Lame pony A 1 year old shetland pony was radiographed because of lameness on the right hindlimb and swelling around the metatarso-phalangeal joint - the owner suggested a possible puncture wound in the limb from a “pitchfork” being used to encourage the pony to move more quickly. Radiographs were made of the fetlock joint - dorsoplantar and lateral views are shown. Radiographic diagnosis Prominent soft tissue swelling is identified with the probability the fluid is both intra- and extra-capsular - bony changes are not clearly seen - the proximal interphalangeal joint laxity is probably due to the pony not being weight-bearing during the examination. Oblique views were made to complete the study. Radiographic diagnosis The oblique views clearly show the bony destruction in one proximal sesamoid bone with a radiopaque bony fragment in the center of the lytic zone (arrows). The radiographic diagnosis was that of an osteomyelitis with a possible sequestrum - the clinical history supported a puncture wound as the source of the infection. The other proximal sesamoid bone was considered radiographically normal. Comments Bone infection often causes a pattern of periosteal response in addition to the bony lysis - the proximal sesamoid bones have a poorly defined periosteum and thus new bone production as a part of the radiographic feature of an osteomyelitis in this bone is minimal, if identified at all. Sequestra are usually formed of dense cortical bone - however, the blood supply in the proximal sesamoid bones is minimal and sequestration is possible in the trabecular bone. It is obvious that oblique views are a necessary part of a radiographic examination of the metatarso-phalangeal joint.
