Reason for performing the study: To identify potential functional-anatomical characteristics of the cranial horn attachment of the medial meniscus (MM) that may help explain the pathogenesis of the common tear patterns that have been reported.
Hypothesis: Full extension of the stifle generates a significant increase in tensile forces within the cranial meniscotibial ligament (CrMTL) of the MM, which may predispose this structure to injury.
Methods: The effect of femorotibial angle (160°, 150°, 140° and 130°) on tensile forces in the axial and abaxial components of the CrMTL was examined in 6 mature cadaver stifles using an implantable force probe. Three additional specimens were used to examine the histological structure of the CrMTL and its connection to the cranial horn of the MM.
Results: Full extension of the stifle (160°) resulted in a significantly greater tensile force in the abaxial component of the CrMTL when compared with the axial component (P = 0.001). The tensile force in the abaxial component of the CrMTL increased significantly between 150° and 160° of stifle extension (P = 0.011). The CrMTL appears to be comprised of 2 functional components, which become more visually distinct as the stifle is extended. Histologically, these components are separated by a cleft of highly vascularised, less organised connective tissue, which becomes less prominent at the junction of the ligament and the cranial horn of the MM.
Conclusion: A 4-fold difference in the tensile forces in the 2 functional components of the CrMTL of the MM was observed with full extension of the stifle.
Potential relevance: The functional anatomy of the CrMTL may place this region at greater risk of injury during hyperextension of the stifle and, therefore, may provide a mechanistic rationale for the commonly reported meniscal tear patterns in the horse.