Introduction: TLIF was developed to achieve circumferential fusion of the lumbar spine, similar to the anterior lumbar interbody fusion and posterior lumbar interbody fusion techniques, with the advantage of a reduced risk of complication. Recent advancements in minimally invasive surgery led to the development of MI-TLIF, which has been reported to reduce intra-operative blood loss, post-operative pain, a nd hospitalization.

Methods: Thirty-six patients with lumbar spinal instability, spondylolisthesis, or degenerative disc disease underwent MI-TLIF. Before surgery and at follow- up, patients completed the Oswestry Disability Index and Visual Analogue Scale for their back and leg, with o utcomes compared between patients with L4- L5 involvement to those with L5-S1 involvement.

Results: The L4-L5 pathology affected an older age group with a mean age of 63.63 ±10.75 compared to 53.23 ±13.31 for the L5-S1 pathology (p-value = 0.014). The mean hospital stay, operating time, intra-operative blood loss, and hospitalization were not significantly different between the two groups (p-values = 0.587, 0.937, 0.627, 0.587). The post-operative questionnaire results s how no significant difference between the two groups (p-value = 0.819 for VAS [back], p-value = 0.626 for VAS [leg], and p-value = 0.962 for ODI). Two complications included the development of a rash from an antibiotic and a case of post-operative nausea which resolved with discontinuation of narcotic analgesia.

Conclusions: There is no difference between the outcomes for patients undertaking MI-TLIF at the L4-L5 level compared to the L5-S1 level.

Patient Care: It will help surgeons to determine the most effective and safe approach to patient's with degenerative lumbar spinal disease at these two common surgical levels.

Learning Objectives: 1. To determine if the level of operation, a common consideration for open approaches, is important for minimally invasive approaches to the lumbar spine.

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