eMedicine Specialties > Emergency Medicine > Trauma & Orthopedics

Knee Injury, Soft Tissue

Author: David B Levy, DO, FACEP, FAAEM, Chairman, Department of Emergency Medicine, St Elizabeth Health Center; Associate Professor of Emergency Medicine, Northeastern Ohio Universities College of Medicine
Coauthor(s): Howard I Dickey-White, MD, Teaching Attending Physician, Department of Internal Medicine, St Elizabeth Hospital Medical Center; June E Sanson CNRP, MSN, Nurse Practitioner, Take Care Health Systems
Contributor Information and Disclosures

Updated: Dec 12, 2008

Introduction

Background

Soft tissue injuries of the knee are some of the most common and clinically challenging musculoskeletal disorders in patients presenting to the ED. Annually, more than 1 million emergency department visits and 1.9 million primary care outpatient visits are for acute knee pain. Therefore, establishing clear-cut diagnostic and therapeutic objectives for these injuries is important.

Knee pain and related symptoms may derive from damage to 1 or more of the soft tissue structures that stabilize and cushion the knee joint (including the ligaments, muscles, tendons, and menisci), from infection to the knee joint or surrounding structures, or from trauma to the bones forming the joint. In addition to the etiology of the patient's presenting complaint, it is important to determine the acuity of the pathologic process as an acute traumatic or infectious event or exacerbation of a chronic overuse or degenerative syndrome.

Accurate and timely diagnosis increases the likelihood of fully restoring normal and pain-free use of the affected knee. For most patients, the severity of the etiology and the injury or pathologic process, acute or chronic, can be determined from a targeted history, focused physical examination, and thoughtful workup including diagnostic imaging (eg, plain radiography).

Pathophysiology

To understand the various injury patterns associated with trauma to the knee, it is important to appreciate the anatomy (see Media file 1).

Two separate but interdependent joints forming the knee are the tibiofemoral articulation and the patellofemoral coupling. Weight-bearing forces, up to 5 times an individual's body weight, are transmitted through the opposing condyles of the femur and the tibia. Two shock-absorbing cartilaginous menisci interpose between the femur and the tibia, forming the largest synovial joint in the body. The medial meniscus is smaller and more fixed than the lateral meniscus; these features predispose it to injury. A fibrous capsule lined by a synovial membrane also surrounds and bolsters the knee joint but does not contribute to the inherent stability of the joint.

Fitness of the knee joint depends largely on the fortifying ligaments and muscles binding together the femur, tibia, and patella. Two sets of knee ligaments are frequently affected. The first set, lying outside of the knee joint proper, are the extracapsular collateral ligaments. These ligaments consist of the medial collateral ligament (MCL), which opposes extreme abductive and/or valgus forces, and its counterpart, the lateral collateral ligament (LCL), which limits excessive adductive and/or varus pressures. The second set, crisscrossing in the knee joint, are the anterior cruciate ligament (ACL) and the posterior cruciate ligament (PCL), which individually brace against excessive translation in the anteroposterior (AP) plane. The ACL serves as the primary knee stabilizer, preventing forward displacement of the tibia on the femur.

Formed primarily by the quadriceps muscles, the extensor apparatus envelops and stabilizes the patella. At its distal aspect, the quadriceps muscle consolidates into the patellar ligament, ultimately inserting onto the tibial tubercle. Several bursae envelop the knee, including the prepatellar, superficial and deep infrapatellar, and pes anserine bursae, which permit friction-free movement between the various structures. Acute trauma or repetitive occupational stress may incite inflammation, with infection and metabolic disorders (eg, gout) being less common etiologies. Inflammation of the bursa then leads to localized tenderness, erythema, and increased warmth. Extensive bursae in this area alleviate potentially damaging frictional forces between the susceptible structures. Fixed in the back of the knee joint, in the popliteal fossa, are vital neurovascular structures, including the popliteal artery.

Definitions and grades of sprains and strains

Sprains to the knee are characterized by the stretching or tearing of noncontractile structures, such as the investing ligaments or of the joint capsule itself, whereas a strain refers to stretching or severing along the course of muscles or tendons. Both collateral- and cruciate-ligament sprains, as well as muscular strains, are relatively common. Ligamentous (sprain) and muscular (strain) injuries may be classified according to the degree of impairment.

