Study Design: A cross-sectional study. Objectives: To examine the relationship between fatty inflitration (morphology) of the lumber multifidus (LM) and changes in LM thickness during contraction using ultrasound imaging in patients with lower back pain (LBP). Background: LBP provides a substantial burden on our healthcare system. The LM muscles appear to play a unique role in lumbar stability and may relate to clinical outcomes if made a priority with rehabilitation programs for patients who experience lumbar spine pain. The purpose of this research was to explore the relationship between LM morphology (structure) and LM activation (function). Confounding factors that may influence patients with LBP were also investigated and compared to the percentage of fat in the LM at each level, including age, gender, disability, BMI, physical-activity level, pain intensity, and clinical signs of instability. Method: Sixty-five subjects filled out the Oswestry Low Back Disability Questionnaire (ODI), the Numeric Pain Rating Scale (NPRS), and the International Physical Activity Questionnaire (IPAQ). A physical exam, lumbar spine MRI, and bilateral rehabilitative ultrasound imaging of the LM at the L4/L5 and L5/S1 level, both at rest and at submaximal contraction were performed. Results: The mean percentage fat content of the multifidus muscle was 16 at L4/L5 and 17 at L5/S1 on the right and on the left 17 L4/L5 and and 16 at L5/S1. The mean percentage change of the LM from rest to activation of L4/L5 and L5/S1, respectively, was 25% and 22% on the right and 21% and 18% on the left. Separate multiple linear regressions were performed with the dependent variable being the percentage of intramuscular fat within the LM. The independent variable was the percentage of LM activation at L4/L5 and L5/S1, bilaterally, and variance associated with age and gender was controlled for. Age was statistically significant for increases in LM at fatter infiltration at each level and side. Percent change of LM thickness was not associated with LM fatty infiltration. Conclusion: No relationship between the fat percentage of the LM at L4/L5 and L5/S1 and the muscles ability to contract was found in this population at these vertebral levels.
