The Lumbar Adjacent Segment Stenosis Trial (LASS)

The Lumbar Adjacent Segment Stenosis (LASS) Trial

The goal of this clinical trial is to learn if there are differences in the effectiveness of decompression surgery alone versus decompression combined with extended fusion in patients with a previous lumbar spinal fusion who now present with symptoms of lumbar adjacent segment stenosis (LASS). The main questions it aims to answer are:

• Does decompression alone differ from decompression combined with extended fusion with regard to clinical outcomes two years after surgery?
• Are there any clinical or radiological characteristics that can predict better or worse outcomes two years after surgery?
• Are there any differences between the treatment groups in terms of health economics?

Researchers will compare decompression surgery alone versus decompression combined with extended fusion to see if there are any differences in treatment effect.

Participants will:

• Be randomized to one of the two surgical procedures
• Visit the clinic four times postoperatively (at three months, 1, 2 and 5 years) for checkups and tests
• Respond to questionnaires before surgery, and three months, 1, 2 and 5 years postoperatively

Study Overview

• Status: Not yet recruiting
• Conditions: Chronic Low Back and Leg Pain; Lumbar Adjacent Spinal Stenosis
• Intervention / Treatment: Procedure: Decompression alone; Procedure: Decompression with extended fusion

Detailed Description

Globally, musculoskeletal disorders are the leading causes of years lived with disability, with spinal disorders contributing to 70% of this burden. The consequences for patients, their families and society are significant.

Lumbar spinal stenosis is a common condition with an increasing prevalence, largely due to an aging population. It is caused by degenerative changes in the supporting structures of the lumbar spine leading to symptoms like low-back pain and radiating pain to the lower extremities as well as numbness and weakness causing walking restrictions. Annually, about 200,000 to 250,000 new cases are diagnosed in the United States alone and this condition is the most frequent indication for spinal surgery in patients older than 65 years of age. Approximately 10% of the population over 50 years suffer from symptomatic lumbar spinal stenosis.

Lumbar surgery may be indicated in patients with various degenerative spinal conditions when non-surgical treatment has failed, and radiological findings are consistent with clinical symptoms. Decompression (removal of stenotic structures to relieve nerve pressure) and spinal fusion (the use of screws, rods, plates, or other devices to assist in achieving fusion between vertebral bodies) remain the cornerstone of operative treatment. The volume of lumbar spine surgery has increased considerably over the past decades, particularly for more complex procedures such as instrumented fusion, and especially among the elderly. In the United States, the hospital costs of lumbar instrumented fusion procedures is reported to be higher than for any other surgical procedure such as percutaneous coronary angioplasty and knee- and hip arthroplasty. In Norway, approximately 700 lumbar spinal fusions are performed every year, with about half of them being reoperations.

Lumbar spinal fusion has the highest complication rates among all spinal surgeries. Complications involving either the segment above or below (=adjacent to) a previously fused segment can arise years after the initial fusion. An annual incidence of 2,5-4% for new subsequent surgery after initial lumbar fusion is reported, 13.6% and 22.2% were re-operated within 5 and 10 years respectively. The majority of reoperations following an initial fusion are due to spinal stenosis adjacent to a previously fused segment (Lumbar Adjacent Segment Stenosis - LASS), and these patients constitute a substantial subgroup within the extensive and growing patient population with spinal stenosis.

At present, there are no guidelines or prospective studies that can advise clinicians on how patients with LASS should be treated, and this issue is emerging as one of the most relevant and debated questions within degenerative spine surgery. According to register data, the most common treatments are either extending the fusion beyond the symptomatic adjacent stenotic segment or just decompression of the stenotic structures, with a tendency of performing just decompression in patients with cranial LASS and decompression with extended fusion in patients with caudal LASS. However, there is large variation in surgical practices both between and even within hospitals. Considering the increasing prevalence of LASS, costs, and risks associated with spinal fusions, there is need for randomized trials to evaluate surgical practice and the relative efficacy of the two most common surgical treatments.

