Bursitis is an inflammatory reaction within a bursa that can range from mild inflammation to sepsis. It is more common and important in horses. It can be classified as true or acquired. True bursitis is inflammation in a congenital or natural bursa (deeper than the deep fascia), eg, trochanteric bursitis and supraspinous bursitis (fistulous withers, see Arthropathies in Large Animals: Fistulous Withers and Poll Evil). Acquired bursitis is development of a subcutaneous bursa where one was not previously present or inflammation of that bursa, eg, capped elbow over the olecranon process, shoe boil over the point of the elbow, and capped hock over the tuber calcaneus.
Bursitis may manifest as an acute or chronic inflammation. Examples of acute bursitis include bicipital bursitis and trochanteric bursitis in the early stages. It is generally characterized by swelling, local heat, and pain. Chronic bursitis usually develops in association with repeated trauma, fibrosis, and other chronic changes (eg, capped elbow, capped hock, and carpal hygroma). Excess bursal fluid accumulates, and the wall of the bursa is thickened by fibrous tissue. Fibrous bands or a septum may form within the bursal cavity, and generalized subcutaneous thickening usually develops. These bursal enlargements develop as cold, painless swellings and, unless greatly enlarged, do not severely interfere with function. Septic bursitis is more serious and is associated with pain and lameness. Infection of a bursa may be hematogenous or follow direct penetration.
The pain in acute bursitis may be relieved by application of cold packs, aspiration of the contents, and intrabursal medication. Repeated injections may result in infection. Treatment of chronic bursitis is surgical. In infected bursitis, systemic antibiotics as well as local drainage are required.
Capped Elbow and Hock
Capped elbow and hock are inflammatory swellings of the subcutaneous bursae (acquired bursitis) located over the olecranon process and tuber calcaneus, respectively, of horses. Trauma from lying on poorly bedded hard floors, kicks, falls, riding the tailgate of trailers, iron shoes projecting beyond the heels, and prolonged recumbency are frequent causes.
Clinical Findings and Diagnosis
Circumscribed edematous swelling develops over and around the affected bursa. Lameness is rare in either case. The affected bursa may be fluctuating and soft at first but, in a short time, a firm fibrous capsule forms, especially if there is a recurrence of an old injury. Initial bursal swellings may be hardly noticeable or quite sizable. Chronic cases may progress to abscessation.
Acute early cases may respond well to applications of cold water, followed in a few days by aseptic aspiration and injection of a corticosteroid. The bursa may also be reduced in size by application of a counterirritant or by ultrasonic or radiation therapy. Older encapsulated bursae are more refractory. Surgical treatment (usually curettage and drainage) is recommended for advanced chronic cases or for those that become infected. A shoe-boil roll should be used to prevent recurrence of a capped elbow if the condition has been caused by the heel or the shoe. With capped hock, behavioral modification so the horse does not kick the stall offers the only hope of permanently resolving the problem.
Fistulous Withers and Poll Evil
Fistulous withers and poll evil are rare, inflammatory conditions of horses that differ essentially only in their location in the respective supraspinous or supra-atlantal bursae. This discussion is of fistulous withers but, except for anatomic details, also applies to poll evil. In the early stage of the disease, a fistula is not present. When the bursal sac ruptures or when it is opened for surgical drainage, and secondary infection with pyogenic bacteria occurs, it usually assumes a true fistulous character.
The condition may be traumatic or infectious in origin. Agglutination titers support an infectious etiology. Brucella abortus and occasionally B suis can be isolated from the fluid aspirated from the unopened bursa, and outbreaks of brucellosis in cattle (see Brucellosis in Large Animals: Brucellosis in Cattle) have followed contact with horses with open bursitis. A Brucella titer should always be evaluated in these cases; if significant, the owners should be made aware of the public health significance.
The inflammation leads to considerable thickening of the bursa wall. The bursal sacs are distended and may rupture when the sac has little covering support. In more chronic, advanced cases, the ligament and the dorsal vertebral spines are affected, and occasionally these structures necrose.
In the early stage, the supraspinous bursa distends with a clear, straw-colored, viscid exudate. The swelling may be dorsal, unilateral, or bilateral, depending on the arrangement of the bursal sacs between the tissue layers. It is an exudative process from the beginning, but no true suppuration or secondary infection occurs until the bursa ruptures or is opened.
Treatment and Prevention
The earlier treatment is instituted, the better the prognosis. The most successful treatment is complete dissection and removal of the infected bursa. The expense of the protracted treatment required in chronic cases often exceeds the value of the animal, and the public health aspects (in cases in which Brucella spp are involved) should be carefully considered. Brucella vaccines have not proved helpful. Sodium iodide therapy is of limited value. It is reasonable to keep horses separate from Brucella-infected cattle, and cattle separate from horses with discharging fistulous withers.
Last full review/revision March 2012 by C. Wayne McIlwraith, BVSc, PhD, DSc, FRCVS, DACVS