Frontal plane knee alignment is associated with a longitudinal reduction in patella cartilage volume in people with knee osteoarthritis.

OBJECTIVES: Varus-valgus alignment of the knee is increasingly becoming recognised as an important biomechanical variable in patellofemoral osteoarthritis (OA). The aim of this study was to determine the cross-sectional and longitudinal relationships between frontal plane knee alignment and patella cartilage volume in people with knee OA. METHODS: Ninety-nine adults with symptomatic knee OA were recruited using a combined strategy including referral from specialist centres, arthritis support groups and media advertising. Both baseline and follow-up X-rays and magnetic resonance imaging (MRI) were performed 2 years apart. Knee alignment and patella cartilage volume were determined from X-ray and MRI, respectively. RESULTS: Annual change in knee alignment was negatively associated with an annual change in the total patella cartilage volume before (P=0.002) and after (P=0.003) adjustment for potential confounders over an average of a 1.9-year period. For every 1 degrees change towards valgus direction, there was a 23.4-mm(3) [95% confidence interval (CI) 8.1 mm(3)-38.7 mm(3)] annual reduction in the total patella cartilage volume. CONCLUSION: This study is the first to clearly demonstrate and quantitate the annual reduction in patella cartilage volume that occurs as knee alignment becomes increasingly valgus in an osteoarthritic cohort. Interventions that aim to minimise change towards valgus alignment may reduce the risk for the onset and progression of patellofemoral OA.