Paraspinal muscle changes of unilateral multilevel minimally invasive transforaminal interbody fusion

PURPOSE: We attempted to identify changes in back muscle atrophy occurring in multilevel minimally invasive transforaminal interbody fusion (MITLIF) and the impact of these changes on clinical outcomes. METHODS: This study was conducted on 92 patients who underwent unilateral MITLIF between 2006 and 2013, had been tracked with a follow-up for at least 1 year, and had been assessed by pre- and postoperative computed tomography (CT). For the clinical evaluation, a pre- and postoperative visualized analog scale (VAS) of the back and legs, and Oswestry Disability Index (ODI) were measured. CT was used for the evaluation of back muscle atrophy and a cross-sectional area (CSA) of the multifidus was measured at the level below a fused segment, excluding metal artifacts. RESULTS: There was no significant difference in the reduction of CSA between groups with one-, two-, or three-plus-segment fusion. In addition, no statistically significant differences were found in the pre- and postoperative VAS of the back, VAS of the legs, and ODI between the three groups. The reduction of CSA showed a statistically significant positive correlation with preoperative VAS of the back (p = 0.025, r = 0.562). On the other hand, no significant difference was found in VAS of the leg (p = 0.437, r = 0.082) and ODI (p = 0.106, r = 0.017). CONCLUSION: When performing unilateral multilevel MITLIF, significant difference was not found in the atrophy of the multifidus according to the number of fused segments. The clinical outcomes also showed no significant difference. Therefore, unilateral MITLIF can be considered to be an effective surgical method to minimize lumbar muscle damage, even at multiple levels.