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Summary Objective To elucidate the role of body mass index (BMI) and knee osteoarthritis (OAK) by evaluating measures of body composition including fat mass and skeletal muscle mass (SMM). Methods Data are from 541 women enrolled in the Michigan Bone Health Study, a longitudinal, population-based study. At visits in 1998 and 2002, radiographs were taken of both knees and were evaluated for the presence of OAK (≥2 on the Kellgren–Lawrence (K–L) scale). Joint space width (JSW) was measured with electronic calipers. Fat mass and SMM were determined using bioelectrical impedance analysis. Results In 2002, the prevalence of OAK was 11% in this population of women whose mean age was 47 years. Fat mass, lean mass, SMM, waist circumference and BMI were greater in women with OAK compared to those without OAK. In multiple variable analyses adjusted for age, fat mass and SMM explained OAK prevalence and increasing OAK severity better than models with BMI; further SMM explained more variation than did fat mass. SMM was positively associated with level of left and right medial JSW while there was no consistent association of JSW and BMI or fat mass. Conclusion Fat mass and SMM were associated with K–L OAK score and the amount of joint space, with more variation explained by SMM. SMM was highly associated with JSW. Therefore, though obesity, frequently characterized by BMI, is a frequently reported risk factor for OAK, this mis-attribution may mean that interventions that focus on weight loss as treatment for osteoarthritis should be aware that this may negatively impact muscle mass.

Osteoarthritis (OA) has been characterized as a slowly evolving degenerative disease affecting cartilage and bone, with a multifactorial etiology that may differ depending on the joint site. Because OA has been considered a disease of the elderly, few population-based studies have examined its frequency and characteristics in persons under the age of 45. Objective In this cross-sectional study, we examined X-rays of both knees and the dominant hand in a population of younger black and white pre- and perimenopausal women in southeastern Michigan ( N =1053) for evidence of osteoarthritis, and reported these outcomes according to the risk factors of age, body size, injury, and smoking behavior. Design Sixteen joints of the dominant hand as well as both knee joints (weight bearing) were evaluated using the Kellgren and Lawrence Atlas of Standard Radiographs of Arthritis. Results By age 40, radiographically-defined osteoarthritis emerges in both the hands and knees. These age characteristics are observed in both black and white women, however prevalence of knee OA was higher in black females (23.1%) compared with white females (8.5%), and although prevalence of hand OA was more comparable between black (25.5%) and white females (19.2%), the joint sites affected differed. The major risk factors reported in studies of older populations are present in this younger population where OA is newly emerging. Conclusions This study provides strong evidence that primary prevention of OA must be implemented in young adulthood to curtail the emergence of radiographically-defined OA at the mid-life.

Objective : To assess whether the presence of subchondral bone marrow abnormalities (bone marrow edema (BME)) and cartilage defects, determined by magnetic resonance imaging (MRI), would explain the difference between painful osteoarthritis of the knee (OAK) compared with painless OAK or pain without OAK. Method : Four groups of women (30 per group), aged 35–55 years, were recruited from the southeast Michigan Osteoarthritis cohort (group 1: painful OAK; group 2: painless OAK; group 3: knee pain without OAK; and group 4: no OAK or knee pain). OAK was defined by a Kellgren–Lawrence score of 2 or greater, while pain was based on self-report. BME and cartilage defects were identified from MRI. Results : BME lesions were identified in 56% of all knees. BME lesions were four times (95% CI=1.7, 8.7) more likely to occur in the painless OAK group as compared with the group with pain, but no OAK. BME lesions >1cm were more frequent (OR=5.0; 95% CI=1.4, 10.5) in the painful OAK group than all other groups. While the frequency of BME lesions was similar in the painless OAK and painful OAK groups, there were more lesions, >1cm, in the painful OAK group.About 75% of all knees had evidence of some cartilage defect, of which 35% were full-thickness defects. Full-thickness cartilage defects occurred frequently in painful OAK. One-third of knees with full-thickness defects and 47% of knees with cartilage defects involving bone had BME >1cm. Women with radiographic OA, full-thickness articular cartilage defects, and adjacent subchondral cortical bone defects were significantly more likely to have painful OAK than other groups (OR=3.2; 95% CI=1.3, 7.6). Conclusion : The finding on MRI of subchondral BME cannot satisfactorily explain the presence or absence of knee pain. However, women with BME and full-thickness articular cartilage defects accompanied by adjacent subchondral cortical bone defects were significantly more likely to have painful OAK than painless OAK.

