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Is hip morphology a risk factor for developing hip osteoarthritis? A systematic review with meta-analysis

The upshot

Is abnormal hip bone shape (cam, dysplasia, or pincer morphology) a risk factor for developing hip osteoarthritis?

This systematic review of 30 studies (over 42,000 hips) examined whether the shape of the hip bones raises the risk of developing hip osteoarthritis. Cam morphology (a bumpy femoral head) and hip dysplasia (a shallow socket) were consistently linked to developing hip OA in prospective studies, each roughly doubling the odds. Pincer morphology (an over-deep socket) was linked to OA only in cross-sectional snapshots, not in studies that followed people over time, so its role is less certain.

SupportsRead paper
Meta-analysis25,898 ParticipantsModerate evidence

Key points

  1. Hip morphology refers to the bony shape of the femoral head and socket, measured on X-rays using angles like the alpha angle and lateral center-edge angle.
  2. Cam morphology (an aspherical femoral head) at baseline roughly 2.5 times the odds of later developing hip OA in prospective studies.
  3. Hip dysplasia (an under-covered, shallow socket) was consistently linked to OA, about 2.4 times the odds, across study designs.
  4. Pincer morphology (an over-covered, deep socket) was associated with OA only in cross-sectional studies, not in prospective ones.
  5. Most cross-sectional studies were low quality, and measuring hip shape in hips that already have OA can overestimate the link.

How it was conducted

Design
Systematic review with meta-analysis of prospective and cross-sectional studies (PRISMA, PROSPERO CRD42019138232)
Search
MEDLINE, EMBASE, Web of Science, Scopus, Cochrane Library, and PEDro from inception to June 2020
Participants
9 prospective and 21 cross-sectional studies; 42,831 hips from about 25,898 individuals (mean age 59, 60% women)
Intervention
Radiographic hip morphology (cam, dysplasia, pincer, and others) compared between hips with and without OA
Outcomes
Prevalence, incidence, or progression of hip OA by radiographic grading or total hip arthroplasty
Analysis
Random-effects (DerSimonian-Laird) odds ratios with 95% CI; Newcastle-Ottawa Scale for risk of bias

What they found

  • Prospective studies, cam morphology (alpha angle >60 degrees): OR 2.52 (95% CI 1.83 to 3.46, P < 0.001) for developing hip OA.
  • Prospective studies, hip dysplasia (LCEA <25 degrees): OR 2.38 (95% CI 1.84 to 3.07, P < 0.001).
  • Prospective studies, pincer morphology (LCEA >39 degrees): OR 1.08 (95% CI 0.57 to 2.07, P = 0.810); not associated.
  • Cross-sectional studies, pincer morphology (LCEA >39 degrees): OR 3.71 (95% CI 2.98 to 4.61, P < 0.001).
  • Cross-sectional studies, acetabular retroversion (crossover sign): OR 2.65 (95% CI 1.17 to 6.03, P = 0.020).
  • Median follow-up of prospective studies was 7.6 years; 92% of prospective but only 13% of cross-sectional studies were good quality.

Limitations

  • Most cross-sectional studies were low quality, with small samples and no adjustment for confounders.
  • Measuring morphology in hips that already have OA (osteophytes) can artificially inflate the association.
  • Pincer morphology may need over 10 years of follow-up and both AP and lateral imaging to detect its slow effect, which most studies lacked.
  • Heterogeneous definitions and measurement methods, especially for pincer morphology and femoral version, limited firm conclusions.

Why it matters

For patients
Certain inherited hip shapes, a bumpy ball or a shallow socket, can raise your long-term risk of hip arthritis.
For clinicians
Cam morphology and dysplasia on hip X-rays are meaningful risk markers for future hip OA and may warrant monitoring or early discussion.
For readers
Prospective evidence links cam morphology and dysplasia to hip OA, while pincer morphology's role remains unproven.

Source

doi:10.1016/j.joca.2021.06.007

Read the original paper
Clinically assessing this area? See the hip & groin special tests.

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