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Fracture-Dislocation of Tarsus

Tia is an 8 year old Chihuahua cross. She was taken to the vet after she chased a cat in the garden, and afterwards couldn’t put any weight through her left back leg at all. Her vets took an x-ray and identified an injury to her hock joint – one of the tiny bones had fractured and dislocated, leaving the joint unstable.

Tia was referred to the YourVets Surgery Service at Smethwick for assessment and repair of her fracture. The injury Tia has sustained is extremely unusual; this type of fracture is seen almost exclusively in racing greyhounds. It always affects their right back leg, because when racing around the track this is on the outside of the curve and so most force is transferred through that leg. With repeated episodes of weight transfer, a stress fracture occurs. Tia must have been pretty determined to catch that cat!

Repairing a fracture associated with a joint space is always a surgical challenge. Normally, when a fracture is repaired, new bone grows across the gap between the fracture fragments and forms a callous which bulges out from the bone surface. Over time, the callous remodels and returns to the normal shape of the bone.

This is an efficient way of building strength rapidly so the bone can bear weight again. However, if a callous were to impinge on a joint space or cause the joint surface to be roughened, then this would create friction and pain when the joint was moved. Therefore, if a fracture involves a joint the surgeon must find a way to compress the two bone fragments together so there is no gap between them, so the bone can heal directly rather than by forming a callous.

Tia’s fracture was repaired using a lag screw. This technique involves placing a screw across the line of a fracture to compress the two fragments. A hole is drilled into the near bone (the fracture fragment) that is the same diameter as the thread diameter of the screw, then a second hole into the deeper bone (that the fracture fragment needs to heal to) that is the same diameter as the shaft diameter of the screw. The screw is then passed through the fracture segment and engages with the deeper bone, where it gains purchase and causes compression of the fracture line as it is tightened.

After her surgery, Tia wore a supportive bandage for 2 weeks, then was strictly rested for a further fortnight before being gradually allowed to build her exercise back up to what she could do before she was injured, over a total of about 4 months. The screw in her joint won’t be removed unless it causes her any problems in the future.

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