Evaluation of change in muscle activity as a result of posterior lumbar spine surgery using a dynamic modeling system.

Study Design: A commercially available musculoskeletal model of the lumbar spine was modified to study the change in muscle activation as a result of posterior lumbar surgery at the L3-L4 and L4-L5 segments.

Objective: To evaluate how graded resection of the lumbar paraspinal muscles as a result of posterior lumbar surgery affects muscle activity for a variety of movement tasks.

Summary Of Background Data: Several in vivo studies compare the change in functional outcome of the paraspinal muscles following surgery. However, due to limitations that exist with current in vivo methods no study to date has been able to quantitatively examine how the function of individual muscles in the lumbar spine change in response to different levels of injury.

Methods: A multibody dynamic musculoskeletal model of the lumbar spine was modified to measure muscle activity using a parametric examination of change in the cross-sectional area of muscles affected by posterior lumbar surgery.

Results: This study shows that the reduction in muscle cross-sectional area as a result of posterior lumbar surgery at L3-L4 and L4-L5 results in a change in trunk muscle activity where the greatest change occurs during axial rotation and lateral bending. The results suggest that preservation of the posterior paraspinal musculature results in greater preservation of the normal muscle activity than traditional open techniques.

Conclusion: Preservation of the paraspinal musculature associated with minimally invasive surgical approaches to the lumbar better preserve postoperative muscle activity. This study suggests that there is a positive correlation between the reduction of paraspinal muscle cross-sectional area following posterior lumbar spine surgery and the alteration in trunk muscle activity.