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Improving hip joint conformation in HD-prone puppies
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Hip dysplasia is a common problem affecting various breeds, and still there are controversies about the best time and method of early recognition to choose the optimal treatment for each individual dog. This article in cooperation of DVM Newsmagazine and the American College of Veterinary Surgeons describes juvenile pubic symphysiodesis (JPS), a very promising minimally invasive surgical procedure for puppies at risk.
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The procedure is still investigational but shows promise for improving hip joint conformation in treated dogs.
The procedure was proposed in 1996, and investigated in a guinea pig model as a possible method of creating acetabular rotation in growing dogs with excessive hip joint laxity. In that study, JPS performed on immature guinea pigs resulted in pubic bone shortening with subsequent external acetabular rotation, and narrowing of the caudal pelvis.
Composition
The canine pelvic symphysis is composed of a fibrocartilagenous center with hyaline cartilage laterally.
This hyaline cartilage is the medial pubic physis and is responsible for much of the longitudinal growth of the pubis. By causing premature closure of both medial pubic physes, JPS results in shortened pubic bones while the rest of the pelvis develops normally. As growth occurs, the acetabula rotate outward theoretically resulting in improved coverage of the femoral heads. This rotation is similar to the effect gained by a triple pelvic osteotomy, but without the potential pain, expense, and gait abnormalities associated with that procedure.
The canine pubic symphysis is approached through a small ventral midline (female) or parapreputial incision. Soft tissues are cleared from the pubic symphysis (approximately 1.5 cm long in most large breed puppies) which is then ablated with electrocautery.
Precautions are taken to protect the soft tissue structures within the pelvic canal. The ischial symphysis (caudal half of the pelvic symphysis) is not disturbed. The animal is neutered during the same anesthetic episode, and can be discharged the same or following day. There has been no need to restrict activity.
What studies say
JPS has been investigated in both normal (Greyhounds) and dysplastic dogs.
The dose of electrocautery needed to result in growth plate closure has also been defined. These studies have found that acetabular rotation has occurred without any significant complications. Measures of hip joint laxity improve when compared to untreated controls i.e. hips that are Ortolani positive often become Ortolani negative following JPS, and PennHIP® distraction indices improve.
At present, we believe that JPS is optimally performed between 16 and 20 weeks of age. This means that puppies, of breeds prone to hip dysplasia, must be screened for hip laxity at 16 weeks of age using the PennHIP method. Puppies with excessive laxity and no radiographic evidence of degenerative joint disease are currently considered candidates for this procedure. It is mandatory that ovariohysterectomy or orchidectomy be performed at the same time to eliminate the dog from the gene pool.
Optimal timing
We hope to learn more about the optimal timing of the procedure in a variety of breeds. Most sporting breeds evaluated to date have approximately a 20o per hip improvement in acetabular rotation if JPS is performed at 16 weeks of age. By 22 weeks of age there is minimal improvement using JPS. It is not currently known if this window of opportunity can be extended for giant breed dogs. It must be stressed that this technique is still investigational and we do not feel that widespread use is warranted at present. A cooperative clinical trial is under way with several surgeons around the country. Longest follow-up to date is three years, and the results continue to be encouraging; however, more information regarding the ultimate outcome of dogs undergoing JPS must be collected.
Source: Kyle G. Mathews (2001): Investigational procedure shows promise for hip dysplasia-prone puppies. In: DVM Newsmagazine May 1, 2001. www.dvmnewsmagazine.com/dvm/
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