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

PURPOSE: 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).

METHODS

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.

RESULTS

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).

CONCLUSION

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 OF EVIDENCE: Level III.