Osteophytes and increasing knee bone size may be causally related to knee cartilage defects. Furthermore, knee cartilage defects may result in increased cartilage breakdown leading to decreased cartilage volume and joint space narrowing suggesting an important role for knee cartilage defects in early knee OA.

Background: Knee cartilage defects may play an important role in early osteoarthritis, but little is known about their natural history.Methods: Knee cartilage defect score (range, 0-4), cartilage volume, and bone surface area were determined using T1-weighted fat-saturated magnetic resonance imaging in 325 subjects (mean age, 45 years) at baseline and 2 years later.Results: Thirty-three percent of the subjects had a worsening (Ն1-point increase) and 37% of the subjects had an improvement (Ն1-point decrease) in cartilage defect score in any knee compartment during 2.3 years. A worsening in cartilage defect score was significantly associated with female sex (odds ratio [OR], 3.09 and 3.64 in the medial and lateral tibiofemoral compartments) and baseline factors, including age (OR, 1.05 per year in the medial tibiofemoral compartment), body mass index (OR, 1.08 in the lateral tibiofemoral compartment), tibiofemoral osteophytes (OR, 6.22 and 6.04 per grade), tibial bone area (OR, 1.24 and 2.07 per square centimeter), and cartilage volume (OR, 2.91 and 1.71 per milliliter in the medial tibiofemoral and patellar compartments). An improvement in cartilage defect score had similar but reversed associations with these factors (except for sex), including a decrease in body mass index (OR, 1.23 in the medial tibiofemoral compartment).Conclusions: Knee cartilage defects are variable, and changes are associated with female sex, age, and body mass index. Increases are associated with baseline cartilage volume, bone size, and osteophytes, suggesting a role for these in the pathogenesis of cartilage defects. Interventions such as weight loss may improve knee cartilage defects.

DING, CHANGHAI, FLAVIA CICUTTINI, FIONA SCOTT, HELEN COOLEY, AND GRAEME JONES. Knee structural alteration and BMI: a cross-sectional study. Obes Res. 2005;13:350 -361. Objective: To describe the associations among BMI, knee cartilage morphology, and bone size in adults. Research Methods and Procedures:A cross-sectional convenience sample of 372 male and female subjects (mean age, 45 years; range, 26 to 61 years) was studied. Knee articular cartilage defect score (0 to 4) and prevalence (defect score of Ն2), volume, and thickness, as well as bone surface area and/or volume, were determined at the patellar, tibial, and femoral sites using T1-weighted fat-saturation magnetic resonance imaging. Height, weight, BMI, and radiographic osteoarthritis were measured by standard protocols. Results:In multivariate analysis in the whole group, BMI was significantly associated with knee cartilage defect scores (␤: ϩ0.016/kg/m 2 to ϩ0.083/kg/m 2 , all p Ͻ 0.05) and prevalence (odds ratio: 1.05 to 1.12/kg/m 2 , all p Ͻ 0.05 except for the lateral tibiofemoral compartment). In addition, BMI was negatively associated with patellar cartilage thickness only (␤ ϭ Ϫ0.021 mm/kg/m 2 ; p ϭ 0.039) and was positively associated with tibial bone area (medial: ␤ ϭ ϩ7.1 mm 2 /kg/m 2 , p ϭ 0.001; lateral: ␤ ϭ ϩ3.2 mm 2 /kg/ m 2 , p ϭ 0.037). Those who were obese also had higher knee cartilage defect severity and prevalence and larger medial tibial bone area but no significant change in cartilage volume or thickness compared with those of normal weight.Discussion: This study suggests that knee cartilage defects and tibial bone enlargement are the main structural changes associated with increasing BMI particularly in women. Preventing these changes may prevent knee osteoarthritis in overweight and obese subjects.

