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

Abstract

Study Design. Prospective cohort study.Objective. The aim of this study was to determine the minimum clinically important difference (MCID) of the 6-minute walking test (6WT) after surgery for lumbar degenerative disc disease (DDD). Summary of Background Data. The smartphone-based 6WT is a valid and reliable tool to quantify objective functional impairment in patients with lumbar DDD. To date, the MCID of the 6WT has not been described in patients with DDD. Methods. We assessed patients pre-and 6-weeks postoperatively, analyzing both raw 6-minute walking distances (6WD; in meters) and standardized 6WT z scores. Three methods were applied to compute MCID values using established patientreported outcomes measures (PROMs) as anchors (VAS back/leg pain, Zurich Claudication Questionnaire [ZCQ], Core Outcome Measures Index [COMI]): average change, minimum detectable change, and the change difference approach. Result. We studied 49 patients (59% male) with a mean age of 55.5 AE 15.8 years. The computation methods revealed MCID values ranging from 81 m (z score of 0.9) based on the VAS back pain to 99 m (z score of 1.0) based on the ZCQ physical function scale. The average MCID of the 6WT was 92 m (z score of 1.0). Based on the average MCID of raw 6WD values or standardized z scores, 53% or 49% of patients classified as 6week responders to surgery for lumbar DDD, respectively. Conclusion. The MCID for the 6WT in lumbar DDD patients is variable, depending on the calculation technique. We propose a MCID of 92m (z score of 1.0), based on the average of all three methods. Using a z score as MCID allows for the standardization of clinically meaningful change and attenuates age-and sexrelated differences.

Digital Biomarkers and the Evolution of Spine Care Outcomes Measures: Smartphones and Wearables

“…Several groups have reported the success of smartphone apps to administer mobility assessments, such as the 6WT and the TUG test, most commonly in patients with degenerative lumbar disorders. 19,23,[41][42][43][44][45] Smartphone administration of these assessments could allow for more frequent testing and a reduction of Hawthorne effects. Zeitlberger et al 46 examined more granular measures of a smartphone app-based 6WT in patients with degenerative lumbar disorders.…”

“…Patients in the DCP group had high engagement and a reduction in their ODI, as well as a 52% decrease in average interest in surgery vs the control group, who showed a 53% increase in average interest in surgery. Intriguingly, this suggests that digital interventions could play a future role in managing patient treatment 41 Maldaner 2020 19 Sosnova 2020 44 Zeitlberger 2022 46 Zeitlberger 2021 42 Zeitlberger 2020 43 DDD Neurogenic claudication and/or radiculopathy 6WT (OFI), TUG (OFI)…”

“…Ahmad et al 49 examined smartphone mobility data during a two-year perioperative period in patients who underwent elective lumbar decompressive surgery. They describe 5 clinical stages characterized by mobility patterns: preoperative baseline, preoperative presentation/ decline, immediate postoperative recovery, full recovery, and possible 49 Ahmad 2021 50 Basil 2021 3 Boaro 2021 26 Cote 2019 22 Maldaner 2021 41 Zaldivar-Jolissaint 2021 51 Zeitlberger 2022 46 Zeitlberger 2021 42 Postoperative secondary decline. These stages correlated with clinical documentation of the patients' courses.…”

“…Others have found similar patterns in perioperative activity trends. 3,50 Zeitlberger et al 42 determined the minimum clinically important difference of a smartphone-based 6WT after surgery for lumbar DDD. They proposed a minimal difference of 92 m walked, which correlated with clinical impressions of these patients.…”