• Grade I sprain - Stretching but no tearing of the ligament, local tenderness, minimal edema, no gross instability with stress testing, firm end point
• Grade II sprain - Partial tears of the ligaments, moderate local tenderness, mild instability with stress testing (but firm end point), moderately incapacitating
• Grade III sprain - Complete tear, discomfort with manipulation but less than expected for degree of injury, variable amount of edema (ranging from negligible to grossly conspicuous), clear instability with stress testing (expressing a mushy end point), severe disability

Specific injuries

• ACL injury: Rupture of the ACL is among the most serious of the common knee injuries and results from a variety of mechanisms. Most patients with ACL damage complain of immediate and profound pain, exacerbated with motion, and inability to ambulate. Disruption of the ACL may occur alone or with other knee injuries, especially a meniscal injury or tear of the MCL.
• PCL injury: Patients typically report falling on a flexed knee or sustaining a direct blow to the anterior aspect of the knee (eg, when the knee strikes the dashboard in a motor vehicle accident). PCL harm signifies a major injury and rarely occurs as an isolated injury.

Frequency

United States

Knee pain is a complaint in up to 20% of the general adult population, accounting for almost 3 million outpatient and emergency department visits per year. Trauma to the knee is the second most common occupational accident. The MCL is the most frequently injured ligament in the knee. ACL damage causes the highest incidence of pathologic joint instability.

In National Collegiate Athletic Association (NCAA) football, 1 major knee injury occurs per team every year. Sports-related activity accounts for approximately 60% of knee injuries producing ligamentous laxity.

International

As in the United States, the incidence of knee injuries is increased in countries where sporting activities, such as skiing, soccer, and basketball, are popular.

Mortality/Morbidity

• Patients receiving inappropriate or ill-timed care of knee dislocations may have undue morbidity (eg, amputation) due to vascular complications in the distal leg.
• Oversight of the magnitude of soft tissue injuries of the knee may result in a failure to expeditiously consider compartment syndrome and its resultant complications, including loss of a limb.
• Misdiagnosis or mismanagement of damage to supporting structures of the knee may lead to chronic knee instability with subsequent development of degenerative joint disease and/or loss of knee function, including but not limited to an inability to bear weight or ambulate.

Sex

• Disorders of the patella and lateral meniscus are generally more common in girls and women than in boys and men. Recent studies also suggest that females are more prone to ACL injuries, which is believed to be due to the fact that the female ACL is both structurally weaker and has a relatively smaller cross sectional diameter.
• Chondromalacia patellae or patellar malalignment syndrome (ie, premature erosion and degeneration of patellar cartilage) predominates in young women.
• Larsen-Johansson disease of the patella, also known as inferior pole patellar chondropathy, is 9 times more prevalent in boys and men than in girls and women, especially in boys aged 10-14 years.

Age

• Ligamentous and meniscal injuries are most likely in young- to middle-aged adults, whereas children and adolescents are most susceptible to osseous damage. Most patients with a meniscal tear are aged 20-30 years, but a second peak occurs in patients older than 60 years. Meniscal injuries are rare in children younger than 10 years with morphologically normal menisci.
• In general, knee dislocations arise from high-energy trauma, such as motor vehicle accidents. The epidemiology of injury follows that of car accidents; therefore, patients tend to be young men.
• Overall, 18.1% of US men and 23.5% of US women aged 60 years and older reported knee pain on most days for 6 weeks prior to their medical examination. Additionally, elderly patients may sustain fractures after minimal trauma that typically produces only soft tissue injuries in younger patients.
• The region of the extensor mechanism susceptible to disruption is correlated with the patient's age. The older the patient, the more proximal the area of rupture. Disruption of the quadriceps tendon most often occurs in elderly patients, whereas more distal severance of the patellar tendon and avulsion of the tibial tubercle occurs in younger patients.

