Hypothesis #1 
_ Trauma Ð fracture left metacarpus +
_ Secondary bacterial / mycotic invasion +
_ Improperly placed bandage / casting




The information presented in the history, physical exam, and orthropedic exam of the calf 
strongly suggest a metacarpal fracture on the left front leg. There is crepitation in the 
metacarpal region, likely due to bone fragments. The marked swelling in the metacarpal 
region is consistent with a fracture response. The etiology of the fracture is most likely 
due to the application of chains and subsequent force applied to the metacarpus during 
the dystocia. When pulling a calf, the chains are placed above and below the metacarpal-
phalangeal joint; this positioning coincides with the lesions on the leg, the decreased 
range of motion of the implicated joint, and the suspected fracture. Improper placement 
of chains (placing the chain only distal to metacarpophalangeal joint) would place 
abnormally high forces on the bones, joint capsule, ligaments, and supporting soft tissues.
This could explain fractures, joint dislocation, and joint ligament damage found on 
radiographic or ultrasound examination. The fracture is not healing properly, which is 
due to blood supply and stabilization provided by the cast / bandage. A left metacarpal 
fracture suffered three months ago should have already progressed through the bone 
healing processes of: initial inflammatory response, increased vascular supply, hematoma 
formation, fibrous tissue production, cartilage formation, new bone formation / 
remodeling. However, in a malunion situation, the normal pathogenesis of bone healing 
is altered leading to malalignment of the bones involved in the fracture. Good blood 
supply combined with some movement at the fracture site will lead to primarily fibrous 
tissue formation between the two bone ends. This fibrous tissue must then be replaced 
with dystrophic calcified tissue, which must THEN be replaced by bone. This is a very 
slow process, which could explain the lack of stabilization even after the cast was 
removed. Less or very poor blood supply to the fracture site further slows ossification 
(endochondral ossification) or prevents new tissue formation at all. The lack of new 
tissue formation is often associated with dead bone at the fracture site, which would be 
detected as a sequestrum on a radiograph. Any of the above scenarios could have resulted 
in the poor healing of the leg in this case. The bandage / cast may not have provided 
enough stabilization, thus allowing movement at the fracture site. Similarly, a disruption 
of the vascular supply could have occurred at the time of injury (trauma Ð chains), or post 
injury with the application of the bandage (too tight, tissue necrosis is present), or from 
the fibrin deposition contracting around arteries and venules in the affected region. The 
fracture fragments in a comminuted fracture could interfere with blood supply completely 
on their own. In large animals, delayed union is very common. Primary bone healing is 
virtually non-existent due to the size and weight of the animals. 

The presence of a draining tract on the wound after removing the cast suggests a 
secondary bacterial or mycotic infection has occurred. There is no reason to suspect an 
infection as a primary lesion; it is most likely to have developed subsequently to the 
fracture. At this point we believe the fracture to be closed, thus environmental 
contamination of the wound is unlikely. The increased blood supply to the area which 
occurs with inflammation predisposes the calf to a hematogenous infection, if there was 
bacteria present in the bloodstream. The metacarpal fracture or a damaged metacarpal-
phalangeal joint is a very nice place for an anaerobic bacteria to colonize. If the fracture 
were ÒopenÓ, then bacterial infection from the environment would be the most likely 
cause of the draining tract. 

The history and physical exam findings suggest improper application of the bandage and 
/ or cast. The presence of tissue necrosis in the affected region is most likely due to the 
bandage material being wrapped to tight around the lesion, cutting off superficial blood 
supply to the skin. Furthermore, neither the bandage nor the cast seems to have provided 
enough stability to the metacarpal bone to allow proper healing, as described above. 
Improper reduction of the fracture fragments could result in a delayed union or a 
malunion situation. Improper bandaging could have allowed abnormal compressive 
forces on the medial aspect of the metacarpal bone, causing the valgus deformity distal to 
the fracture. A bandage that is placed too tight could have caused direct soft tissue 
damage to the extensor tendons in the area (medial, lateral, and common digital extensor 
tendons).