The effects of initial end contact on medial collateral ligament healing: a morphological and biomechanical study in a rabbit model.

In this investigation, the effect of initial end contact on medial collateral ligament (MCL) healing was studied in the rabbit model. Sixty-eight 1-year-old New Zealand white rabbits were separated into two groups. In one group, a 4 mm saggital Z-plasty was performed in the right MCL midsubstance (contact group), and in the other group, an analogous 4 mm midsubstance segment was removed (gap group). Left knees were unoperated to serve as internal contralateral MCL controls. Animals had unrestricted cage activity until sacrifice in groups of eight at 3, 6, 14, and 40 weeks postoperatively. Early results demonstrated that contact and gap injuries healed with what appeared to be scar tissue both morphologically and biomechanically. In both groups, laxities recovered to their contralateral values within 6 weeks and biomechanical viscoelastic behaviors recovered to 68-92% of contralaterals by 14-40 weeks. Despite these similarities, contacts showed morphological and biomechanical evidence of improved healing over gaps. Contact scars remodeled more quickly, recovered laxity more quickly, and were generally closer to contralaterals than gaps in terms of their structural strength, stiffness, and material behaviors, after 40 weeks of healing. With the exception of appearances and failure stress, all measured properties of contact healing MCLs were statistically indistinguishable from contralateral MCLs at 40 weeks of healing. These advantages of contact healing in this model support speculations that there are differences in the early rate and possibly in the later quality of ligament healing when cut rabbit MCL ends are in proximity. Longer-term studies to define end points and mechanisms of healing are required.