Clinical

History

Confirm that an acute traumatic event occurred. Document mechanism of injury, type and location of pain (ie, ask the patient to point to area of pain), associated symptoms, amount of immediate dysfunction, presence and onset of joint swelling, and history of past knee problems. Verify that the cause of the knee problem is mechanical by establishing that pain is exacerbated by movement (eg, walking, climbing, jumping). Inquire about ability to bear weight on the affected limb.

• Mechanism of injury
  • Knowledge of the mechanism can help in predicting which structures may be injured.
  • Determine the circumstances, such as the position of the extremity, whether the foot was anchored to the ground, if the forces were direct or indirect, and the specific details of the injury (eg, direction, magnitude, torque of impact).
  • Direct blows and valgus or varus contact may provoke injury to the contralateral collateral ligaments, fractures to the epiphyseal plates in children with open growth plates, and patellar dislocation.
  • Pure valgus forces, such as those occurring when a football player is struck on the lateral aspect of the knee, are more common than varus-directed contact.
  • The MCL is more prone to injury than the LCL.
  • A combination of valgus or varus stress, whether direct or indirect, delivered to a rotated leg accounts for a wide array of injuries.
  • Vulnerable structures include the collateral and cruciate ligaments, the menisci, and the joint capsule.
    • Consider the intricate damage to the knee of a skier who catches the inside edge of a ski, diverting the tip outward as the body continues to advance forward. This action produces torque, forcing the knee into extreme valgus and external tibial rotation.
    • Depending on the magnitude of the force, this mechanism may tear the MCL, the posteromedial capsule, the lateral meniscus, and the ACL.
  • Rupture of the ACL is among the most serious of the common knee injuries and results from a variety of mechanisms. ACL tears are more common than PCL tears by a ratio of at least 9:1.
    • Most patients with ACL damage complain of immediate and profound pain that is exacerbated with motion and an inability to ambulate.
    • Most patients report a snapping or popping sensation or sound at the time of injury.
    • An acute knee injury heralded by a pop or snap, followed by a rapidly evolving effusion, almost always affirms a rupture of the ACL.
    • Disruption of the ACL may occur alone or with other knee injuries, especially a lateral meniscal injury or tear of the MCL.
    • ACL tears are associated with anterior blows that hyperextend the knee, excessive noncontact hyperextension of the knee, and extreme deceleration forces to the knee.
  • Patients with PCL tears typically report falling on a flexed knee or sustaining a severe direct blow to the anterior aspect of the knee (eg, when the knee strikes the dashboard in a motor vehicle accident).
    • This injury patter displaces the tibia backward and pulls apart the PCL.
    • Patellar injury with disruption of normal articulation or fracture may also result.
    • Look for abrasions, contusions, or lacerations over the knee region.
    • Onset of edema and pain tends to occur within the first 3 hours after injury.
    • PCL harm signifies a major injury and rarely occurs as an isolated injury.
  • Rotational movements may cause a meniscal tear. The most common types of injuries are bucket-handle or flap tear where only one portion has torn free. Given that the medial meniscus is more firmly fixated and attached to the MCL capsule, it is more vulnerable to injury. Menisci are without pain fibers; the tearing and bleeding into peripheral attachments, as well as the traction on the joint capsule, causes discomfort.
• Instability
  • Decide if the patient is describing true instability, characterized by an aberrant displacement of the osseous components of the knee. (The patella dislocates laterally on the femur, or the tibia slides excessively forward in an ACL-deficient knee.)
  • Such terms as giving way or slippage usually denote instability. Buckling tends to be associated with a different phenomenon, often resulting from pain or muscle weakness of the quadriceps.
• Pain
  • Determine if the pain is acute or chronic in nature.
  • Abrupt onset of anterior knee pain with inability to bear weight indicates damage to the extensor mechanism.
  • Acute pain confined to the proximity of medial or lateral regions of the knee joint tends to result from ligamentous and/or meniscal damage.
  • Recent onset of pain at the posteromedial corner of the knee indicates a tear of the medial meniscus or an expanding or ruptured Baker cyst. Menisci are without pain fibers; it is the tearing and bleeding into peripheral attachments as well as the traction on the joint capsule that causes discomfort.
  • Tumors are characterized by chronic pain that is worse at night.
  • Discomfort from bursitis and/or tendinitis is likely to be chronic and bilateral, it is typically worse with rising or walking after sitting than at other times, and it is provoked by prolonged exercise or use.
• Knee effusion
  • The rapidity of onset of knee effusion may corroborate a particular diagnosis. Effusion onset within 6 hours supports the assumption of a cruciate ligament tear, articular fracture, or knee dislocation, whereas delayed edema occurs with meniscal injuries.
  • Nearly one half of patients with an acute ligament rupture have localized edema at the site of injury.
  • Complete ligamentous or capsular disruption can give rise to less-than-anticipated swelling if fluid exudes through the tear. Recurrent knee effusion after activity is consistent with a meniscal injury.
  • Localized distension may originate from bursitis (prepatellar bursitis), meniscal cystic changes, outgrowth of a popliteal cyst (Baker cyst), or dilation of an artery (popliteal-artery aneurysm).
• Locking
  • True locking manifests as a knee joint that is unable to move, usually at 45° of flexion; patients cannot bend further without assistance. It may arise from tears in the meniscus, detached tissue lodging in the knee joint, injury of the cruciate ligament(s), or an osteochondral fracture.
  • Pseudolocking may result from pain and muscle spasm secondary to increasing edema.
  • On occasion, locking of the knee is confused with giving way of the knee. Giving way of the knee may accompany ACL injuries, quadriceps weakness, or patellar disorders.
  • Acute traumatic weakness of the knee often follows a derangement of the extensor mechanism of the knee. Clinically significant atrophy of the quadriceps may appear as early as within 1 week of disuse.
• Degree of immediate dysfunction: Injuries, including meniscal tears, patellar subluxation, or ligament strains or ruptures, may not entirely preclude a patient from bearing weight.
• History of previous knee problems: Knee dislocation can occur after a total joint arthroplasty of the knee. One disastrous complication of a recurrent dislocation of total knee arthroplasty is vascular compromise resulting in an above-knee amputation.

