Healing of the medial collateral ligament following a triad injury: A biomechanical and histological study of the knee in rabbits

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Abstract
The effect of a partial medial meniscectomy and anterior cruciate ligament (ACL) transection on medial collateral ligament (MCL) healing was studied in skeletally mature rabbits. Two groups of animals, group I (isolated MCL rupture) and group II (MCL rupture with ACL transection and partial medial meniscectomy), were examined. At 6 and 12 weeks postoperatively, histological examination of the healing MCL and biomechanical evaluation of the varus-valgus (V–V) knee rotation and tensile properties of the femur-MCL-tibia complex (FMTC) were performed. Group II animals experienced substantial joint degeneration by 6 weeks. Progressive osteophyte formation was observed adjacent to the MCL insertions along with proximal migration of the MCL tibial insertion between 6 and 12 weeks. Histologic examination of the healing MCL substance from both groups showed disorganized collagen, inflammation, and fibroblast proliferation that decreased over time. For group II knees, the V–V knee rotation was found to be significantly elevated (4.7 to 5.2 times the contralateral control), and did not decrease with time. In contrast, the V–V knee rotations of the group I specimens were 1.8 times greater than control immediately following injury, and approached control values by 12 weeks. Tensile testing of the FMTCs revealed that the ultimate load increased with time for both groups, but group I had significantly higher values than group II. The linear stiffness in group I was not different than that group II and did not increase with time. For the mechanical (material) properties of the healed MCL substance, the modulus of the healing tissue for group II was only 40% that of group I. The structural properties of the FMTC and the mechanical properties of the MCL substance from both groups at 6 and 12 weeks were significantly different from the contralateral controls. We further demonstrated that immediately after ACL reconstruction, the V–V rotation of group II knees could be restored to group I levels. Recent clinical studies of MCL healing following isolated complete ligament tears have suggested that nonoperative management without immobilization leads to excellent treatment outcome. However, in more severe injuries involving additional tissues, poor quality of the healed ligament tissue and articular degeneration are observed. Our results demonstrate the deleterious effects of an untreated triad injury on the healing of the MCL substance and its insertions. Examination of the MCL substance suggests that a much larger healing mass is formed following a triad injury, which partially compensates for inferior ligament mechanical properties. Therefore, this study indicates that alternative methods may be necessary to optimize MCL healing following a triad injury. Future studies will determine the consequences of such approaches.