Comparison of paraspinal muscle injury in one-level lumbar posterior inter-body fusion: modified minimally invasive and traditional open approaches.

OBJECTIVE: To determine differences in paraspinal muscle injury between a modified minimally invasive approach (MMIA) and a traditional operative approach (TOPA) for one-level instrumented posterior lumbar inter-body fusion (PLIF). METHODS: From March 2006 to May 2008, a consecutive series of 91 patients who underwent a one-level instrumented PLIF procedure using one of two different approaches (MMIA in 41 patients and TOPA in 50), and who were operated on by one group of surgeons at a single institution, was studied. The following data were compared between the two groups: surgical time, blood loss, and changes in postoperative serum concentration of creatinine kinase (CK). More than 1 year post operation, low back pain was evaluated by a visual analog scale (VAS) and the Oswestry disability index (ODI). Some patients were also evaluated by MRI to allow comparison of the preoperative and postoperative cross sectional area (CSA) and fat degeneration grades at the operative level. RESULTS: There was no statistically significant difference in surgical time, but blood loss, serum concentration of CK, and scores of the VAS and ODI were markedly less in the MMIA group compared with the TOPA group. In the TOPA group, the postoperative CSA of the multifidus muscles was significantly smaller than it was pre-operatively. In contrast, there was no significant difference between the pre- and post-operative CSA of the multifidus muscles in the MMIA group. There was more fatty infiltration postoperatively than preoperatively in both the TOPA and MMIA groups, the increase in fatty infiltration being greater in the TOPA than in the MMIA group. CONCLUSION: Compared with TOPA, MMIA can significantly lessen paraspinal muscle injury, and reduce the incidence of low back pain.