Defining Clinically Meaningful Functional Recovery Following Lumbar Spine Surgery: Minimal Clinically Important Differences for Objective Gait and Balance Biomarkers.

BACKGROUND CONTEXT: Objective gait and balance assessments provide quantitative insights into functional impairment in lumbar degenerative spine disease. However, the absence of minimal clinically important difference (MCID) thresholds limits their clinical interpretability and integration into spine care.

PURPOSE: To define MCIDs for objective gait and balance biomarkers in patients undergoing surgical treatment for lumbar degenerative spine disease.

PATIENT SAMPLE: One hundred eleven patients undergoing surgical intervention for lumbar degenerative spine disease.

OUTCOME MEASURES: Spatiotemporal gait parameters (e.g., walking speed, cadence, stride characteristics), Gait Deviation Index (GDI), and balance metrics including head, center of mass (CoM), and center of pressure (CoP) sway.

METHODS: Patients were evaluated preoperatively and at 3, 6, and 12 months postoperatively using three-dimensional motion analysis. MCIDs were calculated using five complementary approaches: distribution-based (1/2 baseline standard deviation, 1/2 change-score standard deviation), measurement error-based (minimum detectable change at 90% and 95% confidence levels), and anchor-based methods. Final MCID thresholds were derived by averaging distribution-based, change-based, and anchor-based estimates.

RESULTS: Final averaged MCID thresholds demonstrated clinically meaningful change for key gait parameters, including walking speed (0.14 m/s), cadence (7.8 steps/min), stride time (0.11 s), and step length (0.05 m). Balance-related MCIDs included head sway (0.95-0.98 cm), center of mass sway (0.51-0.54 cm), and center of pressure sway (0.57-0.70 cm in planar measures and 28.71 cm for total excursion). MCID estimates were consistent across methods for gait variables, whereas greater variability was observed in balance metrics.

CONCLUSIONS: This study defines clinically interpretable MCID thresholds for objective gait and balance biomarkers in lumbar degenerative spine disease. These thresholds support the integration of motion analysis into clinical practice and enable more precise interpretation of postoperative functional recovery.

STUDY DESIGN/SETTING: Prospective longitudinal cohort study.

LEVEL OF EVIDENCE: Level II.