What is it about?

To assess the safety of L5−S1 inclusion in OLIF, we retrospectively studied 87 patients who underwent lumbar fusion using the OLIF approach. Of these, the L5-S1 level was included in 19 patients and excluded in 68 patients. In the L5-S1 inclusion group, the region was approached using one of three ways: left-sided intrabifurcation, left-sided prepsoas, and right-sided prepsoas. The choice of the technique was partly based on the surgeon’s experience and partly on the relationship of the left common iliac vein with the L5-S1 disc, as seen from preoperative MRI scans. A proposed “facet” line through the medial border of the left L5−S1 facet joint on an MRI axial section helped identify the orientation of the left common iliac vein, and guided the choice of approach.

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Why is it important?

Multi-level lumbar spinal fusion usually entails long periods of rehabilitation and is associated with a high risk of complications, thus creating a need for minimally invasive procedures. One such minimally invasive and versatile option is to use the oblique lumbar interbody fusion (OLIF) or Anterior-To-Psoas (ATP) technique. This allows for a mini-open anterolateral retroperitoneal access to the lumbar spine, with minimal risk of injury to the lumbar plexus (a concern with lateral trans-psoas approaches). The ability to do it in the lateral position and the mini-open muscle-splitting approach allows multiple levels to be addressed with low morbidity (lesser blood loss, lower incidence of ileus, quicker rehabilitation). However, the inclusion of L5−S1 in the OLIF approach—although optimal—can be challenging due to this area’s complex vascular anatomy. Although multiple variations of the oblique approach to L5-S1 have been described, there is no standardization or guidance for the choice of technique. Apprehensive of potentially catastrophic vascular injuries, surgeons may avoid the L5-S1 level entirely or address it posteriorly or with supine anterior methods, leading to increased operative times. L5-S1 is the lowermost mobile disc and has a large role in determining the overall spinal alignment. In multi-level spinal fusion, L5-S1 forms the foundation (base) of the construct. Hence, this level must be addressed with the best technique that would improve alignment and facilitate solid fusion. Using anterior/anterolateral techniques allows placement of larger and taller cages such that alignment and fusion rates are much better than posterior techniques. The oblique anterolateral approach enables multiple levels to be addressed in the same lateral position, saving operative time. To this end, comprehensive guidance on choosing the ideal OLIF technique and risks associated with L5-S1 inclusion is needed.


Overall, our study demonstrates the safety and feasibility of three different OLIF approaches to the L5-S1 level without any significant increase in complications. However, the choice of the surgical technique must be guided by the surgeon’s experience and the patient’s vascular anatomy. The “facet line” on the preoperative MRI may guide the choice of approach. Assistance from an experienced access surgeon is considered critical for these surgeries. Additional learning curve and comfort level in working alongside large venous structures is required, especially for right-sided approaches. These approaches are relatively new but are proven to safe in experienced hands. These techniques are recently gaining popularity due to their safety and low morbidity.

Dr Chirag A Berry
University of Cincinnati

Read the Original

This page is a summary of: Inclusion of L5–S1 in oblique lumbar interbody fusion–techniques and early complications–a single center experience, The Spine Journal, October 2020, Elsevier, DOI: 10.1016/j.spinee.2020.10.016.
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