Injuries to the Distal Skeleton in Sporting Dogs - Carpus

The carpus is a complex joint, consisting or four rows of bones. Three joint levels are present: the antebrachiocarpal joint between the distal end of the radius and ulna and the proximal row of carpal bones, contributing for the 70% of the carpal motion, the middle carpal joint is between the proximal and distal row of carpal bones that contribute to the 25 % of total carpal motion and the carpometacarpal joint between the distal row of carpal bones and the bases of the metacarpal bones that contribute only for a 5 % of the motion. The carpal joint is a complex ginglymus that allows movements of extension, flexion, intra and extra rotation, a minimum of valgus, varus and a few millimeters of translation in palmaro dorsal direction. Several ligaments join the various bones at different levels, the dorsal ligaments tend to be quite thin joining individually the adjacent bones, the robust palmar ligaments are thicker and are in part embedded in the thick palmar fibro cartilage that attaches to the palmar aspect of the carpal bones and bases of the metacarpal bones. This structure provides a strong support to the plantar aspect of the joint that is constantly under tension. The collateral ligaments are strong, especially the medial that is constantly under tension due a normal five degrees of valgus. Unlike the tarsus, the collateral ligaments span only one joint level. The joint capsule separates the antebrachiocarpal joint from the middle carpal and carpometacarpal joints creating two separated compartments. The types of carpal injuries include sprain, hyperextension, luxation and fracture.

Carpal fractures are almost invariably avulsion fractures of ligaments (origin or insertion) and tendons insertion or the result of the combination of shearing and compressive forces acting on the bones during the hyperextension. All these fractures are intra articular with the exception of two types of accessory carpal bone lesions. The clinical examination consists of accurate palpation to localize pain, soft tissue swelling, instability and crepitius. The range of motion of the joint should be tested in flexion, extension, intra and extra rotation in extension and 90 degrees flexion, cranial translation with carpus flexed at 90 degrees.  [...]