Chronic tenosynovitis and associated effusion of the digital flexor tendon sheath is a relatively common condition causing lameness in horses. Initial diagnosis is through palpation revealing heat, pain, and swelling. Sepsis should be ruled out in acute cases. Although some cases of tenosynovitis are primary and respond to conservative therapy with or without treatment of the sheath with corticosteroids, others are secondary to lesions of structures contained within the sheath. Marginal tears of the deep digital flexor tendon and tears of the manica flexoria are the most common tenoscopic diagnoses in surgically treated cases. Treatment of the latter through removal of the affected manica flexoria provides an 80% chance of soundness postsurgery, while debridement of the deep digital flexor tendon marginal tears carries a poor prognosis.

Annular ligament constriction can be primary due to desmitis of the ligament or secondary to longstanding tenosynovitis or enlargement of the flexor tendons contained within the fetlock canal. Clinical signs are similar to other causes of tenosynovitis and include pain on palpation, swelling, and lameness, especially following forced flexion of the distal limb. Careful ultrasonographic examination is recommended to assess accompanying pathology. Treatment can be either conservative (ie, steroids) or surgical (transection of a constricting annular ligament). Surgery is best performed tenoscopically, which allows visualization of the remainder of the sheath for primary pathology and assessment of the degree of constriction.

Other less common causes of tendon or ligament pathology distal to the fetlock include desmitis of the distal oblique sesamoidean ligaments and lesions of the deep digital flexor tendon within the pastern. Both of these can result in tenosynovitis of the digital sheath and can be diagnosed using ultrasonography or MRI.

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