Comparisons of Lumbar Muscle Performance Between Minimally-Invasive and Open Lumbar Fusion Surgery at 1-Year Follow-Up

STUDY DESIGN: Prospective study. OBJECTIVE: Minimally-invasive lumbar fusion surgery (MIS) is a viable alternative to conventional open surgery (COS) for spinal disorders. Although MIS seems to be associated with less para-spinal muscle trauma, the actual back muscle performance after MIS and COS remain controversial. This study investigated post-operative para-spinal muscle performance, and the correlation between muscle dysfunction and clinical outcome. METHODS: In this prospective, non-randomized control study, 50 patients were enrolled and split into 2 groups: COS and MIS. We established a biomechanical model of the para-spinal muscle in the lumbar spine using electromyography (EMG) and specific muscle function tests. Functional outcomes were also reviewed and analyzed. All patients underwent EMG pre-operatively, and at 3 months and 1 year post-operatively. The para-spinal muscle performance was investigated by comparing the back muscle co-contraction ratio and the load transmission zone to the pre-operative data. RESULTS: Twenty-one patients in the COS group and 25 in the MIS group completed the study. Both groups showed a significant improved functional score. The abdominal and back muscle strengths were decreased post-operatively, and were then increased at 12 months post-operatively in both groups. During the perturbed balance task and static task, the MIS group exhibited a trend of recovery in comparison with the COS group. But, the back muscle performance at 12 months was poorer than the pre-op performance in both groups. CONCLUSIONS: There was no significant difference in clinical outcome and para-spinal muscle performance between groups. In both methods, the global muscle function had declined post-operatively.