Alteration of distal tarsal subchondral bone thickness pattern in horses with tarsal pain

REASONS FOR PERFORMING STUDY: Understanding of the development of pathology and source of pain in distal tarsal osteoarthritis is poorly understood. Magnetic resonance imaging is often used in the analysis of human osteoarthritis (OA) because it is sensitive to early changes. HYPOTHESIS: In association with distal tarsal joint (DTJ) pain, there will be an alteration in the characteristic subchondral bone (SCB) thickness pattern of horses with no history of pain when subjected to low-level exercise. METHODS: Sixteen cadaver tarsal joints were collected from 9 mature horses with a history of tarsal pain and radiographic evidence of OA; 3 cadaver tarsi were collected from 2 mature horses with a history of tarsal pain and no radiographic abnormality. Magnetic resonance images were acquired using high-resolution sagittal 3D T1 weighted spoiled gradient echo sequence. Subchondral bone thickness was measured on sagittal images at dorsal and plantar locations on the proximal and distal aspects of the central (CT) and third (T3) tarsal bones and proximal aspect of the third metatarsal bone (MT3). RESULTS: In tarsi with radiographic evidence of OA medial and lateral SCB thicknesses were greater than midline on the proximal and distal aspects of CT and T3. Lateral SCB thickness was greater than medial on the proximal aspect of MT3. There was an increase in SCB thickness at the majority of sites compared with normal horses. There were too few joints in the group without radiographic changes to analyse statistically. In painful tarsi SCB thickness was greater medially than laterally at all sites. In horses without tarsal pain all lateral sites had greater SCB thickness, except the proximal aspect of CT. CONCLUSIONS: There is alteration of normal SCB thickness patterns in painful tarsi. Different thickness patterns could represent different types of pathological processes. Potential clinical relevance: Further work is required to elucidate the pathological processes leading to OA of the DTJs.