism.²⁶
  • In any case, tibial tubercle transfers are likely best avoided in patients with near-normal Q-angles. These procedures do, however, have the capability to correct patella alta, a potentially beneficial component of the corrective process.
• Combined procedures
  • Multiple variations of these procedures are used, in which a distal medialization of the tibial tubercle is combined with a proximal procedure, usually a medial reconstruction and a lateral release. These interventions can also correct for patella alta, with distal movement of the tibial tubercle during the medial transfer. 
  • A study by Cossey and Paterson reported on 21 knees followed for 23 months postoperatively after having undergone a combined procedure consisting of lateral release, distal realignment of the tibial tubercle, and reconstruction of the MPFL with a graft for medial retinacular tissue.³⁴ They reported no redislocations or recurrence of subluxation. The authors also reported that all patients achieved activity levels comparable to or improved from preinjury levels, a functional finding not matched in most other studies.
  • Mikashima et al examined the results of 20 patients who underwent an Elmslie-Trillat distal realignment compared with 20 patients who underwent the same procedure but with the addition of reconstruction of the MPFL.³⁵ At 2-year follow-up, patients in the combined group all had a negative apprehension sign, whereas the distal realignment–only group demonstrated 30% with a positive apprehension sign. The combined group also demonstrated improved radiographic stability on a stress skyline view compared with the distal realignment–only group.³⁵

• More intensive joint reconstructive surgery
  • Procedures such as a trochleoplasty, rotational osteotomy for excessive femoral anteversion or external tibial rotation, and even patellectomy may be performed in cases in which both conservative treatment and less extensive surgery have failed. 
  • Importantly, these are extensive surgeries with significant morbidity and potentially lifelong functional deficit; as such, they are very rarely used in current practice.
• Arthroscopic debridement: In some cases, patients may benefit from arthroscopic debridement for symptomatic relief of arthrosis secondary to the patellofemoral instability.

Postsurgical rehabilitation closely follows nonoperative conservative treatment. All surgical procedures are at risk for complications such as medial tracking, arthrofibrosis, reflex sympathetic dystrophy symptoms, hemarthrosis, and rupture of the quadriceps tendon.

Consultations

If the conservative management is not effective and the patient still experiences symptoms, consult an orthopedic surgeon.

Other Treatment (Injection, manipulation, etc.)

• Bracing and taping can be continued in this phase to decrease pain and increase activity participation.
• Patellar bracing and McConnell taping are viewed as temporary supportive measures whose functions are described in Acute Phase, Other treatment. They should be discontinued when functional activities are performed without pain.

Maintenance Phase

Rehabilitation Program

Physical Therapy

The final phase of rehabilitation emphasizes developing an independence program for the patient. The patient learns how to stretch appropriately, conduct training routines, modify activity, and apply ice after activity routines. Returning the patient to the preinjured functional state often requires progressive functional activity. The rate of progression is limited by the patient’s tolerance. The patient should work toward single-leg standing, deep squatting, and jumping. Once patients are able to adjust activity routines within their optimal loading zones, they are ready to be discharged and only require routine follow-up treatment.

Consultations

If the conservative management is not effective and the patient still experiences symptoms, consult an orthopedic surgeon.

Other Treatment

Manipulation

Wu treated patients who had anterior knee pain, tenderness, quadriceps imbalance, and patellar subluxation with Chinese manipulation.³⁶ The diagnosis was determined by a plain radiography protocol, and his patients were treated with a combination of manipulation and an exercise program. Although his treatment was successful in alleviating symptoms of patellofemoral dysfunction, Wu's study is limited by not having control groups that received either only manipulation or exercise alone. Future studies should take this into account. His manipulation techniques included the following:

• Rolling the metacarpophalangeal joints over the VMO muscle for a deep massage effect
• Circularly kneading the quadriceps with the thenar eminence
• Mobilizing the patella side to side
• Kneading the infrapatellar fat pad
• Peripatellar rubbing with the hypothenar eminences
• Torsion of the tibia on the femur
• Ranging the patella into extension and flexion
• Massaging the gastrocnemius
• Grasping and elevating the patella
• Moving the patella against the resistance of the lateral retinaculum to stretch the latter 

Bracing and taping can be of benefit for symptoms of patellofemoral dysfunction, as discussed in Acute Phase, Other treatment.

Medication

Medications used to treat patellar injury and dislocation include nonsteroidal anti-inflammatory drugs (NSAIDs), acetaminophen, and pain medicines. Allergies, contraindications, and adverse effects should be reviewed before prescribing these medicines.

