Hip dysplasia (HD) is DJD of the hip joints caused by a combination of genetic and environmental / dietary factors.
Specialised distraction radiography (PennHIP or DLS techniques) can predict the likelihood of HD development from the age of 6 months.
Badly affected dogs can be treated with surgery (JPS / DPO) at less than 12 months of age or if older and unresponsive to medical management with THR.
Principally a problem affecting dogs (though it can affect cats), hip dysplasia has been recognised for many years in the veterinary literature as far back as the 1950’s as a collection of radiographic and clinical signs associated with reduced function and degeneration of the coxofemoral joint. Unfortunately incorrect interpretation of the original descriptions by both lay people and the veterinary community led to the term Hip Dysplasia being used as a definition of an etiologic agent rather than a description of a clinical syndrome. There is little doubt now that there are underlying abnormalities of growth and function of the coxofemoral joint that result in degeneration and reduced function of the joint. There are a number of genetic and environmental factors that contribute to this degeneration but they can be broadly broken down into the following groups:
- Factors affecting hip laxity. These are principally genetic BUT excessive weight or physical activity can contribute to stretching a weak coxofemoral joint.
- Factors affecting cartilage and joint biology. These are mostly environmental (e.g. diet) however there is some contribution from genetic factors such as poor capacity to produce proteoglycans.
The combination of these factors causes progressive damage to the cartilage of the hip joint result in arthritis, restriction of movement in the hip and pain.
Clinical signs can be varied and not all dogs show all signs. The most common signs are lameness, “bunny hopping” when running, reluctance to jump, pushing up with the front legs when getting up, slow to sit down, and reluctance to exercise. Most clinical signs with hip dysplasia are progressive and fairly gradual i.e. if the dog (or cat) is suddenly lame and won’t put a foot down that is unlikely to be hip dysplasia.
Diagnosis and radiography
Clinical signs of hip dysplasia can be similar to those of other orthopaedic diseases in dogs and cats as well. Notably cruciate ligament disease and to a lesser extent spinal disease can cause some similar clinical signs. If you suspect your pet has hip dysplasia then it is important to get them examined by a veterinarian and also radiographed to determine if the hips are the cause of the problem and how severe the damage is.
Unfortunately in the past radiographic techniques to assess hip dysplasia really only detected the problem after it had occurred and it was too late to intervene. Recent advanced distraction radiograph techniques such as PennHIP or DorsoLateral Subluxation (DLS) can accurately assess hip laxity and can predict the development of hip dysplasia from as early as 16 weeks and at 6 months have an almost 95% correlation with onset of clinical signs. These techniques measure how loose the hip joints are by putting pressure on the hips to try and distract them out of the joints. In addition as opposed to older techniques that were a sort of yes / no diagnosis of hip dysplasia, PennHIP and DLS actually give an indication of the severity of hip laxity and the likely age of onset of problems.
Treatment has traditionally been based around medical management of the DJD until the animal is no longer responsive at which point the only treatment option available is Total Hip Replacement (THR). The ability to diagnose a predisposition to hip dysplasia with PennHIP or DLS has meant that we have the option to perform procedures that can actually prevent hip dysplasia from occurring. The two procedures that have been most effective are Juvenile Pubic Symphysiodesis (JPS) and Triple / Double Pelvic Osteotomy (TPO/DPO).
Juvenile Pelvic Symphysiodesis (JPS)
- Pubic symphysis is fused at a young age whilst the pup is still growing, either with transsymphyseal staples or ablation of the symphysis growth plate with electrocautery.
- As the pup continues to grow the pelvis grows from the acetabular, ischiatic and ilial growth plates but the restriction at the pelvice symphonies results in the acetabulum “rolling” dorsally over the femoral head as it grows thus increasing femoral head coverage.
- The earlier it is done the greater the amount of “rollover”. Early work suggested that some benefit was possible when the procedure done before the age of 20 weeks, that was later revised to 16 weeks and it is now generally accepted that to get any real benefit it probably needs to be done at 12-15 weeks of age.
- Whilst relatively inexpensive (typical costs would be around $800-$1000 including concurrent desexing) the young age at which the procedure needs to be done, the fact that few animals are showing clinical signs at this age, the variable results particularly in animals with large DI and the development of a viable alternative in the Double Pelvic Osteotomy mean that this procedure is not commonly performed by specialists any more.
Double (Triple) Pelvic Osteotomy
- Originally developed for dogs by veterinarians Barclay Slocum and his engineer wife Theresa Devine as the Triple pelvic osteotomy. The original Slocum and Devine procedure made 3 cuts in the pelvis to essential create a free floating segment that was then rotated secured in a dorsolaterally rotated position to the ilium giving more coverage of the femoral head with a specially designed plate.
- Highly effective but an extremely technically demanding surgery it is prone to complications with a published screw pullout rate of close to 30% and a reoperation rate of 15% or more even in the hands of an experienced specialist with the possibility of catastrophic complications.
- Recently it was shown that the same effect could be achieved with just 2 osteotomies of the pelvis. Essentially the surgery is the same as the original TPO but the osteotomy of the ischium is not performed.
- This apparently relatively minor alteration produces a dramatic improvement in stability and reliability of the surgery. Still technically demanding but now in the hands of an experienced surgeon screw pullout rates are less than 10% and reoperation rates less than 5% with catastrophic complications extremely rare. Due to the dramatic increase in stability it has allowed bilateral DPO to be performed at the one procedure thus reducing cost and morbidity.
- As with TPO if there is already significant DJD then there is marginal benefit in performing the procedure. Consequently the surgery needs to be performed at between 6 months and 12 months of age. STRICT confinement is vital for 4 weeks post operatively. Outcomes though are excellent with various studies clearly demonstrating significant reduction in the incidence of DJD and resolution of clinical signs in early affected dogs.
- Whilst more expensive than JPS at around $7000 for a bilateral DPO the fact that it can be done at a later age when radiographic and clinical assessment is more reliable, and the much more reliable outcome in terms of rotation of the acetabular component of the hip joint compared to JPS (recent experience suggesting that over 30% of dogs undergoing JPS still require DPO), means that we now regard this as the procedure of choice and recommend assessing hips at 6-8 months of age to determine if a DPO is necessary.