Lower Back Muscle Size and Recovery After Lumbar Disc Herniation Surgery

This is a single-center, prospective observational cohort study involving 100 adults undergoing elective surgery for lumbar disc herniation. No treatment, exposure, or anesthetic technique will be assigned by the study protocol. All participants will receive standard general anesthesia, surgery, and postoperative care according to routine clinical practice and the decisions of the responsible clinical teams. No additional imaging, laboratory testing, medication, or invasive procedure will be performed for research purposes.

Existing preoperative lumbar magnetic resonance imaging scans obtained as part of routine clinical care will be evaluated. Muscle measurements will be performed on axial T2-weighted images at the level of the inferior endplate of the L3 vertebra. The right and left psoas muscles will be manually outlined, and their cross-sectional areas will be summed to calculate the total psoas area. The total psoas area will be divided by height squared to calculate the psoas muscle index in cm²/m².

The right and left multifidus muscles will be evaluated on the same MRI section. Their cross-sectional areas will be measured and summed to calculate the total multifidus muscle area. A height-adjusted multifidus muscle index will also be calculated. MRI measurements will be performed by an investigator who is unaware of the participants' clinical outcomes and QoR-15 scores.

Quality of recovery will be assessed using the validated Turkish version of the 15-item Quality of Recovery questionnaire. The QoR-15 evaluates physical comfort, emotional state, physical independence, psychological support, and pain. Total scores range from 0 to 150, with higher scores indicating better recovery. The questionnaire will be administered before surgery and at 24 hours, 48 hours, and 7 days after surgery.

Postoperative pain at rest will be assessed using the Numeric Rating Scale at 2, 6, 12, and 24 hours after surgery. Other routinely collected data will include opioid and other analgesic consumption during the first 24 hours, requirement for rescue analgesia, postoperative nausea and vomiting, antiemetic requirement, length of stay in the post-anesthesia care unit, time to first mobilization, and total length of hospital stay.

The primary analysis will evaluate the associations of the preoperative psoas muscle index and multifidus muscle measurements with the QoR-15 score 24 hours after surgery. Secondary analyses will evaluate their associations with QoR-15 scores at 48 hours and 7 days, postoperative pain scores, analgesic consumption, postoperative nausea and vomiting, recovery unit stay, time to first mobilization, and hospital length of stay.

Correlations will be assessed using Pearson or Spearman correlation analysis, as appropriate. Multivariable linear regression analysis will be used to identify whether the preoperative muscle measurements are independently associated with the 24-hour QoR-15 score after adjustment for relevant demographic and clinical variables.

Inclusion criteria

• Age between 18 and 75 years
• Scheduled for elective surgery for lumbar disc herniation
• American Society of Anesthesiologists physical status I-III
• Availability of a preoperative lumbar MRI obtained as part of routine clinical care
• Scheduled to undergo surgery under general anesthesia
• Sufficient cognitive and communication ability to understand and complete the quality of recovery (QoR-15) questionnaire
• Willingness to participate and provision of written informed consent

Exclusion criteria

• Emergency surgery
• Revision lumbar spine surgery
• Surgery for a spinal tumor, infection, trauma, vertebral fracture, spinal deformity, advanced spinal stenosis, or another condition other than lumbar disc herniation
• Planned spinal fusion or instrumentation
• History of a neuromuscular disorder
• Severe cognitive impairment, inability to communicate, or inability to complete the QoR-15 questionnaire
• Chronic opioid use or a history of opioid dependence
• Preoperative lumbar MRI images of insufficient quality for psoas or multifidus muscle measurement