Related eMedicine topics:
Toxicity, Acetaminophen
Toxicity, Narcotics
Toxicity, Nonsteroidal Anti-inflammatory Agents

Related Medscape topics:
Resource Center Adverse Drug Events Reporting
Resource Center Opioids: A Guide to State Opioid Prescribing Policies
Resource Center Pain Management: Advanced Approaches to Chronic Pain Management
Resource Center Pain Management: Pharmacologic Approaches

Nonsteroidal Anti-inflammatory Drugs

NSAIDs have analgesic, anti-inflammatory, and antipyretic activities. The mechanism of action of NSAIDs is not known, but they may inhibit cyclooxygenase (COX) activity and prostaglandin synthesis. Other mechanisms may exist as well, such as inhibition of leukotriene synthesis, lysosomal enzyme release, lipoxygenase activity, neutrophil aggregation and various cell membrane functions.

Naproxen (Aleve, Anaprox, Naprosyn, Naprelan)

For the relief of mild to moderate pain. Inhibits inflammatory reactions and pain by decreasing the activity of COX, which results in a decrease of prostaglandin synthesis.

Dosing

Adult

500 mg PO followed by 250 mg q6-8h; not to exceed 1.25 g/d

Pediatric

<2 years: Not established
>2 years: 2.5 mg/kg/dose PO; not to exceed 10 mg/kg/d

Interactions

Coadministration with aspirin increases the risk of inducing serious NSAID-related adverse effects; probenecid may increase the concentrations and, possibly, the toxicity of NSAIDs; may decrease the effect of hydralazine, captopril, and beta-blockers; may decrease the diuretic effects of furosemide and thiazides; may increase PT duration when taking anticoagulants (instruct patients to watch for signs of bleeding); may increase the risk of methotrexate toxicity; phenytoin levels may be increased when administered concurrently

Contraindications

Documented hypersensitivity; peptic ulcer disease; recent GI bleeding or perforation; renal insufficiency

Precautions

Pregnancy

B - Fetal risk not confirmed in studies in humans but has been shown in some studies in animals

D - Fetal risk shown in humans; use only if benefits outweigh risk to fetus

Precautions

Acute renal insufficiency, interstitial nephritis, hyperkalemia, hyponatremia, and renal papillary necrosis may occur; patients with preexisting renal disease or compromised renal perfusion risk acute renal failure; leukopenia occurs rarely, is transient, and usually returns to normal during therapy; persistent leukopenia, granulocytopenia, or thrombocytopenia warrants further evaluation and may require discontinuation of the drug.

Ibuprofen (Excedrin IB, Advil, Ibuprin, Motrin)

DOC for patients with mild to moderate pain. Inhibits inflammatory reactions and pain by decreasing prostaglandin synthesis.

Dosing

Adult

200-400 mg PO q4-6h while symptoms persist; not to exceed 3.2 g/d

Pediatric

<6 months: Not established
6 months to 12 years: 4-10 mg/kg/dose PO tid/qid
>12 years: Administer as in adults

Interactions

Coadministration with aspirin increases the risk of inducing serious NSAID-related adverse effects; probenecid may increase the concentrations and, possibly, the toxicity of NSAIDs; may decrease the effect of hydralazine, captopril, and beta-blockers; may decrease the diuretic effects of furosemide and thiazides; may increase PT duration when taking anticoagulants (instruct patients to watch for signs of bleeding); may increase the risk of methotrexate toxicity; phenytoin levels may be increased when administered concurrently

Contraindications

Documented hypersensitivity; peptic ulcer disease; recent GI bleeding or perforation; renal insufficiency; high risk of bleeding

Precautions

Pregnancy

B - Fetal risk not confirmed in studies in humans but has been shown in some studies in animals

D - Fetal risk shown in humans; use only if benefits outweigh risk to fetus

Precautions

Caution in patients with congestive heart failure, hypertension, and decreased renal and hepatic function; caution in the presence of coagulation abnormalities or during anticoagulant therapy

Ketoprofen (Oruvail, Orudis, Actron)

For the relief of mild to moderate pain and inflammation. Small dosages are indicated initially in small and elderly patients and in those with renal or liver disease. Doses >75 mg do not increase therapeutic effects. Administer high doses with caution and closely observe patients for response.