Objective We assessed the probability that mid-aged women with a Kellgren and Lawrence (K–L) score of 1 are likely to progress to a score of 2 or regress to a score of zero at a second time point, 2–3 years later.Methods Osteoarthritis (OA) of measurements (weight-bearing X-rays and interviews) were undertaken in women from the Southeast Michigan population who were ≥40 years of age, and who participated in both the 1995 and 1998 measurements (N=679).Results Of the 17.1 % of women with a 1995 K–L score of 1 in their right knee, 37.1% had a K–L score of 1 in 1998 while 32.8 % had a score of ≥2 and 30.2% had a score of zero. For 26.0% of women, the score progressed by at least one unit over the 2.5 year period whereas scores for only 7.0% of women regressed in the same time period. Women who had a K–L score of 1 in the right knee in 1995 were 2.5 times more likely to have a K–L score of 1 in 1998 (95% CI=1.6–3.8); and were 2.2 times more likely to have a K–L score of 2 or greater (95% CI=1.4–3.5) in 1998 compared with other scores. These women were 74% less likely to have a score of zero in 1998 (95% CI=0.2–0.4). Further, other risk factors, specifically age and BMI were predictors of increasing K–L grade in 1998.Conclusion These findings suggest that a score of 1 is part of the advancement to emergent OAK; and suggest the following criteria to characterize individuals who are at an intervenable stage on the pathway toward OAK: age ≥40, BMI ≥30, and K–L score of ≥1. From the perspective of both the individual and the examiner, these assessment characteristics are relatively simple to assess clinically. Copyright 2002 OsteoArthritis Research Society Intenational. Published by Elsevier Science Ltd. All rights reserved.

Discrepancies exist between radiographic osteoarthritis of the knee (OAK) and report of knee joint pain. Little is known about how these two definitions of osteoarthritis (OA) and their correlates differ between African American (AA) and Caucasian (CA) women.Objective We compared the prevalence of radiographic OAK and knee joint pain in AA and CA women, and the congruency of these outcomes according to age, body size, and knee injury.Design A cross-sectional study of African American and Caucasian women aged 40–53 years (N=829) in Southeast Michigan used the Kellgren and Lawrence Atlas of Standard Radiographs of Arthritis to characterize radiographs of both knee joints (weight bearing) and self-report of knee pain.Results Current pain was a significantly more sensitive predictor of radiographic OAK among AA women (Se=0.51) compared to CA women (Se=0.35). Specificity was similar between AA women (Sp=0.77) and CA women (Sp=0.82). Positive predictive value was significantly greater for AA compared with CA women (PV+=0.40 and PV+=0.15, respectively). The odds of having radiographic OAK increased with BMI >32kg/m2in both groups. Knee pain was related to BMI in CA women, but not AA women. Previous knee injury was associated with knee pain in both AA and CA women (OR=3.0 and OR=2.4).Conclusions Joint pain in AA women was more likely to be associated with radiographic OAK as compared with CA women. This suggests differences in these two groups in both how pain is experienced in the OAK process and in the prevalence of non-OAK related pain in knee joints.

Objective We evaluated C-reactive protein (C-RP), a quantitative marker of the acute phase response, as a potential biomarker of prevalent and incident osteoarthritis of the knee (OAK). Methods Serum C-reactive protein concentrations were characterized with ultrasensitive rate nephelometry in a population-based sample of 1025 women (318 African-American and 707 Caucasian) who are enrollees in a study of musculoskeletal conditions at the mid-life. Assignment of OAK was based on Kellgren-Lawrence (K–L) scores of 2 or more on radiographs. Prevalent OAK was based on the baseline (1996) score while the classification of incident OAK was based on a score of 2 or greater at the follow-up examination 2.5 years later amongst those with a baseline K–L scores of 0 or 1. Results At baseline, the prevalence of radiographic OAK was 12% in participants who were aged 27–53 years and 18% in the subgroup of women aged 40–53 years. The mean C-RP value was 2.31mg/L, with values ranging from below detection (0.3mg/L) to 47.4mg/L. Higher C-RP concentrations were associated with both prevalent and incident OAK ( P 0.0001, and P 0.0001, respectively). For each K–L score increase from 0 to 3, there was a significantly higher mean C-RP value. Compared to women without incident OAK, women who developed OAK in the 2.5-year follow-up had significantly higher baseline C-RP concentrations. Women with bilateral OAK had higher C-RP concentrations than women with unilateral OAK (6.65mg/L±0.56 vs 3.63mg/L±0.42, P 0.007). BMI was highly correlated with C-RP ( r =0.58) and obesity was an effect modifier with respect to OAK and C-RP concentrations. When stratified according presence or absence of OAK and obesity (BMI >30kg/m 2 ), mean C-RP values were: obesity and OAK, 6.3±0.4mg/L; obesity but not OAK, 4.3mg/L±0.2; no obesity but OAK, 1.7mg/L±0.8; and neither obesity nor OAK, 1.3mg/L±0.2mg/L. These stratum means were significantly different from each other, indicating a higher C-RP with OAK after accounting for obesity. Conclusion C-RP, as a measure of an acute phase response and inflammation, is highly associated with OAK; however, its high correlation with obesity limits its utility as an exclusive marker for OAK. Copyright 2002 OsteoArthritis Research Society International. Published by Elsevier Science Ltd. All rights reserved .