Cat, male castrated, less than 1 year of age. Found on the street, suspicious of trauma/HBC. At the clinical examination the cat was in good general condition, crepitus was felt on the right hind limb. Radiographic diagnosis
- Radiographs were taken of the thorax and of the right tibia/fibula.
- Thorax was interpreted as normal.
- There was a comminuted fracture of the right tibial diaphysis with 2-etage fracture of the proximal right fibula with accompanying moderate soft tissue swelling (compatible with bleeding, edema, cellulitis). There was moderate dislocation of the fracture fragments.
- The fracture was fixed with a DCP plate.
Pre OP (only ML view) and post OP (CrCa and ML view) of the fracture of the right tibia and fibula with documentation of the reposition and fixation of the tibial fracture.
- 2 months post OP radiographs show advanced but incomplete healing of the right tibial fracture and advanced healing of the fibula (not shown).
- 2 years later, the private vet tried to remove the plate. It was not possible to remove the implant completely, so the cat was referred to the veterinary hospital were the complete removal of the implant was performed.
CrCa and ML view after complete implant removal from the right tiba. Radiographic findings
- There is severe thinning of the cortex (thin arrows) and of the tibial diameter at the level of the original fracture.
- The bone opacity in this area is very heterogenous, with areas of decreased opacity in the medulla (big arrow).
The following day, after jumping from the bed, the cat was presented at the clinic again for acute lameness in the same limb. Radiographs were taken again. CrCa and ML view of the right tibia and fibula, showing transverse fracture at the level of the thinned tibial diaphysis and transverse fibular fracture. Mild dislocation and angulation also present. Comments
- There exist minimal data to suggest refractures rates or predisposing factors. The factors that have been suggested to influence refracture include initial fracture pattern (including comminution and displacement), implant characteristics, early removal of implants, and the lack of protection of the healed bone following implant removal.
- When an implant is removed, the biggest practical problem is that the limb is loaded too quickly or too often before adaptive changes can be made by the bone to areas of high stress created by the removal.
- It is a well known principle that any sudden change in the cross-section or shape of a uniform loead-bearing structure leads to localized high stresses. The most commonly proposed or clinical observed mechanical factors appear to be stress protection under an area of a plate.
- Over many years, rigid plate fixation has been associated with stress protection and subsequent bone loss. The clinical significance of this bone loss, whether by an increase in porosity or a decrease in bone mineral density is still matter of discussion.
- The main mechanisms of the loss of bone which occurs beneath the plates is due to interference with the local vasculature or protection form natural stress.
- The refractures are usually not really fractures through the old fracture plane, but fractures in the area where repair processes have been taking place.The total bone mass in the region of the refracture is usually reduced. In addition, the bone structure is not homogeneous. Histologically, the juxtaposition of fibrous and lamellar bone, new osteons and porosity might lead to stress concentration.
To be continued...
