Osteoarthritis of the knee: multicompartmental or compartmental disease?

Objective. Knee OA has been conceptualized as a multicompartmental disease, as a compartmental disease or as a combination of these two disease processes. The aim of this study was to determine the associations between four radiographic features (joint space narrowing, osteophyte formation, sclerosis and cysts) across and within the three knee compartments (medial tibiofemoral, lateral tibiofemoral and patellofemoral compartment) in knee OA. Methods. Data from the Amsterdam OA Cohort were used. In 298 patients diagnosed with knee OA, radiographic features were examined in three knee joint compartments. Radiographic features were scored according to standardized scoring methods. Factor analysis was used to examine associations between the four radiographic features across and within compartments. Results. A bifactor model showed a general multicompartmental factor: 10 of 12 radiographic features across the entire joint were associated with the general factor. The bifactor model also showed three compartmental factors-one for each compartment: joint space narrowing, sclerosis and to a lesser extent osteophyte formation were associated with these compartmental factors. Conclusion. These findings suggest a multicompartmental disease process in the knee, characterized by associations among features across the entire joint, as well as compartmental disease processes in each knee compartment, characterized by associations among features within specific compartments. Longitudinal studies are needed to explore the possibility of the development from a compartmental disease to a multicompartmental disease and the impact of contributing factors on the development.