I am presenting a brief overview of the natural history of hip dysplasia. There are several classic articles, including the two listed by Dr. Weinstein and Dr. Wedge. More recent reviews and publications, including those listed here, provide in-depth discussion on the natural history of hip dysplasia, and I highly recommend reading them. In general, we use the term hip dysplasia to refer to any abnormal development of the acetabulum, femoral head, or both. In our practice, however, we typically are using this term to describe inadequate coverage of the femoral head by the acetabulum. This inadequate coverage leads to focal chondral overload of the lateral acetabular rim and labrum, which can lead to degenerative arthritis. A systematic review by O'Connor et al. reported on 10,000 hips, all asymptomatic, and noted approximately a 2.3% prevalence of radiographic hip dysplasia. There have been multiple studies and estimates from the late 1980s that associated acetabular dysplasia with about 20% to 40% of patients with hip osteoarthritis. We are very particular in defining the dysplasia as developmental hip dysplasia versus congenital hip dysplasia, and this is supported by an article looking at universal hip ultrasound screening programs in Germany, which had been universally applied, and noted that despite this effort, 50% of patients undergoing periacetabular osteotomy for correction of developmental hip dysplasia had normal infant screening ultrasounds. Murphy et al. followed 286 patients who had undergone unilateral hip replacement for hip dysplasia. They evaluated the contralateral dysplastic hip and assessed parameters that would lead to advanced arthritis by the age of 65, and found several that were universally problematic, the first being lateral center edge with a degree of less than 16, acetabular index with a degree of greater than 15, femoral head undercoverage approximately 31%, acetabular index depth to width ratio of less than 38%, and those hips with the most proximal part of the sore seal was the lateral margin. And I've shown this from A, B, C, D, E as a pictorial representation of those measurements. Most orthopedic surgeons understand that hip dislocation and severe subluxation lead to osteoarthritis, however the evaluation of the mildly dysplastic hip is still somewhat of a challenge. There are a couple studies that looked at more mild hip dysplasia and the relative risk of osteoarthritis, the first one being a check study that looked at approximately 720 patients aged 45 to 65 and presented an odds ratio. If the lateral center edge was less than 25 degrees, it was a 2.83 odds ratio. If the anterior center edge was less than 25 degrees, it was also a odds ratio of 2.62, but having both parameters being less than 25 degrees increased the odds ratio to 5.45. Another prospective cohort of about 1,000 women aged 44 to 67 at enrollment obtained an AP pelvis x-ray at two years and then again at 20-year follow-up. What they noted was that for each degree of lateral center edge less than 28 degrees, there was a 13% increased risk of radiographic osteoarthritis and about an 18% increased risk of total hip arthroplasty. I think the caveats with these studies are that the relative risk was increased, however the overall absolute risk was still relatively low. A case example from my practice is a 40-year-old male that presented with right hip pain after activities. He had radiographic indices suggesting mild acetabular dysplasia and after a long discussion, he elected to proceed non-operatively. He avoided his impact activity and progressed with a strengthening program. He returned four years later with progressive pain and loss of motion. On radiographic evaluation, he's now developed significant joint space narrowing and evidence of osteoarthritis. Periacetabular osteotomy has been hypothesized to alter the natural history of hip dysplasia. Wiles et al. looked at 144 patients after PAO and compared the natural history progression to that of normal hips as well as hips with dysplasia. Their mean follow-up time was about 9.2 years and what they found is that PAO did alter the natural history progression of arthritis compared to the natural history of the untreated hip dysplasia hips. Specifically with hips treated with PAO with tonus 0, there was a 3% progression compared to 5% in the natural history and those with tonus 1, there was an 11% progression compared to 25% progression of the natural history of DDH hips. With tonus 2 hips, however, despite PAO, still progressed similarly to osteoarthritis. And what they noted was that the PAO shifted the osteoarthritis progression more closely to that of the non-dysplastic hip pattern. I've included references for further reading and in-depth discussion. Thank you.

hip dysplasia

acetabulum

osteoarthritis

periacetabular osteotomy

chondral overload