The third carpal bone

Abstract

equal prevalence of distal radial carpal (DRC) and third carpal (C3) injury but in Standardbreds, C3 is more commonly damaged. The medial aspect of the intercarpal joint is highly susceptible to overload because of the greater load on the medial aspect of the joint and the hinge-type closing of the joint. The typical distalradial carpal (DRC) chip fracture occurs in the middle of its articular rim just lateral or adjacent to the attachment of a small ligament that courses distally and medially to merge with the capsular attachments to the face of the second carpal bone. The typical chip is therefore best visualized on the DLPMO and flexed lateral views. The flexed view is important to assess since loss of normal subchondral density extending palmarly away from the fracture is a sign of extensive articular damage and a poor prognosis. Thebest DRC chips are triangular in outline and relatively narrow along their articular margin. A second very common site of DRC injury is the dorsal lateral comer of the bone. This is the most common site for an osteophyte to develop (and subsequently fracture) in the horse. Such lesions can be difficult to diagnose radigraphically and are best seen on a well-positioned, well-exposed skyline or a wellpenetrated DMPLO projection. They are rarely found as a solitary lesion. Arthroscopic removal is the preferred management for most carpal fractures although it certainly should be acknowledged that many small carpal chips can be managed medically. If surgery is an option, in terms of the horse's value, repeated injections should be avoided and, in particular, repetitive corticosteroids should be avoided. Early intervention affords a better prognosis so a decision concerning surgery should be made shortly after diagnosis. Following ar throscopic surgery for atypical chip fracture, horses are rested for about two weeks with hand grazing only allowed. They then begin a program of handwalking that begins with five minutes/day and increases weekly by five minute increments until they are walking 30-40 minutes/day. Swimming is also a rehabilitative option that can begin any time after two weeks. Passive flexion is advised for the first month following surgery. Sodium hyaluronate is usually injected five to seven days following surgery and repeated when the horse returns to training if an effusion persists. A horse with a typical distal lateral radius chip fracture will start jogging about six weeks postoperatively, whereas most serious intercarpal injuries receive two to three times as long a convalescence. THE THIRD CARPAL BONE