Physical

Developing a standard routine to avoid omitting important aspects of the knee joint examination is important.

• When performed by properly trained physicians, the physical examination is reasonably sensitive (74-81%) for detecting meniscal, ACL, PCL, and collateral ligament injuries. However, accurate examination becomes difficult with greater elapsed time because of swelling secondary to bleeding and inflammation.
• Ensure adequate exposure of both lower extremities, from the groin to the toes, and examine the patient in a supine position. It is important to compare the symptomatic knee to the contralateral, normal knee joint.
• Attempt to alleviate the patient's fears, and convince the patient to relax as much as possible during palpation and during stress testing of the injured knee joint.
• Examine the uninjured knee first to approximate baseline values and to allow the patient to understand what will be done to the injured knee.
• Focus the initial examination on inspection, palpation, and neurovascular evaluation. In the event of a suspected knee dislocation, any discrepancy in distal pulses compared to the unaffected leg, or an ankle-brachial index less than 0.8, an arteriogram is needed to rule out a vascular injury.
• Begin distal to the injury. If possible, observe the patient standing and/or walking.
  • A grossly antalgic gait indicates a clinically significant problem with 1 or both lower limbs.
  • When an uninjured patient stands with feet together, the medial aspects of both knees and ankles are normally in contact.
• Inspect the knee for edema, ecchymosis, effusion, masses, patella location and size, muscle mass, erythema, and evidence of local trauma, such as abrasions, contusions, or lacerations. Carefully check for a communication of a skin defect with the underlying knee joint (eg, open intra-articular injury).
• The knee appears ordinarily hollow on either side of the patella and slightly indented just above the patella.
  • Small accumulations of fluid cause these gaps to swell.
  • Large effusions are most conspicuous above the patella, where the joint cavity is most spacious.
  • Classify the edema as localized (bursal) or generalized (intra-articular).
  • Ballottement of the patella assists the examiner in detecting an effusion (see Media file 2). With the dominant hand superior to the patella, compress the tissues (and possibly fluid) inferiorly. Maintain pressure with the hand in this position. Next, apply downward compression to the patella. In the normal knee with minimal joint fluid, the patella moves directly onto the femoral condyle. In the knee with a large effusion the patella is floating, and ballottement results in the patella tapping against the femoral condyle; this is noted in the fingertips.

