Tendon sheaths are "sleeve-like" structures that contain synovial fluid and provide a lubricated environment for the facilitated movement of tendons over (flexing and extending) joint surfaces. The presence of inflammation within a tendon sheath is termed tenosynovitis.
Tenosynovitis of the horse's tarsal sheath is also known as thoroughpin. The tarsal sheath encloses the deep digital flexor tendon (DDFT) of the hindlimb as it courses along the back of the hock. Thoroughpin is a morphologic description of the swelling rather than a clinical diagnosis. Like many other swellings associated with the hock region, thoroughpin may or may not occur in conjunction with pain or lameness.
Thoroughpin is characterized by fluid-filled swellings which are visible along both medial (inside) and lateral (outside) aspects of the hindlimb just above the point of the hock.
Although effusion of the plantar pouches of the tibiotarsal joint (the plantar component of bog spavin) can closely mimic the appearance of thoroughpin, swellings representative of the latter are more intimately associated with the tendons (gastrocnemius, superficial digital flexor and deep digital flexor) along the back of the limb.
Thoroughpin is typically unilateral and considered to be a consequence of trauma to the DDFT within the sheath or to the sheath lining itself. Although it can vary in size, thoroughpin usually constitutes a cosmetic blemish and is therefore of greater concern in show horses.
Although thoroughpin (tendon sheath inflammation) is not the same as arthritis (joint inflammation), conformational abnormalities and activities that predispose horses to thoroughpin can also lead to arthritis, tendinitis and other problems. Therefore trimming/shoeing strategies, footing materials, conditioning programs, work scheduling and soundness in horses with thoroughpin should evaluated to prevent the development of additional issues.
Stall rest. This is most effective in acute cases (i.e. if injury is recent).
Cold-water hosing and/or application of ice. Again, more effective in the acute stage.
Topical therapy (we recommend Dexamethasone Sweat Spray). Although this strategy is most effective in the acute phase, we have also observed positive response in subacute and chronic cases.
External pressure via wrapping of the area. Although this method can be effective at reducing swelling, bandaging of the hock area is very difficult and often results in secondary complications, such as skin compromise/ devitalization along the point of the hock and associated gastrocnemius (Achilles) tendon. We therefore try to avoid wrapping of the hock in most cases.
Drainage of sheath fluid via needle aspiration. Although this provides temporary relief, fluid quickly re-accummulates within the sheath unless some measure(s) are taken to prevent recurrence.
Intrathecal injection. Although this technique doesn't work in every situation, it has proven to be an effective approach for treatment of thoroughpin. In some instances, serial (multiple) injections are required to produce a permanent result.
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.
At The Atlanta Equine Clinic we typically drain the extra fluid and subsequently infuse a combination of steroid, atropine and antimicrobial (antibiotic) in an attempt to “dry up” synoviocytes (synovial fluid-producing cells) lining the sheath. Following treatment, a thin layer of Dexamethasone Sweat Spray is applied daily to support and enhance the effect of the injection.
Usually one treatment is adequate, although chronic (long-term) cases are generally more therapeutically challenging than acute (more recent) ones. As with most issues, the sooner treatment is implemented the better it tends to work.