Pelvic incidence–lumbar lordosis mismatch is associated with knee extension discrepancy between the supine and standing positions in patients with knee osteoarthritis

BackgroundSome knee osteoarthritis (KOA) patients show knee flexion in standing despite full extension in supine.ObjectiveThis study examined whether sagittal spinopelvic alignment is associated with the discrepancy between supine and standing knee extension.MethodsIn this retrospective cross-sectional study, 124 KOA patients undergoing preoperative evaluation were reviewed. Standing sagittal hip-knee-ankle angle (sHKA) was measured on full-length standing lateral radiographs, and supine sHKA was measured with a handheld two-arm goniometer. The difference between standing and supine sHKA (ΔsHKA) was examined. Patients were classified as having a ΔsHKA of ≥10° or <10°.Age, sagittal vertical axis (SVA), lumbar lordosis (LL), pelvic tilt, pelvic incidence (PI), and PI-LL were analyzed using multivariable logistic regression and receiver operating characteristic (ROC) analysis.Results21 patients (16.9%) had ΔsHKA ≥10°. These individuals were older and had larger SVA, pelvic tilt, and PI-LL. PI-LL was associated with ΔsHKA of ≥10° (odds ratio: 1.08; 95% CI: 1.01-1.11; p = 0.03). ROC curve showed a PI-LL cutoff of 42.5° (AUC: 0.796; sensitivity: 47.6%; specificity: 96.1%).ConclusionsLarger PI-LL was associated with standing knee flexion, even in patients with full extension in the supine position. Therefore, sagittal spine alignment should be evaluated in KOA patients.