Introduction: OLIF has been purported to provide indirect decompression of nerve roots by increasing foraminal and axial area. We sought to evaluate the effect of OLIF on foraminal and axial area using CT and MRI and to evaluate the rate of subsequent posterior direct decompression.
Methods: A retrospective review of OLIF cohort was undertaken. Demographic information was obtained in addition to operative levels. Only patients with both pre- and post-operative CT or MRI were included. Foraminal and cross-sectional axial area were measured pre- and post-operatively. Operative levels incurring further posterior decompression were also recorded.
Results: A total of 76 operative levels from 33 patients were analyzed, with 19 of these levels being imaged both with CT and MRI. Nineteen of these patients were female (57.6%) with the average age being 67.6 +/- 6.6 years old. Operative levels were stratified as follows: 7 L1-2, 19 L2-3, 25 L3-4, 22 L4-5, 3 L5-S1. Axial cross-section on CT was found to be significantly larger after OLIF (232.3mm2 v. 275.6mm2; p=0.048). Foraminal height (15.9mm2 v. 18.5mm2; p=0.0027) and foraminal area (106.3mm2 v 146.6mm2; p=0.000016) both had statistically significant increases on CT after OLIF. Concerning MRI, there was a significant difference in foraminal height (15.6mm2 v. 17.7mm2; p=0.035); however, axial cross-section (132.9mm2 v. 158.9mm2; p=0.12) and foraminal area (114.8mm2 v. 133.8mm2; p=0.096) were not found to be significantly different. Posterior decompression was performed on twenty-seven levels after OLIF, primarily at L4-5.
Conclusions: Our results illustrate that OLIF is effective in indirectly decompressing neural elements, with nearly two-thirds of levels not requiring posterior decompression. OLIF resulted in increased foraminal area, foraminal height, and cross-sectional area by CT. MRI detected less changes than CT, and thus, may not be as accurate in measuring foraminal area and cross-sectional area as compared to CT.
Patient Care: With these results, we can better predict and tailor management following oblique lateral interbody fusion such that we can avoid potentially unnecessary posterior decompression given the radiographic evidence of indirect decompression with OLIF.
Learning Objectives: By the conclusion of this session, participants should be able to better understand the role of OLIF in indirect decompression, imaging modalities that best capture changes in axial cross-section area, foraminal height, and foraminal area, as well as better predict the likelihood of needing posterior decompression after OLIF.