The Impact of Paraspinal Muscle Atrophy in Lumbar Spinal Fusion Outcomes

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%.