Radiographic case definitions and prevalence of osteoarthrosis of the hip: A survey of 4 151 subjects in the Osteoarthritis Substudy of the Copenhagen City Heart Study

Background The diagnosis of osteoarthrosis (OA) is founded on radiographic evidence of joint degeneration and characteristic subjective symptoms. Due to the lack of consensus radiographic case definitions, the prevalence and incidence of OA reported in the literature varies. The aims of the current study were to establish an accurate and workable radiographic definition of OA in hip joints and to examine the association of OA (thus defined) with self-reported pain.

Methods Radiographic features of hip OA were classified in pelvic radiographs of 3 807 subjects (1 448 males and 2 359 females) according to the OA classifications of Kellgren and Lawrence (1957) and Croft (1990), and according to minimum joint space width (JSW) of 2.0 mm regardless of other radiographic features of OA. The relationships between these radiographic discriminators and self-reported hip pain were investigated.

Results Formation of cysts, osteophytes and subchondral sclerosis was significantly more frequent in men. Average minimum JSW was narrower in women than in men (p < 0.001). In both sexes, minimum JSW decreased after the fourth decade of life, but progressively more so in women. Women reported hip pain more frequently than men (p < 0.001). When the cut-off JSW value of 2.0 mm was applied regardless of other radiographic features of OA, prevalences of hip OA ranged from 4.4% to 5.3% in subjects ≥ 60 years of age. The radiographic discriminator with the strongest association with self-reported hip pain in men and women ≥ 60 years of age was minimum JSW ≤ 2.0 mm; OR = 3.3 (95% CI 1.9 − 5.7) for men, and OR = 3.2 (95% CI 1.9 − 5.2) for women.

Interpretation We found that minimum JSW ≤ 2.0 mm was the radiographic criterion having the closest association with self-reported hip pain. Using composite OA scores emphasizing the relatively inconsequential formation of cysts, osteophytes and subchondral sclerosis runs the risk of over-inflating the prevalence of hip OA in men and of underestimating hip OA prevalence in women.