Diagnosis: Iatrogenic fracture of the distal diaphysis of the left metacarpus and subsequent valgus deformity due to delayed union and probable inappropriately applied cast. Difficulties were encountered during the calving period most likely due to increased size of the calf. Because of birthing difficulties, obstetric chains and Franks Calf jack were used to aid fetal extraction. Fetal extraction with excessive forelimb traction commonly causes fractures in assisted calvings. We speculate this was the beginning of this calfŐs problem. Before radiographs, we suspect there probably is a metacarpal fracture because the normal placement of obstetric chains is in this area and because of the instability and crepitance of the leg upon manipulation. The most serious complicating factor in neonatal fractures is not usually the fracture itself; rather, it is the soft tissue damage and resultant interference with vascular supply distal to the fracture site when using chains. It should be assumed in most cases of forced extraction leading to fractures that moderate to severe trauma to the major vessels will occur and that there will be delayed healing. In this particular case a heavy bandage was applied for one month immediately post calving due to the suspected fracture in an attempt to provide stability. We do not know if radiographs were taken at this time to aid in fracture reduction but considering that the animal now has a valgus deformity, we assume that attempts to align the fracture appropriately were not made. In young calves, casts should ideally be replaced every 3 weeks; however, with vascular compromise the healing progress should be monitored rigorously with radiographs and cast applied accordingly. In this case, this did not happen and at 2 weeks post initial cast placement, areas of skin fell off, indicating possible necrosis of the damaged skin due to lack of blood supply. In addition there is no mention of antibiotics being used when the initial injuries occured and this probably lead to the infection seen at our exam with pus exuding from draining tracts. We do not have any indication of what type of cast was actually applied in this instance. After the one month bandage, the fracture was found to still not be stable so a half limb cast was applied for 3 weeks. As previously mentioned, delayed healing should be expected with any vascular compromise and this may have been overlooked in this case and another inappropriate bandage may have been applied. We are unsure as to where exactly the half limb bandage started and ended; however ideally a cast should at least cover/stabilize the joints above and below the fracture site. If this cast did not go over the carpal joint ( the more proximal joint of the fracture, and instead ended in the midmetacarpal or proximal metacarpal region then this would have lead to increase stressed on the fracture site and would also cause severe sore rubs. When dealing with fractures, whether placing a cast or doing internal/external fixation you need to take into account orthopedic biomechanics. Special consideration needs to be given to young growing animals since any change in compressive or tensile forces can cause an alteration in the growth pattern since the growth plates are still susceptible. Five forces need to be considered: 1) Stress: the force per unit area acting on material in a specific plane; 2) Strain: the resulting deformation oor change in dimension of material. Strain may be produced by stresses of tension, compression or sheer;3) Compression: a force such as weight bearing that tends to reduced the dimension of the pane in which it operates;4) Tension: a force that tends to increase the dimesion of the plane in which it operates. 5)Shear: forces generated when opposing foces operate in different regions of the same plane. Depending on bone shape, and loading characteristics, different aspects of weight bearing bones have regions of compression and tension forces. The regions are usually termed the tension and compression sides of the bone and are CRITICAL to the placement of stabilizing materials. In large animals, delayed unions are common. This is due to the size/weight of the animals, usually of adults. Even with proper fixation, rigid stabilization often does not occur. Local factors that can lead to delayed union include instability, vascular compromise, large fracture gaps, interposed soft tissue, infections, and inappropriate fixation techniques. Instability, vascular compromise, large fracture gap, infection and inappropriate stabilization with the cast may have all contributed to the delayed union in this calf. When there is less than ideal vascular supply and movement of the fracture site, the pluripotential cells become chondroblasts instead of fibroblasts. The cartilage plate that forms at the fracture site must be replaced by bone thru the slow process of endochondral ossification. Because of the plane in which the fracture occurred, upon weight bearing the forces on the medial aspect of the limb would cause the limb to turn out laterally since there was less support on the lateral side of the fracture. Perhaps if a splint had been placed on the lateral aspect of the limb for extra support this would not have occurred. Healthy, well vascularized bones heal to functional union usually by 3 weeks in calves due to their ability to quickly form new periosteal bone and substantial callus formation and usually do not lead to abnormal conformation. The fact that there was still instability at 3 weeks may also indicate compromised vasculature of the area. In summary, the pathogenesis of the lameness of this calf is as follows: the distal metacarpal region was fractured during forced extraction and there was also soft tissue damage. Due to the probable vascular compromise and possibly improper stabilization as well as infection of the area ( no antibiotics, skin sloughing off) there was delayed union. In addition the leg may not have been stabilized such that the compressive forces on the medial and lateral side were equal leading to excess compression on the medial side, forcing the leg out laterally during the rapid growth period of this calf. The original bandage was only described as being a heavy bandage. If this bandage was placed too tightly, the vascular supply may have been further compromised leading to the swelling seen. The healing process would normally be delayed in such circumstances but after one month when there was still instability of the leg, only a half limb cast was placed on the limb. If this cast did not cover/stabilize the joints above and below the fracture site then compressive forces were again most likely not equal leading to further deformity in angulation.