Data from 3,187 individuals were assessed; after exclusion of women under 50 years of age, individuals with evidence of inflammatory disease (on hip or knee radiographs) or bilateral hip joint replacement, and those missing K-L grades (including 24 with unilateral joint replacements), 2,739 participants (1,184 men and 1,555 women) remained for analyses (). Of the analyzed individuals, 57% were women and 31% were AA.
Characteristics of the sample, stratified by sex, are shown in . The mean age was higher among women than men, due to the exclusion of women under 50 years of age, with no significant differences in age between racial groups by sex. AA women had a significantly higher mean BMI compared to White women; White men had a higher BMI compared to AA men. More white men and white women (66% and 60%, respectively) had a high school education or beyond, compared to AA men and women (46% and 45%, respectively). There was no difference by race for history of prior hip injury among men or women.
Characteristics of the sample, by sex and race.
AA and white women had a similar prevalence of rOA, defined by K-L grade ≥ 2 in at least one hip (23% vs. 22%). No differences were seen between white and AA women by specific K-L grades (p=0.14, ). Unilateral disease was more common than bilateral in both groups of women, with no difference by race (p=0.64). In unadjusted analyses, significant differences were identified in several of the radiographic features. Mild axial JSN was seen more frequently among White compared to AA women (26% compared to 20%), and while AA women had more frequent moderate/severe axial JSN, this finding was quite rare in both groups (1-2% affected, ). AA women had more frequent superior JSN, and slightly higher frequencies of medial JSN, although the numbers for medial JSN were small and not significantly different by race. AA women had a slightly higher frequency of subchondral cysts, but there was no racial difference for sclerosis (). AA women had an increased frequency of medial OST, especially on the femoral side of the joint, compared to white women (). Lateral OST were also more frequent among AA women, and more often on the acetabular side, compared to white women. The combination of both acetabular and femoral OST was also increased in AA compared to white women, both laterally and medially. When assessed across the entire joint without separating lateral from medial, AA women were more likely to have OST in any site (acetabular only 47.1%, femoral only 5.1%, or both 16.0%) compared to White women (42.5%, 3.6%, and 13.2%, respectively, p<0.001).
Frequencies of K-L grade by race among women and men
Unadjusted frequencies for joint space narrowing (JSN), subchondral cysts, and sclerosis at the hip, by sex and race.
Unadjusted frequencies for medial and lateral osteophytes (OST) at the hip, by sex and race.
In adjusted analyses, no significant differences were seen between AA and white women for K-L grade or laterality (data not shown). After adjustment, estimates did not significantly change from unadjusted models (). For axial JSN, where the proportional odds assumption did not hold, AA women had more than twice the odds of moderate or severe axial JSN compared to whites, with mild disease 30% less likely among AA women. The proportional odds ratio for superior JSN indicated that AA women were 70% more likely to have superior JSN, and to have it be more severe, compared to white women. Results were similar for medial JSN, but did not reach statistical significance, likely due to the infrequency of this pattern of JSN. The odds of having subchondral cysts were 50 % higher for AA women, but sclerosis did not differ by race (). AA women had 40% increased odds for more frequent and severe medial OST compared to white women, with twice the odds of medial femoral OST alone, but there were no significant differences by race for medial acetabular OST alone or for the combination of both medial femoral and medial acetabular OST in the adjusted analyses. AA women had more frequent and severe lateral OST compared to white women, and had 30% increased odds for the combination of lateral femoral and acetabular OST, with no differences for isolated femoral OST or acetabular OST in the lateral compartment. For overall pattern of OST, without separation into lateral and medial compartments, AA women were 30% more likely to have acetabular only OST, 80% more likely to have femoral OST alone, and 50% more likely than White women to have both acetabular and femoral OST (data not shown).
Adjusted ORs for individual radiographic features in AAs compared to Whites, by sex.
Among the men, 17% of white and 21% of AA men had a K-L grade ≥ 2 in at least one hip, with most of the difference in the milder categories (p=0.02, ). In unadjusted analyses, unilateral disease was more common than bilateral in both groups, with no difference by race (p=0.08). AA men had a lower frequency of mild axial JSN compared to white men (). Similar to findings in the women, AA men had more frequent superior JSN than white men. There were no differences by race in medial JSN for the men, as the numbers of affected men were very small. There was no difference by race for the frequency of subchondral cysts, but AA men had a slightly higher frequency of sclerosis than did white men (). While the men had similar frequencies of medial OST, AA men had significantly more frequent and more often severe lateral OST, especially on the acetabular side of the joint (). Again similar to findings for the women, the combination of both acetabular and femoral OST was more frequent among AA compared to white men, but only on the lateral side of the joint. When OST were assessed across both medial and lateral compartments, AA men more frequently had acetabular only (36.6%) and both acetabular and femoral OST (19.1%) compared to White men (33.4% and 13.0%, respectively, p<0.001).
In adjusted analyses, despite a trend toward a difference by race for K-L grade ≥ 2 (OR 1.3, 95% CI 1.0, 1.8), there were no differences by specific K-L grades (and therefore by global OA severity) at the hip among men (data not shown). AA men were, however, more likely to have bilateral hip rOA compared to White men (OR 1.4, 95% CI 1.0, 1.8). As in the women, unadjusted and adjusted models did not significantly differ, and adjusted ORs are presented (). Compared to white men, AA men were significantly less likely to have mild axial joint space narrowing; no differences by race were seen for moderate/severe axial JSN. AA men had twice the odds of more frequent and severe superior JSN compared to white men. There was a borderline significant racial difference in medial JSN among the men, but very few men in either group had this pattern of JSN, and the model fit was questionable. No significant racial differences were seen among men for sclerosis or subchondral cysts. Medial OST also did not differ significantly by race among the men; no differences were seen for medial acetabular or medial femoral OST alone or for the presence of OST on the acetabular or femoral side of the joint in the medial compartment. However, and similarly to the women, AA men had about 40% higher odds of having, and having more severe, lateral OST, with 80% increased odds for the combination of both femoral and acetabular OST on the lateral side, and 40% increased odds for isolated lateral acetabular OST, with no difference for isolated femoral OST. Finally, when OST were considered regardless of medial or lateral compartment, AA men were 40% more likely to have acetabular only OST, and 80% more likely to have both acetabular and femoral OST, compared to White men (data not shown).