Prevalence of malformations of the hip joint and their relationship to sex, groin pain, and risk of osteoarthritis: a population-based survey.

BACKGROUND: Although the clinical consequences of femoroacetabular impingement have been well described, little is known about the prevalence of the anatomical malformations associated with this condition in the general population, the natural history of the condition, and the risk estimates for the development of osteoarthritis.
METHODS: The study material was derived from a cross-sectional population-based radiographic and questionnaire database of 4151 individuals from the Copenhagen Osteoarthritis Substudy cohort between 1991 and 1994. The subjects were primarily white, and all were from the county of Østerbro, Copenhagen, Denmark. The inclusion criteria for this study were met by 1332 men and 2288 women. On the basis of radiographic criteria, the hips were categorized as being without malformations or as having an abnormality consisting of a deep acetabular socket, a pistol grip deformity, or a combination of a deep acetabular socket and a pistol grip deformity. Hip osteoarthritis was defined radiographically as a minimum joint-space width of <or=2 mm.
RESULTS: The male and female prevalences of hip joint malformations in the 3620 study subjects were 4.3% and 3.6%, respectively, for acetabular dysplasia; 15.2% and 19.4% for a deep acetabular socket; 19.6% and 5.2% for a pistol grip deformity; and 2.9% and 0.9% for a combination of a deep acetabular socket and pistol grip deformity. The male and female prevalences of a normal acetabular roof were 80.5% and 77.0%. We found no significantly increased prevalence of groin pain in subjects whose radiographs showed these hip joint malformations (all p > 0.13). A deep acetabular socket was a significant risk factor for the development of osteoarthritis (risk ratio, 2.4), as was a pistol grip deformity (risk ratio, 2.2). Acetabular dysplasia and the subject's sex were not found to be significant risk factors for the development of hip osteoarthritis (p = 0.053 and p = 0.063, respectively). The prevalence of hip osteoarthritis was 9.5% in men and 11.2% in women. The prevalence of concomitant malformations was 71.0% in men with hip osteoarthritis and 36.6% in women with hip osteoarthritis.
CONCLUSIONS: In our study population, a deep acetabular socket and a pistol grip deformity were common radiographic findings and were associated with an increased risk of hip osteoarthritis. The high prevalence of osteoarthritis in association with malformations of the hip joint suggests that an increased focus on early identification of malformations should be considered.