Dosing

Adult

25-50 mg PO q6-8h prn; not to exceed 300 mg/d

Pediatric

<3 months: Not established
3 months to 12 years: 0.1-1 mg/kg PO q6-8h
>12 years: Administer as in adults

Interactions

Coadministration with aspirin increases the risk of inducing serious NSAID-related adverse effects; probenecid may increase the concentrations and, possibly, the toxicity of NSAIDs; may decrease the effect of hydralazine, captopril, and beta-blockers; may decrease the diuretic effects of furosemide and thiazides; may increase PT duration when taking anticoagulants (instruct patients to watch for signs of bleeding); may increase the risk of methotrexate toxicity; phenytoin levels may be increased when administered concurrently

Contraindications

Documented hypersensitivity

Precautions

Pregnancy

B - Fetal risk not confirmed in studies in humans but has been shown in some studies in animals

D - Fetal risk shown in humans; use only if benefits outweigh risk to fetus

Precautions

Caution in patients with congestive heart failure, hypertension, and decreased renal and hepatic function; caution in the presence of coagulation abnormalities or during anticoagulant therapy

Analgesics

Pain control is essential to quality patient care. Analgesics ensure patient comfort and have sedating properties, which are beneficial for patients who have sustained trauma or who have sustained injuries.

Acetaminophen (Aspirin-free Anacin, Tempra, Feverall, Tylenol)

DOC for pain in patients with documented hypersensitivity to aspirin or NSAIDs, with upper GI disease, or who are taking oral anticoagulants.

Dosing

Adult

325-650 mg PO q4-6h or 1000 mg tid/qid; not to exceed 4 g/d

Pediatric

<12 years: 10-15 mg/kg/dose PO q4-6h prn; not to exceed 2.6 g/d
>12 years: 325-650 mg PO q4h; not to exceed 5 doses in 24 h

Interactions

Rifampin can reduce the analgesic effect; coadministration with barbiturates, carbamazepine, hydantoins, and isoniazid may increase hepatotoxicity.

Contraindications

Documented hypersensitivity; known G-6-PD deficiency

Precautions

Pregnancy

B - Fetal risk not confirmed in studies in humans but has been shown in some studies in animals

Precautions

In long-term alcoholism, hepatotoxicity is possible following various dose levels; severe or recurrent pain or high or continued fever may indicate a serious illness; acetaminophen is contained in many OTC products and combined use with these products may result in cumulative doses that exceed the recommended maximum dose.

Acetaminophen and codeine (Tylenol-3)

Indicated for the treatment of mild to moderate pain.

Dosing

Adult

30-60 mg/dose PO based on codeine content q4-6h or 1-2 tab q4h; not to exceed 4 g/d of acetaminophen

Pediatric

0.5-1 mg/kg/dose PO based on codeine q4-6h; 10-15 mg/kg/dose based on acetaminophen content; not to exceed 2.6 g/d of acetaminophen

Interactions

The toxicity of codeine increases with CNS depressants, TCAs, MAOIs, neuromuscular blockers, phenothiazines, and narcotic analgesics; rifampin can reduce the analgesic effects of acetaminophen; coadministration with barbiturates, carbamazepine, hydantoins, and isoniazid may increase the hepatotoxicity of acetaminophen.

Contraindications

Documented hypersensitivity

Precautions

Pregnancy

C - Fetal risk revealed in studies in animals but not established or not studied in humans; may use if benefits outweigh risk to fetus

Precautions

Caution in patients who are dependent on opiates because this substitution may result in acute opiate withdrawal symptoms; caution in patients with severe renal or hepatic dysfunction; hepatotoxicity with acetaminophen is possible following various dose levels in those with long-term alcoholism; severe or recurrent pain or high or continued fever may indicate a serious illness; acetaminophen is contained in many OTC products, and combined use with these products may result in cumulative doses that exceed the recommended maximum dose.

Follow-up

Return to Play

Patients with patellar injury and dislocation may return to play after (1) all symptoms and episodes or exacerbations have resolved and (2) full ROM and preinjury strength have been achieved in the affected limb. The timeline for return to play varies from patient to patient. In a 2000 study, Atkin et al found that at 6 months, 58% of their study population still reported deficits in function.³⁸

Some variability exists in the time required to return to play, and it depends on multiple factors, including the underlying anatomy and physiology, whether conservative or surgical treatment was used, and the type of surgical treatment performed. In a review article in 2003, Hinton et al suggested that following surgical correction of a patellar injury or dislocation, return to sports can be anticipated to occur 4-6 months after the procedure.³⁹

Prevention

Prognosis

The prognosis for patellofemoral dysfunction and dislocation has been studied and reports of outcomes vary. Overall, conservative treatment for acute patellar dislocations yields a 30-50% chance of continuing to have long-term symptoms of instability or pain.

