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Femoral Neurogram Before Transpsoas Spinal Access at L4-5 Intervertebral Disk Space: A Proposed Screening Tool
Timothy T Davis1, Thomas F Day, Hyun W Bae
1*Cedars Sinai Medical Center, The Spine Institute, Los Angeles †Kaiser Permanente Orthopedic Surgery Department, Spine Services, Downey, CA.
Study Design:
Observational study.
Objective:
To illustrate the variability of the course of the femoral nerve across the L4-5 disk space, and to present a novel application of transforaminal epidural steroid injections (TFESI) in the visualization of femoral nerve roots.
Summary Of Background Data:
A concern regarding the lateral retroperitoneal transpsoas approach is the proximity of the lumbar plexus. Current techniques of assessing the proximity of neural tissue to the L4-5 disk space have limited capabilities.
Methods:
A total of 100 patients were selected for L4-5 TFESI (L4 selective nerve root blocks) because of lumbar radiculopathy. L4 neurograms were obtained while performing L4-5 TFESI under flouroscopic guidance, using a retroneural technique. The course of the L4 root/femoral nerve was then evaluated under fluoroscopy in the anteroposterior and lateral planes. Images were then reviewed by a radiologist, physiatrist, and 2 orthopedic spine surgeons.
Results:
Fluoroscopic evaluation revealed that the pattern of location of the femoral nerve was highly variable. In males, it was located 4.7% in zone 2, 32.5% in zone 3, 53.5% in zone 4, and 9.3% in zone P. In female patients, it was located 7.0% in zone 2, 14% in zone 3, 54.4% in zone 4, and 24.6% in zone P.
Conclusions:
An L4 neurogram will provide an accurate trajectory of L4 root/femoral nerve as it crosses the L4-5 intervertebral disk space. An accurate assessment is essential to help minimize the increasing frequency of thigh pain, paresthesias, and weakness associated with the lateral access to the L4-5 intervertebral disk space. Femoral nerves that fall within zones 2 and 3 will require more manipulation during retraction and may be better suited with a different surgical approach.
