Puppies have growth plates at the ends of the femur bones from which the bone grows. These growth plates are susceptible to developing fractures in immature animals. One such growth plate is called the capital physis and is located at the head of the femur bone. This head forms the ball of the hip joint. When a fracture occurs through this growth plate the cap of the head of the femur slips off; hence this fracture is referred to as a “slipped cap.”
Cause of fracture
This type of fracture only occurs in dogs that are less than one year of age and cats that are just under 2 years of age. The most common cause of a femoral fracture is trauma, such as being struck by a vehicle or taking a fall.
Slipped cap fractures require surgery for a successful outcome. The surgery should be done as soon as possible so that broken end of the bone does not get worn down, thus preventing the fracture from fitting together properly. In small dogs and cats, a simple procedure called a femoral head and neck excision is a very acceptable treatment. This involves removing the broken fragment and the neck of the femur bone to allow a false joint to form (see figure right).
In medium to large dogs, primary repair of the fracture is always recommended. Generally two pins are inserted in the bone to stabilize the fracture.
Surgery usually gives an acceptable outcome; however, it is possible that the dog may no longer be as athletic (such as a hunting dog). Dogs that are four months and younger tend to develop much more arthritis than older puppies with the same fracture. Uncommon complications include infection, breakage of the pins, and sciatic nerve damage. In general, most small dogs and cats that receive a femoral head and neck excision surgery regain very good function on the limb. Primary repair of the fracture has been reported to be successful in 80% of the cases; whereas, no surgery will result in persistent lameness and hip pain.
For more information on this subject, speak to the veterinarian who is treating your pet.