The epidemiology and interaction of knee alignment and body mass on knee osteoarthritis

The growing prevalence of knee osteoarthritis (KOA) is fuelled by the rising obesity epidemic and an ageing population. The lack of a KOA cure drives the need to identify prevention strategies with alternative treatments to surgery a priority. This requires careful investigation of risk factors and their interaction. Knee mal-alignment and excess body mass are KOA risk factors but their combined effect is less understood.These five studies examine knee alignment and body mass as separate risk factors, describing their natural history and their association with prevalence and incidence of symptomatic radiographic knee osteoarthritis (SRKOA), radiographic knee osteoarthritis (RKOA) and knee pain outcomes in a long-standing female cohort. The cross-sectional interaction of these risk factors and outcomes is examined. One-point (1P) versus two-point (2P) anatomic axis (AA) knee alignment measurements, and body mass index (BMI) versus waist circumference (WC) measurements are also compared. Differences between 1P and 2P measurements indicate method specific alignment categories are required. Improvements are identified in AA angle measurement that require further validation to establish a gold standard AA alignment method. Changes in AA alignment over 10 years were small, but limited by identification of rotated knees.Over 19 years the tripling amount of obese women, was associated with increased prevalence and incidence of SKROA, RKOA and knee pain. WC measurement offers no advantage over BMI in predicting SRKOA, but it could be substituted where height or weight measurement is difficult.Results suggest a cross-sectional interaction between BMI and alignment with SRKOA and RKOA but not with knee pain, indicating that it may be driven by structure. This is important for targeting timely treatment of these risk factors.This new knowledge should assist in identification of individuals who would benefit from early intervention and treatment, to reduce pain, suffering and high future costs of KOA.