The goal of this clinical trial is to evaluate the theory of epidural pressure by comparing a surgical procedure that aims to perform less bone resection compared to conventional surgery in patients with lumbar spinal stenosis.

The main questions it aims to answer is:

Is bony decompression of the lumbar canal performed until normalization of epidural pressure not inferior to conventional surgery in achieving clinical improvement in patients with symptomatic lumbar canal stenosis?

Researchers will:

Compare conventional open laminectomy to bony decompression of the lumbar canal until normalization of epidural pressure is achieved.

Participants will:

• Be randomized to one of the two surgical interventions: laminectomy guided by epidural pressure measure or conventional laminectomy.
• Visit the clinic for checkups and tests until 1 year of follow-up.

This is a non-inferiority, controlled, randomized, single-blind clinical trial comparing the effectiveness of full lumbar canal bony decompression up to normalization of epidural pressure versus open laminectomy in patients with symptomatic lumbar canal stenosis. The study will not involve any medical industry sponsorship.

Surgical intervention decisions will be made by a single neurosurgeon at Hospital Clínico San Carlos, based on clinical scales and imaging as specified in the inclusion criteria. After the patient signs the informed consent form and is placed on the surgical waiting list, they will be randomized in a 1:1 ratio (simple randomization implemented via SPSS software). Baseline clinical scales will be administered (Zurich Claudication Questionnaire, ZCQ; Numeric Pain Rating Scale, NPRS; Oswestry Disability Index, ODI; Japanese Orthopaedic Association Back Pain Evaluation Questionnaire, JOABPEQ) to establish the patient's baseline status. The patient will remain blinded to the assigned intervention group.

Study Interventions:

• Pressure-guided laminectomy (PGL): An open laminectomy with complete decompression of the posterior elements. This is defined as the classic technique. After muscle dissection, a Codman microsensor (Integra LifeSciences) is inserted into the epidural space under direct visualization, performing careful dissection of the inferior aspect of the ligamentum flavum on the right hemilamina to obtain the patient's baseline epidural pressure. The sensor is then removed, and resection of the spinous process, supraspinous and interspinous ligaments, bilateral hemilaminae, and ligamentum flavum is performed until an adequate decompression of the thecal sac is achieved.
• Non-pressure-guided laminectomy (NPGL): After muscle dissection, the Codman microsensor is inserted into the epidural space as described above. The patient's baseline epidural pressure is recorded, and then bony decompression is initiated using the "unilateral laminotomy for bilateral decompression" technique from the left side, continuing until the epidural pressure decreases to 10 mmHg, a value established as the median within normal range.

The CODMAN Microsensor pressure catheter (Integra LifeSciences) is a transducer with a distal strain gauge that records pressure changes in a given medium. Its proximal end has an electrical connector that must be attached to the ICP Express monitor. This particular microsensor model was chosen due to its availability in the operating room inventory and because it has been used in previous studies published in the scientific literature.

All surgeries will be performed by a single neurosurgeon at Hospital Clínico San Carlos. Patients will be evaluated two weeks after surgery, at which time clinical scales will be applied and the surgical wound will be checked. Subsequently, patients will be evaluated at 3 and 6 months postoperatively via telephone follow-up, and at 12 months with an in-person visit, during which clinical outcome scales will be administered.

Additionally, a lumbosacral MRI will be obtained 3 months after surgery to qualitatively assess the degree of decompression achieved in each patient.

Sociodemographic data and clinical outcome variables will be collected during the preoperative consultation and at the follow-up visits at 1, 3, 6, and 12 months post-surgery. Imaging data will be collected from the patient's preoperative lumbar spine MRI (baseline) and from the lumbar MRI obtained 3 months postoperatively. T2-weighted axial sequences will be used to qualitatively assess the extent of bony decompression.

The database generated for the study will not contain any patient identifiers, thus maintaining confidentiality of patient identity. Study data will be recorded in a de-identified manner linked to a unique code per patient, such that only the researcher can associate these data with an individual medical record. Access to participants' clinical documentation will be limited to the investigators and personnel responsible for data quality assurance and analysis.

All procedures will adhere to Regulation (EU) 2016/679 of the European Parliament and of the Council of 27 April 2016 (General Data Protection Regulation), and to Spanish Organic Law 3/2018 of December 5 on Personal Data Protection and Guarantee of Digital Rights (LOPDGDD). The entity responsible for data processing is Hospital Clínico San Carlos, whose Data Protection Officer is the DPO Committee of the Regional Health Authority of the Community of Madrid. This entity will handle data for the purposes outlined in this document.

