Diagnostic Imaging and Cytological Analysis Aid the Clinical Investigation of Long Digital Extensor Tendon Subtendinous Bursitis in a Horse.

The fetlock joint is a high mobility structure that accommodates enormous loading during locomotion. An injury of the superficial constituent such as subtendinous bursitis may occur due to repeated trauma. An 8-year old school riding horse was presented with dorsomedial distension in the left hindlimb fetlock region. The lesion was noted following routine exercise. The horse demonstrated no lameness and a negative response to the fetlock flexion test. Radiographic findings revealed a smooth surface cortical thickening on the medial aspect of the distal third metatarsal bone. Furthermore, the ultrasonography showed synovial thickening and proliferation, fibrous thickening with an irregular border in the inner synovial lining, and local protuberance of the fibrous layer within the bursa beneath the long digital extensor tendon. Cytological examination of the fluid from the distended lesion discovered multiple nucleated cells, including synoviocytes, nondegenerate neutrophils, lymphocytes, and macrophages. Eventually, the horse suffered subtendinous bursitis of long digital extensor tendon in the left hindlimb fetlock region. Intrabursa administration of 10 mg triamcinolone acetate alongside 25 mg hyaluronan (HA) and subsequent pressure bandaging were performed in the affected fetlock area. The distension was substantially reduced after the 4-week recovery period post medical administration. In summary, the horse was diagnosed with long digital extensor subtendinous bursitis that can occur accidentally. The diagnostic imaging and cytological analysis of accumulated fluid benefited a critical evaluation and facilitated the selection of the appropriate therapeutic plan for this defect.