Radiographic evaluation of sclerosis of the third carpal bone associated with exercise and the development of lameness in Standardbred racehorses.

Abstract

REASONS FOR PERFORMING STUDY: Sclerosis of the third carpal bone is a common radiographic finding in both lame and sound racehorses, but there are no guidelines correlating degree of sclerosis and incidence of lameness. OBJECTIVES: To develop a protocol for describing subchondral bone sclerosis in C3 on dorsoproximal-dorsodistal oblique (DPr-DDiO) radiographs of the carpus and to correlate these changes with exercise history and carpal lameness. METHODS: One hundred and six Standardbreds entering their first year of training (exercise group) and 7 age-matched Standardbreds at pasture (controls) were examined at approximately 3 month intervals over 12-18 months. Examinations consisted of lameness evaluation and carpal radiographs (DPr-DDiO and flexed lateromedial projections). A grading system (very mild, mild, moderate and severe) for C3 sclerosis seen on the DPr-DDiO radiograph was developed that utilised a combination of the criteria of trabecular thickening (trabecular score; TS) and total percent area of the C3 radial facet affected (TAA). RESULTS: Exercise group horses showed significant increase in TS and TAA throughout training compared to control horses. Middle carpal joint lameness developed in 32/106 (30%) exercise group horses and none of the control horses. Incidence of middle carpal joint (MCJ) lameness was lower in horses with mild (2/30, 6.7%) than moderate (10/32, 31.2%) and severe (20/44, 45.4%) sclerosis throughout training. CONCLUSIONS: Horses with higher grades of sclerosis, as defined by this novel grading system, were more likely to develop MCJ lameness at some point of training. The proposed grading system gave a quantitative assessment of radiographic sclerosis that could then be used to correlate increasing severity of sclerosis with increasing incidences of lameness. POTENTIAL RELEVANCE: These results serve as a basis for further investigation into determining the degree of C3 sclerosis at which pathological changes and lameness can be expected.