Personal data, including health data, will be retained for the duration of the project and up to three years after its conclusion. Patients may exercise their rights of access and rectification of data, as well as the right to restrict data processing and to request a copy of their data or transfer of their data to a third party.

Descriptive statistics will be used to summarize the demographic and clinical data. Quantitative variables will be summarized by their mean and standard deviation (SD) if normally distributed. Quantitative variables with a skewed distribution will be summarized by median and interquartile range (IQR). Qualitative variables will be presented as frequency distributions.

No interim efficacy analysis will be performed.

Efficacy analysis will be conducted on both the Per-Protocol (PP) and Intention-to-Treat (ITT) populations. Safety analysis will be performed only on the ITT population. Data will be examined longitudinally, and the primary analysis will focus on differences in effectiveness between the two intervention modalities as measured by the ZCQ and the other clinical scales over time. Interaction terms between treatment group and time will also be included to explore whether effects differ across follow-up time points.

Non-inferiority efficacy analysis will be carried out using linear regression models with a one-sided α of 0.05 and using the non-inferiority margins. Multiple non-inferiority hypotheses will be tested (one for each clinical scale); adjustments for multiple comparisons will be applied to control the overall Type I error rate, progressively tightening the alpha for each additional hypothesis so that the study maintains the required overall error threshold.

In addition to unadjusted analyses, all analyses will be adjusted for potential confounding factors such as age, sex, and comorbidities using multiple linear regression.

For the safety analysis, any complications occurring during the study period will be analyzed. Their association with the type of intervention will be evaluated using logistic regression models. In this case, a two-sided α level of 0.05 will be considered.

All results from the analyses will be expressed as estimated mean effects with 95% confidence intervals, and these estimates will be compared against the non-inferiority margin to infer non-inferiority of the intervention. The analyses described above will be conducted using IBM SPSS Statistics v26 and R v4.4.1.

Resources for the Study

• Human resources: Neurosurgeon; Neurosurgery resident; Methodological research support unit (UAMI).
• Physical resources: Scheduled surgery operating room; Outpatient clinic office (with chair, desk, computer, and examination table); Data analysis room with computer.
• Specific materials: Intracranial pressure monitoring catheter (Codman); Intracranial pressure monitor.

Timeline The expected duration of the trial is 2 years, subdivided into a 12-month patient recruitment period and 1 year of follow-up.

Adverse Events It is the investigator's responsibility to detect and document any occurrence meeting the criteria and definition of an adverse event (AE). Adverse events will be reported as per the guidelines established by the CONSORT Statement for Randomized Trials of Nonpharmacologic Treatments: 2017 Update and Extension for Nonpharmacologic Trial Abstracts.

Ethical Considerations The trial will be conducted in accordance with the principles of the Declaration of Helsinki and the current legal regulations in Spain. It will commence only after obtaining approval from the relevant Research Ethics Committee (Comité Ético de Investigación Clínica, CEIC).

Plan for Dissemination of Results Upon completion of the study, publications will be prepared to disseminate the findings in national or international journals, and the results will also be presented at conferences. The principal investigator commits to complying with current Spanish legislation, which mandates the publication of all results (positive or negative) in scientific journals, including reference to the approving CEIC and the study's funding source.

Inclusion Criteria:

• Surgical indication determined by:

  • Lower back pain and/or lower extremity pain for more than 3 months.
  • Pain refractory to conservative medical management (analgesics, physical therapy, epidural block).
  • Clinical criterion of neurogenic claudication defined as a score ≥11 on the N-CLASS scale.
  • Preoperative magnetic resonance imaging (MRI) showing lumbar canal stenosis.

• Patient consents to the proposed surgical intervention.

• Patient agrees to participate in the study by signing the informed consent form.

Exclusion Criteria:

• Foraminal or lateral recess stenosis.
• Symptomatic disc herniation at the segment to be treated.
• Spondylolisthesis > Grade I (Meyerding) (translation >25% of the vertebra) or spondylolysis.
• Radiological instability defined as >5 mm of anteroposterior translation on dynamic flexion-extension spine X-rays.
• Scoliosis with Cobb angle >30°.
• Compression fracture at the level to be treated.
• Prior surgery at the same segment to be treated.
• Prior infection at the segment to be treated.
• Contraindication for MRI.
• Diagnosis of major depressive disorder or dysthymia according to DSM-V criteria.

At this time, a decision has not yet been made regarding the sharing of individual participant data (IPD). The research team is currently evaluating the ethical, legal, and logistical considerations involved, including participant privacy concerns and data governance policies. A final decision will be made upon completion of the study and in accordance with institutional guidelines and applicable regulations.