Diagnosis: delayed union of left metacarpal fracture With the difficult birth, chains were placed on the metacarpals of the calf. The calf was pulled incorrectly, placing too much force on the metacarpals with the chains. The chains not only caused wounds on the outside of the metacarpals, but also resulted in fracture of the left metacarpal. In order to stabilize the fracture, a bandage was placed on the metacarpal. The bandage, however, was improperly placed, not taking a proper amount of force off of the fracture area, and cutting off the blood supply to the area, so that healing was not allowed. Since radiographs were not taken and the leg was just bandaged initially, the fractured bone fragments were not aligned properly. The instability of the fracture fixation (bandaging), large fracture gap, and infection led to delayed union (evidenced by persistence of the fracture gap 3 months after fracture treatment, causing continued lameness and instability, angular deformity, and enlargement of fracture ends). Delayed union can be caused by inadequate fracture fixation or a loss of blood supply to the area. In this calf, both of these causes contributed to the delayed union. The necrotic, sloughing skin indicates that the bandage was applied improperly and cut off the blood supply. This compromised the extraosseous blood supply, which is essential in the initial stages of bone healing. Also, the excess movement of the fracture site due to improper fixation inhibited angiogenesis in the area and impaired the ability to form a callus. In fact, there is very little callus formation indicating an oligotrophic or slight hypertrophic delayed union. The classification would be made easier if the infection was not present causing bone lysis. This fracture has the potential to heal if the infection is cleared up and the bone is aligned properly. This would not be considered a non-viable delayed union due to lack of blood supply because there is evidence that the blood supply in the area has returned, as indicated by the newly formed granulation tissue, a highly vascularized tissue. Depending on the blood supply, the pleuropotential cells were led to become either fibroblasts, which created fibrous tissue between the fracture ends or chondroblasts, which build a cartilage plate at the fracture site. If the blood supply was severely impaired, no tissue formation between the ends is a possibility (cartilage and fibrous tissue are too radiolucent to be distinguished radiographically from an empty space). Fibrous tissue would need be destroyed and replaced by dystrophic calcification, then ossification, while a cartilage plate would be replaced with bone via endochondral ossification Đ both slow processes. The infection of the fracture is likely from skin (S. aureus) and dirt (E. coli) contamination via the skin wounds caused either by the chains, the fracture, or the cast/bandage. 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. This explains the infectious contribution to the delayed union. These changes can be seen radiographically. The radiographs show dramatic periosteal proliferation and bone lysis, signs of osteomyelitis. The draining tract seen on the skin also supports the diagnosis of osteomyelitis. 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, thus explaining the decreased range of motion. This would contribute to the severe swelling in the metacarpal region. As for the tight bands of tissue, there are still 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 calfŐs leg has been bandaged for so long, the tendons could have gotten tight from disuse. With moderate, regulated exercise, this will get better. Based on the radiograph, it does not look like growth plates were damaged, improving the prognosis of the healing process.