Non-inferiority of Osseous Decompression of the Lumbar Canal Until Normalization of Epidural Pressure Compared to Conventional Open Laminectomy in Patients With Symptomatic Lumbar Spinal Stenosis.

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.