Objective: To describe the associations between age, knee cartilage morphology, and bone size in adults. Methods: A cross sectional convenience sample of 372 male and female subjects (mean age 45 years, range 26-61) was studied. Knee measures included a cartilage defect five site score (0-4 respectively) and prevalence (defect score of >2 at any site), cartilage volume and thickness, and bone surface area and/or volume. These were determined at the patellar, medial, and lateral tibial and femoral sites using T 1 weighted fat saturation MRI. Height, weight, and radiographic osteoarthritis (ROA) were measured by standard protocols. Results: In multivariate analysis, age was significantly associated with knee cartilage defect scores (b = +0.016 to +0.073/year, all p,0.01) and prevalence (OR = 1.05-1.10/year, all p,0.05) in all compartments. Additionally, age was negatively associated with knee cartilage thickness at all sites (b = 20.013 to 20.035 mm/year, all p,0.05), and with patellar (b = 211.5 ml/year, p,0.01) but not tibial cartilage volume. Lastly, age was significantly positively associated with medial and lateral tibial surface bone area (b = +3.0 to +4.7 mm 2 /year, all p,0.05) and patellar bone volume (b = +34.4 ml/ year, p,0.05). Associations between age and tibiofemoral cartilage defect score, cartilage thickness, and bone size decreased in magnitude after adjustment for ROA, suggesting these changes are directly relevant to OA. Conclusion: The most consistent knee structural changes with increasing age are increase in cartilage defect severity and prevalence, cartilage thinning, and increase in bone size with inconsistent change in cartilage volume. Longitudinal studies are needed to determine which of these changes are primary and confirm their relevance to knee OA.

Objective. To describe the association between prevalent and incident knee cartilage defects and loss of knee cartilage in male and female adults.Methods. A convenience sample of 325 subjects (mean age 45 years; age range 26-61 years) was evaluated at baseline and ϳ2 years later. Knee cartilage volume, cartilage defect scores (0-4 scale), and joint surface area were determined using T1-weighted fatsuppression magnetic resonance imaging techniques. Height, weight, and radiographic evidence of osteoarthritis were measured by standard protocols.Results. Multivariable analysis revealed that baseline cartilage defect scores at the medial tibia, lateral tibia, and patella had a dose-response association with the annual rate of change in knee cartilage volume at the corresponding site (␤ ‫؍‬ -1.3% to -1.2% per grade; P < 0.05 for all comparisons). In addition, an increase in knee cartilage defect score (change of >1) was associated with higher rates of knee cartilage volume loss at all sites (␤ ‫؍‬ -1.9% to -1.7% per year; P < 0.01 for all comparisons). Furthermore, a decrease in the knee cartilage defect score (change of less than or equal to ؊1) was associated with an increase in knee cartilage volume at all sites (␤ ‫؍‬ 1.0% to 2.7% per year; P < 0.05 for all comparisons).Conclusion. Prevalent knee cartilage defects are predictive of compartment-specific cartilage loss over 2 years. Both increases and decreases in knee cartilage defects are associated with changes in knee cartilage volume, which implies a potential for reversal of knee cartilage loss.

Within the age range we studied, knee cartilage volume declines at a faster rate with increasing age. This is partly mediated by ROA at the medial tibial site only. Furthermore, women have substantially higher knee cartilage loss than men, and these sex differences first appear at age 40 and become more marked with increasing age, which has implications for prevention of cartilage loss from middle age.

Men have substantially higher knee cartilage volumes than women. These sex differences appear to be mediated in part by body and bone size but a significant amount remains unexplained. Furthermore, the differences become more marked over the age of 50 yr suggesting that both cartilage development and cartilage loss in later life contribute to sex differences in cartilage volume. Further longitudinal studies in large samples will be required to confirm these findings.

Early medial compartment ROA is associated with substantial reductions in cartilage volume and increases in bone area. These large changes, when combined with similar measurement error for MRI and radiographs, suggest that MRI may be superior at detecting and hence understanding early osteoarthritis of the knee in humans.