Surgical Treatment of Adjacent Segment Stenosis (STASS)

The goal of this clinical trial is to learn whether microdecompression alone is as effective as decompression with extension of fusion surgery in patients with symptomatic adjacent segment stenosis after previous lumbar fusion surgery.

The main questions it aims to answer are:

Is microdecompression alone non-inferior to decompression with extension of fusion in improving disability 24 months after surgery, as measured by the Oswestry Disability Index (ODI)? Does microdecompression alone result in similar or lower rates of complications, reoperations, pain, and radiological progression compared with decompression and fusion?

Researchers will compare microdecompression alone to decompression with extension of lumbar fusion to determine whether the less invasive procedure can achieve similar clinical outcomes while reducing surgical burden and preserving spinal structures.

Participants will:

Be randomly assigned to one of two treatment groups: microdecompression alone or decompression with extension of lumbar fusion.

Undergo the assigned surgical treatment. Attend clinical and radiological follow-up visits at 6, 12, and 24 months after surgery.

Complete questionnaires assessing disability, pain, quality of life, sleep quality, and mental health.

Undergo routine imaging and clinical examinations to evaluate treatment outcomes and possible complications.

Study Overview

• Status: Not yet recruiting
• Conditions: Lumbar Spinal Stenosis; Adjacent Segment Disease
• Intervention / Treatment: Procedure: Microsurgical Decompression with Extension of Fusion; Procedure: Microsurgical Decompression Alone

• Study Type: Interventional
• Enrollment (Estimated): 338
• Phase: Not Applicable

Contacts and Locations

• Study Contact: Name: Anton Früh, PD MD M.Sc.; Phone Number: +49 030 450 660 376; Email: anton.frueh@charite.de

Study Locations

• Germany
  • State of Berlin
    • Berlin, State of Berlin, Germany, 10117
      • Charité - Universitätsmedizin Berlin

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Adult; Older Adult
• Accepts Healthy Volunteers: No

Description

Inclusion Criteria:

• Age ≥18 years.
• Oswestry Disability Index (ODI) between 30% and 80% at screening.
• Symptomatic adjacent segment stenosis following degenerative lumbar fusion surgery.
• Persistent symptoms despite at least 6 weeks of appropriate conservative treatment.
• Radiological evidence of adjacent segment spinal stenosis on magnetic resonance imaging (MRI).
• Ability to understand the study procedures and complete patient-reported outcome questionnaires.
• Ability to provide written informed consent.

Exclusion Criteria:

• Adjacent segment kyphosis or scoliosis greater than 10 degrees.
• Screw loosening or pseudarthrosis of the previous fusion construct.
• Known current pregnancy or breastfeeding.
• Acute traumatic spinal injury or fracture.
• Active inflammatory disease of the spine.
• Active neoplastic disease of the spine.
• Contraindication to spinal surgery.
• Inability to provide informed consent or complete study questionnaires.
• Symptoms attributable to spinal stenosis are not the predominant clinical complaint
• Foraminal stenosis grade ≥2 according to the Lee classification.
• Dynamic spondylolisthesis ≥3 mm on flexion-extension radiographs.
• Persons involuntarily detained by judicial or administrative order.

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Treatment
• Allocation: Randomized
• Interventional Model: Parallel Assignment
• Masking: Single

Number of Arms

2

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Active Comparator: Control; Decompression and fusion	Procedure: Microsurgical Decompression with Extension of Fusion; Participants undergo microsurgical decompression of symptomatic adjacent segment stenosis combined with extension of the existing lumbar fusion.
Active Comparator: Intervention; Mircosurgical decompression only	Procedure: Microsurgical Decompression Alone; Participants undergo microsurgical decompression of symptomatic adjacent segment stenosis after previous lumbar fusion surgery without extension of the existing fusion.

