THE MERCK VETERINARY MANUAL
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Fractures of the Third Metatarsal Bone in Horses

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Generally, the same type of fractures can be acquired as in the third metacarpal bone (see Fracture of the Third Metacarpal (Cannon) Bone in Horses). Kicking injuries or other external influences are usually responsible for the development of the different types of shaft fractures (transverse, oblique, spiral, fissure, and multifragment fractures). Lateral condylar fractures occur more frequently in Standardbred horses and may be present bilaterally with marginal lameness; medial condylar fractures are rare. Nondisplaced, incomplete fractures of the proximal third of the third metatarsal bone that extend into the tarsometatarsal joint are seen only in this bone. Stress fractures that occur in the forelimb do not occur in the hindlimb. Horses with third metatarsal bone fractures are usually severely lame (4–5/5). Weight bearing and axial deformation during loading depend on the type of fracture(s) present. Diagnosis is usually confirmed by radiography and/or other diagnostic imaging techniques.

Fissure fractures may be treated by stall rest, bandaging, and maintenance in a sling to prevent the animal from lying down. This type of management prolongs recovery time but is an option. Other conservative management techniques, such as cast application, are possible in certain fractures, but are no longer advocated for several reasons. They prevent early active motion and induce fracture disease and, frequently, pressure sores at predilection sites (region of the ergot, dorsal aspect of the proximal third metatarsal with half casts), and may lead to rupture of the peroneus tertius tendon if a full cast is applied. Additionally, many horses do not tolerate casts that prevent flexion of the talocrural joint. Internal fixation is the treatment of choice. Locking compression plates allow solid, rigid fixation of most load-preventing fractures. The plate allows the introduction of regular cortex screws and where desired, locking head screws. Condylar fractures and proximal incomplete fractures of the third metatarsal are best treated by means of cortex screws inserted in lag fashion through stab incisions. With this type of treatment, the fragment can be compressed onto the parent portion of the bone to facilitate rapid bone healing, usually without callus formation. If the horse is to be returned to athletic activity, plate removal 5–6 mo postoperatively is indicated. If 2 plates were applied, staggered removal is performed 3 mo apart. In most cases, fractures repaired only with cortex screws do not require implant removal after healing.

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, DACVSMR; 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

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