The "Wind Surf" Deformity-Correcting Fixed Flexion Deformity and Hyperextension in Bilateral CAS TKA.

Severe knee arthritis can result in complex coronal and sagittal angular deformities. Windswept deformity is used to describe a varus deformity and contralateral valgus deformity. We recognized a new sagittal pattern at the time of computer-assisted surgery (CAS) in total knee arthroplasty (TKA) in which one knee has a fixed flexion deformity (FFD), while the contralateral knee has a hyperextension deformity. We propose to define it as "wind surf" deformity mimicking the opposite pull of the wind and a surfer. The incidence of "wind surf" deformity in this series was 0.96% among a cohort of 2,291 bilateral TKAs performed between 2013 and 2018. Twenty-two patients were identified with an FFD of 5° to 20° on one knee and recurvatum of -5° to -20° on the contralateral knee. Additional bone resection and soft-tissue releases were performed for the FFD with a goal to maintain residual 1° to 3° of flexion. Minimal bone resection and soft-tissue disruption were performed on the knee with hyperextension with a goal to maintain 5° to 7° of flexion. These opposite strategies applied with the help of CAS prevented recurrence resulting in satisfactory clinical results at 2-year follow-up. The "wind surf" deformity variant should be identified in patients presenting with severe knee arthritis to guide surgical treatment, prevent recurrence, and obtain favorable clinical patient outcomes.