SUMMARY
Changes in coronal alignment in osteoarthritic knees evolving from extension to flexion remain poorly studied. Using an imageless computer-navigation system (Stryker©) we prospectively collected measurements of dynamic coronal pre-implant alignment during primary total knee arthroplasty. Coronal alignment of the osteoarthritic knee was determined at maximal extension and 90° flexion. Measurements were subgrouped as varus (=-3°), neutral (>-3°, <+3°) or valgus (=+3°). Of 545 osteoarthritic knees (347 females), coronal alignment in extension was 261 (48%) varus, 197 (36%) neutral and 87 (16%) valgus. Varus extension alignment was more common in male versus female knees (p< .0001). Valgus extension alignment was more common in female versus male knees (p= .002). In flexion, 174 (66%) of varus knees remained varus. Coronal alignment remained unchanged (within +3°; -3°) in flexion versus extension in approximately half of the OA knees observed. This insight into a changing coronal deformity might contribute to a better understanding of osteoarthritic knee behaviour.