566


EQUINE VETERINARY EDUCATION


Equine vet. Educ. (2022) 34 (11) 566-568 doi: 10.1111/eve.13622


Clinical Commentary


Fracture of the accessory carpal bone—conservative or surgical therapy? A. F€


urst* and M. Jackson


Vetsuisse Faculty, University of Zurich—Equine Hospital Zurich, Zurich, Switzerland *Corresponding author email: afuerst@vetclinics.uzh.ch


De Preux et al. (2022) describe the successful treatment of a multiple fracture of the accessory carpal bone (ACB) in a horse. This is a remarkable report because surgical repair of ACB fractures is difficult, and thus, successful treatment has seldom been reported. Computer-assisted orthopaedic surgery (CAOS) undoubtedly contributed to the desired outcome in this case. Fractures of the ACB are not uncommon in horses and


can have many different configurations. Nevertheless, since the aetiopathogenesis of fracture of this particular bone is typically unique, the resulting fracture shows a characteristic course. It is thought that the ACB becomes compressed between the radius and the cannon bone similar to a nut in a nutcracker. At the same time, asynchronous traction of the extensor and flexor carpi ulnaris muscles promotes bone fracture; these two muscles are innervated by different nerves, the radial and ulnar nerves, which may contribute to asynchronous traction of the two muscles. For unknown reasons, the ACB is not displaced medially during flexion, which predisposes it to fracture. These events usually lead to a fracture configuration similar to that described by de Preux et al. (2022); the fracture is characterised by a vertical course with an additional fragment in the dorsoproximal region of the ACB (Figs 1 and 2). However, other configurations have also been described. It is extremely important to obtain different radiographic views because dislocation of the


fragments can often only be detected with the carpus flexed. Computed tomographic (CT) images are particularly


helpful, and modern equipment allows imaging to be done in standing horses. In most cases, CT images show a more complicated fracture course compared with radiographs. Conservative treatment of ACB fractures has also been


associated with a good outcome (Carson, 1990). Some horses returned to compete in equestrian events after conservative therapy, and one horse went on to win in the Olympics (Dyson, 1990). Therefore, conservative management of ACB fractures is probably the treatment option elected in most horses today. However, in our experience, nonunion or malunion often


occurs, and delayed fracture healing is almost always encountered with conservative treatment. This is attributable to the constant movement of the bone fragments because of the numerous ligaments and tendons that attach to the ACB. In addition, the ACB has no periosteum or bone marrow and has a poor blood supply. Conservative management also fails to provide compression of the fracture ends, which is exacerbated by the constant pull of the various tendons and ligaments on the bone, creating an unfavourable environment for healing. For these reasons, surgical treatment of ACB fractures


offers many advantages. Fragments can be fixed in the correct position and compression applied to the fracture, but the unique anatomy of the ACB means that surgical fixation of fractures is not that easy. Fracture fixation has been achieved with lag screws (Easley & Schneider, 1981; Rijkenhuizen & Nemeth, 1994) or a plate (Ruggles, 2019), but


Fig 1: Illustration of the typical configuration of a fracture of the accessory carpal bone: vertical fracture with a dorsoproximal fragment.


Fig 2: Lateromedial radiographic view of a typical fracture of the accessory carpal bone: vertical fracture with a dorsoproximal fragment.


© 2022 The Authors. Equine Veterinary Education published by John Wiley & Sons Ltd on behalf of EVJ Ltd. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.


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