Normative data of a smartphone app–based 6-minute walking test, test-retest reliability, and content validity with patient-reported outcome measures

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  • 1 Department of Neurosurgery, University Hospital Zurich and Clinical Neuroscience Center, University of Zurich, Switzerland;
  • 2 Department of Neurosurgery, Cantonal Hospital St. Gallen, St. Gallen, Switzerland;
  • 3 Department of Neurosurgery, Leiden University Medical Center, Leiden, The Netherlands;
  • 4 Department of Neurosurgery, Bergman Clinics, Amsterdam, The Netherlands;
  • 5 Center for Neuroscience, Queens University, Kingston, Ontario, Canada;
  • 6 Department of Neurosurgery, Hospital Universitario La Paz, Madrid, Spain;
  • 7 Department of Neurosurgery, Stanford University Hospital and Clinics, Stanford, California; and
  • 8 Neuro and Spine Center, Hirslanden Clinic St. Anna, Lucerne, Switzerland
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OBJECTIVE

The 6-minute walking test (6WT) is used to determine restrictions in a subject’s 6-minute walking distance (6WD) due to lumbar degenerative disc disease. To facilitate simple and convenient patient self-measurement, a free and reliable smartphone app using Global Positioning System coordinates was previously designed. The authors aimed to determine normative values for app-based 6WD measurements.

METHODS

The maximum 6WD was determined three times using app-based measurement in a sample of 330 volunteers without previous spine surgery or current spine-related disability, recruited at 8 centers in 5 countries (mean subject age 44.2 years, range 16–91 years; 48.5% male; mean BMI 24.6 kg/m2, range 16.3–40.2 kg/m2; 67.9% working; 14.2% smokers). Subjects provided basic demographic information, including comorbidities and patient-reported outcome measures (PROMs): visual analog scale (VAS) for both low-back and lower-extremity pain, Core Outcome Measures Index (COMI), Zurich Claudication Questionnaire (ZCQ), and subjective walking distance and duration. The authors determined the test-retest reliability across three measurements (intraclass correlation coefficient [ICC], standard error of measurement [SEM], and mean 6WD [95% CI]) stratified for age and sex, and content validity (linear regression coefficients) between 6WD and PROMs.

RESULTS

The ICC for repeated app-based 6WD measurements was 0.89 (95% CI 0.87–0.91, p < 0.001) and the SEM was 34 meters. The overall mean 6WD was 585.9 meters (95% CI 574.7–597.0 meters), with significant differences across age categories (p < 0.001). The 6WD was on average about 32 meters less in females (570.5 vs 602.2 meters, p = 0.005). There were linear correlations between average 6WD and VAS back pain, VAS leg pain, COMI Back and COMI subscores of pain intensity and disability, ZCQ symptom severity, ZCQ physical function, and ZCQ pain and neuroischemic symptoms subscores, as well as with subjective walking distance and duration, indicating that subjects with higher pain, higher disability, and lower subjective walking capacity had significantly lower 6WD (all p < 0.001).

CONCLUSIONS

This study provides normative data for app-based 6WD measurements in a multicenter sample from 8 institutions and 5 countries. These values can now be used as reference to compare 6WT results and quantify objective functional impairment in patients with degenerative diseases of the spine using z-scores. The authors found a good to excellent test-retest reliability of the 6WT app, a low area of uncertainty, and high content validity of the average 6WD with commonly used PROMs.

ABBREVIATIONS 6WD = 6-minute walking distance; 6WT = 6-minute walking test; ASA = American Society of Anesthesiologists; COMI = Core Outcome Measures Index; COPD = chronic obstructive pulmonary disease; DDD = degenerative disc disease; GPS = Global Positioning System; HRQoL = health-related quality of life; ICC = intraclass correlation coefficient; LDH = lumbar disc herniation; LSS = lumbar spinal stenosis; MRC = Medical Research Council; OFI = objective functional impairment; PROM = patient-reported outcome measure; SEM = standard error of measurement; TUG = Timed Up and Go; VAS = visual analog scale; ZCQ = Zurich Claudication Questionnaire.

Supplementary Materials

    • Supplemental Table 1 and Figs. 1 and 2 (PDF 5.45 MB)

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Contributor Notes

Correspondence Martin N. Stienen: University Hospital Zurich & Clinical Neuroscience Center, University of Zurich, Switzerland. mnstienen@gmail.com.

INCLUDE WHEN CITING Published online May 29, 2020; DOI: 10.3171/2020.3.SPINE2084.

L.T. and E.G. contributed equally to this work and share first authorship.

Disclosures Dr. Desai reports being a consultant to DePuy Synthes and Stryker.

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