Evaluation of the medial soft-tissue restraints of the extensor mechanism of the knee.

TLDR

The study aimed to determine the relative contributions of medial soft‑tissue restraints to preventing lateral patellar displacement. Anatomical dissection and biomechanical testing of 25 fresh‑frozen knee specimens were performed to rank the soft‑tissue restraints by their force contribution to lateral patellar displacement. The medial patellofemoral ligament provided the largest restraint (≈53 % of total force), the patellomeniscal ligament and deep capsular retinacular fibers contributed about 22 %, and the patellotibial band was functionally insignificant.

Abstract

We performed an anatomical dissection of the medial soft-tissue retinacular fibers that restrain lateral patellar displacement and found that the medial patellofemoral ligament inserts not only on the patella but also on the undersurface of the distal aspect of the quadriceps mechanism. The deep capsular layer contained substantial retinacular fibers that were associated with the medial patellomeniscal ligament. Functional studies of the relative contributions of the medial soft-tissue restraints in the prevention of lateral patellar displacement were also performed. Twenty-five fresh-frozen specimens of the knee, obtained after amputations (nineteen specimens) or from cadavera (six specimens) were tested biomechanically on a universal testing instrument. We ranked the soft-tissue restraints, in order of their relative contributions to the restraining force, on the basis of the percentage of force provided by the retinacular and ligamentous tissue that resisted the lateral displacement of the patella. The medial patellofemoral ligament, although varying in size and importance, was found to be the major medial soft-tissue restraint that prevented lateral displacement of the distal knee-extensor mechanism, contributing an average of 53 per cent of the total force. The patellomeniscal ligament and associated retinacular fibers in the deep capsular layer of the knee, which were previously thought to be functionally unimportant in the stabilization of the patella, contributed an average of 22 per cent of the total force. The previously described retinacular fibers (the patellotibial band) were functionally unimportant in the prevention of lateral displacement.