Improvements in lower-extremity patient-reported outcomes after lumbar interbody fusion

OBJECTIVE Recently, new patient-reported outcome measures (PROMs) of the spine were designed to overcome the limitations of previous spinal PROMs and to consider the whole spine as a single kinetic functional unit. Owing to the significance of spine-hip-knee and global body balance, the spine and lower extremities cannot be considered separately. However, no reports have evaluated lower-extremity functional outcome using PROMs after lumbar spine surgery. The authors aimed to elucidate changes in hip and knee PROMs after lumbar interbody fusion and to evaluate the sagittal spinopelvic radiographic parameters that were most strongly correlated with lower-extremity PROMs. METHODS In 2018, the authors consecutively evaluated patients who underwent lumbar interbody fusion surgery with at most three levels. Preoperative and 1-year postoperative clinical and radiographic data were assessed. Spinal functional outcomes were measured with the Oswestry Disability Index (ODI), visual analog scale (VAS) for pain, and Scoliosis Research Society-22r (SRS-22r) questionnaire. Lower-extremity functional outcomes were evaluated with the Harris Hip Score (HHS) and Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC). Linear regression was used to evaluate the relationship between spinal and lower-extremity PROMs and spinopelvic radiographic parameters. RESULTS The authors enrolled 67 patients, with a mean age of 66.4 years. The average number of surgical levels was 1.7. All assessed PROMs improved significantly after surgery (p < 0.001 for ODI, p < 0.001 for VAS, p = 0.017 for SRS-22r, p = 0.042 for HHS, and p = 0.033 for WOMAC). Spinopelvic parameters, including lumbar lordosis (LL), pelvic tilt (PT), C7 sagittal vertical axis, and sagittal radiographic parameters of hip and knee, significantly improved after surgery. On linear regression analysis, HHS and WOMAC correlated with LL and PT, respectively (beta = 0.554 and p = 0.043 for correlation of HHS with LL; beta = 1.573 and p = 0.021 for correlation of WOMAC with PT). CONCLUSIONS The current study demonstrated that lumbar fusion surgery may induce postoperative improvements in lower-extremity functional and radiological outcomes. However, among radiographic parameters, changes in LL and PT were the most strongly associated with lower-extremity PROMs.