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Proportion of Participants Achieving at Least 30% Reduction in Oswestry Disability Index (ODI)	The primary endpoint is the proportion of participants achieving a reduction of at least 30% in the Oswestry Disability Index (ODI) compared with baseline. The ODI is a validated patient-reported outcome measure assessing disability related to lumbar spine disorders on a scale from 0% to 100%. A reduction of at least 30% is considered clinically meaningful.	24 months after surgery

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Pain related disability	Disability related to low back pain assessed using the Oswestry Disability Index (ODI). The ODI score ranges from 0 to 100%, with higher scores indicating greater disability and worse functional impairment.	Baseline (before surgery), 6 months after surgery, 12 months after surgery, and 24 months after surgery.
Leg Pain Intensity at Rest	Pain intensity assessed using the Numeric Rating Scale (NRS; 0-10) for leg pain at rest.The NRS ranges from 0 to 10, where 0 indicates no pain and 10 indicates the worst imaginable pain. Higher scores indicate greater pain intensity.	Baseline (before surgery), 6 months after surgery, 12 months after surgery, and 24 months after surgery.
Leg Pain Intensity during Movement	Pain intensity assessed using the Numeric Rating Scale (NRS; 0-10) for leg pain during movement.The NRS ranges from 0 to 10, where 0 indicates no pain and 10 indicates the worst imaginable pain. Higher scores indicate greater pain intensity.	Baseline (before surgery), 6 months after surgery, 12 months after surgery, and 24 months after surgery.
Back Pain Intensity at Rest	Pain intensity assessed using the Numeric Rating Scale (NRS; 0-10) for back pain at rest.The NRS ranges from 0 to 10, where 0 indicates no pain and 10 indicates the worst imaginable pain. Higher scores indicate greater pain intensity.	Baseline (before surgery), 6 months after surgery, 12 months after surgery, and 24 months after surgery.
Back Pain Intensity during Movement	Pain intensity assessed using the Numeric Rating Scale (NRS; 0-10) for back pain during movement.The NRS ranges from 0 to 10, where 0 indicates no pain and 10 indicates the worst imaginable pain. Higher scores indicate greater pain intensity.	Baseline (before surgery), 6 months after surgery, 12 months after surgery, and 24 months after surgery.
Maximum Walking Distance	Maximum walking distance measured in meters.	Baseline (before surgery), 6 months after surgery, 12 months after surgery, and 24 months after surgery.
Health-Related Quality of Life Assessed by the 36-Item Short Form Health Survey (SF-36)	generates eight domain scores (physical functioning, role limitations due to physical health, bodily pain, general health perceptions, vitality, social functioning, role limitations due to emotional problems, and mental health), each transformed to a scale ranging from 0 to 100, with higher scores indicating better health-related quality of life and functional status. Unit of Measure: Points on a scale (0-100).	Baseline (before surgery), 6 months after surgery, 12 months after surgery, and 24 months after surgery.
Health-Related Quality of Life Assessed by the EuroQol 5-Dimension 5-Level Questionnaire (EQ-5D-5L) Index Score	Health-related quality of life assessed using the EuroQol 5-Dimension 5-Level questionnaire (EQ-5D-5L). The EQ-5D-5L evaluates five dimensions of health status (mobility, self-care, usual activities, pain/discomfort, and anxiety/depression), each with five response levels. Responses are converted into a single EQ-5D-5L Index Score using an established country-specific value set. Higher index scores indicate better health-related quality of life. Unit of Measure: Utility index score (higher scores indicate better health-related quality of life).	Baseline (before surgery), 6 months after surgery, 12 months after surgery, and 24 months after surgery.
Mood Assessed by the German General Depression Scale - Short Form (ADS-K)	Depressive symptoms assessed using the German General Depression Scale - Short Form (ADS-K). The ADS-K is a self-report questionnaire comprising 15 items, each rated on a 4-point Likert scale (0-3 points). Total scores range from 0 to 45 points, with higher scores indicating more severe depressive symptomatology and worse mood status. Unit of Measure: Points on a scale (range: 0-45; higher scores indicate more severe depressive symptoms)	Baseline (before surgery), 6 months after surgery, 12 months after surgery, and 24 months after surgery.
Sleep Quality Assessed by the Pittsburgh Sleep Quality Index (PSQI)	Sleep quality assessed using the Pittsburgh Sleep Quality Index (PSQI). The PSQI is a self-administered questionnaire evaluating sleep quality and disturbances over the previous month across seven domains: subjective sleep quality, sleep latency, sleep duration, habitual sleep efficiency, sleep disturbances, use of sleeping medication, and daytime dysfunction. Component scores are summed to generate a global PSQI score ranging from 0 to 21 points, with higher scores indicating poorer sleep quality and greater sleep disturbance. Unit of Measure: Points on a scale (range: 0-21; higher scores indicate worse sleep quality).	Baseline (before surgery), 6 months after surgery, 12 months after surgery, and 24 months after surgery.
Length of hospital stay	Length of hospital stay measured in days from surgery until hospital discharge.	From date of surgery until hospital discharge, up to 30 days postoperatively
Intensive Care Unit Stay	Duration of intensive care unit stay measured in days.	From admission to the intensive care unit after surgery until discharge from the intensive care unit, up to 30 days postoperatively.
Additional or Revision Spine Surgery	Proportion of participants requiring additional spinal surgery or revision surgery during follow-up.	Up to 24 months after surgery
Perioperative Complications	Number and type of perioperative complications associated with the surgical procedure.	Perioperative/Periprocedural
Operative Parameters	Operative duration, intraoperative blood loss	Perioperative/Periprocedural
Dynamic Spondylolisthesis	Presence of dynamic spondylolisthesis defined as a translation of ≥3 mm on flexion-extension radiographs.Unit of Measure: Participants with dynamic spondylolisthesis.	24 month after surgery
Central Stenosis Severity Assessed by the Schizas Classification	Central canal stenosis at the adjacent segment assessed on MRI using the Schizas classification (Grades A-D).Unit of Measure: Grade (A-D; higher grades indicate more severe stenosis).	24 months after surgery
Foraminal Stenosis Severity Assessed by the Lee Classification	Foraminal stenosis at the adjacent segment assessed on MRI using the Lee classification (Grades 1-4).Unit of Measure: Grade (1-4; higher grades indicate more severe foraminal stenosis).	24 months after surgery.
Implant Integrity	Implant integrity assessed on radiographs, including evidence of implant loosening, breakage, or material dislocation.Unit of Measure: Participants with implant failure.	24 months after surgery.
Segmental Lordosis	Segmental lordosis measured on standing lateral radiographs.Unit of Measure: Degrees (°).	24 months after surgery.

