Fractures of the first phalanx are not uncommon in racehorses. They may be small “chip” fractures along the dorsal margin of the proximal joint surface, longitudinal fractures (split pastern), or comminuted. Another category involves fragments of the palmar or plantar proximal aspect of the first phalanx, which may be associated with osteochondrosis.
Signs of longitudinal fractures involve acute weightbearing lameness after work or a race. There may be little or no swelling initially, but there is intense pain on palpation or flexion of the fetlock. Lameness may be less pronounced with chip or avulsion fractures, but flexion of the joint usually exacerbates the problem.
Diagnosis is confirmed by radiography or by scintigraphy for small nonradiographically visible fractures. A number of oblique radiographic views may be necessary to ensure visibility of the fracture line, which may be seen initially as a fine fissure, usually extending distally from the sagittal groove of the proximal phalanx in the dorsopalmar/plantar view.
Chip and avulsion fractures can be removed by arthroscopic surgery. Longitudinal fractures can be repaired by internal fixation using two or more cortical bone screws by the technique of interfragmentary compression. Careful attention should be paid to the fracture configuration to ensure that all components are incorporated in the repair. In some circumstances CT may aid an accurate diagnosis. Conservative treatment of severely comminuted fractures involves immobilization with a plaster or fiberglass cast for up to 12 wk, with or without the use of transfixation pins through the third metacarpal/tarsal. However, complications include poor alignment at the fracture site, secondary arthritis, and contralateral laminitis.
Fractures of the second phalanx are similar to those of the first phalanx but less common. Treatment and prognosis are similar, although as they tend to be more comminuted, secondary arthritis of the PIP or DIP joints is common.
Fractures of the proximal sesamoid bones are relatively common. They are caused by overextension and often are associated with suspensory ligament damage, as in the forelimb or hindlimb of Standardbreds and Thoroughbreds. The lateral proximal sesamoid in the hindlimb of Standardbreds may be fractured as a result of torque forces induced by shoeing with a trailer-type shoe. The fractures may be apical, mid-body, basilar, abaxial, axial, or comminuted, and they may involve one or both sesamoids. Most, apart from some abaxial fractures, are articular. Clinical signs include heat, pain, and acute lameness, which is exacerbated by flexion of the fetlock. There is often hemarthrosis and synovial effusion of the metacarpo/tarso phalangeal joint. Diagnosis is confirmed radiographically. The prognosis is fairly good if small articular fragments are promptly removed by arthroscopy. Apical fractures in adult racehorses (≥2 yr old) removed arthroscopically have an 83% favorable prognosis for return to racing for the hindlimb and 67% for the forelimb. Mid-body fractures require internal fixation using 1–2 lag screws. The prognosis in large basilar fractures is poor, regardless of surgical approach. Complete disruption of the suspensory apparatus, including fractures of both sesamoid bones, is a catastrophic injury accompanied by vascular compromise of the foot; however, some horses can be salvaged for breeding by surgical arthrodesis of the fetlock joint.
Last full review/revision March 2012 by Stephen B. Adams, DVM, MS, DACVS; Joerg A. Auer, DrMedVet, Dr h c, MS, DACVS, DECVS; James K. Belknap, DVM, PhD, DACVS; Jane C. Boswell, MA, VetMB, CertVA, CertES (Orth), DECVS, MRCVS; Peter Clegg, MA, Vet MB, PhD, CertEO, DECVS, MRCVS; Andrew L. Crawford, BVetMed, CertES (Orth), MRCVS; Jean-Marie Denoix, DVM, PhD, Agregé; Marcus J. Head, BVetMed, MRCVS; C. Wayne McIlwraith, BVSc, PhD, DSc, FRCVS, DACVS; James Schumacher, DVM, MS, DACVS, MRCVS; John Schumacher, DVM, MS, DACVIM; Roger K. W. Smith, MA, VetMB, PhD, DEO, DECVS, MRCVS; Chris Whitton, BVSc, FACVSc, PhD