Observations on the anatomy and pathology of the palmar intercarpal ligaments in the middle carpal joints of thoroughbred racehorses.

Ten carpi from juvenile Thoroughbred horses were dissected in detail to record the anatomy of the palmar intercarpal ligaments (PICLs). These were found not to be substantially attached to the palmar carpal ligament. The lateral PICL was sited at the convergence of the palmar aspects of the third, fourth, intermediate and ulnar carpal bones and aligned predominantly in a proximodistal direction. The medial PICL had a large origin distally on the lateral aspect of the radial carpal bone (Cr) and attached to third (C3) and second (C2) carpal bones with apparently separate fibre orientations. Fibres between Cr and C3 aligned obliquely from dorsoproximomedial to palmarodistolateral which corresponds to the direction of movement of Cr relative to C3 during carpal extension. Video recordings of arthroscopic evaluations of 67 middle carpal joints of juvenile Thoroughbred horses in race training were reviewed retrospectively and the osteochondral and ligamentous pathology visible in each recorded. Damage to the Cr-C3 part of the medial PICL was present in 47 (70%) joints and, in 6 joints, comprised complete rupture of this branch. A significant (P < 0.001) relationship was found between the presence of remodelling of the dorsodistal margin of Cr and the severity of ligament damage. It is considered that the orientation of fibres of the Cr-C3 branch of the MPICL is consistent with a putative role to alternate forces borne by Cr and C3 during axial loading of the limb and that the injuries of this structure seen in young racehorses may represent a fatigue-type pathology analogous to that seen concurrently in the related osteochondral tissues.