Background Knee osteoarthritis (KOA) is more common in African-Americans (AAs) than Whites (WHs) in the United States. The prevalence and severity of osteophytes, bone sclerosis and joint space narrowing (JSN) are also greater among AAs than among WHs. Radiographic KOA features between the two races may also vary according to sex.
Objectives To determine if the pattern of radiographic progression in KOA varies by race and sex
Methods Knees of AAs and WHs with minimal or no radiographic KOA (Kellgren-Lawrence [K-L] grades 0 or 1) at baseline in the Osteoarthritis Initiative (OAI) were selected for analysis. Serial fixed-flexion knee x-rays through the 96 month visit were scored for K-L grade and tibiofemoral JSN based on Osteoarthritis Research Society International grade. A subset, enriched for those that developed radiographic KOA, were assessed for joint space width (JSW) using digital imaging software. Mixed models for repeated measures were used to estimate race- and sex-specific mean JSW and 95% confidence interval at fixed locations in the medial (x=0.250mm) and lateral (x=0.725mm) compartments, as well as average annual loss in fixed JSW (fJSW). Generalized estimating equation logistic regression models were used to estimate the effect of race and sex on: summary radiographic grade progression (defined by any increase in K-L grade ≥1), and JSN progression (defined by any increase in OARSI grade ≥1) in the medial and lateral compartments. Models were adjusted for time to progression, baseline age, body mass index (BMI), family history of joint replacement, bony enlargements in the distal interphalangeal joints, frequent knee-bending, and history of knee injury or surgery.
Results 3,776 knees were studied from 695 WH men, 932 WH women, 93 AA men, and 168 AA women, with mean age of 59 years and BMI of 28 kg/m2. Mean baseline medial fJSW was as follows: 6.53 in WH men, 5.43 in WH women, 6.51 in AA men, and 5.48 in AA women. Figure 1 displays the race and sex-specific mean medial fJSW during the study period, after adjustment, with 95% CIs. Annual medial fJSW loss (mm/year) over 8 years was significantly greater in AA men (-0.13) than in all other subgroups (-0.07 WH men, -0.06 WH women, -0.07 AA women, p<0.0001). There was no evidence of difference in annual loss of JSW in the lateral compartment.
In the adjusted models, odds of radiographic K-L grade progression were significantly higher in AA men (adjusted odds ratio [aOR] 2.18, 95%CI [1.22–3.91], p=0.009) and in WH men (aOR 1.53, 95% CI [1.18–1.98], p=0.002), in comparison to WH women. The odds did not significantly differ between AA and WH women (p=0.476). In fully adjusted models, the odds of having OARSI grade progression in medial JSN was slightly higher in AA women in comparison to WH women (aOR 1.38, 95% CI [0.91–3.46]), p=0.090), though this was not significant. Compared to WH women, WH men had greater odds of lateral JSN progression (aOR 2.25, 95% CI [1.29–3.92], p=0.004). There was no significant difference in lateral JSN progression among AA women (p=0.542) and AA men (p=0.509), in comparison to WH women.
Conclusions Compared to WHs and AA women, AA men were more likely to have radiographic knee OA progression over time. Loss of JSW and progression of JSN in specific compartments may vary based on race and sex. Further research to characterize and identify causes of differential KOA progression by race and sex is warranted.
Disclosure of Interest None declared
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