07/24/2026
Thoroughpin in Horses
Brian S. Burks, DVM
Diplomate of the American Board of Veterinary Practitioners®
394 Fox Road
Apollo, PA 15613
(724) 727-3481
www.foxrunequine.com
Thoroughpin is tenosynovitis of the tarsal sheath, which encloses the deep digital flexor tendon (DDFT) of the hindlimb as it travels along the back of the hock. The swelling in the tendon sheath may or may not cause pain or lameness. Tendon sheaths are synovial filled sleeves lubricate tendons as they pass over joint surfaces. Inflammation of a tendon sheath is termed tenosynovitis.
Clinically, thoroughpin is noted by fluid filled swellings along the medial or lateral aspects of the hindlimb just above the point of the hock. These swellings are sometimes mistaken for effusion of the plantar pouches of the tibiotarsal joint, which is part of bog spavin. In thoroughpin, the swelling is associated with the tendons- gastrocnemius, superficial digital flexor, and deep digital flexor- along the back of the hock.
Thoroughpin is usually unilateral and is idiopathic but may be caused by trauma to the DDFT within the tendon sheath or to the sheath lining itself. Idiopathic tenosynovitis is not associated with inflammation or lameness. There is usually no history of trauma, and the effusion is insidious in nature. Varying in size, thoroughpin is usually a cosmetic blemish, and is of greater concern in show horses.
Acute tenosynovitis is often associated with greater effusion and lameness, accompanied by heat and pain to palpation. Ultrasound should be used to look for damage to the tendon.
Chronic tenosynovitis is characterized by synovial effusion and a thickened tendon sheath. There may be adhesions between the layers of the tendon sheath or the sheath and the tendon. There may be loss of function. Thoroughpin is rarely associated with lameness.
The same conformational abnormalities and athletic endeavors that predispose horses to thoroughpin can also lead to arthritis. Therefore trimming/shoeing strategies, footing materials, exercise program, and soundness in horses with thoroughpin should be evaluated to prevent the occurrence of other lameness issues.
TREATMENT
Stall rest. This is most effective in acute cases (e.g. if a recent injury).
Cold-water hosing and/or application of ice. Again, this is more effective in the acute stage.
Topical therapy with a steroid sweat. Although this strategy is most effective in the acute phase, we have also observed positive response in subacute and chronic cases.
Bandaging can be very effective, but bandaging the hock is difficult and can result in compromise of the skin over the point of the hock. Thus, this is not used often.
The fluid can be aspirated from the tendon sheath, which provides temporary relief as fluid quickly accumulates once more. Therefore, the sheath can be injected with a combination of steroid, atropine, and antibiotic to stop fluid production by the synoviocytes lining the tendon sheath. Serial injections are usually required to produce a permanent result. As with most injuries, early treatment is more likely to be successful.
The fluid obtained from this type of lesion is likely to be not only voluminous, but lacking in mucin, making the fluid quite thin. The white blood cell count and protein of the fluid should be measured to ensure that early septic tenosynovitis is not overlooked.
Radiation therapy. Radiation therapy has also been implemented with some degree of success. This technique works by diminishing secretory properties of the tendon sheath lining.
Surgery can be used to break up adhesions that form inside the tendon sheath or when injections have proven ineffective. Cases that require surgery have a guarded prognosis for full recovery.
The use of shock wave therapy or laser therapy in cases where there is tendon damage may be helpful. If there is no tendon damage, laser therapy is more appropriate to reduce the swelling.
As with any disease or disorder, early intervention is recommended to result in the best possible outcome. Chronic tenosynovitis is less likely to respond to conservative therapy.
Fox Run Equine Center
www.foxrunequine.com
(724) 727-3481