Central osteophytes develop in cartilage with abnormal structure and composition: data from the Osteoarthritis Initiative cohort.

To investigate the natural history of central osteophytes (COs) by analyzing the structure and matrix composition of CO-associated cartilage using 3-T MRI at and 1-3 years before the onset of COs. Baseline, 4- and 6-year knee MRIs of 400 participants in the Osteoarthritis Initiative were screened for the appearance of new COs. Twenty-eight subjects developed 31 COs. Using MRIs at CO onset and 1-3 years before CO onset, cartilage T2 values were calculated for the local cartilage preceding COs and the surrounding cartilage. Cartilage lesions local to the site of COs and bone marrow edema like lesions (BMELs) subjacent to COs were graded using whole organ MRI scores (WORMS). Wilcoxon tests were used to compare T2 values from the local and the surrounding cartilage at each time point and to compare T2 and WORMS between time points. Knee symptoms were recorded during this period. All subjects showed local cartilage lesions before the development of COs. Mean cartilage WORMS increased from 1.56 ± 0.66 a period of 3 years before to 2.39 ± 0.75 with onset of COs (p = 0.008). Local T2 values in the area of the later-appearing COs were significantly higher compared with T2 values of the surrounding cartilage 3 (p = 0.044) and 2 years earlier (p = 0.031) and with the onset of COs (p = 0.025). No significant increase in symptoms was found with the onset of COs. This study provides evidence that focal cartilage structural and compositional degeneration precedes COs. No significant aggravation of knee symptoms was reported during the evolution of COs.