• Cash et al reported on a 30-year noninvasive rehabilitation treatment course for patients with and without congenital anomalies of the extensor mechanism who had an acute patellar dislocation.⁴⁰ Of the 54 patients with congenital anomalies, 28 (52%) reported good or excellent results. Of the 20 patients without congential anomalies, 15 (75%) reported good or excellent results.⁴⁰
• Buchner et al evaluated a total of 126 patients who had a primary traumatic patella dislocation and were treated either conservatively, with arthroscopic exploration, or with immediate surgical repair of the parapatellar ligaments.²⁵ After a mean follow-up of 8.1 years, the study reported long-term functional results as excellent or good in 85% of patients. However, the investigators also noted a recurrence rate of 26% in the total study population.²⁵
• Atkin et al investigated 74 young athletes who received standardized rehabilitation after acute patellar dislocation during sporting events.³⁸ After full passive ROM and quadriceps strength were at least 80% compared with the uninvolved knee, these patients returned to sports activity. Up to 6 months after the initial insult, participation in strenuous activity, especially kneeling and squatting, was significantly reduced. At 6 months, 58% continued to note a reduced ability to fully participate.³⁸

Education

See Prevention.

Multimedia

Media file 1: Apprehension sign. The knee is placed at 30° flexion, and lateral pressure is applied. Medial instability results in apprehension by the patient.

Media file 2: Anatomic morphology of patellar insertion into the intercondylar notch.

Media file 3: Muscles influencing patellar biomechanics.

Media file 4: The Q angle can be measured while the patient is standing or while the knee is at 20° of flexion (ie, at neutral), with maximum internal or external rotation of the tibia.

Media file 5: Ligament constraints of the patella.

References

1. Räty HP, Kujala UM, Videman T, et al. Lifetime musculoskeletal symptoms and injuries among former elite male athletes. Int J Sports Med. Nov 1997;18(8):625-32. [Medline].

2. Thijs Y, De Clercq D, Roosen P, Witvrouw E. Gait-related intrinsic risk factors for patellofemoral pain in novice recreational runners. Br J Sports Med. Jun 2008;42(6):466-71. [Medline].

3. Hahn T, Foldspang A. Prevalent knee pain and sport. Scand J Soc Med. Mar 1998;26(1):44-52. [Medline].

4. Aoyagi K, Ross PD, et al. Prevalence of joint pain is higher among women in rural Japan than urban Japanese-American women in Hawaii. Ann Rheum Dis. May 1999;58(5):315-9. [Medline]. [Full Text].

5. Zhang Y, Xu L, Nevitt MC, et al. Comparison of the prevalence of knee osteoarthritis between the elderly Chinese population in Beijing and whites in the United States: The Beijing Osteoarthritis Study. Arthritis Rheum. Sep 2001;44(9):2065-71. [Medline]. [Full Text].

6. Nietosvaara Y, Aalto K, Kallio PE. Acute patellar dislocation in children: incidence and associated osteochondral fractures. J Pediatr Orthop. Jul-Aug 1994;14(4):513-5. [Medline].

7. Andrikoula S, Tokis A, Vasiliadis HS, Georgoulis A. The extensor mechanism of the knee joint: an anatomical study. Knee Surg Sports Traumatol Arthrosc. Mar 2006;14(3):214-20. [Medline].

8. Escala JS, Mellado JM, Olona M, et al. Objective patellar instability: MR-based quantitative assessment of potentially associated anatomical features. Knee Surg Sports Traumatol Arthrosc. Mar 2006;14(3):264-72. [Medline].

9. Dejour H, Walch G, Nove-Josserand L, Guier C. Factors of patellar instability: an anatomic radiographic study. Knee Surg Sports Traumatol Arthrosc. 1994;2(1):19-26. [Medline].

10. Post WR, Teitge R, Amis A. Patellofemoral malalignment: looking beyond the viewbox. Clin Sports Med. Jul 2002;21(3):521-46, x. [Medline].

11. Bongers EM, van Kampen A, van Bokhoven H, Knoers NV. Human syndromes with congenital patellar anomalies and the underlying gene defects. Clin Genet. Oct 2005;68(4):302-19. [Medline].

12. Amin S, Goggins J, Niu J, et al. Occupation-related squatting, kneeling, and heavy lifting and the knee joint: a magnetic resonance imaging-based study in men. J Rheumatol. Aug 2008;35(8):1645-9. [Medline].

13. Grelsamer RP, Dubey A, Weinstein CH. Men and women have similar Q angles: a clinical and trigonometric evaluation. J Bone Joint Surg Br. Nov 2005;87(11):1498-501. [Medline].

14. Verma A, Su A, Golin AM, O'Marrah B, Amorosa JK. A screening method for knee trauma. Acad Radiol. May 2001;8(5):392-7. [Medline].

15. Stanciu C, Labelle HB, Morin B, Fassier F, Marton D. The value of computed tomography for the diagnosis of recurrent patellar subluxation in adolescents. Can J Surg. Aug 1994;37(4):319-23. [Medline].

