Hip Dysplasia in Adults
Patient information — Dr Christopher Spelman, Orthopaedic Surgeon
Why hip dysplasia turns up in adulthood
Hip dysplasia is usually thought of as a condition of babies. But newborn screening does not detect every case, and milder forms cause no problem in childhood at all. A shallow socket can function adequately for two or three decades before the extra load on the rim begins to tell.
The result is that a significant number of people first learn they have hip dysplasia in their twenties or thirties, when they present with groin pain — often having been told for years that it was a muscle strain, a labral tear, or nothing.
What is actually wrong
In a normal hip, the socket covers the ball well and the load passing through the joint is spread across a broad surface. In a dysplastic hip the socket is shallow, tilted, or facing the wrong direction, so the ball is under-covered.
Two things follow. The load concentrates on a small area at the rim of the socket, at pressures the cartilage was not built for. And the hip is subtly unstable, so the labrum and surrounding muscles work harder to hold it in place.
Over time this produces labral tears, cartilage loss at the rim, and eventually arthritis — typically decades earlier than would otherwise occur.
Symptoms
• Groin pain, worse with activity, standing or walking distances
• A sense of the hip giving way, catching, or feeling unstable
• Pain on the outside of the hip from the muscles working overtime
• Fatigue in the hip after prolonged activity
• Sometimes a limp late in the day
Many patients are hypermobile, and many have been very active — dancers, gymnasts and runners are over-represented.
Diagnosis
Diagnosis rests on a weight-bearing AP pelvis X-ray, from which the coverage of the femoral head is measured. Additional views assess the front and back coverage of the socket. MRI shows labral and cartilage damage. CT is sometimes used for surgical planning.
An important point: the severity of symptoms does not track neatly with the severity of the dysplasia on X-ray. Mild dysplasia can be very symptomatic, and the decision to operate is based on the whole picture, not a single measurement.
Treatment
Non-operative treatment — physiotherapy to build the muscles that stabilise the hip, activity modification, and weight management where relevant. This helps symptoms and is always worth doing. It does not change the shape of the hip or the long-term course.
Periacetabular osteotomy (PAO) — the socket is cut free from the pelvis and rotated into a position that covers the femoral head properly, then fixed with screws. This redistributes load across a broader surface and stabilises the joint. It is the definitive treatment for symptomatic dysplasia in a hip that has not yet developed significant arthritis.
Hip replacement — where arthritis is already established, joint preservation is no longer possible and replacement is the appropriate operation.
Hip arthroscopy alone is generally not appropriate for a dysplastic hip. Treating the labral tear without addressing the under-coverage that caused it can worsen instability. This is a well-documented pitfall.
What the evidence shows
PAO changes the natural history of the dysplastic hip. A systematic review and meta-analysis of 24 studies covering 3,471 patients and 3,655 hips found survivorship of the native hip — that is, not having progressed to hip replacement — of approximately 75.9% at 10 years and 36.5% at 20 years (Tan et al., 2022). These number are much better in patients that do not have pre-existing arthritis and are younger.
Patient selection is what determines the result. The same analysis identified two significant negative prognostic factors: age over 40, and pre-operative Tönnis grade 2 or above — meaning arthritis already established on X-ray. The authors concluded the ideal candidate is under 40 with a Tönnis grade of 0 or 1 (Tan et al., 2022).
This is the single most important thing to understand about PAO: it works well in hips that have not yet worn out, and less well in hips that have. Which is an argument for diagnosing dysplasia early rather than watching it.
Patient-reported outcomes improve substantially. A systematic review of patients with no prior intervention found Harris Hip Scores improving from a mean of 68.9 before surgery to 89.1 after, with six of seven included studies achieving a minimally important clinical difference (Akhtar et al., 2023).
Complications
PAO is major surgery and the complication rate is not trivial — the meta-analysis reported an overall rate of 23.5%, though most complications were manageable and did not require further surgery (Tan et al., 2022).
The most frequently reported were:
• Numbness over the front or outer thigh (lateral femoral cutaneous nerve dysaesthesia) — around 8.2%. Usually improves, sometimes permanent
• Stress fracture — around 5.3%
• Delayed union, non-union or pseudarthrosis of the pubic ramus not requiring surgical correction — around 3.7%
Other recognised risks include sciatic or femoral nerve injury, bleeding requiring transfusion, infection, blood clots, prominent screws requiring removal once the bone has healed, intra-articular extension of the bone cut, and under- or over-correction.
Recovery
PAO recovery is measured in months rather than weeks. Expect a period of protected weight-bearing while the pelvis heals, followed by a progressive rehabilitation programme. Most patients are back to low-impact activity within a few months and continue improving over a year or more.
Depending on patient factors, Dr Spelman will generally have patients touch weight bearing up until 4-6 weeks post-operatively with crutches and then gradually increase from this point. Patients cannot run or jump until the pelvis is united at 4-6 months after surgery.
Why it matters to get this diagnosis right
Untreated symptomatic hip dysplasia does not stay still. The distinction between a hip that can be preserved and one that can only be replaced is largely a question of how much cartilage remains — and that is a function of time.
A young adult with groin pain, a labral tear on MRI and an unmeasured X-ray is a common and consequential miss. If your hip pain has been attributed to a labral tear without anyone measuring your socket coverage, it is worth asking the question.
References
1. Tan JHI, Tan SHS, Rajoo MS, Lim AKS, Hui JH. Hip survivorship following the Bernese periacetabular osteotomy for the treatment of acetabular dysplasia: a systematic review and meta-analysis. Orthop Traumatol Surg Res. 2022;108(4):103283. DOI
2. Akhtar M, Razick DI, Wen J, et al. Patient-reported outcomes and factors impacting success of the periacetabular osteotomy. Cureus. 2023;15(4):e37320. DOI