• Swelling of the infrapatellar fat pad may result from premenstrual fluid retention, causing pain on knee extension. This condition is referred to as fat-pad syndrome and must be differentiated from patellar tendonitis, or superficial or deep patellar bursitis.
• Confirm the position of the patella.
  • A superiorly displaced patella (patella alta) may accompany a disruption of the patellar ligament, while a breach of the quadriceps tendon might cause an inferior position of the patella (patella baja).
  • If time permits and it is relevant to the patient's complaint, measure the Q angle which is calculated by drawing a line from the tibial tubercle to the center of the patella and then from the center of the patella to the anterior superior iliac spine. Any angle exceeding 15° may make the patella vulnerable to subluxation or dislocation.
• Conspicuous atrophy of the quadriceps muscles indicates the presence of a long-standing or preexisting disorder. Atrophy of the vastus medialis muscle commonly follows surgical repair of the knee.
• Inspect and palpate the popliteal fossa; this evaluation is best performed with the patient prone.
  • The only palpable structure in this space is ordinarily the popliteal artery.
  • Abnormal bulges may derive from popliteal-artery aneurysms, popliteal thrombophlebitis, or Baker cysts. A Baker cyst originates from a herniation of the synovial membrane through the posterior aspect of the joint capsule, and tends to be associated with intra-articular disease. Rupture of a Baker cyst with subsequent dissection of the synovial fluid results in a clinical picture often indistinguishable from that of thrombophlebitis of the calf.
• Palpation
  • Palpate the knee in slight flexion. This position is facilitated by placing a pillow under the popliteal fossa. Direct palpation at specific areas.
  • Tenderness strictly confined to the joint line suggests a meniscal tear.
  • The Bragard sign indicates a medial meniscus injury. It refers to point sensitivity along the medial aspect of the joint line. The tenderness intensifies with internal rotation and extension of the tibia.
  • Additional clinical clues suggestive of meniscal disease are the first and second Steinmann signs and the Payr sign.
    • With the patient supine and the hip and knee flexed to 90° the examiner vigorously and quickly rotates the tibia internally and externally. Pain in the lateral compartment with forced internal rotation indicates a lateral meniscus lesion. Medial-compartment pain during forced external rotation indicates a lesion of the medial meniscus. Test for a second Steinmann sign when the point of tenderness is most pronounced along the anterior joint line. When the examiner moves the knee from extension into flexion, the meniscus is displaced posteriorly, and the point of tenderness is displaced from the anterior joint line back towards the collateral ligaments. This maneuver helps in differentiating meniscal injuries from ligamentous problems, as ligament pain does not shift with flexion.
    • Test for Payr sign with the patient sitting cross-legged and exerting downward pressure along the medial aspect of the knee. Medial knee pain indicates a posterior horn lesion of the medial meniscus.
  • Damage to the MCL may reveal tenderness along the entire course of the ligament.
    • The tenderness can be present from the origin on the medial femoral condyle to its tibial insertion.
    • Tenderness of the MCL limited to the insertion or origin can occur with avulsion-type fracture.
  • A damaged LCL may be tender from its attachment on the lateral femoral epicondyle to its insertion on the fibular head.
  • Placing the knee in slight flexion with the patient supine optimizes palpation of the MCL and improves LCL evaluation by positioning the affected knee in a figure 4 arrangement.
  • A positive patellar apprehension sign implies a preceding patellar dislocation.
    • With the leg held and supported in 30° of flexion, apply a firm, laterally directed force toward the medial aspect of the patella. A positive test manifests as trepidation on the patient's part, such as grabbing for the examiner's arm when pressure is applied.
    • Tenderness or edema about the medial retinaculum is associated with spontaneously reduced patellar dislocation.
  • Quadriceps rupture
    • Palpate the anterior aspects of both thighs, particularly noting any muscle wasting.
    • A rupture in the quadriceps commonly emerges just proximal to the tibia, revealing a transverse tract more pliable than the surrounding musculature. The extent and completeness of the tear correlates with the size of the defect. This palpable defect above the patella is known as the gap test or sulcus sign.
  • Bursal injuries
    • Palpate the clinically significant bursae accordingly.