16. Shea KP, Fulkerson JP. Preoperative computed tomography scanning and arthroscopy in predicting outcome after lateral retinacular release. Arthroscopy. 1992;8(3):327-34. [Medline].

17. McNally EG, Ostlere SJ, Pal C, et al. Assessment of patellar maltracking using combined static and dynamic MRI. Eur Radiol. 2000;10(7):1051-5. [Medline].

18. Brossmann J, Muhle C, Büll CC, et al. Evaluation of patellar tracking in patients with suspected patellar malalignment: cine MR imaging vs arthroscopy. AJR Am J Roentgenol. Feb 1994;162(2):361-7. [Medline]. [Full Text].

19. Mäenpää H, Lehto MU. Patellar dislocation. The long-term results of nonoperative management in 100 patients. Am J Sports Med. Mar-Apr 1997;25(2):213-7. [Medline].

20. Neptune RR, Wright IC, van den Bogert AJ. The influence of orthotic devices and vastus medialis strength and timing on patellofemoral loads during running. Clin Biomech (Bristol, Avon). Oct 2000;15(8):611-8. [Medline].

21. Shellock FG, Mink JH, Deutsch AL, Molnar T. Effect of a newly designed patellar realignment brace on patellofemoral relationships. Med Sci Sports Exerc. Apr 1995;27(4):469-72. [Medline].

22. Gilleard W, McConnell J, Parsons D. The effect of patellar taping on the onset of vastus medialis obliquus and vastus lateralis muscle activity in persons with patellofemoral pain. Phys Ther. Jan 1998;78(1):25-32. [Medline]. [Full Text].

23. Mohr KJ, Kvitne RS, Pink MM, Fideler B, Perry J. Electromyography of the quadriceps in patellofemoral pain with patellar subluxation. Clin Orthop Relat Res. Oct 2003;415:261-71. [Medline].

24. Earl JE, Schmitz RJ, Arnold BL. Activation of the VMO and VL during dynamic mini-squat exercises with and without isometric hip adduction. J Electromyogr Kinesiol. Dec 2001;11(6):381-6. [Medline].

25. Buchner M, Baudendistel B, Sabo D, Schmitt H. Acute traumatic primary patellar dislocation: long-term results comparing conservative and surgical treatment. Clin J Sport Med. Mar 2005;15(2):62-6. [Medline].

26. Arendt EA, Fithian DC, Cohen E. Current concepts of lateral patella dislocation. Clin Sports Med. Jul 2002;21(3):499-519. [Medline].

27. Sillanpää P, Mattila VM, Visuri T, Mäenpää H, Pihlajamäki H. Ligament reconstruction versus distal realignment for patellar dislocation. Clin Orthop Relat Res. Jun 2008;466(6):1475-84. [Medline].

28. Panagopoulos A, van Niekerk L, Triantafillopoulos IK. MPFL reconstruction for recurrent patella dislocation: a new surgical technique and review of the literature. Int J Sports Med. May 2008;29(5):359-65. [Medline].

29. Krause F, Kolling C, Brantschen R, Sieber HP. [Medium-term results after m. vastus medialis obliquus-plasty for lateral patellar dislocation] [German]. Orthopade. Jan 2006;35(1):94-101. [Medline].

30. Christoforakis J, Bull AM, Strachan RK, et al. Effects of lateral retinacular release on the lateral stability of the patella. Knee Surg Sports Traumatol Arthrosc. Mar 2006;14(3):273-7. [Medline].

31. Haspl M, cicak N, Klobucar H, Pecina M. Fully arthroscopic stabilization of the patella. Arthroscopy. Jan 2002;18(1):E2. [Medline].

32. Nam EK, Karzel RP. Mini-open medial reefing and arthroscopic lateral release for the treatment of recurrent patellar dislocation: a medium-term follow-up. Am J Sports Med. Feb 2005;33(2):220-30. [Medline].

33. Mäenpää H, Lehto MU. Surgery in acute patellar dislocation--evaluation of the effect of injury mechanism and family occurrence on the outcome of treatment. Br J Sports Med. Dec 1995;29(4):239-41. [Medline]. [Full Text].

34. Cossey AJ, Paterson R. A new technique for reconstructing the medial patellofemoral ligament. Knee. Apr 2005;12(2):93-8. [Medline].

35. Mikashima Y, Kimura M, Kobayashi Y, Asagumo H, Tomatsu T. Medial patellofemoral ligament reconstruction for recurrent patellar instability. Acta Orthop Belg. Dec 2004;70(6):545-50. [Medline].

36. Wu LS. Evaluation and manipulative therapy of patellar malalignment: a clinical review and preliminary report. J Manipulative Physiol Ther. Sep 1991;14(7):428-35. [Medline].

