THE ROLE OF COMPUTED-TOMOGRAPHY IN EVALUATION OF SUBCHONDRAL OSSEOUS LESIONS IN 7 HORSES WITH CHRONIC SYNOVITIS

Seven horses with severe, persistent lameness of sudden onset were eva luated with scintigraphy and/or computed tomography. The lameness was localised to the front fetlock joint in 2 horses and to the tibiotarsa l joint in 5 horses. Five of the horses had a history of intra-articul ar injections of the involved joint prior to presentation. All horses had effusion of the affected joint and were positive to flexion tests. Intra-articular anaesthesia eliminated or improved the lameness in 4 cases and a nerve conduction block proximal to the affected joint impr oved the lameness in another. Cytology examination of fluid from affec ted joints identified normal joint fluid (one horse) or elevations in nucleated cell counts of 0.9 x 10(9)/l-36.8 x 10(9)/l and total protei n 20-42 g/l (6 horses). The joint fluid of 2 of these horses cultured positive for bacteria. Initial radiographs were either normal (4 cases ) or the changes seen were not sufficient to explain the degree of lam eness. In the 6 cases where scintigraphy was performed, intense focal isotope uptake was found in the suspected region, which corresponded t o the proximal portion of the first phalanx (2 cases), distal tibia (2 cases), or talus (3 cases). Computed tomography (CT) was performed be cause occult fracture or osteomyelitis was suspected; and knowledge of the precise anatomical location of the lesion was considered necessar y to assess the need for surgery and to plan the surgical approach. Hy podense focal lesions with hyperdense haloes were found in the subchon dral bone deep to the sagittal groove of the first phalanx (P1) (2 cas es) in the cochlea of the distal tibia (2 cases), and in the intertroc hlear portion of the talus (3 cases). Communication between the lesion and the joint space was demonstrated by CT in 5 cases. Post mortem ex amination of one case revealed synovitis and a chronic bone abscess (B rodie's abscess) communicating with the joint space.