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Definition and Epidemiology

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Idiopathic anterior knee pain has been described by various other terms (Table 27-1). It refers to nonspecific, vague, mostly activity-related anterior knee pain and is the most common cause of knee pain in adolescents. Anterior knee pain has been reported in half of adolescent athletes at some time.

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Table 27-1. Synonyms for Anterior Knee Pain
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Mechanism

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Many factors have been postulated to contribute to the development of anterior knee pain in adolescents (Table 27-2).1–4 Intense physical activity overloading the patellofemoral mechanism (Figure 27-1) appears to be the most consistent factor leading to the development of anterior knee pain. The patellofemoral unit provides the mechanism for knee extension and deceleration. The stability of the patella in the femoral groove is provided by the surrounding soft tissue attachments and the bony supporting structures (Figure 27-2). Malalignment and abnormal tracking of the patella have been postulated to contribute to anterior knee pain. Vastus medialis obliquus plays an important role in stabilizing the patella in the femoral groove and its proper tracking. A chondromalacia patella is a pathologic diagnosis indicating softening and erosion of the cartilage of the patellofemoral joint; in some athletes, it is a cause of severe anterior knee pain.2

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Table 27-2. Factors Postulated to Contribute to Anterior Knee Pain
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Figure 27-1
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Patellofemoral mechanism. Patellofemoral mechanism provides the basis for effective knee extension. During the movement of the knee from flexion to extension there is increasing patellofemoral compression force.

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Figure 27-2
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Soft tissue patellofemoral stabilizers.

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Clinical Presentation

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The young active athlete presents with either acute or gradual onset anterior knee pain affecting one or both knees, usually seen following a recent increase in physical activity. The pain is increased after prolonged sitting (theater sign), ascending or descending stairs, and repeated squatting exercises. Usually, the pain has been present for few weeks with intermittent activity-related exacerbations and improvement with a period of rest. Deterioration of sports performance because of increased frequency and worsening of the pain, leads the athlete to seek medical attention. The athlete may give a history of the knee catching, pseudolocking, ...

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