37. Brosseau L, Casimiro L, Robinson V, et al. Therapeutic ultrasound for treating patellofemoral pain syndrome. Cochrane Database Syst Rev. 2001;CD003375. [Medline]. [Full Text].

38. Atkin DM, Fithian DC, Marangi KS, et al. Characteristics of patients with primary acute lateral patellar dislocation and their recovery within the first 6 months of injury. Am J Sports Med. Jul-Aug 2000;28(4):472-9. [Medline].

39. Hinton RY, Sharma KM. Acute and recurrent patellar instability in the young athlete. Orthop Clin North Am. Jul 2003;34(3):385-96. [Medline].

40. Cash JD, Hughston JC. Treatment of acute patellar dislocation. Am J Sports Med. May-Jun 1988;16(3):244-9. [Medline].

41. Beaconsfield T, Pintore E, Maffulli N, Petri GJ. Radiological measurements in patellofemoral disorders. A review. Clin Orthop Relat Res. Nov 1994;308:18-28. [Medline].

42. Beasley LS, Vidal AF. Traumatic patellar dislocation in children and adolescents: treatment update and literature review. Curr Opin Pediatr. Feb 2004;16(1):29-36. [Medline].

43. BenGal S, Lowe J, Mann G, Finsterbush A, Matan Y. The role of the knee brace in the prevention of anterior knee pain syndrome. Am J Sports Med. Jan-Feb 1997;25(1):118-22. [Medline].

44. Bensahel H, Souchet P, Pennecot GF, Mazda K. The unstable patella in children. J Pediatr Orthop B. Oct 2000;9(4):265-70. [Medline].

45. Boden BP, Pearsall AW, Garrett WE Jr, Feagin JA Jr. Patellofemoral Instability: Evaluation and Management. J Am Acad Orthop Surg. Jan 1997;5(1):47-57. [Medline].

46. Brody LT, Thein JM. Nonoperative treatment for patellofemoral pain. J Orthop Sports Phys Ther. Nov 1998;28(5):336-44. [Medline].

47. Chapman MW, ed. Chapman's Orthopaedic Surgery. Vol 2. 3^rd ed. Baltimore, Md: Lippincott Williams & Wilkins; 1993.

48. [Best Evidence] Christiansen SE, Jakobsen BW, Lund B, Lind M. Isolated repair of the medial patellofemoral ligament in primary dislocation of the patella: a prospective randomized study. Arthroscopy. Aug 2008;24(8):881-7. [Medline].

49. Connolly JF. Fractures and Dislocations: Closed Management. Philadelphia, Pa: WB Saunders Co; 1995.

50. Eckstein F, Adam C, Sittek H, et al. Non-invasive determination of cartilage thickness throughout joint surfaces using magnetic resonance imaging. J Biomech. Mar 1997;30(3):285-9. [Medline].

51. Eckstein F, Schnier M, Haubner M, et al. Accuracy of cartilage volume and thickness measurements with magnetic resonance imaging. Clin Orthop Relat Res. Jul 1998;352:137-48. [Medline].

52. Elias DA, White LM. Imaging of patellofemoral disorders. Clin Radiol. Jul 2004;59(7):543-57. [Medline].

53. Fithian DC, Paxton EW, Cohen AB. Indications in the treatment of patellar instability. J Knee Surg. Jan 2004;17(1):47-56. [Medline].

54. Fulkerson JP. Alternatives to patellofemoral arthroplasty. Clin Orthop Relat Res. Jul 2005;436:76-80. [Medline].

55. Gagliardi JA, Chung EM, Chandnani VP, et al. Detection and staging of chondromalacia patellae: relative efficacies of conventional MR imaging, MR arthrography, and CT arthrography. AJR Am J Roentgenol. Sep 1994;163(3):629-36. [Medline]. [Full Text].

56. Grelsamer RP, Klein JR. The biomechanics of the patellofemoral joint. J Orthop Sports Phys Ther. Nov 1998;28(5):286-98. [Medline].

57. Grood ES, Suntay WJ, Noyes FR, Butler DL. Biomechanics of the knee-extension exercise. Effect of cutting the anterior cruciate ligament. J Bone Joint Surg Am. Jun 1984;66(5):725-34. [Medline].

58. Handelberg F, Shahabpour M, Casteleyn PP. Chondral lesions of the patella evaluated with computed tomography, magnetic resonance imaging, and arthroscopy. Arthroscopy. 1990;6(1):24-9. [Medline].

59. Handelberg F, Shahabpour M, Van Betten F, et al. CT arthrography and MRI of the patella. Acta Orthop Belg. 1989;55(3):331-8. [Medline].

