Veterinary Practice March 2014

FOR any given fracture the normal time to healing will vary according to the breed, age, general health, the bone involved, severity of the fracture (especially comminuted fractures), soft tissue damage and type of fixation. Delayed union can be diagnosed when no or minimal union of the bone is observed in what would be considered a “normal” healing time. “Normal” relates to that of a similar fracture, in the same bone of a patient of similar breed, age and general health, which has been repaired in the same way, and heals without complication. The causes of delayed union are typically one or more of: inadequate immobilisation, distraction, excessive compression, impaired blood supply, infection, excessive implant quantities or excessive fracture gap. Fracture gap may be the prime cause of delayed union because it often leads to other causes such as excessive motion at the site. This may cause soft tissue disruption, affecting vascular supply and ultimately callus formation. With internal fixation, external fixation and external coaptation, adequate stability is the key to the progress of healing. Cast immobilisation allows relatively large amounts of movement between fracture ends during the progression through haematoma, fibrin clot, cartilage and finally bone. Each stage will tolerate varying degrees of movement within the limits of each tissue. This tolerance varies over time and is susceptible to slight changes in treatment such as modification of casts or splints. This means re-examination and regular radiographic assessment is required as it may be necessary to modify support depending on whether the delay in healing is temporary or evolves into non-union. Following internal fixation, bone ends are fixed relative to each other and the gap between them is maintained. This may delay healing as lack of stimulation may prevent effective ingrowth of granulation tissue.