Inflammation of a tendon can be acute or chronic, with varying degrees of tendon fibril disruption. Tendinitis is most common in horses used at fast work, particularly racehorses. The problem is seen in the digital flexor tendons and is more common in the forelimb than in the hindlimb. In racehorses, the superficial digital flexor is involved most frequently. The primary lesion is a central rupture of tendon fibers with associated hemorrhage and edema.
Tendinitis usually appears after fast exercise and is associated with overextension and poor conditioning, fatigue, poor racetrack conditions, and persistent training when inflammatory problems in the tendon already exist. Improper shoeing may also predispose to tendinitis. Poor conformation and poor training also have been implicated.
During the acute stage, the horse is severely lame and the involved structures are hot, painful, and swollen. In chronic cases, there is fibrosis with thickening and adhesions in the peritendinous area. The horse with chronic tendinitis may go sound while walking or trotting, but lameness may recur under hard work. Ultrasonography delineates the cross-sectional and longitudinal extent of the tendinitis.
Tendinitis is best treated in the early, acute stage. The horse should be stall-rested, and the swelling and inflammation treated aggressively with cold packs and systemic anti-inflammatory agents. Some degree of support or immobilization should be used, depending on the amount of damage to the tendon. Intratendinous corticosteroid injections are contraindicated. When a distinct hypoechoic or anechoic core lesion is present on ultrasound examination, tendon splitting has been recommended (the rationale is to decrease intratendinous pressure due to serum or hemorrhage). Cases also have been treated with shock wave therapy, intralesional injection of fat-derived stromal cells or cultured bone marrow−derived mesenchymal stem cells, or platelet-rich plasma products. The levels of evidence for these modalities are variable. The horse should be rehabilitated using a regimen of increasing exercise. Superior check ligament desmotomy has been used as an adjunctive treatment to minimize recurrence of the problem before the horse is returned to training.
Other treatments for chronic tendinitis have included superficial point firing (of questionable benefit) and percutaneous tendon splitting. Annular ligament desmotomy is also used when tendinitis occurs within the confines of the digital tendon sheath.
The prognosis for a flat-racing Thoroughbred racehorse to return to racing after a bowed tendon is guarded, regardless of treatment. However, increasing success is seen with eventers, show jumpers and show hunters, and dressage horses, respectively.