In residents aged 45 years and older in the sampled 6 townships of Johnston County, these hip OA-related measures occurred at surprisingly high but different frequencies, with hip symptoms occurring most commonly, followed by radiographic hip OA, symptomatic hip OA, and moderate/severe radiographic hip OA. This is the first U.S. study to provide prevalence estimates for these 4 outcomes by age, sex, and race. Contrary to previous indirect comparisons, African-Americans did not have lower prevalence of radiographic hip OA or moderate/severe radiographic hip OA and were at least as likely, if not more likely, as Caucasians to have these 4 hip outcomes.
For hip symptoms, the only previous population-based prevalence estimates of hip-related OA outcomes in men and women in the United States came from the 1971–1975 NHANES-I and the 1988–1994 NHANES-III. NHANES-I focused on the civilian, non-institutionalized population age 25–74 (for hip outcomes, men ages 25–74 years and women 50–74 years) in the contiguous United.States. Defining hip pain as “ever having significant pain in your hips on most days for at least 1 month”, this study reported an overall prevalence of 6.6%, and found generally increasing rates by age and roughly similar rates by sex and white/black race (11
). The more recent NHANES-III defined hip pain as “significant hip pain on most days over the preceding 6 weeks” and in analyses confined to those 60 years of age and older, found hip pain reported by 14.3% overall with higher estimates in women than men, a higher estimate among non-Hispanic black men (14.8%) than non-Hispanic white men (12.4%), and the opposite race effect among women (26
). The higher prevalence of hip pain in NHANES-III compared with NHANES-I was speculated to be related to possible non-articular source of pain in older individuals, or potentially an increase in incidence of hip OA(26
). Our Johnston County prevalence estimates for hip symptoms were about 4–5 times higher for comparable age ranges than NHANES-I and 2–3 times higher than NHANES-III; higher among women; and similar by race. Our prevalence estimates are probably higher in part than these other studies as a result of applying a broader case definition (aching or stiffness as well as pain) without requiring a specific duration criterion (“at least 1 month” or “over the preceding 6 weeks”) or “significant” pain.
For radiographic hip OA outcomes, the only previous population-based prevalence estimates came from NHANES-I, which defined radiographic hip OA based on the overall K-L grade of non-weight-bearing hip radiographs subjectively synthesized by the non-radiologist readers (11
), using the 1963 Atlas of Standard Radiographs (14
). Prevalence of radiographic hip OA among those 45–54, 55–64, and 65–74 years were about 0.7%, 2.7%, and 3.6%, respectively and was higher in men than women ages 65–74 years (4.6% in men, 2.7% in women) (11
). Comparable overall age-specific prevalence figures from our study were 8–30 times higher than those from NHANES-I (at 21%, 23%, and 31%, respectively) and were similar for men and women ages 65–74 years. There may be several reasons for the difference. First, NHANES-I radiographs may have been under-read, resulting in an underestimate of the true prevalence (27
). Second, men in rural or non-metropolitan areas such as Johnston County may have a higher prevalence of radiographic hip OA than those in urban or metropolitan areas (28
). Third, geographic variation in risk factors for hip OA may exist between NHANES-I and our study (the contiguous United States and the South, respectively). Finally, differences in radiographic techniques and secular trends in underlying risk factors in the 20 year interval may preclude direct comparisons of estimates between the 2 studies.
A special contribution of this study is the finding that African-Americans were at least as likely, if not more likely, to have radiographic and symptomatic hip OA than Caucasians. Prior studies had suggested a much lower prevalence of hip OA among native black Africans (12
), as did studies comparing African and Caribbean blacks to European Caucasians (29
). In addition, it has been unclear if the lower rate of total hip replacement surgery among blacks in the United States (30
) was related to a lower prevalence of hip OA in this demographic group, or to patient preferences, health care system, cultural, or other reasons for lower utilization of this treatment modality, as seen in racial disparities of utilization of total knee replacement for knee OA(31
). Our data, as well as the report by Tepper and Hochberg showing no significant racial difference in radiographic hip OA in the NHANES-I (11
), together suggest that African-Americans are not spared radiographic and symptomatic hip OA, and that alternate explanations for racial disparities in the use of joint replacement for hip OA should be investigated. These data also suggest the possibility of unmet need in this group and the need for education of health care providers about this issue.
This study has several limitations. First, as is typical for most population-based studies utilizing radiographs for diagnosis, it occurred in a limited geographic region that may not be representative of the United States as a whole in terms of geography, rurality, and important factors such as obesity. However, about 70% of our sample was overweight or obese, similar to current figures for the rest of the country (32
) suggesting that the high prevalence of obesity may not be such a limitation. Second, this study focused only on those 45 and older, although these are the ages when OA begins to be detected more commonly. Finally, symptoms were not defined using groin pain, a more specific hip symptom than what people perceive to be hip symptoms, which can mistakenly include sciatica and lumbar pain (33
On the other hand, this study has several significant strengths. It occurred relatively recently in a well-defined population with a large sample size and a sizable proportion of African-Americans and men. The 2 racial groups were recruited from the same geographic location, decreasing the systematic bias that inevitably occurs by comparing racial groups recruited from different geographic regions. Both racial groups underwent identical examination using the same techniques, with very high reproducibility of the radiographic reading procedure. Additionally, participants were well-characterized for OA using radiographs and symptoms, allowing 4 outcomes to be examined. Specifically, our estimates of radiographic outcomes excluded people with findings consistent with inflammatory arthritis, thereby sharpening the distinction between those with and those without radiographic hip OA, in contrast to other studies that did not make this clarification (11
). Our estimates may be conservative because we excluded those with hip replacements, most of whom probably had OA (9
). Finally, our exclusions of those with missing symptom or radiographic data were unlikely to bias our results because those with missing data were similar to those with complete data.
Our results have demonstrated that these 4 outcomes represent a common occurrence for many persons aged 45 years and older, for both sexes, and for African-Americans as well as Caucasians. Although these estimates can strictly apply only to the target population in which the study was conducted, it appears likely that the frequencies of these outcomes have substantially increased over the last 20 to 30 years. In the future as our population ages, and the obesity epidemic goes unchecked (32
), the prevalence of these hip related OA outcomes and accompanying disability can be expected to increase for all ages, both sexes, and these racial groups. Reducing this impact will require educating the public and health care community about modifiable risk factors for hip OA occurrence and progression, finding new modifiable risk factors, and developing effective interventions to treat, slow progression, and ultimately prevent OA.