Effect of local alignment on compartmental patterns of knee osteoarthritis

Background: Previous studies have shown that lower-extremity malalignment increases the risk and rate of progression of knee osteoarthritis. The authors of such studies have used full-length lower-extremity radiographs to quantify alignment. However, a radiograph that includes only the knee is commonly ordered for a patient with early symptoms of knee osteoarthritis. The purpose of this study was to investigate whether local malalignment, as determined with use of a standing short knee radiograph, is associated with an increased risk of having osteoarthritis and having more severe compartmental disease. Methods: Short fluoroscopically guided standing anteroposterior knee radiographs of 306 patients (608 knees) with radiographic evidence of knee osteoarthritis were used to determine the compartment-specific Kellgren-Lawrence grade of osteoarthritis and the local (distal femoral to proximal tibial) knee alignment. The relationship between local alignment and compartmental patterns of osteoarthritis was assessed. Results: Each degree of increase in the local varus angle was associated with a significantly increased risk of having predominantly medial compartment osteoarthritis, even when we adjusted forage, sex, and body mass index (odds ratio, 1.39; 95% confidence interval, 1.29 to 1.49; p < 0.001). A similar association was found between valgus angulation and lateral compartment osteoarthritis (odds ratio, 1.55; 95% confidence interval, 1.36 to 1.75; p < 0.001). Analysis of the 362 knees with predominantly medial compartment osteoarthritis showed that each degree of increase in the varus angle was associated with a significantly increased adjusted risk of having severe medial disease (odds ratio, 1.52, p < 0.001). In the forty-seven knees with predominantly lateral compartment osteoarthritis, a similar trend was found between an increase in the valgus angle and the severity of the lateral disease, with the results approaching but not reaching significance. Conclusions: In patients with early symptomatic knee osteoarthritis, there is a clear relationship between local knee alignment, as determined from short standing knee radiographs, and the compartmental pattern and severity of the knee osteoarthritis. This study provides data with which physicians can assess how knee alignment contributes to the observed patterns and severity of osteoarthritis in an individual patient.