eMedicine Specialties > Physical Medicine and Rehabilitation > Lower Limb Musculoskeletal Conditions

Patellofemoral Syndrome

Author: Patrick J Potter, BSc, MD, FRCP(C), Associate Professor, Physical Medicine and Rehabilitation, The University of Western Ontario; Consulting Staff, Department of Physical Medicine and Rehabilitation, St Joseph's Health Care Centre
Coauthor(s): Keith AJ Sequeira, MD, Associate Director of Spinal Cord Medicine, Assistant Professor, Department of Physical Medicine and Rehabilitation, Parkwood Hospital, University of Western Ontario
Contributor Information and Disclosures

Updated: Jul 15, 2009

Introduction

Background

Patellofemoral syndrome (PFS) is characterized by a group of symptoms that are easily diagnosed and often respond to simple management. The common presentation is knee pain in association with positions of the knee that result in increased or misdirected mechanical forces between the kneecap and femur.¹ Ironically, as simple as its presentation is, lack of consensus on the fundamental factors associated with PFS remains. Accordingly, synonyms for the syndrome go in and out of fashion. No agreement exists on the exact pathophysiology, but significant work is being completed on the extent and direction of the associated forces on the patella, as well as on the tracking and alignment of the patella.

Pathophysiology

While theories regarding the pathophysiology of patellofemoral syndrome vary, identification of the resultant forces involved in dynamic and static knee positions has been fundamental to the research on this syndrome. Factors believed to contribute to production of retropatellar pain include impairments affecting the patellofemoral joint interface. Such impairments may be a consequence of an unbalanced muscle pull, malalignment between the joint surfaces, excessive knee valgus (ie, increased Q-angle) resulting in increased lateral forces, and quadriceps contractures causing production of excessive leverage forces on the patellofemoral joint surface. Excessive use of the joint, either in frequency of loading or excessive loading, also contributes to the symptoms.

Frequency

United States

Patellofemoral syndrome is common in the United States, especially among physically active persons.

International

Patellofemoral syndrome has an estimated prevalence rate of 20% in student populations.

Mortality/Morbidity

Morbidity associated with patellofemoral syndrome is directly proportional to the activity level of the patient. Curtailing physical activities that place unnecessarily stressful demands upon the patellofemoral articulation may be necessary (preferably while substituting other activities into the exercise program).

Race

No racial predilection has been identified for patellofemoral syndrome.

Sex

Patellofemoral syndrome more frequently affects females than males.

Age

Patellofemoral syndrome occurs most frequently in adolescents and young adults.

Clinical

History

• Knee pain is the most common presentation of patellofemoral syndrome.
  • The pain characteristically is located behind the kneecap (ie, retropatellar) and most often manifests during activities that require knee flexion and forceful contraction of the quadriceps (eg, during squats, ascending/descending stairs).
  • Pain may worsen in intensity, duration, and rapidity of onset if the aggravating activity is performed repeatedly.
  • Pain may be exacerbated by sitting with the knee flexed for a protracted period of time, such as while watching a movie, hence leading to the terms "theatre sign" and "movie-goer's knee." Patients with this condition often may prefer to sit at an aisle seat, where they may more frequently keep the knee extended.
• Symptoms often occur during the activity, such as playing volleyball for 30 minutes, or may occur later after the activity has been completed.
• Sometimes symptoms manifest as late as the next day.

Physical

Physical examination of a patient with patellofemoral syndrome should include examination of the musculoskeletal system, including the following² :

• The upper and lower body should be examined to exclude generalized diseases that make up the differential diagnoses (eg, osteoarthritis).
• The usual physical findings are localized around the knee.
• Tenderness often is present along the facets of the patella. The facets are most accessible to palpation by manipulation of the patella while the knee is fully extended and the quadriceps muscle is relaxed. Manual positioning of the patella medially, laterally, superiorly, and inferiorly allows for palpation of the respective facets.
• An apprehension sign may be elicited by manually fixing the position of the patella against the femur and having the patient contract the ipsilateral quadriceps.
• Crepitus may be present, but if present in isolation, crepitus does not allow for definitive diagnosis.
• Determine the Q-angle by measuring the angle between the tibia and femur. Use the attachment of the patella to the patellar tendon as the intersection point.
• Examination of gait may demonstrate excessive foot pronation, excessive knee valgus, or an antalgic gait pattern.
• Repetitive squatting may reproduce knee pain.
• Use the physical examination and historical details to help exclude other diagnoses.
• Examination of the contralateral limb is equally important, as the syndrome often is bilateral. However, one side usually manifests more symptoms.
• Palpation of the tibial tuberosity may detect tenderness suggesting that other impairments also are present.
• Determining the bulk of the vastus medialis is possible, because it is situated superficially and has little overlying tissue. Bulk may be observed by direct visualization during contraction. The vastus medialis is believed to be the most active muscle in the last 15° of resisted knee extension, making this the best arc of movement for assessing its strength.
• Genu recurvatum and hamstring weakness may contribute to the occurrence of PFS, and therefore, identifying such impairments may aid in the choice of management.

Causes

The potential causes of patellofemoral syndrome remain controversial and are therefore more appropriately referred to as associated factors.¹ Overuse, overloading, and misuse of the patellofemoral joint seem to be the cornerstone factors on which most authors agree.

• Search for CME/CE on This Topic »

• Limping Child (Orthopedic Surgery)
• Patellofemoral Arthritis (Orthopedic Surgery)

• Foot, Ankle, Knee, and Hip Center
• Arthritis Center
• Bone Health Center
• Knee Pain Introduction

• Supervised Exercise Therapy May Be Helpful for Patellofemoral Pain Syndrome
• ACSM 2009: Exercise Improves Patellofemoral Pain

• Palliation of Patellofemoral Pain: A Review of Treatment Techniques