60. Hawkins RJ, Bell RH, Anisette G. Acute patellar dislocations. The natural history. Am J Sports Med. Mar-Apr 1986;14(2):117-20. [Medline].

61. Holmes SW Jr, Clancy WG Jr. Clinical classification of patellofemoral pain and dysfunction. J Orthop Sports Phys Ther. Nov 1998;28(5):299-306. [Medline].

62. Ireland ML, Chang JL. Acute fracture bipartite patella: case report and literature review. Med Sci Sports Exerc. Mar 1995;27(3):299-302. [Medline].

63. King JB, Perry DJ, Mourad K, Kumar SJ. Lesions of the patellar ligament. J Bone Joint Surg Br. Jan 1990;72(1):46-8. [Medline]. [Full Text].

64. Kujala UM, Osterman K, Kormano M, et al. Patellofemoral relationships in recurrent patellar dislocation. J Bone Joint Surg Br. Nov 1989;71(5):788-92. [Medline]. [Full Text].

65. Leblanc JM. Patellar complications in total knee arthroplasty. A literature review. Orthop Rev. Mar 1989;18(3):296-304. [Medline].

66. Levine J. Chondromalacia patellae. Physician Sportsmed. 1979;7:41-9.

67. Lindberg U, Lysholm J, Gillquist J. The correlation between arthroscopic findings and the patellofemoral pain syndrome. Arthroscopy. 1986;2(2):103-7. [Medline].

68. Mangine RE, Eifert-Mangine M, Burch D, Becker BL, Farag L. Postoperative management of the patellofemoral patient. J Orthop Sports Phys Ther. Nov 1998;28(5):323-35. [Medline].

69. Miller MD, Hinkin DT, Wisnowski JW. The efficacy of orthotics for anterior knee pain in military trainees. A preliminary report. Am J Knee Surg. Winter 1997;10(1):10-3. [Medline].

70. Miller PR, Klein RM, Teitge RA. Medial dislocation of the patella. Skeletal Radiol. 1991;20(6):429-31. [Medline].

71. Moore KL. Clinically Oriented Anatomy. 3^rd ed. Baltimore, Md: Lippincott Williams & Wilkins; 1992.

72. Mow VC, Ateshian GA, Ratcliffe A. Anatomic form and biomechanical properties of articular cartilage of the knee joint. J Biomech Eng. 1991;113(2):198-207.

73. Mäenpää H, Lehto MU. Patellar dislocation has predisposing factors. A roentgenographic study on lateral and tangential views in patients and healthy controls. Knee Surg Sports Traumatol Arthrosc. 1996;4(4):212-6. [Medline].

74. Nissen CW, Cullen MC, Hewett TE, Noyes FR. Physical and arthroscopic examination techniques of the patellofemoral joint. J Orthop Sports Phys Ther. Nov 1998;28(5):277-85. [Medline].

75. Nomura E, Inoue M, Kurimura M. Chondral and osteochondral injuries associated with acute patellar dislocation. Arthroscopy. Sep 2003;19(7):717-21. [Medline].

76. Powers CM. Rehabilitation of patellofemoral joint disorders: a critical review. J Orthop Sports Phys Ther. Nov 1998;28(5):345-54. [Medline].

77. Powers CM, Shellock FG, Beering TV, et al. Effect of bracing on patellar kinematics in patients with patellofemoral joint pain. Med Sci Sports Exerc. Dec 1999;31(12):1714-20. [Medline].

78. Rauschning W, Nordesjö LO, Nordgren B. Isokinetic knee extension strength and pain before and after correction of recurrent patellar dislocation. Arch Orthop Trauma Surg. 1983;102(2):102-6. [Medline].

79. Sanders TG, Morrison WB, Singleton BA, Miller MD, Cornum KG. Medial patellofemoral ligament injury following acute transient dislocation of the patella: MR findings with surgical correlation in 14 patients. J Comput Assist Tomogr. Nov-Dec 2001;25(6):957-62. [Medline].

80. Schonholtz GJ, Zahn MG, Magee CM. Lateral retinacular release of the patella. Arthroscopy. 1987;3(4):269-72. [Medline].

81. Shellock FG. Effect of a patella-stabilizing brace on lateral subluxation of the patella: assessment using kinematic MRI. Am J Knee Surg. Summer 2000;13(3):137-42. [Medline].

82. Shellock FG. Patellofemoral joint abnormalities in athletes: evaluation by kinematic magnetic resonance imaging. Top Magn Reson Imaging. Sep 1991;3(4):71-95. [Medline].

83. Tecklenburg K, Dejour D, Hoser C, Fink C. Bony and cartilaginous anatomy of the patellofemoral joint. Knee Surg Sports Traumatol Arthrosc. Mar 2006;14(3):235-40. [Medline].

