Equis ISSN 2398-2977

Carpus: sheath tenosynovitis

Synonym(s): Carpal tunnel syndrome, Carpal canal syndrome

Contributor(s): Bud G E Fackelman, Graham Munroe, Chris Whitton




  • Primary or idiopathic synovitis of the sheath post-trauma:
    • No evidence of physical damage on palpation and imaging, but marked synovial inflammation.
  • Chronic synovitis and enlargement of the carpal sheath following trauma to sheath:
    • Acute injury and moderate to severe lameness that does not resolve.
    • No physical cause of the persistent inflammation but gradually becomes chronic with thickening of the sheath wall, palmar retinaculum and surrounding perisheath tissue.
    • The synovium becomes chronically damaged and thickened with adhesions, synovial masses and clumps. There may or may not be enlargement of the SDFT/DDFT.
  • Frontal plane or comminuted fracture Accessory carpal: fracture of the accessory carpal bone can affect the carpal canal and sheath:
    • Fracture fragments can impinge on the DDFT and more rarely, comminuted bone fragments may be displaced into the carpal sheath.
    • Both can lacerate or damage the DDFT to varying degrees.
  • Superficial digital flexor tendonitis in the carpal sheath has been occasionally reported in older horses (15 years) and Standardbred racehorses:
    • Acute cases have sheath distension without any obvious signs involving the SDFT elsewhere.
    • Injury to the SDFT may also occur at the musculotendinous junction often subsequent to a fall or other severe trauma. If complete rupture occurs the horse may require humane destruction.
    • Focal tears lead to a moderate to severe lameness with sheath distension.
  • Primary deep digital flexor tendonitis in the carpal sheath is uncommon:
    • Occasionally marginal tears are detected on tenoscopy in chronically lame horses with carpal sheath distension.
  • Tearing of the radial head of the DDFT can cause tenosynovitis of the carpal sheath:
    • The amount of distension of the sheath and presenting lameness is variable.
  • Osteochondroma Carpus: osteochondroma of the caudal distal radius:
    • Most present in young horses (2-6 years old) with distension of the sheath and variable, often recurrent, lameness.
    • The lesion is most likely to be in the lateral one-third of the radius.
    • Most are single, sharply pointed protuberances situated between 7 and 33 mm proximal to the distal radial physis.
    • They are variable in size but when clinical signs are present they are impinging on the overlying DDFT.
  • Desmitis and tearing of the accessory ligament of the SDF:
    • This is an uncommon injury mainly in European Standardbred trotters, and occasional show jumpers, eventers, dressage horses and Thoroughbred racehorses.
    • The primary injury to the ligament leads to a secondary sheath synovitis and may be associated with other injuries in the carpal canal such as SDFT tendinitis SDFT: tendinitis and flexor retinaculum fibrosis.
  • Intrathecal hemorrhage which may be idiopathic, traumatic, eg fall, or secondary to damage to the SDFT/DDFT/ALSDFT or accessory carpal bone.
  • Exostosis of the caudal margin of the bony remnant of the distal radial physis:
    • One or two caudally directed physeal remnants can occur with variable shapes from sharp to irregular and blunted.
    • Similar interference to the DDFT, as in the radial osteochondroma, occurs with fraying and tearing of fibers, sometimes over an extensive area.
  • Deep DDFT tendon injuries, whether due to tendinitis Deep digital flexor tendon: tendinitis or rubbing on the distal radial osteochondroma/physeal exostosis:
    • Can lead to an expanded flexor tendon volume within the carpal canal and may lead to restriction and carpal tunnel-like syndrome.
    • Additionally, some chronic carpal sheath problems, such as desmitis of the ALSDFT, sheath tenosynovitis, and ALSDFT tendonitis, may lead to secondary perisheath and carpal retinacula fibrosis, further constricting the carpal canal.


  • Acute or chronic.


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Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Hawthorn A et al (2016) Post operative synovial sepsis following endoscopic surgery: Increased risk associated with the carpal sheath. Equine Vet J 48 (4), 430-433 PubMed.
  • Jorgensen J S et al (2015) Musculoskeletal lesions and lameness in 121 horses with carpal sheath effusion (1999-2010). Vet Radiol Ultrasound 56 (3), 307-316 VetMedResource.
  • Minshall G J & Wright I M (2014) Frontal plane fractures of the accessory carpal bone and implications for the carpal sheath of the digital flexor tendons. Equine Vet J 46 (5), 579-584 PubMed.
  • Taintor J, Caldwell F & Almond G (2013) Aseptic tenosynovitis of the carpal flexor sheath caused by rupture of the accessory ligament of the deep digital flexor tendon. Can Vet J 54 (8), 765-768 PubMed.
  • Minshall G J & Wright I M (2012) Tenosynovitis of the carpal sheath of the digital flexor tendons associated with tears of the radial head of the deep digital flexor: Observations in 11 horses. Equine Vet J 44 (1), 76-80 PubMed.
  • Wright I M & Minshall G J (2012) Clinical, radiological and ultrasonographic features, treatment and outcome in 22 horses with caudal distal radial osteochondromata. Equine Vet J 44 (3), 319-324 PubMed.
  • Byron C R et al (2010) Modified tenoscopic method for carpal flexor retinaculum release in a horse. Vet Surg 39 (2), 239-243 PubMed.
  • Nixon A J, Schachter B L & Pool R R (2004) Exostoses of the caudal perimeter of the radial physis as a cause of carpal synovial sheath tenosynovitis and lameness in horses: 10 cases (1999-2003). J Am Vet Med Assoc 224 (2), 264-270 VetMedResource.
  • Textor J A, Nixon A J & Fortier L A (2003) Tenoscopic release of the equine carpal canal. Vet Surg 32 (3), 278-284 PubMed.
  • Southwood L L et al (1998) Tenoscopic anatomy of the equine carpal flexor synovial sheath. Vet Surg 27 (2), 150-157 PubMed.
  • Cauvin E R J et al (1997) Gross and ultrasonographic anatomy of the carpal flexor tendon sheath in horses. Vet Rec 141 (19), 489-495 PubMed.
  • Cauvin E R J et al (1997) Endoscopic examination of the carpal flexor tendon sheath in horses. Equine Vet J 29 (6), 459-466 PubMed.
  • Munroe G A & Cauvin E (1997) Surgical treatment of a comminuted articular fracture of the accessory carpal bone in a thoroughbred horse. Vet Rec 141 (2), 47-49 PubMed.
  • Redding W R (1993) Evaluation of equine digital flexor tendon sheath using diagnostic ultrasound and contra radiography. Vet Radiol Ultrasound 34, 42-48 WileyOnline.

Other sources of information

  • McIlwraith C W, Wright I & Nixon A (2014) Diagnostic and Surgical Arthroscopy in the Horse. 4th ed. Mosby, USA.
  • Dyson S J (2011) The Carpal Canal and Carpal Synovial Sheath. In: Diagnosis and Management of Lameness in the Horse. 2nd edn. Eds: Ross M K & Dyson S J. Elsevier Saunders. pp 777-779.