Background/Purpose: While intra-articular (i.a.) mineralization can be visualized on knee radiographs, the sensitivity of its identification is low with this modality, hampering efforts to understand its pathogenic role and consequences in knee OA. Computed tomography (CT) is highly sensitive for the detection and localization of i.a mineralization. We report the prevalence of CT-detected i.a. mineralization in older adults with or at risk of knee OA.
Methods: The Multicenter Osteoarthritis (MOST) Study is a NIH-funded longitudinal cohort study of persons with or at risk of knee OA. Participants have undergone bilateral knee CT scans and PA knee radiographs, and completed standardized questionnaires to ascertain frequent knee pain. A musculoskeletal radiologist scored multiplanar CT images using an ordinal score (0-3) for degree of mineralization in each of the WORMS subregions of cartilage and menisci, as well as ligaments, capsule, and vasculature using a new CT scoring system, the Boston University Calcium Knee Score (BUCKS), for evaluating i.a. mineralization. A random sample of 50 subjects was re-scored after a period of at least 2 months, by the same reader for intra-reader reliability and by a second MSK radiologist for inter-reader reliability. Prevalence of i.a. mineralization was computed for the total sample, and stratified by age, sex, and presence of frequent knee pain and radiographic knee OA (ROA) (Kellgren and Lawrence grade ≥2).
Results: To date, 621 subjects (1242 knees) have been scored during the ongoing study visit (58% female, mean age 71.8, mean BMI 29.8). Overall, 12% of knees had calcium crystal deposition on radiograph, while CT-detected mineralization was present in 24% of knees in either cartilage, meniscus, and/or capsule. The prevalence in specific locations was: 17% articular cartilage, 20% meniscal, and 12% capsular. 14% of knees without calcium crystal deposition on radiograph had articular cartilage and/or meniscal mineralization detected by CT. Of the knees with CT-detected articular cartilage mineralization, the majority had it present in 1-4 WORMS cartilage subregions (out of 14), and 81% also had meniscal mineralization. For the knees with meniscal mineralization, the majority had it in 5 or 6 WORMS meniscus subregions (out of 6), and 41% also had articular cartilage mineralization. Articular and meniscal mineralization increased with age, was similar among men and women, and was more prevalent in those with ROA. Prevalence of CT-detected i.a mineralization was comparable in subjects with and without frequent knee pain. Capsular mineralization was similar across age and gender, but more prevalent in those with frequent knee pain and ROA. Overall, 52% of knees had vascular calcification, which increased with age and was more prevalent in men. The intra-reader reliability (weighted-kappa) ranged from 0.95 for cartilage to 1.0 for joint capsule. The inter-reader reliability (weighted-kappa) ranged from 0.92 for cartilage to 1.0 for joint capsule.
Conclusion: CT of the knee provides greater visualization of i.a. mineralization than radiographs, including locations within the hyaline articular cartilage, meniscus, and soft tissue, as well as its co-localization. BUCKS demonstrated high reliability. These data will provide opportunity to evaluate the longitudinal relation of i.a. mineralization to adjacent articular tissue pathology and overall OA progression.