Objective: Jumper's knee, or chronic patellar tendinitis, can be a source of considerable pain in athletes. The changes that occur with shearing of the tendinous fibers from repeated microtrauma can progress to significant degeneration and increase the risk of tendon rupture. In order to better understand this phenomenon, a correlative study relating the MR imaging and pathologic findings was performed.
Subjects and methods: Nine high-performance athletes 18-22 years old (mean age, 20 years) underwent operation of 11 knees for long-standing jumper's knee. The average period of symptoms was 3 years (range, 2 to 6 years). MR knee examinations were performed before surgery in all athletes. The symptoms, MR findings, and pathological findings were correlated.
Results: There was focal thickening in the proximal one third of the patellar tendon (range, 9-16 mm; mean, 12 mm) in all 11 knees, involving the medial portion of the tendon in 10 and the center in one. On proton-density-weighted MR images, all knees demonstrated a focus of abnormal signal intensity in the proximal one third of the patellar tendon. On T2-weighted MR images, 10 knees demonstrated abnormal signal intensity; eight were isointense to that seen on proton-density-weighted images, and two were relatively hyperintense. Ten tendons demonstrated a poorly defined posterior margin. Pathologically, the areas of abnormal signal intensity corresponded to tissue containing tenocyte hyperplasia, prominent angiogenesis with endothelial hyperplasia, loss of longitudinal collagenous architecture, and microtears with collagen fiber separation. Hyaline degeneration was present in specimens from every patient.
Conclusion: In athletes with chronic patellar tendinitis, areas of abnormal signal intensity on MR imaging corresponded to degenerative pathologic changes consistent with angiofibroblastic tendinosis. In nearly all patients, the tendon thickening occurred eccentrically. Disproportionate medial tendon thickening may be related to unequal tensile forces across the knee joint, resulting in greater stress on the medial portion of the extensor mechanism of the knee.