Tenosynovitis of the deep digital flexor tendon in horses.

TENOSYNOVITIS of the deep digital flexor tendon (thoroughpin) in horses is manifested by distention of its tarsal synovial sheath due to formation of an excessive synovial effusion. Unless tenosynovitis is acute, signs of inflammation, pain or lameness are absent (1). Tendinitis can and does occur in conjunction with inflammation of the tarsal synovial sheath. As tendons function they are frequently subjected to considerable strain, peritendinous pressure, and friction between the parietal and visceral layers of the tendon sheath (2). Acute direct trauma or trauma that is multiple and minor can precipitate tenosynovitis. In acute tenosynovitis of the deep digital flexor tendon, the ensuing inflammatory reaction affects the tarsal synovial sheath, which responds to inflammation by formation of an excessive synovial effusion. Chronic tenosynovitis follows the acute form or it can be insidious in onset. It is characterized by persistent synovial effusions, stenosis of the tendon sheath, or adhesions between the parietal and visceral layers of the tendon sheath and the enveloped tendon (6, 8). Riziform bodies may be present in synovial effusions in chronic tenosynovitis. Therapy in this group of horses was directed at preventing formation of excessive synovial effusion by aspiration of the tarsal synovial sheath and the intrathecal injection of an adrenocortical steroid or one of its synthetic analogues. Presented in this report are clinical signs, response to intrathecal injection of synthetic steroids, and results of synovial effusion analyses. Analyses of synovial effusions were performed to characterize synovial effusions produced in horses affected with tenosynovitis of the deep digital flexor tendon.