Collaborators and Investigators

• Sponsor: Charite University, Berlin, Germany

Study record dates

Study Major Dates

• Study Start (Estimated): October 1, 2026
• Primary Completion (Estimated): September 30, 2030
• Study Completion (Estimated): March 1, 2031

Study Registration Dates

• First Submitted: May 29, 2026
• First Submitted That Met QC Criteria: June 18, 2026
• First Posted (Actual): June 22, 2026

Study Record Updates

• Last Update Posted (Actual): June 22, 2026
• Last Update Submitted That Met QC Criteria: June 18, 2026
• Last Verified: June 1, 2026

More Information

Terms related to this study

• Keywords: Lumbar Spinal Stenosis; Adjacent Segment Disease; Adjacent Segment Stenosis
• Additional Relevant MeSH Terms: Bone Diseases; Musculoskeletal Diseases; Spinal Diseases; Spinal Stenosis
• Other Study ID Numbers: STASS-Trial; 574896382 (Other Grant/Funding Number: Deutsche Forschungsgemeinschaft (DFG))

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: YES

IPD Plan Description

Individual participant data underlying the results reported in publications arising from this study, after de-identification, will be made available upon reasonable request to the corresponding investigator.

Supporting documents including the study protocol, statistical analysis plan, and data dictionary will also be made available.

• IPD Sharing Time Frame: Beginning 12 months following publication of the primary study results and ending 5 years after publication.

IPD Sharing Access Criteria

De-identified individual participant data (IPD) underlying the results reported in publications arising from this study, as well as the study protocol, statistical analysis plan, and analytic code, will be made available to qualified researchers.

Access will be granted to investigators who provide a scientifically sound research proposal that is approved by the study steering committee. Requests must be submitted to the study sponsor and should specify the intended use of the data.

Data will be shared only after publication of the primary study results and following execution of an appropriate data-sharing agreement. Access will be provided through a secure electronic data transfer system in accordance with applicable data protection regulations.

• IPD Sharing Supporting Information Type: STUDY_PROTOCOL; SAP; ANALYTIC_CODE

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No