Effect of Sequential Removal of Parts of the Second Metacarpal Bone on the Biomechanical Stability of the Equine Carpus

Objective To quantify changes in biomechanical stability and stiffness within the equine carpus after removal of 50%, 80%, and 100% of the second metacarpal bone ( MC 2). Study Design In vitro biomechanical study. Methods Cadaveric equine forelimbs (n = 16) were evaluated. Intact constructs were loaded in axial compression from 0 to 5000 N and compression + torsion (5000 N ± 20°) for 5 cycles. This was repeated after removal of 50%, 80%, and 100% of MC 2. The primary biomechanical outcome variables were the compressive stiffness and compressive + torsional stiffness of the carpus. Relative kinematic motion was also evaluated between the second carpal bone ( C 2) and the radial carpal bone ( RC ), C 2 and the third metacarpal bone ( MC 3) and C 2 and the third carpal bone ( C 3). Results A significant decrease in compressive + torsional stiffness was found after 100% removal of MC 2. Compressive stiffness of the carpus did not change after 100% MC 2 removal. A significant increase in relative rotation around the z‐axis (rotation around the long axis) was observed for C 2 versus MC 3 and C 2 versus C 3 when 100% of MC 2 was removed as compared to 80%, 50%, and 0% removal. No significant difference in relative rotation between C 2 and RC was detected. Conclusions The biomechanical results reported here suggest that the torsional stability of the equine carpus is significantly decreased only after complete resection of MC 2.