History
Knee pain is the most common presentation of patellofemoral syndrome (PFS). 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, shortly thereafter, or sometimes even the following day.
PFS is also known as "runner's knee" or "biker's knee," as PFS is highly associated with running and biking.
Patellofemoral weight bearing increases with knee flexion as follows:
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Walking - 0.5 times body weight
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Ascending or descending stairs - 3.3 times body weight
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Squatting - 6 times body weight
Physical
Physical examination of a patient with patellofemoral syndrome should include examination of the musculoskeletal system, including the following [4] :
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The upper and lower body should be examined to exclude generalized diseases that make up the differential diagnoses (eg, osteoarthritis).
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The usual physical findings are localized around the knee.
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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.
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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.
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Crepitus may be present, but if present in isolation, crepitus does not allow for definitive diagnosis.
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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.
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Examination of gait may demonstrate excessive foot pronation, excessive knee valgus, or an antalgic gait pattern.
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Repetitive squatting may reproduce knee pain.
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Use the physical examination and historical details to help exclude other diagnoses.
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Examination of the contralateral limb is equally important, as the syndrome often is bilateral. However, one side usually manifests more symptoms.
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Palpation of the tibial tuberosity may detect tenderness suggesting that other impairments also are present.
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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.
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Genu recurvatum and hamstring weakness may contribute to the occurrence of patellofemoral syndrome, and therefore, identifying such impairments may aid in the choice of management.
A literature review by Arazpour et al found that compared with healthy subjects, persons with patellofemoral syndrome tend to have the following [5] :
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Reduced gait velocity
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Reduced cadence
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Decreased knee extensor moment in association with the loading response and terminal stance
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Delayed peak rear foot eversion in association with gait
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Increased hip adduction
The reports used in the review differed as whether hip rotation in patellofemoral syndrome increased, decreased, or remained the same.
Causes
The potential causes of patellofemoral syndrome remain controversial and are therefore more appropriately referred to as associated factors. [2] Overuse, overloading, and misuse of the patellofemoral joint seem to be the cornerstone factors on which most authors agree.
In a 2011 study of high school running athletes, the results suggest that stronger preinjury hip abductors and weaker preinjury hip external rotators are linked to PFS development. Also, patients exhibiting PFS seem to lose hip abduction and external rotation strength in comparison with their preinjury strength. A higher hip external-to-internal rotation strength ratio was found to possibly protect against PFS development. [6]
