Endoscopic Foraminal Decompression Preceding Oblique Lateral Lumbar Interbody Fusion To Decrease The Incidence Of Post Operative Dysaesthesia

Introduction

Lumbar interbody fusion has become a widely accepted treatment for painful conditions of the lumbar spine from degenerative disc disease, instability, and stenosis.¹ Axial back pain and radicular symptomatology can be dramatically improved from interbody fusion. When outcomes are evaluated, higher fusion rates and improved pain reduction can be anticipated than from posterolateral fusion alone.²

The benefits of interbody fusion indirectly decompressing the neural elements have been known since the 1990s. Morphometric assessment of neural canal and neural foraminal dimension after anterior lumbar interbody fusion supports the concept of indirect decompression.³

Interbody fusion does pose a risk for complications. In an attempt to lessen the risk of severe complications that may occur with anterior or posterior approaches to the spine and to offer less invasive surgical alternatives, lateral lumbar interbody fusion has become popularized. Although this technique recommends electromyography (EMG) monitoring to safely transverse the psoas muscle and lumbar plexus, nerve root injury remains a concern. In a large review of 919 lumbar lateral interbody fusion (LLIF) levels performed at the Hospital for Special Surgery in New York, Lykissas et. al. reported an incidence of sensory deficit in 38% of patients, motor deficits in 23.9% of patients, and anterior thigh and groin pain in 38.5% of patients.⁴ While many published series, such as that reported by Rodgers reviewing 600 cases of lateral lumbar interbody fusions, never discuss dysaesthesia at all,⁵ studies where this problem is considered routinely have reported dysaesthesia rates from 20-60%.^{6, 7} Residual sensory deficits at one year post-op are typically between 1-3% and motor weakness between 2-3%.^{6, 8}

Oblique lateral lumbar interbody fusion is a newer technique employed to achieve interbody fusion. This is also a bone and muscle preserving minimally invasive technique. Although the incidence of neurologic injury is lower than in lateral interbody fusion cases, neural injury remains a concern. This approach utilizes Kambin’s triangle to gain access to the disc space for discectomy and endplate preparation. Of course, the superior margin of this space is the exiting nerve root. As such, due to nerve root retraction or tension, nerve root irritation is not uncommon. In a retrospective analysis of our first 55 consecutive cases, transient dysaesthesia occurred between 20-25% of cases. Since the technique also recommends utilizing EMG monitoring to gain access safely to the disc space, sensory neurologic injury lasting greater than 3 months has an incidence less than 1% and motor deficit is even less frequent. Our dysaesthesia occurrences involved the L5-S1 level almost exclusively, although one patient treated with an L2-3 and L3-4 OLLIF did experience transient dysaesthesia.

The results of this study suggest that foraminotomy lessens the incidence of dysaesthesia in patients who failed to meet EMG safety thresholds. This technique can also be utilized for patients with facet hypertrophy and foraminal stenosis.