Contact pressures in chondromalacia patellae and the effects of capsular reconstructive procedures.

We measured patellofemoral contact areas and pressures using pressure sensitive film in ten human cadaver knees exhibiting degenerative lesions of patellar cartilage. We studied a flexion range from 20 degrees to 90 degrees and compared contact pressures before and after capsular reconstructive procedures. With an intact, normal capsule, localized lesions of grade I-II exhibited a 50% reduction in pressure (from 3.4 +/- 0.7 MPa to 1.6 +/- 0.9 MPa) directly over the lesion. Grade III-IV lesions exhibited a loss of contact pressure greater than 90%. This reduction in pressure appears to result from a loss of stiffness in the low-grade cartilage lesions and from a loss of cartilage thickness in higher grade lesions. Highly localized peak pressures were also observed on the normal cartilage bordering the lesions. Capsular reconstructive procedures (medial plication, lateral plication, lateral release, and bilateral release) did not result in consistent pressure reductions or in the creation of more uniform pressure distributions. In particular, lateral capsular release, a popular surgical procedure, resulted in no change in three knees and four different pressure patterns in the other seven knees.