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The effect of immobilization on ligamentous healing and strength of the medial collateral ligament of the rat knee Pisesky, Wayne Anthony


The purpose of this study was to determine the effects of varying periods of immobilization on ligamentous healing and strength in a rat experimental model. Sixty-one mature male Wistar rats were used. The left knee medial collateral ligament was surgically exposed, divided, and repaired. The rats were randomly placed into one of four groups: Group A, no immobilization, Group B, 2 weeks' immobilization, Group C, 6 weeks' immobilization, and Group D, 10 weeks' immobilization of the operated limb. The right knee served as a control. The ligaments were studied histologically and biomechanically at 2 weeks, 6 weeks, 10 weeks and 20 weeks post-operatively. Histologic samples were objectively evaluated with the light microscope using a Maturity Index Score and Scale that were devised based on the numbers and orientation of the fibroblasts and the amount and orientation of the collagen fibres. Ligament-bone preparations were studied using an Instron material testing machine to determine the biomechanical properties of the ligament until failure. Utilizing the Maturity Index Score and Scale, it was shown that Group A, with no immobilization, matured more rapidly than the other groups, and achieved full maturity at 20 weeks post-operatively. The other groups all showed a retarded rate of healing while immobilized. The electron microscopic study supported this data by demonstrating the level of metabolic activity of the fibroblasts which decreased with increasing maturity and by demonstrating that the size, amount and orientation of the collagen fibers increased with mobilization. The biomechanical testing showed that at 2 weeks post-operative, Group A had achieved a strength which was 46% of controls while Group B was only 29% of controls (p = 0.055). At 6 weeks Group A was 65% of controls, Group B was 56% of controls and Group C was 39% of controls (p = 0.0004). At 20 weeks Group A was 83% of controls, Group B was 71% of controls, Group C was 66% of controls and Group D was 48% of controls (p = 0.0005). Group A was 71% stronger than Group D at this time, indicating that the healing medial collateral ligament attained a greater strength and histologically matured more rapidly if mobilization is begun immediately.

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