Hip Dysplasia is a malformation of the hip joint which leads to degenerative joint disease and often times crippling arthritis in dogs. While breeds of all sizes can get hip dysplasia, large breed dogs are more prone to it.
Understanding Hip Dysplasia
The hip is a ball and socket joint where the head of the femur (thigh bone) is the ball and the acetabulum of the pelvis forms the socket. In dysplastic dogs, the shape of the head of the femur or the acetabulum or both are abnormal. As a result, the ball cannot rotate smoothly in the socket. The head of the femur slips partially out of the joint (sub-luxates) and bangs around in the acetabulum which causes trauma to the joint and leads to arthritis. Hip Dysplasia is an inherited trait. About 60% of the likelihood of developing hip dysplasia is based on the genes of the parents. The other 40% is based on environmental factors such as growth rate, amount of exercise during growth and trauma to the joint.
Diagnosing hip dysplasia can be done with a great degree of certainty by 14 weeks of age using a special radiographic technique called the Pennhip system. This procedure (developed at the University of Pennsylvania) allows us to determine exactly how loose the hip joint is by providing a view of the hips where we can measure how far the femur can be pulled out of the acetabulum. These measurements are calculated and a value known as the distractive index (DI) is determined. This value is compared to the averages of the breed and from that we can tell what the probability is that the pet will develop hip dysplasia and whether or not they are acceptable for breeding. In general, if the DI is greater than 0.45, the pet has over an 80% probability of developing dysplasia. Because dysplasia is heritable, we can select only pets with DI values that are better than the breed average to breed. In doing so, we can eventually reduce and hopefully eliminate dysplasia from that line of dogs.
The following video explains a comparison between PennHip and OFA Testing.
Preventing the clinical symptoms of dysplasia
Recently a minimally invasive technique known as the Juvenile Pubic Symphysiodesis (JPS) surgery has been developed to dramatically (80-90% reduction) reduce the chances that a pet at risk of developing hip dysplasia will actually get the disease. This surgery is performed on pets between 12 and 20 weeks and operates on the principle that if we can close the growth plate between the left and right halves of the pubis (the bones on the bottom of the pelvis), it will force the acetabuli to move further out to the sides and cover the femoral heads more effectively thus reducing the instability of the hip joint.
- The pelvis when viewed from a dog’s rear end is a circular
- The dark area at the bottom of the left drawing is the growth center (growth plate) of the pubic bone of the pelvis
- When the growth from this growth center (pubis) is stopped, yet the remaining parts of the pelvis grow, the sockets of the hips rotate over the ball of the hip (femoral head)
- Take note of the lack of coverage (shading) of the ball of the femur prior to surgery (below left) versus after the dog has finished growing (below right)
- The result is a stable hip that has much less chance of developing significant arthritis
How does our veterinary clinic select candidates for JPS surgery?
Hip dysplasia occurs more frequently in large breed dogs, but almost all breeds do have it. Because this procedure is only beneficial between the ages of 12 and 20 weeks of age, we recommend that all pets should be evaluated for potential hip dysplasia at 14 weeks of age using the Pennhip system. Pets with distractive index values above 0.45 should have JPS surgery and sterilization performed at 16 weeks of age.
What happens during the surgery?
- Your pet will be put under general anesthesia
- A small incision is made between the hind limbs to expose the pubic bone of the pelvis
- The growth plate of the pubis is cauterized to destroy the growing cells of this part of the pelvis
- Your pet will stay over night and go home the next day with pain medication and antibiotics to take for a few days.
- An Elizabethan plastic collar will be dispensed to prevent your pet from licking the wound.
Success of the JPS procedure
The earlier the procedure is performed in the 12-20 week age bracket, the greater chance that it will prevent significant development of arthritis of the hips. In general, there is a 90% chance that your pet will benefit from this surgery if he/she is predisposed to dysplasia based on a distractive index greater than 0.45.
This is a very safe and minimally invasive procedure when performed in young pets. Potential complications include:
- Failure of the pubic growth center to be successfully ablated by the cauterization surgery, thus the pelvis grows as it would naturally and the hip dysplasia progresses
- Seroma (a serum pocket) formed at the surgical site
- Infection is uncommon
- The Pennhip system allows us to reliably diagnose hip dysplasia at an early age.
- JPS surgery offers a minimally invasive and financially affordable method for reducing arthritis resulting from hip dysplasia if performed between 12 to 20 weeks of age.
- For information on interpreting Penn-Hip Results view this video and/or visit this Penn-hip.org