Anaesthesia of the Carpus/metacarpus and Hock/metatarsus

In athletic horses, forelimb lameness associated with the carpal joints and proximal metacarpus is common. Similarly, pain arising from the structures of the proximal metatarsus and distal tarsus is a common cause of hindlimb lameness in working horses of all disciplines. The synovial articulations of the carpus and distal tarsus may be affected by synovitis, osteoarthritis, fractures and soft tissue injuries. Pain arising from the proximal metacarpus and metatarsus is frequently considered to result from inflammation of the proximal one third of the suspensory ligament (PSL), often termed proximal suspensory desmitis (PSD); however, lesions of the enthesis of the PSL, the proximal metacarpal/tarsal bones and other important soft tissue structures such as the accessory ligament to the deep digital flexor tendon may also be the cause of lameness that is isolated to that region. Effusion of the carpal joints is readily identified on palpation; however, other palpable abnormalities that could be used to reliably identify lesions of the proximal metacarpus/carpus or metarsus/distal tarsus are infrequently encountered. A reduced range of motion on examination and an exacerbation of lameness following flexion of the carpus or proximal hindlimb may lead to a suspicion of carpal or tarsal pain but such findings should be corroborated by diagnostic regional analgesia or diagnostic imaging. Abnormalities seen on radiographic and ultrasonographic examination may be subtle or incidental with a substantial overlap of the normal and abnormal appearance of the structures affected. Thus, the diagnosis of lameness in the region of the proximal metacarpus/ carpus and proximal metatarsus/tarsus is heavily reliant on the findings of diagnostic regional analgesia. As there is considerable overlap of the effects of nerve and joint blocks in this region it is vital that the diagnostician is fully aware of the structures that may be anaesthetised by each nerve and joint block. Ultimately, more advanced imaging techniques such as MR imaging may be required to establish a diagnosis in challenging cases. [...]