    • Prepatellar bursitis (ie, housemaid's knee) presents with tenderness, erythema, warmth, and swelling superficial to the patella, and does not usually restrict ROM of the knee.
    • With superficial infrapatellar bursitis, tenderness is present over the tibial tubercle and can be confused with Osgood-Schlatter disease, as tenderness and edema at the site where the infrapatellar bursa inserts into the tibial tubercle accompanies this disease.
    • The deep infrapatellar bursa is located under the patellar tendon (separating it from the underlying fat pad and tibia). When inflamed, it causes pain during active ROM, but no pain during passive flexion-extension.
    • Located between the pes anserine tendon and MCL, inflammation of this bursa (anserine bursitis) causes marked tenderness approximately 5 cm below the medial joint line. Pain is often times worst at night and particularly pronounced when the patient walks up stairs or rises from a sitting position. Anserine bursitis may be mistaken for an injury to the MCL.
    • Bursitis can be distinguished from an intra-articular injury by both location of the pain and the fact that movement of the joint itself should not cause discomfort (up to the point of skin tension).
  • In children, be sure to palpate the epiphyses, as growth plate injuries may be confused with soft-tissue injuries.
  • Patellar tendonitis or jumper's knee is an overuse syndrome caused by repetitive actions presenting with localized tenderness along the superior or inferior aspects of the patella. Pain increases with active resistance against extension.
  • Traumatic prepatellar neuralgia presents with persistent, intense point tenderness over the middle or outer borders of the patella. The pain may be exacerbated even with the slight pressure of clothing.
  • Discrete tenderness over the lateral femoral epicondyle (approximately 3 cm above the lateral joint line) is seen with iliotibial band tendonitis. Soft tissue swelling and crepitus may also be present. Pain is most pronounced with weight bearing on a flexed knee and occurs most commonly in long-distance runners.
• ROM testing
  • Evaluate the knee for active flexion and extension. Inability to extend the knee to any extent implies damage to the extensor mechanism.
  • Clinically significant effusions may hinder complete extension of the knee joint and may be incorrectly identified as locking of the knee.
• Stress testing
  • Assess knee joint stability by applying various stresses to the joint.
  • Clarify the examination by employing a standard routine and directing gentle firm pressure, rather than applying sudden forceful manipulation, causing reflexive contraction of adjacent muscles.
  • Excessive joint motion (laxity) indicates an injury.
  • The appearance of a soft or mushy end point versus the healthy hard (ie, abrupt increase in joint stiffness) end point implies possible ligament damage.
  • Assess the quantity and the quality of translation, comparing the injured knee to the unaffected side. Side-to-side differences in knee translation hold greater significance than absolute measurements of motion.
  • Characterize knee joint unsteadiness by the direction of tibial displacement. For example, medial knee instability means that the tibia moves abnormally away from the femur on the medial side.
  • Assess the collateral stability in 30° flexion and in full extension. Position the patient supine with the thigh resting on the edge of the examination table and support the foot. The MCL is assessed by applying valgus stress to the knee. The LCL is assessed by applying varus stress to the knee.
    • Provide valgus stress by pressing with 1 hand on the lateral aspect of the knee; with the other hand, direct the ankle laterally, attempting to open the knee joint on the medial side.
    • Inducing a substantial gap in the medial aspect of the knee joint implies impairment of the MCL.
    • Increased laxity of the medial side of the knee with the knee in extension indicates additional damage to posterior structures, such as the posterior joint capsule and the PCL.
    • Test for lateral knee joint stability by reversing the hand positions.
    • Push medially upon the knee and laterally against the ankle (varus stress), trying to open the knee joint on the lateral side.
    • Gapping of the knee joint may be visible and palpable.
    • A difference in the degree of lateral knee tautness when comparing the affected knee to the uninjured side indicates disruption of the LCL.
    • Lateral instability with the knee extended suggests injury to the LCL and the lateral capsule, as well as likely damage to the ACL or the PCL.
    • Relieving stress on the injured knee when following testing for collateral ligament impairment may provoke a clunking sensation.
  • The Lachman maneuver confirms ACL integrity.
    • This maneuver is the most sensitive bedside test, about 87% for ACL tear (see Media file 3).

