Responsiveness of the Zurich Claudication Questionnaire in Patients With Lumbar Spinal Stenosis Undergoing Nonsurgical Treatment: A Secondary Analysis of a Randomized Controlled Trial.

STUDY DESIGN

Secondary analysis of a randomized controlled trial.

OBJECTIVE

We investigated the ability to distinguish patients with lumbar spinal stenosis (LSS) who improved from those who did not after receiving nonsurgical treatment. We used the disorder-specific Zurich Claudication Questionnaire (ZCQ) satisfaction subscale as an external anchor and estimated the minimal clinically important differences (MCIDs) for the ZCQ symptom severity and physical function subscales.

SUMMARY OF BACKGROUND DATA

The ZCQ satisfaction subscale effectively distinguishes surgical patients who improved from those who did not for LSS. However, its responsiveness in nonsurgical treatment has not been evaluated yet.

METHODS

Eighty-four patients with LSS who received supervised physical therapy or a home exercise program were included. Patients were classified as responders or nonresponders according to the cutoff of 2.5 for the ZCQ satisfaction subscales at six weeks and one year. The external responsiveness of the ZCQ satisfaction subscale was assessed using correlational and receiver-operating characteristic (ROC) curve analyses. MCIDs for the ZCQ symptom severity and physical function subscales were estimated using anchor and distribution approaches.

RESULTS

Pearson correlation coefficients between the changes in outcomes and the ZCQ satisfaction subscale at six weeks and one year were 0.37 to 0.58 (symptom severity) and 0.40 to 0.45 (physical function subscales) (>0.30 is considered a good anchor). The area under the ROC curve values were 0.66 to 0.72 and 0.63 to 0.71 for the symptom severity and physical function subscales, respectively (>0.7 is considered acceptable). The MCIDs at six weeks and one year estimated from anchor-based approaches were -0.64 to -0.13 (symptom severity) and -0.39 to 0.10 (physical function), and those from the distribution-based approaches were -0.31 to -0.30 and -0.29 to -0.27, respectively.

CONCLUSIONS

The findings of this study suggest that the ZCQ satisfaction subscale has less ability to distinguish patients with LSS who improved in the ZCQ symptom severity and physical function subscales from those who did not after nonsurgical treatment, compared to those after surgical treatment.