Statistical Hypothesis: The primary objective is to evaluate the effect of Decompression alone versus Decompression with extended Fusion at two-year FU. Thus, the null hypothesis to be tested in relation to the primary endpoint is as follows:

• Null hypothesis: The proportions of participants reaching a minimum 30% ODI improvement from baseline to two-year FU is equal in the Decompression alone and the Decompression with extended Fusion treatment groups.
• Alternative hypothesis: The proportions of participants reaching a minimum 30% ODI improvement from baseline to two-year FU is greater in one of the treatment groups than the other Secondary, the researchers in the current project aim to conduct a cost-utility analysis and evaluate the impact of radiological parameters. Main endpoint is at 2-year follow-up, but each participant will be followed for 5 years after surgery.

Patients will be randomly assigned in a 1:1 ratio to undergo decompression surgery alone or decompression combined with extended instrumented fusion. Procedure for decompression will be mid-line preserving technique, and with the use of vision-enhancing aid (microscope magnifying glasses). The procedure for extended fusion will involve bilateral pedicle screws and with an aim to transplant a minimal amount of bone volume. All surgeons need to have at least senior surgeon experience.

Statistical analysis: The effect measure for the primary endpoint will be the difference between the treatment groups in the probability of reaching a minimum 30% ODI improvement from baseline to one-year FU. It will be estimated by the difference in observed proportions with a 95% Newcombe hybrid score confidence interval. A two-sided P-value for the null hypothesis of a zero difference will also be calculated with the Fisher mid-P test. Safety endpoints will be tabulated and presented with descriptive statistics.

Further details of the statistical methods will be provided in the SAP. The SAP will be finalized before the database lock and will include a more technical and detailed description of the statistical analyses.

Interim analysis: An interim analysis for safety will be performed when 50% of the patients in each group have completed the 12-month FU. If one of the proposed stop criteria is fulfilled the study will be terminated:

1. The proportion of patients needing reoperation due to any condition in the operated level(s) is statistically significantly (p<0.05) higher in one of the groups.
2. The change in NRS leg pain from baseline to 12-month FU is statistically significantly (p<0.05) lower in one of the groups.

An independent statistician blinded for treatment adherence will perform the interim analysis. Only data on reoperations and on NRS for leg pain will be available to the statistician. Following the analysis, the statistician will inform the steering committee, via the central monitor (at Clinical Trial Unit, Oslo University Hospital) whether the study can continue. Further information about the analysis will not be disclosed or available by anyone else than the independent statistician until the main analysis at 2-year FU.

Sample Size Determination: This study is powered for the main outcome (ODI) to be able to detect at least a 20% absolute difference between the proportions of responders (ODI improvement of minimum 30% from baseline) assessed at two-year follow-up between the two treatment groups. For the sample size determination, we anticipated that 55% from the decompression with extended fusion arm and 35% from the decompression alone arm will reach the primary outcome. The statistical power selected is 80%, and the accepted type I error rate 5% (β =0.2, α = 0.05). Considering these assumptions with a superiority two-sided test, 96 patients are required in each group (192 total). The significance level will be set at 0.05 and all estimates will be reported with 95% CI and the exact p-value.

• Study Type: Interventional
• Enrollment (Estimated): 192
• Phase: Not Applicable

Contacts and Locations

• Study Contact: Name: Kjersti Storheim, Professor; Phone Number: 0047-22117740; Email: uxskje@ous-hf.no
• Study Contact Backup: Name: Eira K Ebbs, PhD; Phone Number: 0047-22118080

Study Locations

• Norway
  • Gjøvik, Norway
    • Innlandet Hospital Gjøvik
    • Contact: Håvard Furunes, PhD; Phone Number: 0047 62 33 30 00; Email: havardfurunes@gmail.com
  • Oslo, Norway
    • Oslo University Hospital HF
    • Contact: Christian Hellum, Professor; Email: CHRHEL@ous-hf.no
  • Tromsø, Norway
    • University Hospital of North Norway
    • Contact: Tore K Solberg, Professor; Phone Number: 0047 77 62 60 00; Email: tore.solberg@unn.no

Participation Criteria

Eligibility Criteria

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

Description

Inclusion Criteria:

Participants must meet all the following criteria to be eligible for the study:

1. Clinical symptoms of spinal stenosis, defined as neurogenic claudication or radiating pain into the lower limbs with duration >6 months
2. MRI-confirmed adjacent segment stenosis, proximal to a previously fused lumbar segment (fusion of maximum two levels between L1 and S1, any type of previous lumbar fixation procedure).
3. CT-verified solid fusion
4. Minimum time since previous fusion: one year
5. Eligible for both treatment alternatives: decompression with extended fusion and decompression alone.
6. Age between 18 and 80 years.
7. Insufficient improvement after at least 3 months of non-operative treatment.
8. Understand Norwegian language, spoken and written.

