Evaluating Paraspinal Muscle Response and Compensation via Musculoskeletal Modeling in Spinal Stenosis Surgeries

IntroductionLumbar spinal stenosis is a common cause of lower back pain and weakness in elderly patients. The gold standard treatment for this is lumbar laminectomy which involves widespread muscle damage to the multifidus, a complete loss of the posterior tension band which contains the supraspinous and interspinous ligaments. However, in recent years minimally invasive techniques such as bilateral and unilateral laminotomy have become more popular and are showing efficacy in the decompression of spinal stenosis. Due to its minimally invasive approach, the muscle retraction required for laminotomy is less intensive than that required for laminectomy. The overall body of literature on the surgical treatment of spinal stenosis is sparse in its interrogation of the biomechanical outcomes of these techniques and to our knowledge, there are no current publications that incorporate muscle forces. MethodsA previously validated thoracolumbar ribcage finite element (FE) model was used for this study. Three different surgeries, traditional laminectomy, unilateral and bilateral midline sparing approaches at L4-L5 segment were simulated by removing the spinous process, supraspinous, and interspinous ligaments. The segmental range of motion (ROM) for all models were acquired and input into a musculoskeletal modelling software to calculate muscle forces. ResultsUnilateral and bilateral laminotomy showed similar muscle forces for every muscle group in both flexion and extension motion. While comparing the muscle forces in laminotomy to the laminectomy in extension motion displayed an increase in Iliocostalis lumborum (IL) by 12 % and multifidus (MF) by 16% and decrease in transverse abdominus (TA) by 138% and erector spine (ES) by 12%. For flexion, there was an increase in IL by 35%, and MF by 12%. ConclusionOur results highlight that laminectomy, which involves the removal of paraspinal muscles and posterior ligamentous structures to relieve stenosis, can lead to increased instability and necessitate muscle compensation, particularly in adjacent and thoracic spine segments. Conversely, midline sparing approaches such as laminotomies, are associated with decreased muscle compensation across spinal segments and enhanced stability.