Reduced spinopelvic mobility does not correlate with knee flexion deformity in patients undergoing total knee arthroplasty.

Abstract

The aim of this study was to evaluate the impact of reduced spinopelvic mobility (SM) on knee flexion deformity (KFD) in patients undergoing total knee arthroplasty (TKA). A retrospective analysis on 213 patients (271 knees) undergoing robotic-assisted primary TKA was conducted. Sagittal spinopelvic alignment (SSA) parameters-sacral slope (SS), pelvic incidence (PI), and pelvic tilt (PT)-were measured on lateral standing and sitting spinopelvic radiographs. Patients were stratified according to established SM classifications: standing-sitting difference in SS ≥ 10° versus < 10°, PT ≥ 20° versus < 20°, and Dorr's classification (DC). KFD was assessed intraoperatively using a robotic-assisted surgical platform after placement of arrays: first in the native state (KFDb), and again after osteophyte removal and maximum manual correction (KFDa). Correlations between standing-sitting changes in SSAs and KFDb/KFDa, as well as differences in mean KFDb/KFDa between SM groups, were analysed. The mean differences between standing and sitting was 11.3° (SD 9.1) for SS and 6.9° (SD 9.8) for PT. Based on SM classifications, 129 knees (48%) showed a SS difference < 10°, 30 knees (11%) a PT difference ≥ 20°, and DC categorised 131 (48%) as normal, 64 (24%) as stuck standing, 74 (27%) as stuck sitting, and 1% as kyphotic. The mean KFDb and KFDa were 5° (SD 6) and 2° (SD 2), respectively. No significant correlations were found between standing-sitting changes in SSAs and KFDb or KFDa (correlation coefficients < 0.1 for all). No significant differences in mean KFDb or KFDa were observed across SM classification groups (p > 0.2 for all). Spinopelvic mobility does not correlate with intraoperative knee flexion deformity in patients undergoing TKA suggesting that the increased knee flexion found among these patients is a dynamic rather than a permanent compensatory mechanism. Level III.