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Nicolai Maldaner, Marketa Sosnova, Anna M. Zeitlberger, Michal Ziga, Oliver P. Gautschi, Luca Regli, Astrid Weyerbrock, Martin N. Stienen, and for the International 6WT Study Group

OBJECTIVE

Digital transformation enables new possibilities to assess objective functional impairment (OFI) in patients with lumbar degenerative disc disease (DDD). This study examines the psychometric properties of an app-based 6-minute walking test (6WT) and determines OFI in patients with lumbar DDD.

METHODS

The maximum 6-minute walking distance (6WD) was determined in patients with lumbar DDD. The results were expressed as raw 6WDs (in meters), as well as in standardized z-scores referenced to age- and sex-specific values of spine-healthy volunteers. The 6WT results were assessed for reliability and content validity using established disease-specific patient-reported outcome measures.

RESULTS

Seventy consecutive patients and 330 volunteers were enrolled. The mean 6WD was 370 m (SD 137 m) in patients with lumbar DDD. Significant correlations between 6WD and the Core Outcome Measures Index for the back (r = −0.31), Zurich Claudication Questionnaire (ZCQ) symptom severity (r = −0.32), ZCQ physical function (r = −0.33), visual analog scale (VAS) for back pain (r = −0.42), and VAS for leg pain (r = −0.32) were observed (all p < 0.05). The 6WT revealed good test-retest reliability (intraclass correlation coefficient 0.82), and the standard error of measurement was 58.3 m. A 4-tier severity stratification classified patients with z-scores > −1 (no OFI), −1 to −1.9 (mild OFI), −2 to −2.9 (moderate OFI), and ≤ −3 (severe OFI).

CONCLUSIONS

The smartphone app-based self-measurement of the 6WT is a convenient, reliable, and valid way to determine OFI in patients with lumbar DDD. The 6WT app facilitates the digital evaluation and monitoring of patients with lumbar DDD.

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Nicolai Maldaner, Marketa Sosnova, Anna M. Zeitlberger, Michal Ziga, Oliver P. Gautschi, Luca Regli, Oliver Bozinov, Astrid Weyerbrock, and Martin N. Stienen

OBJECTIVE

The 6-minute walking test (6WT) and the Timed Up and Go (TUG) test are two of the most commonly applied standardized measures of objective functional impairment that help support clinical decision-making for patients undergoing surgery for degenerative lumbar disorders. This study correlates smartphone-app–based 6WT and TUG results to evaluate their responsiveness.

METHODS

In a prospective study, 49 consecutive patients were assessed preoperatively and 6 weeks postoperatively using the 6WT, the TUG test, and commonly used patient-reported outcome measures. Raw values and standardized z-scores of both objective tests were correlated. An external criterion for treatment success was created based on the Zurich Claudication Questionnaire patient satisfaction subscale. Internal and external responsiveness for both functional tests was evaluated.

RESULTS

The mean preoperative 6WT results improved from 401 m (SD 129 m), z-score −1.65 (SD 1.6) to 495 m (SD 129 m), z-score −0.71 (SD 1.6, p < 0.001). The mean preoperative TUG test results improved from 10.44 seconds (SD 4.37, z-score: −3.22) to 8.47 seconds (SD 3.38, z-score: −1.93, p < 0.001). The 6WT showed a strong negative correlation with TUG test results (r = −66, 95% CI 0.76–0.53, p < 0.001). The 6WT showed higher internal responsiveness (standardized responsive mean = 0.86) compared to the TUG test (standardized responsive mean = 0.67). Evaluation of external responsiveness revealed that the 6WT was capable of differentiating between patients who were satisfied and those who were unsatisfied with their treatment results (area under the curve = 0.70), whereas this was not evident for the TUG test ( area under the curve = 0.53).

CONCLUSIONS

Both tests adequately quantified functional impairment in surgical candidates with degenerative lumbar disorders. The 6WT demonstrated better internal and external responsiveness compared with the TUG test.

Clinical trial registration no.: NCT03977961 (clinicaltrials.gov)