Comparison of tibial cartilage volume and radiologic grade of the tibiofemoral joint

Objective. To compare tibial cartilage volume as measured by magnetic resonance imaging (MRI) with radiologic assessment of the tibiofemoral joint. Methods. The MRI-determined tibial cartilage volume was compared with the radiologic grade of individual features of osteoarthritis (osteophytes and joint space narrowing [JSN]) in 252 subjects (mean +/- SD age 60.2 +/- 10 years, 62% female) who were participating in studies of knee cartilage. Results. JSN seen on both medial and lateral radiographs of the tibiofemoral joint was inversely associated with the respective tibial cartilage volume. This inverse relationship was strengthened with adjustment for age, sex, body mass index (BMI), and bone size. After adjustment for these confounders, for every increase in JSN grade (0-3), the medial tibial cartilage volume was reduced by 257 mm 3 (95% confidence interval [95% CI] 193-321) and the lateral tibial cartilage volume by 396 mm 3 (95% CI 283-509). The relationship between mean cartilage volume and radiologic grade of JSN was linear. Based on results in the subgroup of subjects with normal radiographic findings, we have proposed a model to estimate average "normal" cartilage volume in men and women for a given age, BMI, and bone size. Conclusion. The results of this study demonstrate a strong negative, linear association between medial and lateral tibial cartilage volume and increasing grade of JSN. Using data from radiographically normal subjects, we have proposed a simple model for estimating "normal" cartilage volume. However, larger studies will be needed to confirm these findings and to determine whether they are valid in younger subjects.