Content area
Abstract
This study examines the question of how increased tension affects the biomechanical, biochemical and histological properties of both normal and healing medial collateral ligaments. Medial collateral ligaments (MCL) in the left hindlimb of rabbits were subjected to increased tension by placing a stainless steel pin perpendicularly underneath the distal end of the ligament at the time of operation. Transected MCL in another set of rabbits were allowed four weeks of healing before the addition of the s.s. pin. Six or twelve weeks postoperation, all ligaments were subjected to biomechanical testing which included quantitative measurements of the in-situ stresses and strains and cyclic tensile tests. The stress-strain results were represented by a pseudo-strain energy function and material constants were determined. The material constants for control and experimental MCL's were then compared statistically. Samples were also analyzed for total collagen content and the ratio of the Schiff base cross-link dihydroxylysinonorleucine (DHLNL) to that of hydroxylysinonorleucine (HLNL).
The results demonstrated that the increase in ligament tension did not change the normal varus-valgus knee joint laxity. However, the comparison of material constants from the derived constitutive equation showed that, at six weeks, the stress-strain curves for MCL which had undergone the increased stress regimen had significant changes such that there was a lower stress for a given strain compared to the control. At twelve weeks, though, this trend had reversed showing a significant improvement in stress-strain properties.
For the healing group, no experimental knee achieved normal varus-valgus joint laxity. Knees which had a transected MCL had a value over twice that of the control knee at six weeks post-operation. With the addition of the tension pin this value was reduced to 1.5 times the control. At twelve weeks, the addition of the pin resulted in no statistical differences between control and experimental knees. With regard to the stress-strain curves (or mechanical properties), the best results relative to the control side were achieved by the twelve week group with the addition of the tension pin. These MCL had the highest stress for a given strain compared to any other experimental group. Qualitative histological improvements were seen which included a more longitudinal arrangement of collagen fibers and decreased cellularity. (Abstract shortened with permission of author.)
