Minimal Clinically Important Differences in Gait and Balance Ability in Patients Who Underwent Corrective Long Spinal Fusion for Adult Spinal Deformity

Study Design: Retrospective observational study. Background: The risk of a femoral neck fracture due to a fall after adult spinal deformity surgery has been reported. One of the most significant factors among walking and balance tests in post-operative ASD patients was the timed up-and-go test (TUG). This study aims to calculate the minimal clinically important difference (MCID) in balance tests after ASD surgery. Methods: Forty-eight patients, 4 males and 44 females, were included by exclusion criteria in 66 consecutive patients who underwent corrective surgery as a treatment for ASD at our institution from June 2017 to February 2022. The inclusion criteria for this study were age >= 50 years; and no history of high-energy trauma. The exclusion criteria were dementia, severe deformity of the lower extremities, severe knee or hip osteoarthritis, history of central nervous system disorders, cancer, and motor severe paralysis leading to gait disorders. The surgeries were performed in two stages, first, the oblique lumber interbody fusion (OLIF) L1 to L5 (or S1), and second, the posterior corrective fusion basically from T10 to pelvis. For outcome assessment, 10 m walk velocity, TUG, ODI, and spinopelvic parameters were used. Results: Ten meter walk velocity of pre-operation and post-operation were 1.0 +/- 0.3 m/s and 1.2 +/- 0.2 m/s, respectively (p < 0.01). The TUG of pre-operation and post-operation were 12.1 +/- 3.7 s and 9.7 +/- 2.2 s, respectively (p < 0.01). The ODI improved from 38.6 +/- 12.8% to 24.2 +/- 15.9% after surgery (p < 0.01). All post-operative parameters except PI obtained statistically significant improvement after surgery. Conclusions: This is the first report of MCID of the 10 m walk velocity and TUG after ASD surgery. Ten meter walk velocity and the TUG improved after surgery; their improvement values were correlated with the ODI. MCID using the anchor-based approach for 10 m walk velocity and the TUG were 0.10 m/s and 2.0 s, respectively. These MCID values may be useful for rehabilitation after ASD surgery.