The fetlock region

Horses undergoing any activity may sustain an injury to the metacarpophalangeal/metatarsophalangeal (MCP/MTP) joint. This chapter refers to the MCP/MTP joint as the fetlock joint and addresses the differences between the fore and hind joints. Magnetic resonance imaging (MRI) of the fetlock region can be used as a method of further evaluating known or suspected pathology, localized to the region by diagnostic local analgesia. Slice positioning should aim to evaluate the entire joint including distal third metatarsal bone, proximal phalanx and proximal sesamoid bones (PSBs) and the supporting soft tissues. Subchondral bone (SCB) pathology is an important cause of fetlock joint lameness and is thought to play a role in the pathogenesis of osteoarthritis (OA), osteochondral fragmentation, fractures and SCB necrosis, which represent the most common causes of fetlock lameness in all types of athletic horse. Suspensory ligament branch injuries may be detected using MRI when they are not apparent ultrasonographically.