Nerve Root and Lumbar Plexus Proximity to Different Extraforaminal Lumbar Interbody Fusion Trajectories: A Cadaver Study.

STUDY DESIGN: Cadaver study.

OBJECTIVE: To investigate the safety of the extraforaminal lumbar interbody fusion approach.

SUMMARY OF BACKGROUND DATA: Over the last decade the number of techniques available for lumbar interbody fusion has increased. Recent interest has developed in an extraforaminal approach to the intervertebral disc to reduce the morbidity associated with facetectomy. The safety of this extraforaminal corridor with regards to the exiting nerve root and lumbar plexus has yet to be assessed.

METHODS: With the cadaver prone, the C-arm was positioned over the disc of interest and aligned perpendicular to the superior endplate of the inferior vertebral body, with the superior articular process bisecting the available disc space. Three needles were passed into the disc and labeled medial, middle, and lateral. After needle placement, each nerve root and the lumbar plexus were dissected. The distance of each needle to these structures was measured and discectomy was performed to assess potential graft length from a transforaminal and extraforaminal approach.

RESULTS: We performed the method on levels L1-L5 bilaterally on 2 cadavers, totaling 16 attempts for each needle position. The average distance to nerve of the medial approach (3.2±1.1 mm) was statistically greater than both the middle (1.1±1.4 mm) and lateral (-0.2±2.9 mm) approaches (P<0.0001 for both). The distance to plexus of the medial approach (14.3±6.2 mm) was greater than the middle (9.2±6.1 mm) approach and statistically greater than the lateral (5.2±5.6 mm) approach (P=0.001). There was a greater graft length available by the extraforaminal lumbar interbody fusion approach (36.1±2.7 mm) than the transforaminal lumbar interbody fusion approach (29.3±3.5 mm, P<0.0001).

CONCLUSIONS: The safest trajectory was the medial, passing adjacent to the superior articular process. The close proximity, however, means that neuromonitoring and tubular dilators would be necessary to use this technique in a clinical setting.

LEVEL: Level V.