Range of Extension Correlates with Posterior Capsule Length after Knee Remobilization

Knee injuries are common in sports, and postinjury immobilization is often required to protect healing tissues and alleviate pain, but both the injury and the immobilization can lead to a knee contracture. Knee flexion contractures limit performance. Previous research has identified posterior knee capsule fibrosis as a contributor to immobility-induced knee flexion contractures. This study aims to measure posterior knee capsule length at various durations of remobilization after knee immobilization and to correlate with the recovery of knee range of motion.

Two hundred fifty-nine male Sprague-Dawley rats had one knee extra-articularly immobilized in flexion with a Delrin® plate at a 45° angle for one of six durations: 1, 2, 4, 8, 16, or 32 wk, followed by spontaneous remobilization after plate removal, which lasted zero, one, two, and four times the duration of immobilization. The contralateral knees served as controls. The posterior knee capsule length was measured by histomorphometry. These measures were correlated with previously published range of motion data from the same cohort of specimens.

Knees immobilized for 1 and 2 wk partially recovered posterior capsule length (P > 0.05). Knees immobilized beyond 2 wk failed to recover posterior capsule length, irrespective of the duration of remobilization (P < 0.05). The residual posterior capsule shortening correlated with the lack of knee extension (P < 0.003).

For knee injuries requiring more than 2 wk of immobilization, unassisted remobilization will not restore posterior knee capsule shortening and the reduction in knee extension. These results support the role of the posterior capsule in knee joint contracture and the need to minimize the duration of immobility and to assist the recovery of the range of knee extension after a sport injury.