Bog spavin refers to a chronic synovitis of the talocrural joint characterized by distention of the joint capsule. Faulty conformation may lead to weakness of the hock joint and increased production of synovia. In such cases, both limbs are affected. The unilateral case is more likely to be a sequela of a sprain or some underlying problem within the joint (eg, osteochondrosis). The most frequent cause of unilateral or bilateral joint distention, at least in Warmblood horses, is osteochondrosis dissecans (OCD) of the intermediate ridge of the distal tibia. Radiography of the region is indicated in all cases. In horses with unilateral joint distention, it is advisable to also examine the opposite hock. In cases of OCD, frequently an identical lesion can be seen there (see Lameness in Horses: Osteochondrosis of the Stifle in Horses).
The horse usually is not lame unless the condition is complicated by additional bone and cartilage involvement. The primary distention of the joint capsule occurs on the dorsal medial surface of the hock, while smaller swellings develop on each side of the proximal caudal aspect. Uncomplicated bog spavin rarely interferes with the usefulness of the horse but is an unsightly blemish and indicates the need for radiographic evaluation. The distention may spontaneously appear and disappear in weanlings and yearlings.
The excess fluid within the joint capsule may be aspirated; however, this is only of temporary benefit, as the distended joint space is rapidly refilled by synovial fluid. Through external bandage support or the application of a commercial boot for several weeks, the stretched joint capsule slowly reverts to normal size. Injection of intra-articular corticosteroids provides variable and transient relief and is best applied in conjunction with rest and external support. The injection may be repeated 3 wk later if necessary. Arthroscopy should be performed when osteochondral involvement is suspected. Bog spavin tends to recur, especially if poor conformation is an inciting factor.
Last full review/revision March 2012 by Stephen B. Adams, DVM, MS, DACVS; Andrew L. Crawford, BVetMed, CertES (Orth), MRCVS; 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; Marcus J. Head, BVetMed, MRCVS; C. Wayne McIlwraith, BVSc, PhD, DSc, FRCVS, DACVS; James Schumacher, DVM, MS, DACVS, MRCVS; John Schumacher, DVM, MS, DACVS, MRCVS; Roger K. W. Smith, MA, VetMB, PhD, DEO, DECVS, MRCVS; Chris Whitton, BVSc, FACVSc, PhD; Jean-Marie Denoix, DVM, PhD, Agregé; Joerg A. Auer, DrMedVet, Dr h c, MS, DACVS, DECVS