Hypothesis 1: mal-union of fracture site The obstetric chains caused a fracture (or fractures-will be determined on radiographs). Since radiographs were not taken and the leg was just bandaged initially, the fractured bone fragments were not aligned properly. The hematoma formed around the mis- aligned bone fragments bringing in macrophages and osteoclasts to remove the dead bone and promote angiogenesis. Fibrin deposited in the hematoma to organize it and the macrophages initiate fibroplasia. Osteoprogenitor cells migrated into the fracture site from the medullary cavity and the periosteum. New blood vessels form from the surrounding soft tissue. During the remodeling phase, the fracture site is bridged by a callus and the mineralized cartilage is remodeled into woven bone. This remodeling phase lasts for awhile after the trauma, but once the callus forms the bone must be rebroken to set the limb properly. The following applies to all hypotheses: There can always be an infection with this kind of trauma and there is evidence of this in the calf since there is a purulent draining tract, severe limb edema and crepitus. The infection could have gained access into the bone and joint cavity through the wounds caused by the chains, the fracture or the actual casting/bandaging. With osteomyelitis, the bacterial multiplication causes an abscess and bone necrosis. The low pH and pO2 caused by the bacteria incite the death of the osteocytes and bone reabsorption. As the abscess progresses, pressure increases and there is further bone necrosis. Death of bone fragments (sequestra) and the growing abscess leads to the growth of the abcess to the skin (fistula). This would account for the draining tract. These changes can be seen radiographically. Since this is a young calf, the infection has probably spread to the joint cavity due to the architecture of the metaphyseal vessels (the metaphyseal vessels are connected with the epiphyseal vessels). The joint capsule would be distended and filled with fluid. As for the tight bands of tissue, there are two possible explanations. Since the skin was necrotic and sloughed off, the tight tissue could be due to contracture of the skin during the healing process. Also, since the calfÕs leg has been bandaged for so long, the tendons could have gotten tight from disuse. With moderate, regulated exercise, this will get better.