BUTCHER, M.T.*; BERTRAM, J.E.A.; BENZUIDENHOUT, A.J.; Florida State University, Tallahassee; Florida State University, Tallahassee; College of Veterinary Medicine, Cornell University, Ithaca, NY: Putative role of the collateral ligaments of the distal sesamoid bone in Equus

The distal forelimb of the horse displays a complexity of ancillary ligaments. For some of these the function is known, but for many the function is not clear. From their anatomical arrangement, it was hypothesized that the collateral ligaments of the distal sesamoid bone provide passive support for the pastern joint during limb loading. To test this hypothesis six forelimbs were removed from three horses and placed in a materials testing frame (hoof flush with base plate) and underwent trials of compression while force and video records were taken. Trials compared loading with collateral ligaments of the distal sesamoid bone intact and after cutting (transverse plane) at the level of the pastern joint. Compressive force data were combined with kinematic records of angular changes in the three distal-most limb segments: metacarpus (3MC), phalanx 1 (P1) and phalanx 2 (P2). Kinematics were corrected relative to angular excursions of the 3MC segment and normalized. Angular profiles were characterized using 2nd order polynomial coefficients and these were used to test for statistical differences between the intact and cut trials. Analysis showed the collateral ligaments of the distal sesamoid bone prevented flexion of the pastern joint during compressive loading. Pastern flexion was evident in cut trials and suggests that the collateral ligaments act as lever arms to facilitate dorsal rotation of the P2 and P3 (hoof) and ensure the digit elements rotate in unison with limb loading.