Injury size affects long-term strength of the rabbit medial collateral ligament

Long-term effects (104 weeks) of 2 extremes of gap size on the mechanical behavior of the rabbit medial collateral ligament were examined. In the midsubstance of each right medial collateral ligament, either an 8 mm gap injury was created or a 4 mm Z plasty injury was created and repaired. Each group was subdivided into a healing interval of 40, 78, or 104 weeks. Femur-medial collateral ligament-tibia complexes were tested mechanically or examined with light microscopy. Both injuries healed with histologically similar tissue and showed improved mechanical behavior 78 weeks after injury. No further improvement was measurable 104 weeks after injury. Scar material properties remained markedly inferior to normal regardless of injury. Low load and viscoelastic behavior recovered relatively well regardless of gap size. However, gap injuries showed significantly inferior structural properties at all intervals. These results suggest that a large initial gap between ligament ends in the extraarticular space predisposes scars to long term structural weakness. If this principle is true clinically, then patients with large gaps between torn ligament ends (caused by displacement, folding, or retraction) may function well at lower loads, but they may be chronically at greater risk of reinjury at high loads.