• Place the patient supine and flex the knee 20-30°.
• With 1 hand, grasp and stabilize the patient's thigh just above the patella. With the opposite hand, try to dislodge the proximal tibia forward.
• In patients with large thighs, the position may need to be modified. Position the large thigh of the patient over the knee of the examiner. Push downward on the patient's femur with one hand, while the other hand grasps the proximal tibia and attempts to move it anteriorly.
• Damage to the ACL manifests as excessive forward motion of the tibia without a firm end point.
• If viewed from the lateral aspect, the natural concave silhouette of the knee, extending from the tibial tubercle to the superior aspect of the patella, obliterates when ACL damage occurs.
• Anterior drawer testing also evaluates the soundness of the ACL (see Media file 4).

• Place the patient in the supine position, flex the hip to 45°, and bend the knee to 90° with the patient's foot planted firmly on the examination table.
• Sitting on the dorsum of the foot, place both hands behind the knee.
• Once the hamstrings appear relaxed, discreetly try to displace the proximal leg anteriorly.
• The anterior drawer test is less sensitive for ACL damage than the Lachman maneuver.
• Posterior drawer testing is done in a similar manner to anterior drawer testing, except that the pressure is directed backward on the proximal tibia.
  • Posterior instability arising from PCL injury manifests as an abnormal increase in posterior tibial translation.
  • Confusion may occur when trying to distinguish whether abnormal translation of the tibia on the femur originates from excessive ACL or PCL laxity.
  • Unless the examiner knows prior to testing that the resting position of the tibia is shifted posteriorly, anterior drawer testing may yield a false perception of instability.
• To distinguish disorders of the ACL from those of the PCL, employ the tibial sag test.
  • Flex the patient's hips and knees to 90° while supporting the patient's heels.
  • In this position, the PCL impaired knee will clearly sag backward from the effects of gravity (also referred to as the Godfrey sign).
• The pivot-shift test helps substantiate capsular tears and injury to the ACL (see Media file 5).

• Elicit by lifting the tibia of the affected side. If the ACL is impaired, the tibia subluxates anteriorly during knee extension.
• In addition, apply a moderate valgus stress while flexing the knee.
• As the knee joint approaches 20-40° of flexion, an abrupt jerking movement occurs in the ACL-impaired knee, indicating a reduction in prior anterior subluxation.
• McMurray testing substantiates meniscal disorders (see Media file 6).

• With the patient supine and the knee in maximum flexion, palpate the posteromedial margin of the affected knee joint with one hand and support the foot with the opposite hand.
• Externally rotate the lower leg as far as possible, affix varus pressure, and cautiously extend the knee joint.
• If a tear is present in the medial meniscus, an audible, palpable, and painful clunk transpires, as the femur passes over the damaged portion of the meniscus.
• To check the lateral meniscus, repeat the above technique, but place one hand over the posterolateral aspect of the knee joint and internally rotate the lower leg to its maximum extent.
• Slowly extend the leg again, listening and feeling for a click or pop, and observe the patient for distress.
• Clicks unassociated with pain or joint-line tenderness, especially during lateral meniscus testing, may represent a normal variant and should not be interpreted as evidence of a meniscal tear.
• Unfortunately, the McMurray test is neither sensitive nor specific for meniscal damage.
• Another method for establishing the soundness of the menisci, especially the posterior horn of the menisci, is the Apley compression or grind test (see Media file 7).

• Place the patient in the prone position and flex the knee to 90°.
• Stabilize the patient's thigh against the examination table with the knee of the examiner, and apply a downward-directed force onto the patient's foot and leg.
• Rotate the leg, while mildly flexing and extending the knee joint. Any pain in the joint should be noted, as well as any resonance or irritation emanating from the knee.
• Two additional tests recently cited in the literature are the Thessaly test and Ege's test.
  • Advocates of the Thessaly test state it is a safe and reliable method to detect meniscal injuries. The Thessaly test is performed with the patient standing first on the good leg, and then on the symptomatic leg, with the knee in 5 degrees of flexion and again with the knee in 20 degrees of flexion. Next, the patient rotates the body internally and externally 3 times, and the test is considered positive if there is joint line discomfort and/or a sense of locking or catching.
  • To perform the Ege's test, the patient assumes a squatting position with the lower extremities held in maximum external rotation (to detect a medial meniscal tear) and repeated in maximum internal rotation (to detect a lateral meniscal tear). Pain and/or an audible click during the maneuver are consistent with a positive test.

