Courtesy of Dr. Hilary Rice.
The calcaneal bursa in horses, which is considered a true (congenital) bursa, is composed of three bursal structures:
The subcutaneous calcaneal bursa lies between the skin and the superficial digital flexor tendon.
The intertendinous calcaneal bursa lies between the superficial digital flexor tendon and the gastrocnemius tendon.
The gastrocnemius bursa lies deep to the gastrocnemius tendon.
The intertendinous bursa communicates with the gastrocnemius bursa 100% of the time, so for therapeutic purposes, these two bursae are usually considered to be one structure. The subcutaneous and intertendinous bursae occasionally communicate.
Inflammation of the bursa (bursitis) can be aseptic in cases of trauma that does not result in penetration of the skin. Horses with aseptic calcaneal bursitis show mild to moderate effusion of the bursa and varying degrees of lameness, usually exacerbated by flexion of the tarsus.
The term "capped hock" refers to distention of the subcutaneous bursa over the tuber calcanei in horses. Capped hock usually results from repetitive trauma (eg, kicking or leaning on stable walls). It is not generally associated with lameness, but it is a cosmetic blemish.
In occasional cases of capped hock, a subcutaneous abscess results from a penetrating injury and leads to painful swelling and lameness. Treatment of an abscess requires surgical excision and appropriate antimicrobial therapy.
Management of calcaneal bursitis in horses requires accurate diagnosis of the inciting cause, which typically requires ultrasonographic and radiographic evaluation. Septic calcaneal bursitis results most commonly from penetrating injury to the point of the hock (see septic calcaneal bursitis image). Initially, horses might not show substantial lameness; however, they progress to non-weight-bearing when infection develops within the intertendinous bursa.
Calcaneal bursitis is managed with systemic and local antimicrobial therapy, along with early bursoscopic lavage and debridement as needed. The prognosis for long-term soundness in horses with septic calcaneal bursitis after bursoscopic lavage varies by the duration of infection and the presence of calcaneal osteomyelitis.
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Also see pet owner content regarding joint disorders in horses.
