Minimal Clinically Important Difference of the 6-Minute Walk Distance in Patients Undergoing Lumbar Spinal Canal Stenosis Surgery: 12 Months Follow-Up

Abstract

Study design: Retrospective review of prospectively collected data.

Objective: We evaluated the responsiveness of the 6-minute walk distance (6MWD) and determined the threshold of the minimal clinically important difference (MCID) in patients who underwent lumbar spinal stenosis (LSS) surgery.

Summary of background data: Little evidence exists on the MCID of 6MWD after LSS surgery. The 6MWD is an objective gait assessment that can be measured quickly.

Materials and methods: In total, 126 patients (74 men; average age, 72.2 ± 6.5 yr) were included and assessed preoperatively and at 12 months postoperatively. We used the Oswestry Disability Index (ODI), as an anchor to calculate the MCID for the 6MWD and measured internal and external responsiveness of the 6MWD. The external responsiveness was assessed in 2 ways: (1) One based on the anchoring questionnaire and (2) another based on the scale distribution. The anchor-based approach was evaluated using the Spearman rank correlation coefficient and receiver-operating characteristic curve. The distribution-based approach was evaluated using the minimal detectable change.

Results: The ODI scores and 6MWD for each anchor significantly improved postoperatively. The change in the 6MWD was significantly correlated with change in the ODI (6 mo, r = -0.45; 12 mo, r = -0.49). The receiver-operating characteristic analysis demonstrated good discriminative properties for the 6MWD using the ODI anchor (6 mo, 0.72; 12 mo, 0.78). The cutoff values for 6MWD were 102.3 and 57.5 at 6 and 12 months, respectively. In the distribution-based approach, the minimal detectable change for the 6MWD was 95.7 m.

Conclusions: We validated both the internal and external responsiveness of the 6MWD using the ODI and estimated the MCID in the 6MWD for patients undergoing LSS surgery. However, there was lower validity for the MCID among those participants with the high walking ability and low disability at baseline.