THE MERCK VETERINARY MANUAL
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Osteoarthritis in Horses (Fetlock and Pastern)

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Deterioration of articular cartilage within the metacarpal/tarsal-phalangeal joint is a common injury in racehorses and can lead to the development of periarticular osteophytes, enthesiophytes, and joint space collapse. In young, training horses, periosteal bone formation can occur on the dorsal aspect of the distal metacarpus and the proximal aspect of the proximal phalanx, often involving the joint capsule (osselets). Osteoarthritis is often secondary to a primary abnormality such as a chip fracture or osteochondrosis (see Osteochondrosis of the Stifle in Horses). Treatment can be limited. The use of intra-articular steroids can provide pain relief, but the deterioration of the cartilage is inevitable. In severe, advanced cases, arthrodesis of the joint is necessary to provide pain relief.

Osteoarthritis of the proximal interphalangeal joint (articular ringbone) often creates new bone formation and a bell-shaped appearance to the pastern region. Rarely this may progress to ankylosis. Clinical diagnosis is based on visualization and palpation of soft-tissue thickness and new bone proliferation in the pastern region. Usually, the range of joint movement is restricted, and there is pain on forced flexion of the involved articular surfaces. Intra-articular and regional diagnostic analgesia identify the pastern region as the site of pain. Radiography confirms the diagnosis in established cases. Anti-inflammatory medication may relieve the signs of lameness temporarily. Surgical arthrodesis of the pastern joint is frequently required to successfully restore performance.

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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