The synovial membrane from the carpometacarpal joint contributes to uniting the bases of adjacent metacarpal bones. The intermetacarpal joints are joints between the proximal ends of adjacent metacarpal bones. Ossification is usually complete at 5 to 6 months of age. 29 Metacarpal I has its epiphysis at the proximal end, and metacarpals II through V have a single epiphysis at the distal end. A dorsal sesamoid bone articulates with the head of the metacarpal bone at metacarpophalangeal joints II through V. Metacarpal I has one small palmar sesamoid that is not numbered. The metacarpophalangeal joint sesamoid bones are numbered from I through VIII from medial to lateral. Each metacarpal bone articulates with the proximal phalanx of the corresponding numbered digits and two palmar sesamoid bones. Metacarpals II through V are all weight bearing, but metacarpals III and IV are longer than metacarpals II and V. 29 Metacarpal I is usually present, but it is not weight bearing because it is shorter than the level of the second metacarpophalangeal joint. ![]() Each metacarpal bone has a proximal base, a middle body, and a distal head. The five metacarpal bones are numbered from medial to lateral. Metacarpal Bones and Joints and Sesamoid Bones The palmar fibrocartilage is attached to all the proximal carpal bones with the exception of the accessory carpal bone, to all the numbered carpal bones, and to the proximal palmar aspect of the base of metacarpal bones III through V ( Figure 56-4). 29, 64, 72 The flexor retinaculum extends from the medial aspect of the accessory carpal bone to the radial styloid process, and distally to the radial and first carpal bones. Multiple short intercarpal ligaments unite the numbered carpal bones, and the numbered carpal bones to the metacarpal bones (Figure 56-3). ![]() The accessory carpal bone is attached distally to the proximal aspect of metacarpals IV and V by two separate ligaments (accessorometacarpal ligaments), and to the fourth and ulnar carpal bones by separate ligaments. On the palmar side, the short radial collateral ligament, the palmar radiocarpal ligament, and the palmar ulnocarpal ligament are the major deep ligaments of the carpus. The short ligaments that attach the radial carpal bone to the ulnar carpal bone, the radial and ulnar carpal bones to the numbered carpal bones, and the numbered carpal bones to each other and to the corresponding metacarpal bones are also visible (see Figure 56-1). The ligaments present on the dorsal surface of the carpus are the radioulnar ligament (articular disc), the dorsal radiocarpal ligament, the short ulnar collateral ligament, and the short radial collateral ligament. Antebrachial muscles and tendons cross all three joints of the carpus, but the carpal ligaments themselves do not. The carpal joints as a whole act as a ginglymus (hinge) joint stabilized by short extra-articular and intra-articular ligaments, an articular disc (sometimes known as the radioulnar ligament that connects the radius to the ulna), palmar fibrocartilage, and the joint capsule. The intercarpal joints exist between the individual bones of each row. The metacarpophalangeal joint exists between the distal row of carpal bones and the joint surface of the base of the metacarpal bones. The middle carpal joint exists between the proximal and distal rows of carpal bones. 29 The antebrachiocarpal joint occurs between the distal radius and ulna and the proximal row of carpal bones. The carpus is a composite joint composed of all the articulations to which the seven carpal bones contribute. General fracture repair techniques are presented in other chapters, but techniques unique to the carpus, metacarpus, and digits will be addressed in this chapter. In general, fractures that involve joint surfaces, ligament injuries that cause significant instability, and shearing injuries are approached surgically using the same principles applied when those injuries occur in other parts of the skeleton. Although these studies highlight diverse treatment options and theorize causation of the injuries, many questions remain regarding the best clinical approach for treating many of these conditions. ![]() The scientific literature regarding treatment options consists primarily of observational studies and biomechanical laboratory studies. Yet the mechanism of injuries to these structures and best treatment options for those injuries in the dog and cat are poorly understood. 29 The manus has a complex anatomy that is well documented and studied. The manus of the canine thoracic limb consists of the carpus, metacarpal bones, phalanges, and associated sesamoid bones. Kapatkin, Tanya Garcia-Nolen and Kei Hayashi
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