Fractures of the third metacarpal/metatarsal condyles: Hong Kong perspective

Pathogenesis

Parasagittal fractures of the distal condyles of Mc/MtIII originate from pathological defects in the palmar aspect of the distal condyles of the third metacarpal or metatarsal bone. The majority involve linear fissures in the mineralised cartilage and subchondral bone, which arise in either the medial or lateral condylar groove [1]. The pathological origin of these fissures remains elusive although there is evidence that some may be developmental while others result from coalescence of fatigue-induced microdamage [2,3]. The remainder originate from larger, focal defects in the subchondral bone that are located more centrally within the condyle, associated with palmar osteochondral disease (POD) lesions. Whatever the origin of the defects, they are likely to be associated with fatigue damage of underlying subchondral bone. The defects act as flaws, which concentrate stress, thereby further accelerating the rate of damage accumulation and crack growth. Once the initial crack reaches a critical length it will propagate explosively. Orientation of trabeculae in the distal condyles provides little resistance to crack growth and tends to guide the fracture proximally.

Diagnosis

Complete displaced fractures are relatively easily diagnosed because of profound distension of the joint as a result of haemorrhage, obvious pain on flexion of the fetlock and the presence of swelling associated with the displacement of fracture fragments. Short incomplete fractures can be difficult to diagnose. There are often few, if any, localising signs. Lameness is abolished by perineural anaesthesia of the palmar and palmar metacarpal nerves at the level of the distal extremity of the splint bone but may be only partially improved by intra-articular analgesia of the fetlock joint. Usually these fissures are only visible on the flexed dorsal 125° distal to palmaroproximal oblique projection of the metacarpophalangeal joint and plantar 60° proximal–dorsodistal oblique projection of metatarsophalangeal joint [4].  […]