Although often referred to as patellar tendonitis, a more accurate description of ''Jumper's knee,'' based on histologic studies, is of overuse tendinopathy. This is the most common tendinopathy in skeletally mature athletes, occurring in up to 20% of jumping athletes. Jumper's knee primarily affects the proximal posterior fibers of the patellar tendon and is a cause of significant functional disability in professional and recreational athletes . Biomechanically, to squat and land softly from a jump, the quadriceps muscle lengthens in eccentric contraction and creates high tension on the patellar tendon. Patellar tendinopathy occurs secondary to repetitive microtrauma caused by tendon overload without adequate repair. This overuse can lead to pain, tenderness, swelling, and decreased performance.
Most commonly, an athlete will present with anterior knee pain of insidious onset that is aggravated by activity (jumping, squatting, kneeling, and going down stairs). Symptoms can range from pain after activity to pain that persists
Fig. 2. Sinding-Larsen-Johannsen Syndrome (SLJS). There is fragmentation of the distal aspect of the patella, consistent with SLJ syndrome in the right clinical setting.
throughout an activity. Many individuals experience no decrease in performance, while severely affected individuals may suffer a substantial decrease in athletic ability. On physical examination, localized tenderness over the inferior patella/proximal patellar tendon is commonly found .
Imaging of patellar tendinopathy remains somewhat controversial. Radiographs are occasionally useful in identifying ossification of the tendon or associated osseous abnormalities, but ultrasonography and MRI are the modalities of choice for diagnosis. Ultrasonography, the accepted modality in much of Europe, demonstrates lower pole irregularity, fragmentation, chondral changes, and thickening of the tendon insertion at the patella . Ultrasound evaluation of tendinopathy is quite dependent on equipment and operator experience. MRI also demonstrates tendon thickening with increased signal particularly on spin-echo and gradient-echo imaging. T2-weighted imaging best demonstrates partial tears with high signal intensity in the area of injury. Although the exact modality of choice for evaluation of this condition is debatable, ultrasound and MR have both been proven effective (Fig. 3) .
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