84. Wessel LM, Scholz S, Rüsch M. Characteristic pattern and management of intra-articular knee lesions in different pediatric age groups. J Pediatr Orthop. Jan-Feb 2001;21(1):14-9. [Medline].

Keywords

patellar injury and dislocation, patellofemoral dysfunction, patellofemoral dislocation, patella subluxation, patellofemoral joint dysfunction, patellofemoral joint syndrome, patellofemoral pain, patellofemoral pain syndrome, PFPS, patellofemoral stress syndrome, PFSS, kneecap injury, dislocated kneecap, knee pain, knee injury, knee dislocation, dislocated knee, patella fracture, knee fracture

Contributor Information and Disclosures

Author

Gerard A Malanga, MD, Founder and Director, New Jersey Sports Medicine Institute; Director of Pain Management, Overlook Hospital; Director of Sports Medicine, Sports Medicine Fellowship Director, Mountainside Hospital; Clinical Chief, Rehabilitation Medicine and Electrodiagnosis, St Michael's Medical Center; Medical Director, Consultant, Horizon Healthcare Worker's Compensation Services, Blue Cross and Blue Shield Worker's Compensation
Gerard A Malanga, MD is a member of the following medical societies: Alpha Omega Alpha, American Academy of Physical Medicine and Rehabilitation, American College of Sports Medicine, North American Spine Society, and Physiatric Association of Spine, Sports and Occupational Rehabilitation
Disclosure: Nothing to disclose.

Coauthor(s)

Brian F White, DO, Staff Physician, Department of Physical Medicine and Rehabilitation, Kessler Institute for Rehabilitation, University of Medicine and Dentistry of New Jersey
Brian F White, DO is a member of the following medical societies: American Academy of Physical Medicine and Rehabilitation, American Osteopathic Association, and Wilderness Medical Society
Disclosure: Nothing to disclose.

Wah Sang Lee, DO, MS, Staff Physician, Department of Physical Medicine and Rehabilitation, New Jersey Medical School/Kessler Institute of Rehabilitation
Wah Sang Lee, DO, MS is a member of the following medical societies: American Osteopathic Association
Disclosure: Nothing to disclose.

Thomas Agesen, MD, Assistant Clinical Professor, Department of Physical Medicine and Rehabilitation, UMDNJ, New Jersey Medical School; Consulting Staff, Mountainside Hospital, Summit Overlook Hospital
Thomas Agesen, MD is a member of the following medical societies: American Academy of Physical Medicine and Rehabilitation, American College of Sports Medicine, and Physiatric Association of Spine, Sports and Occupational Rehabilitation
Disclosure: Nothing to disclose.

Medical Editor

Andrew L Sherman, MD, MS, Associate Professor of Clinical Rehabilitation Medicine, Vice Chairman, Chief of Spine and Musculoskeletal Services, Program Director, SCI Fellowship and PMR Residency Programs, Department of Rehabilitation Medicine, Leonard A Miller School of Medicine, University of Miami
Andrew L Sherman, MD, MS is a member of the following medical societies: American Academy of Physical Medicine and Rehabilitation, American Association of Neuromuscular and Electrodiagnostic Medicine, American College of Sports Medicine, American Medical Association, American Paraplegia Society, American Spinal Injury Association, and Association of Academic Physiatrists
Disclosure: Nothing to disclose.

Pharmacy Editor

Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicine
Disclosure: Nothing to disclose.

Managing Editor

Russell D White, MD, Professor of Medicine, Department of Community and Family Medicine, University of Missouri-Kansas City School of Medicine, Truman Medical Center Lakewood
Disclosure: Nothing to disclose.

CME Editor

Jon B Whitehurst, MD, Clinical Instructor of Surgery, University of Illinois College of Medicine; Partner and Executive Board Member, Rockford Orthopedic Associates; Orthopedic Chairman, Rockford Memorial Hospital
Jon B Whitehurst, MD is a member of the following medical societies: American Academy of Orthopaedic Surgeons, American Orthopaedic Society for Sports Medicine, and Arthroscopy Association of North America
Disclosure: Nothing to disclose.

Chief Editor

Craig C Young, MD, Professor, Departments of Orthopedic Surgery and Community and Family Medicine, Medical Director of Sports Medicine, Sports Medicine Fellowship Director, Medical College of Wisconsin
Craig C Young, MD is a member of the following medical societies: American Academy of Family Physicians, American College of Sports Medicine, American Medical Society for Sports Medicine, Phi Beta Kappa, and Wilderness Medical Society
Disclosure: Nothing to disclose.

© 1994- by Medscape.
All Rights Reserved
(http://www.medscape.com/public/copyright)