Exclusion Criteria:

Participants will be excluded if any of the following criteria are met:

1. Previous surgery at the actual adjacent stenotic level.
2. More than two fused lumbar levels.
3. Non-union (pseudoarthrosis) at the previously surgically fused level, radiologically verified.
4. Foraminal stenosis grade 3 at the adjacent level.
5. Spinal fracture.
6. Presence of cauda equina syndrome.
7. Complete motor deficit.
8. ASA physical status classification IV or V.
9. Alcohol or drug abuse.
10. Active cancer
11. Contradictions to MRI (e.g., Cardiac pacemaker electrodes, metal implants in the eye or brain, claustrophobia)
12. Disabling chronic neurological disease (e.g., Parkinson's disease, ALS, MS)
13. Ongoing serious psychiatric disease&
14. Any condition that in the view of the investigator would suggest that the patient is unable to comply with the study protocol and procedures
15. Declining specific treatment arm
16. Are participating in another clinical trial that may interfere with this trial

Study Plan

How is the study designed?

Design Details

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

Number of Arms

2

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Experimental: Decompression alone; Patients allocated to decompression alone will be offered mid-line preserving decompression technique	Procedure: Decompression alone; Patients allocated to decompression alone will be offered mid-line preserving decompression technique with the use of a vision-enhancing aid (microscope or magnifying glasses).
Active Comparator: Decompression with extended fusion; Patients allocated to decompression with extended fusion will be offered decompression with the use of vision enhancement, in addition to the procedure for the extended fusion involving bilateral pedicle screws with autologous bone transplant and/or bone substitutes.	Procedure: Decompression with extended fusion; Patients allocated to decompression with extended fusion will be offered decompression with the use of vision enhancement (microscope or magnifying glasses). The procedure for the extended fusion will involve bilateral pedicle screws with autologous bone transplant and/or bone substitutes. The use of an interbody device (cage) or not and decompression technique will be at the discretion of the surgeon. Bone grafts should be placed in the interbody device and either posteriorly and/or anteriorly to the interbody device. Autologous bone can be placed in the intervertebral space without a cage if it is not feasible e.g., due to a too narrow intervertebral disc space. Alternatively a posterior or posterolateral bone grafting can be performed.

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Oswestry Disability Index (ODI): Change in percent	Improvement in the ODI score of a minimum of 30% from baseline (dichotomized variable: yes / no (yes = improved 30% or more, no = improved less than 30%)). The ODI is a questionnaire examin the level of disability based on 10 everyday activities of daily living. Each item consists of 6 statements which are scored from 0 to 5, with 0 indicating the least disability and 5 the highest level of disability. The total score is calculated as a percentage, with 0% indicating no disability and 100% indicating the highest level of disability.	From enrollment to five years postoperatively (main endpoint is two years after surgery, but ODI will also be assessed before surgery, 3 months, one- and five years postoperatively)

