The study determines the reliability and validity of the 6-Minute Walking Test (6MWT) in patients with lumbar degenerative disc disease (DDD).

The purposes of the study is to assess the ability of the 6-Minute Walking Test (6MWT) as a reliable and standardized objective outcome assessment and its relation to already established subjective patient reported outcome measures in patients suffering from lumbar degenerative disc disease. We want to use an existing smartphone-application that uses global positioning system (GPS) coordinates to measure walking distance. Applying self- measurement of the 6MWT before and after a therapeutic intervention, we determine objective functional impairment (OFI) in patients. The results of this study add to the understanding of achievable objective outcomes after therapeutic interventions applied to patients with DDD and examines patients acceptance for smartphone based self-measurement.

Primary Objectives The primary objective is to determine the reliability and validity of the 6-Minute Walking Test (6MWT) in patients with lumbar degenerative disc disease (DDD)

Secondary objectives are

1. to correlate objective functional impairment (OFI) with already established patient-rated outcome measures (PROMs) in the sense of cross-validation.
2. To correlate OFI, as determined by the 6MWT with OFI that is determined by another objective test, the TUG test
3. to then analyze the change in OFI in patients before and after surgical intervention
4. to determine whether patients prefer the objective (6MWT) or subjective (PROMs) repeated assessment of their functional condition.

Inclusion Criteria:

• Patient scheduled for spine surgery with one of the following diagnosis (1) lumbar disc herniation (LDH), (2) lumbar spinal stenosis lumbar (LSS) or lumbar DDD with or without instability requiring lumbar fusion (transforaminal lumbar interbody fusion, posterior lumbar interbody fusion, or extreme lateral interbody fusion)
• Male and Female subjects ≥ 18 years
• Written informed consent

Exclusion Criteria:

• Pregnancy
• Inability to walk (extreme pain or severe neurological deficits)
• Severe Chronic Obstructive Lung Disease (COPD) corresponding to ≥ Gold III
• Severe heart failure corresponding to ≥ New York Heart Association (NYHA) III
• Lung cancer and diffuse parenchymal lung disease
• Other medical reasons interfering with the patient's ability to walk and perform the 6MWT (e.g., osteoarthritis disease of the lower extremities, Parkinson's disease, heart failure, hip or knee prosthesis etc.)
• Unavailability for follow up and/or inability to complete assessment (planning to move, no smartphone, etc.).

All patients presenting to the neurosurgical department of the Kantonsspital St. Gallen (KSSG) with a diagnosed DDD fulfilling the inclusion criteria and scheduled for surgery will be considered for this study.