LIGAMENT TENSION AFFECTS NUCLEAR SHAPE IN-SITU - AN IN-VITRO STUDY

This study was carried out to test the hypothesis that a relationship exists between ligament tension and ligament cell geometry. Rabbit kne e joints were positioned at 70 degrees of joint flexion and the medial collateral ligament (MCL) was mechanically isolated and the femur-MCL -tibia complex was stretched or compressed by displacing the crosshead of a materials testing machine: -2.0 mm (relative compression), 0.0 m m (a reproducible no-load starting point), +0.7 mm or +1.4 mm (relativ e tension). Each MCL complex was then fixed immediately in 10% neutral buffered formalin. Contralateral knees were dissected similarly with MCLs exposed and fixed in situ at 70 degrees of flexion. Subsequent to histological processing, measurements were made of the profiles of fi brocyte nuclei (since previous work has shown that nuclear shape close ly approximates fibrocyte shape) that were located in the central port ion of each MCL midsubstance using a video-based computerized morphome try system. Results showed that the dimensions of nuclei in the midsub stance of experimental MCLs were significantly longer and thinner at c rosshead displacements that corresponded to increased ligament tension . At +1.4 mm of displacement fibrocyte nuclei were approximately 4 mu m longer and 1 mu m thinner than those fixed at 0.0 mm, an observation supported by a statistically significant increase in the mean maximum -to-minimum-diameter ratio and a significant decrease in mean cell rou ndness. These results strongly suggest that mechanical load can direct ly affect ligament fibrocyte geometry in sim. If a similar phenomenon also occurs in vivo, the metabolism of ligament fibrocytes may be infl uenced considerably by their loading history.