The goal of this observational study is to learn about the role of pre-operative paraspinal muscle atrophy in outcomes of lumbar spine fusion surgeries in patients with degenerative lumbar spine diseases. The main question it aims to answer is:

Does paraspinal muscle atrophy worsen lumbar spine fusion surgeries outcomes? Participants undergoing lumbar spine fusion surgeries as part of their treatment for degenerative lumbar spine diseases will answer survey questions about their low back pain and daily activities for 1 year.

Lumbar spine fusion surgery is a widely performed intervention worldwide with the rate steadily increasing. This trend reflects the growing burden of degenerative spinal disorders (DSD) and low back pain (LBP), which globally affect an estimated 266 million individuals (3.63% of the global population) each year. Socioeconomic factors are important risk aspects for lumbar pain and disability both directly and indirectly. Despite the widespread use of lumbar fusion surgery, outcomes are not uniformly successful. A significant proportion of patients experience poor postoperative results, with studies indicating that 33% of patients report treatment failure, including a 22% worsening rate after surgery for lumbar spinal stenosis. Factors associated with these poor outcomes include prolonged back pain duration (>12 months), prior spinal surgery, and advanced age (>70 years). One critical yet often overlooked factor contributing to poor outcomes is paraspinal muscle atrophy. The paraspinal muscles and vertebrae are interdependent tissues, and the health of these muscles plays a vital role in spinal stability and function. The multifidi, erector spinae, psoas, and quadratus lumborum muscles provide support for the lower back. Numerous studies have explored the degeneration or atrophy of back muscles and the reduction in back extensor muscle strength in patients with lower back pain. Patients with high lumbar muscularity and mild fatty infiltration ratio observed on preoperative MRI demonstrated more promising clinical and radiographic outcomes after lumbar interbody fusion. As the prevalence of degenerative spinal conditions continues to rise globally, understanding the role of paraspinal muscle health in surgical success is critical. By prioritizing patient selection based on modifiable risk factors, clinicians can enhance postoperative outcomes and mitigate the economic and clinical burdens associated with lumbar fusion surgery.

• Sample Size Calculation:

Based on determining the main outcome variable, The estimated minimum required sample size is 55 patients.

The sample size was calculated using Epi-info version 7 software, based on the following assumptions:

Main outcome variable is to determine the impact of paraspinal muscle atrophy on lumbar spine fusion outcomes. Previous studies indicate a significant decrease in paraspinal muscle volume one year after surgery, dropping from 67.8% to 60.4%. This reduction correlates significantly with physical and mental outcomes, as well as pain levels. With 80% confidence, the margin of error for these findings is estimated to be within 3%.

- Study tools (in detail, e.g., lab methods, instruments, steps, chemicals, …):

A. Preoperative:

• Magnetic resonance imaging (MRI) of lumbar spine will be used to measure the total cross-sectional area (TCSA), functional cross-sectional area (FCSA) and fatty infiltration (FI) of erector spinae (ES), multifidus (MF) and psoas major (PM) at the level of diseased segment together with one level above & below using ImageJ software v1.54p.
• plain X-rays will be used to measure local kyphotic angle and lumbar lordosis using Surgimap software v2.3.2.1.
• Oswerty disability index Arabic version (ODI)
• EuroQol-5-dimension 5-level Arabic version (EQ-5D-5L)
• Visual analogue scale (VAS) B. Day one postoperative: Postoperative X-ray. C. Two weeks postoperative: Wound check. ODI, EQ-5D-5L, Visual Analogue Score. D. Six weeks postoperative: Wound check. ODI, EQ-5D-5L, Visual Analogue Score. E. Three months postoperative: ODI, EQ-5D-5L, Visual Analogue Score. F. Six months Postoperative: ODI, EQ-5D-5L, Visual Analogue Score, X-ray. G. One year Postoperative: ODI, EQ-5D-5L, Visual Analogue Score, X-ray, MRI if the patient is still complaining.

Inclusion Criteria:

• Patients with degenerative lumbar spine diseases undergoing lumbar spinal fusion.

Exclusion Criteria:

• Long-level fusion ≥ 3 levels.
• History of previous lumbar surgery.
• Patients diagnosed with spondylolysis.
• Other pathological conditions such as fractures, infections or tumors.
• Uncontrolled comorbidities.

Patients undergoing lumbar spinal fusion at Assiut University Hospitals, Department of Orthopedic surgery and Traumatology.