Fractures of the stifle

Fractures involving the stifle joint are most commonly found in immature animals. There are a wide variety of fracture types involving the distal femur, proximal tibia and patella. Detailed radiographic investigations are required to provide exact definition of the fracture and allow the surgeon to select the most appropriate method of fixation. Clinical findings on initial examination may be limited due to swelling associated with the fracture and pain experienced by the patient. It is however essential, to clinically evaluate both the soft tissue and bony structures in the joint. When fractures are present accurate reduction (especially if the joint surface is involved), proper regard for functional growth plates and careful handling of small fragments of bone, are of prime importance. Fracture stabilisation is achieved by basic principles. Since many of these animals are immature, bone healing will be optimal and fracture healing is normally not a problem.

Fracture of the distal femur

I) Supracondylar fracture of the femur

This is the most commonly seen fracture affecting the joint and is generally found in dogs 6-12 months of age and in cats up to 2yrs. A history of trauma either directly from a blow or following a fall may be provided. The animal is non weight-bearing on the affected limb and the joint is grossly swollen. Radiographs must be obtained to confirm the diagnosis. A lateral view of the stifle is the most useful film to establish this. It is essential that a cranio-caudal view should also be obtained to ensure that there is not an accompanying inter-condylar fracture.

Management

These fractures should be dealt with as rapidly as is reasonably possible. If fixation is delayed remodelling will occur and the bones may be fixed in the wrong location by the rapid production of a healing callus thus necessitating surgical break-down and the possibility of further damage. Early reduction is simple and achieved by fixing the fracture site and then carefully pushing the epiphysis forward so that it toggles into position when the fracture is moved into extension.

Factors affecting the selection of method of stablisation are:

• The age of the animal and therefore the remaining growth potential.
• The small size of epiphysis.
• Minimal compromise of the articular surface by implants

Reduction and stabilisation can be affected by many methods both closed and open. In younger animals the use of Rush pins, parallel placed K wires, crossed K-wires or a bone plate are all methods which give good stability. Rush pins and parallel K wires give minimal compromise to growth plate function. Specially designed condylar plates may be used in older or chondrodystrophoid animals. It is important whichever method is selected, to achieve accurate reduction of the fracture. Under-reduction of the fracture may lead to limited joint movement or fracture failure with re-displacement of the epiphysis caudally

II) Y or T fractures of the distal femur

These are encountered in immature animals. Cats or small breed dogs seem most prone to this injury. Clinically there may be swelling of the joint and movement may be accompanied by crepitus and pain. Radiographs will reveal the true extent of the injury and it is particularly important to differentiate these from simple supra-condylar fractures before surgery is commenced. These fractures are often un-displaced and require careful inspection of the pre-op films to confirm the diagnosis. Surgery involves reconstruction of the distal femoral condyle using pins and screws. Particular attention must be paid to obtaining accurate reduction of articular fractures. In most cases reduction of the intercondylar fracture or fractures is attempted first then the supra-condylar fracture is stabilised as described above.

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