An examination of the mechanism of ligament contracture.

It has been proposed that the mechanism of ligament contraction involves conversion of fibroblasts to a contractile form similar to the phenomenon recently documented in wound contraction. In this study rat knees were surgically immobilized in flexion and a sham operation was performed on the contralateral knees. Mechanical studies revealed that the flexion contracture increased rapidly for two weeks. The anterior cruciate ligaments (ACL) were contracted and contributed to the flexion contractures. Histologic studies of the ACL showed no increase in the cellularity of the contracted ligaments. In the contracted ligaments, staining for the contractile protein actin was heavy. Previous transmission electron microscopy studies have demonstrated fibroblast cytoplasm in processes far from the visible cell body and it is hypothesized that this cytoplasm was responsible for increased actin staining away from the visible cell body. This study supports the concept that ligament fibroblasts, modulated to a form containing increased quantities of the contractile protein actin, play an active role in the contraction of ligamentous tissue.