Causes

The intrinsic structural framework of the knee and its exposure to the environment account for particular injuries.

• Harm may arise from direct impact, such as in contact or collision sports or blows to the knee connected to motor vehicle accidents.
• Most soft-tissue injuries sustained by the knee do not, however, involve direct trauma but arise from actions producing excessive torque on the knee joint, especially those activities involving twisting, rapid deceleration, or landing from a jump.
• If tensile forces placed on the knee exceed the intrinsic tone of the ligaments, injury to the ligaments results.
• Low-intensity forces may provoke a reversible injury, with only transient deformation of the elastic ligament; however, profound loads applied to the knee joint produce irreversible rupture of the ligament fibers.
• Valgus-directed blows sustained by the externally rotated knee occur commonly.
• High-intensity impact to the lateral side of the knee tends to be serious and befalls skiers when catching a ski tip or football players following a blind-side clipping type of injury.
• Valgus contact injuries may cause a series of injuries to the knee, including a tear of the MCL, followed by damage to the posterior medial capsule, and, finally, damage to the ACL. This combination of injuries is referred to as O'Donahue or unhappy triad.
• An intense varus stress to the knee joint gives rise to a sequence of injuries, depending on the position of the knee.
• Impact to the medial side of the knee in a neutral position causes disruption of the LCL, the iliotibial band, and/or the biceps femoris.
• Profound varus strain to the extended and internally rotated knee harms not only the LCL and the ACL, but also may mar the PCL and the lateral posterior capsule.
• Undue varus stress to the flexed and internally rotated knee brings about LCL injury, proceeding to damage of the lateral posterior capsule and/or lateral meniscus and, if extreme, impairment of the PCL.
• Extensor-mechanism injuries result from direct or indirect forces.
  • Direct injuries result from a blow to the anterior aspect of the knee, often causing the patella to fracture.
  • Indirect injury occurs when forced flexion of the knee occurs against a contracted quadriceps.
  • Depending on the patient's age and the type of force applied, disruption of the extensor mechanism can occur by means of quadriceps tendon tear, patellar fracture, rupture of the patellar tendon, or avulsion of the tibial tuberosity.
  • Many conditions have been reported to be associated with rupture of the quadriceps tendon including hyperparathyroidism, chronic renal failure, gout, obesity, leukemia, rheumatoid arthritis, diabetes, systemic lupus erythematosus, steroid use (both local injection and systemic use), and fluoroquinolone use. A considerable delay may exist between the administration of a fluoroquinolone and the spontaneous rupture of a tendon.
  • Bilateral simultaneous ruptures of the quadriceps tendon are rare, but they have been reported numerous times in the literature. In one series of bilateral quadriceps rupture, 41 (65%) were attributed to falls or missteps, and 22 (35%) occurred spontaneously while the patient was walking.
• Patients with meniscal injuries frequently report pain after twisting (rotational force) their knee while bearing weight on the affected side.
• Imposing extreme hyperextension force may disrupt the cruciate ligaments, conceivably anywhere along their span.
• ACL tears
  • Rupture of the ACL is among the most serious of the common knee injuries and results from a variety of mechanisms.
  • ACL tears are associated with anterior blows that hyperextend the knee, excessive noncontact hyperextension of the knee, and extreme deceleration forces to the knee.
  • Disruption of the ACL may occur alone or with other knee injuries, especially a meniscal or MCL tear.
• PCL tears
  • Patients typically report falling on a flexed knee or sustaining a direct blow to the anterior aspect of the knee (eg, when the knee strikes the dashboard in an motor vehicle accident).
  • PCL harm signifies a major injury and rarely occurs as an isolated injury.

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