Thoroughpin refers to a distention of the tarsal sheath of the deep digital flexor tendon just above the hock. It is characterized by plantar fluid-filled swellings visible on both medial and lateral sides proximal to the tibiotarsal joint, which distinguish it from bog spavin (see Lameness in Horses: Bog Spavin in Horses). It is usually unilateral and varies in size. The lesion is referred to as a tenosynovitis of traumatic origin, but it may not be associated with any detectable inflammation, pain, or lameness. It essentially constitutes a blemish and so is of major clinical importance in show horses. Treatment is by withdrawal of the fluid and injection of hyaluronate and/or a long-acting corticosteroid, which may need to be repeated until the swelling does not recur.

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