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Oswestry Disability Index (ODI): Continuous	Change in ODI from baseline (continuous variable)	From enrollment to five years postoperatively (main endpoint is two years after surgery, but ODI will also be assessed before surgery, 3 months, one- and five years postoperatively)
Numeric Rating Scale leg pain (NRS leg pain)	Change in NRS leg pain from baseline. The NRS is a 11-point numeric scale (patient reported) ranging from '0' (e.g. "no pain") to '10' (e.g. "worst possible pain")	From enrollment to five years postoperatively (main endpoint is two years after surgery, but NRS leg pain will also be assessed before surgery, 3 months, one- and five years postoperatively)
Numeric Rating Scale back pain (NRS back pain)	Change in NRS back pain from baseline. The NRS is a 11-point numeric scale (patient reported) ranging from '0' (e.g. "no pain") to '10' (e.g. "worst possible pain").	From enrollment to five years postoperatively (main endpoint is two years after surgery, but NRS back pain will also be assessed before surgery, 3 months, one- and five years postoperatively)
Global perceived effect (GPE)	The GPE scale asks the participant to rate, on a 7 point Likert scale, how much their condition has improved or deteriorated. GPE 1-2 defined as success (completely recovered (1), much better (2)), GPE 3-5 defined as no change (somewhat better (3), no change (4), somewhat worse (5)), GPE 6-7 defined as worsening (much worse (6), worse than ever (7))	From three months after surgery to five years postoperatively (main endpoint is two years after surgery, but GPE will also be assessed 3 months, one- and five years postoperatively)
Oswestry Disability Index (ODI): Change in percent	Less than 20% improvement in ODI defined as failure. Dichotomized variable: yes / no (yes = less than 20% improvement from baseline, no = improved 20% or more from baseline).	From enrollment to five years postoperatively (main endpoint is two years after surgery, but ODI will also be assessed before surgery, 3 months, one- and five years postoperatively)
EuroQol-5 dimensions-5 levels (EQ-5D-5L)	Change in EQ-5D-5L from baseline. The descriptive system comprises five dimensions: mobility, self-care, usual activities, pain/discomfort and anxiety/depression. Each EQ-5D-5L dimension has 5 levels: no problems, slight problems, moderate problems, severe problems and extreme problems. The participant is asked to indicate his/her health state by ticking the box next to the most appropriate statement in each of the five dimensions. This decision results in a 1-digit number that expresses the level selected for that dimension. The digits for the five dimensions can be combined into a 5-digit number that describes the patient's health state. Index scores range from -0.59 to 1, where1 is the best possible health state.	From enrollment to five years postoperatively (main endpoint is two years after surgery, but EQ-5D-5L will also be assessed before surgery, 3 months, one- and five years postoperatively)
Occupational status and return to work	To evaluate the effect of decompression alone versus decompression combined with extended fusion on ability to work, the participants will be asked about their occupational status and return to work	From enrollment to five years postoperatively (main endpoint is two years after surgery, but participants will also be asked about their occupational status before surgery, 3 months, one- and five years postoperatively)
Radiology	A- Total lumbar lordosis on standing radiograph, B- Sagittal imbalance (difference between pelvic incidence and lumbar lordosis > 10 °) on standing radiograph, and C- Fusion (evaluated on CT in patients undergoing decompression combined with extended fusion). Standing X-ray is taken six times, CT-scan one time.	From enrollment to five years postoperatively. Standing X-ray is taken six times (before surgery, postoperatively before discharge from hospital, and 3 months, 1 year, 2 years, and 5 years after surgery). CT 2 years after surgery (extended fusions only)
Reoperations	The incidence, type and number of reoperations	During the whole study period (five years)

Other Outcome Measures

Outcome Measure	Measure Description	Time Frame
Adverse Events of special interest (AESI) and Serious Adverse Events (SAEs)	Safety assessments: Incidence of adverse events of special interest (AESI) and serious AE (SAEs)	During the whole study period (five years)
Cost-effectiveness	Change in the EQ-5D-5L, hospital costs, community costs including sick leave, co-interventions (pharmacological and non-pharmacological).	During the whole study period (five years)

Collaborators and Investigators

• Sponsor: Oslo University Hospital
• Collaborators: University Hospital of North Norway; Sykehuset Innlandet HF

Study record dates

Study Major Dates

• Study Start (Estimated): August 1, 2026
• Primary Completion (Estimated): August 1, 2032
• Study Completion (Estimated): October 1, 2032

Study Registration Dates

• First Submitted: June 19, 2026
• First Submitted That Met QC Criteria: June 19, 2026
• First Posted (Actual): June 26, 2026

Study Record Updates

• Last Update Posted (Actual): June 26, 2026
• Last Update Submitted That Met QC Criteria: June 19, 2026
• Last Verified: June 1, 2026

More Information

Terms related to this study

• Keywords: Surgery; Randomized trial; Spinal stenosis; Previous lumbar spinal fusion
• Additional Relevant MeSH Terms: Bone Diseases; Musculoskeletal Diseases; Spinal Diseases; Spinal Stenosis; Therapeutics; Mechanical Phenomena; Physical Phenomena; Pressure; Decompression
• Other Study ID Numbers: 869043; 2025049 (Other Grant/Funding Number: Health South-East RHF, Norway (public research funding from a non-commercial governmental body))

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: NO

Drug and device information, study documents

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