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Brief description/objective

Background:
Lumbar spinal stenosis (LSS) is a progressive, degenerative disorder of the aging spine presenting with lower back pain, which commonly progresses into neurogenic claudication which impedes walking. The precise measurement of symptom severity and functional restriction is crucial when considering surgery and at follow-up, when the efficacy of the treatment is critically evaluated. Therefore, analyzing objective functional impairment (OFI), in contrast to patient reported subjective outcome measures (PROMs), is an emerging field in the clinical evaluation of spine patient as well as in research. However, an established test to reliable measure OFI and correlate it with subjective PROMs in LSS is still lacking. Given the typical symptoms of neurogenic claudication in LSS patients the Six-Minute-Walking Test (6WT), a test in which patients are instructed to walk as long and quick as possible for six minutes, can fulfill this need of a standardized way to determine OFI in patients with LSS.

Objective:
To determine the reliability and validity of the 6WT in patients with LSS. Our project will enable physicians to evaluate the success of a surgery for LSS on the OFI metric. Furthermore, it will provide the patient with the unique possibility of direct feedback on their performance. Once systematically characterized the 6WT has the potential to become the future “gold standard” for the objective evaluation of LSS patients.

Design:
This is a multi-center prospective observational study with the Kantonsspital St. Gallen as the main and coordinating study center and the University Hospital Zurich, Hirslanden Clinic St. Anna and University Clinic Balgrist as participating project sites. The study encompasses a duration of 30 months and will include n=160 patients with LSS scheduled for a surgical intervention and n=150 control subjects.

Methods:
We will use a smartphone-application (the 6WT app) developed by our team that uses GPS coordinates to measure the walking distance of LSS patients over six minutes in their home environment. Patients can indicate occurrence of neurogenic claudication by pressing a designated button, allowing for the determination of time and distance to first symptoms. Applying the smartphone app-based self-measurement of the 6WT before and after surgery, we thus determine OFI at baseline and follow up. Based on the 6WT results of the age- and sex-adjusted control population range we will be able to stratify OFI results by their severity into groups and express deviation from the norm by means of an adjusted z-score/t-score. We will correlate OFI with already established PROMs in the sense of cross-validation and determine the minimum clinically important difference (MCID) as the smallest change that is important to patients, in order to describe a critical threshold that defines treatment effectiveness.