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

Abstract

<jats:sec><jats:title>OBJECTIVE</jats:title><jats:p>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.</jats:p></jats:sec><jats:sec><jats:title>METHODS</jats:title><jats:p>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/m<jats:sup>2</jats:sup>, range 16.3–40.2 kg/m<jats:sup>2</jats:sup>; 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.</jats:p></jats:sec><jats:sec><jats:title>RESULTS</jats:title><jats:p>The ICC for repeated app-based 6WD measurements was 0.89 (95% CI 0.87–0.91, p &lt; 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 &lt; 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 &lt; 0.001).</jats:p></jats:sec><jats:sec><jats:title>CONCLUSIONS</jats:title><jats:p>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.</jats:p></jats:sec>

Effects of self-quarantine during the COVID-19 pandemic on patients with lumbar spinal stenosis

“…Before case-control matching, the SQ group reported a significantly higher baseline NRS score for low back pain than that reported by the remaining patients. Walking ability in patients with lumbar degenerative disease has a reported inverse correlation with back pain severity; [ 16 ] thus, it is reasonable that patients with severe back pain limited outings and exercise after the order from the government. This difference led to failure in yielding 1:1 matching.…”

Assessment of the Minimum Clinically Important Difference in the Smartphone-based 6-minute Walking Test After Surgery for Lumbar Degenerative Disc Disease

“…A 34-year-old female with lumbo-radicular pain resulting from a L4/5 LDH was admitted for sequestrectomy. At the preoperative assessment she walked 422 m, which corresponds to a OFI z score of −2.4 (age- and sex-adjusted reference population: 605 ± 75 m 12 ). The surgery was uneventful, and she was discharged home shortly after.…”

“…Furthermore, normative population data have recently become available, which allows to adjust 6WT results for age and sex to express OFI in the form of standardized z scores. 12 App-based 6WT results demonstrated excellent intrarater reliability and good correlation with several commonly used PROMs. 12,13 Reporting the clinical relevance in addition to statistical significance in the assessment of treatment outcomes has gained increasing importance for cohort studies and clinical trials.…”

“…10 At first consultation patients were instructed on usage of the 6WT app and instructions how to perform the 6WT (level and straight path in their home environment) were handed out, as described previously. 12,13 Patients were asked to perform the 6WT twice before surgery and twice 6 weeks postoperatively.…”

Distance to first symptoms measured by the 6-min walking test differentiates between treatment success and failure in patients with degenerative lumbar disorders

“…The 6-min walking test (6WT) is increasingly applied as an objective outcome measure in patients with lumbar DLD [5]. We recently developed a smartphone app-based version of the 6WT, which demonstrated excellent reliability [6,7]. The 6WT can be self-performed by the patient in his/her home environment, and results are standardized with respect to age and sex [6,8,9].…”