The Science and Decision Making Behind Surgical Treatments for Hip Dysplasia
Amy Kapatkin, DVM, Dip ACVS, Assistant
Professor of Surgery
Canine hip dysplasia is a prevalent disease but its true incidence is still unknown. OFAa reports the incidence at 1.8 - 48.1 % of dogs of certain breeds. 1 This is biased because radiographs rarely get submitted to the OFA if the veterinarian taking them finds evidence of DJD already present. 2,3 The extended view used by OFA masks laxity, (the number one risk factor for developing degenerative joint disease in the future), and therefore dogs may look normal on the extended view, yet be in a high risk group for developing DJD later in life. 2-5 A survey done by board-certified radiologist at The University of Pennsylvania's veterinary school determined that the incidence was probably 2-3 times higher than what OFA reports for each breed. 2,3 Until mandatory testing and submission of hip radiographs by breeders are instituted, the incidence of this disease is probably underestimated.
Although canine hip dysplasia can be a severely debilitating disease in certain individual dogs, 76% of dogs that have radiographic signs of hip osteoarthritis function normally without surgery. 6 Another study showed similar success rates with nonsurgical management of hip osteoarthritis. 100% of the owners were satisfied with their decisions not to do surgery and 86% indicated the dogs maintained soundness at high activity levels. The other 14% had only intermittent lameness. (Unpublished data presented by GK Smith at the VOS 26th annual conference, 1999).
In this era of rapid access to information and sophistication in veterinary surgery, it is important for surgeons to recommend treatments for canine hip dysplasia that are evidence-based instead of opinion based. This applies particularly to procedures that are touted as "preventative" surgeries. It is accepted that certain dogs with hip dysplasia will be clinical for their osteoarthritis, not respond to medical treatments, and need either a total hip replacement or femoral head and neck excision arthroplasty salvage procedure. What is still unclear is whether or not procedures such as the triple pelvic osteotomy (TPO), public symphysiodesis (PS), intertrochanteric osteotomy (ITO), femoral neck lengthening (FNL) or DARthroplasty truly affect or stop the natural progression of hip osteoarthritis. We have already seen procedures such as the pectinectomy and BOP/Sertl shelf arthroplasty that claimed to alleviate clinical signs of hip dysplasia, fall out of favor by surgeons. Some of this was due to a good evidence based study, showing that the Bob/Sertl shelf arthrosplasty was not osteoconductive, and did not change joint mobility or halt degenerative joint disease. 7 Studies have never shown a correlation between cutting the pectineal muscle and its relationship to alleviating signs of osteoarthritis long term even though abnormalities of certain pelvic musculatures may play a role in the development of hip dysplasia.8-12
The question is why certain procedures are considered by reputed surgeons as ineffective to prevent hip DJD while other procedures that have not been scientifically tested, are recommended and praised as the preclusion of osteoarthritis? Follow up has shown that DJD still occurs after these surgeries and therefore their efficacy has not really been established. 13-15 Why are there conflicting recommendations from experts in the same specialty and each person vehemently believes their advise is correct? It is because most clinical recommendations for treatment or prevention of disease come from global, subjective judgments and not evidence- based studies. 16
The common reasons for failures of treatment efficacy studies include poorly designed or nonrandomized groups, selection and response bias, variation of surgical procedures between patients in the same study and inadequate follow up (length of follow up and poor compliance with follow up). When applying this concept to "preventative" surgeries recommended for hip dysplasia, it is evident that the literature has articles that are descriptive studies or results from uncontrolled studies. Although there is some value in these types of studies, true outcome probabilities or guidelines for intervention can rarely be made from them. These descriptive studies, such as in the Schrader's publications, should be used as preludes to properly designed randomized clinical studies before the treatment is promoted for use. 17,18 If the treatment improves health outcomes, the benefits outweigh harms of outcome compared with no treatment, then the procedure should be applied to clinical use. 16 Combine that with tailoring treatment for severity of signs of the patient, owner expectations from the procedure, cost and invasiveness, it becomes clear that TPO, PS, FNL ITO and the DARthroplasty have not yet been properly investigated to determine if final outcome of our patients are better with these procedures than with no treatment at all. In the human medical field, demonstrating positive patient-oriented outcomes is viewed as more important than disease-oriented outcomes. 16 Applying this to "preventative" hip surgeries, it is not so important if the surgery changes radiographic coverage of the femoral head or if the dog has less DJD after surgery compared to non-operated dogs. It is important to know if after the surgical procedure the dog will have a better clinical result, will not need any medical treatment, and not need further surgical treatment compared to non-operated dogs. To accomplish this, a randomized, large, all- inclusive clinical trial of each of these surgeries compared to non-treated dogs must be performed. Since 76%- 86% of the dogs do well without surgery, then perhaps the surgical successes reported in the literature are simply because they would have done as well without any treatment.
This presentation will focus on surgeries that claim to prevent hip dysplasia. What is known and not known about each procedure and how performing some of these procedures can permanently affect genetic control of hip dysplasia in the future.
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