Summary

Patients with a greater posterior tilt of the pelvic alignment had restrictions in knee extension postoperatively, and those with a greater varus alignment of the lower extremity preoperatively had a lower knee flexion after UKA.

Abstract

Introduction

Although the knee range of motion (ROM) is an important factor affecting postoperative clinical outcomes, evidence regarding the relationship between spinopelvic alignment and the knee ROM or clinical outcomes after knee arthroplasty is lacking. We aimed to evaluate whether the anteroposterior alignment of the lower extremity and sagittal spinopelvic alignment affect the postoperative knee ROM and clinical outcomes after medial unicompartmental knee arthroplasty (UKA).
Patients and Methods: Thirty-two patients (a total of 37 knees: 6 men, 7 knees; 26 women, 30 knees) who underwent navigation-assisted UKA were included in this retrospective study. Preoperative radiographic examinations of the anteroposterior hip-knee-ankle (HKA) angle were conducted and lateral spinopelvic parameters, including sagittal vertical axis, lumbar lordosis, sacral slope, pelvic tilt (PT), and pelvic incidence, were calculated. Correspondingly, the relationship of the knee ROM at 1 year after UKA and the postoperative new Knee Society Score (KSS) with radiographic parameters was investigated.

Results

At 1-year post-UKA, the postoperative knee flexion angle was found to be significantly associated with the preoperative knee flexion angle (p=0.041, 95% confidence interval [CI]: 0.025–1.141) and the preoperative HKA angle (p=0.012, 95% CI: -2.377–-0.342) in the multiple linear regression analysis. A knee extension restriction angle =10° was significantly correlated with the PT (p=0.007, 95% CI: 0.772–0.959) in the logistic regression analysis. When the cutoff value of the PT was 24.5° for a postoperative knee extension restriction angle =10°, the sensitivity was 70.4% and the specificity was 100% based on receiver-operating characteristic curves. The PT in patients with postoperative knee extension restriction =10° (32.0° ± 6.6°) were significantly greater than that in patients with postoperative knee extension restriction <10° (19.3° ± 9.0°) (p=0.001). There was no significant relationship between the KSS and the HKA angle or spinopelvic parameters.

Conclusion

Patients with a greater posterior tilt of the pelvic alignment had restrictions in knee extension postoperatively. Moreover, those with a greater varus alignment of the lower extremity preoperatively had a lower knee flexion after UKA.