Faculty Bibliography

Detecting potential intraoperative injuries to the femoral nerve should be the main goal of neuromonitoring of lateral lumber interbody fusion (LLIF) procedures. We propose a theory and technique to utilize motor evoked potentials (MEPs) to protect the femoral nerve (a peripheral nerve), which is at risk in LLIF procedures. MEPs have been advocated and widely used for monitoring spinal cord function during surgical correction of spinal deformity and surgery of the cervical and thoracic spine, but have had limited acceptance for use in lumbar procedures. This is due to the theoretical possibility that MEP recordings may not be sensitive in detecting an injury to a single nerve root considering there is overlapping muscle innervation of adjacent root levels. However, in LLIF procedures, the surgeon is more likely to encounter lumbar plexus elements than nerve roots. Within the substance of the psoas muscle, the L2, L3, and L4 nerve roots combine in the lumbar plexus to form the trunk of the femoral nerve. At the point where the nerve roots become the trunk of the femoral nerve, there is no longer any alternative overlapping innervation to the quadriceps muscles. Insult to the fully formed femoral nerve, which completely blocks conduction in motor axons, should theoretically abolish all MEP responses to the quadriceps muscles. On multiple occasions over the past year, our neuro-monitoring groups have observed significantly degraded amplitudes of the femoral motor and/or sensory evoked potentials limited to only the surgical side. Most of these degraded response amplitudes rapidly returned to baseline values with a surgical intervention (i.e., prompt removal of surgical retraction).

BACKGROUND CONTEXT/BACKGROUND:Lateral spacers (LSs) are the standard of care for a lateral lumbar interbody fusion. However, various types of fixation, such as bilateral pedicle screws (BPSs), unilateral pedicle screws (UPSs), bilateral facet screws (BFSs), and lateral plates (LPs) have been reported to increase the stability of LSs. The biomechanics of a novel lateral interbody implant, which is an interbody spacer with an integrated plate and two bone screws (lateral integrated plate-spacer [IPS-L]), has not been investigated yet. PURPOSE/OBJECTIVE:To compare the biomechanical stability of IPS-L and LS with and without supplemental instrumentation. STUDY DESIGN/METHODS:Human lumbar cadaveric study evaluating the biomechanical stability of an IPS-L. METHODS:Each of the six (L2-L5) spines was sequentially tested in intact; IPS-L; IPS-L+UPS; IPS-L+BPS; IPS-L+BFS; LS+BFS; LS+UPS; LS+BPS; LS; and LS+LP, using a load-control protocol in which a ±8 Nm moment was applied, for three cycles each, in flexion-extension (FE), lateral bending (LB), and axial rotation (AR). Data results were obtained from the third cycle. RESULTS:The IPS-L construct significantly reduced the range of motion (ROM) by 75% in FE, 70% in LB, and 57% in AR, compared with intact. Lateral integrated plate-spacer demonstrated similar biomechanical stability as LS+LP, and higher stability than the LS-alone construct, but the difference was not statistically significant. CONCLUSIONS:The IPS-L evaluated in the present study demonstrated equivalent biomechanical stability compared with standard lateral interbody fusion constructs. The addition of BPSs to the IPS-L showed significant reduction in ROM in FE, and the addition of BFSs showed significant reduction in ROM in FE and AR, compared with the integrated plate-spacer alone construct. The IPS-L with supplemental fixation may be a viable option for lateral interbody fusion. Long-term clinical studies are further required to confirm these results.

STUDY DESIGN/METHODS:A retrospective analysis of a case series was performed. OBJECTIVE:To describe a novel technique to monitor femoral nerve function by analyzing the saphenous nerve somatosensory evoked potential (SSEP) during transpsoas surgical exposures of the lumbar spine. SUMMARY OF BACKGROUND DATA/BACKGROUND:During transpsoas direct lateral approaches to the lumbar spine, electromyography monitoring is frequently advocated; however, sensory and motor neurological complications are still being reported. Femoral nerve injury remains a feared complication at the L3-L4 and L4-L5 levels. The current neurophysiological monitoring modalities are not specific or sensitive enough to predict these injuries after the retractors are placed. The authors have developed a technique that is hypothesized to reduce femoral nerve injuries caused by retractor compression by adding saphenous nerve SSEPs to their neurophysiological monitoring paradigm. METHODS:Institutional review board approval was granted for this study and the medical records along with the intraoperative monitoring reports from 41 consecutive transpsoas lateral interbody fusion procedures were analyzed. The presence or absence of intraoperative changes to the saphenous nerve SSEP was noted and the postoperative symptoms and physical examination findings were noted. RESULTS:SSEP changes were noted in 5 of the 41 surgical procedures, with 3 of the patients waking up with a femoral nerve deficit. None of the patients with stable SSEP's developed sensory or motor deficits postoperatively. No patient in this series demonstrated intraoperative electromyography changes indicative of an intraoperative nerve injury. CONCLUSION/CONCLUSIONS:Saphenous nerve SSEP monitoring may be a beneficial tool to detect femoral nerve injury related to transpsoas direct lateral approaches to the lumbar spine. LEVEL OF EVIDENCE/METHODS:4.

BACKGROUND/OBJECTIVE/OBJECTIVE:Postprocedural infections are a significant cause of morbidity after spinal interventions. METHODS:Literature review. An extensive literature review was conducted on postprocedural spinal infections. Relevant articles were reviewed in detail and additional case images were included. RESULTS:Clinical findings, laboratory markers, and imaging modalities play important roles in the detection of postprocedural spinal infections. Treatment may range from biopsy and antibiotics to multiple operations with complex strategies for soft tissue management. CONCLUSIONS:Early detection and aggressive treatment are paramount in managing postprocedural spinal infections and limiting their long-term sequelae.

Methemoglobinemia, a condition associated with cyanosis and diminished pulse oximetry values, has been reported after use of local anesthetics to facilitate fiberoptic intubation. The majority of reports in the literature detail this development during diagnostic procedures such as endoscopy and bronchoscopy. A case of methemoglobinemia in a multiple-injury patient with an unstable compressive-flexion injury of the cervical spine undergoing fiberoptic intubation is presented. A literature review of this entity is also presented. The patient underwent fiberoptic intubation using topical pharyngeal anesthetics before planned cervical corpectomy, strut grafting and instrumentation. He became acutely cyanotic with abruptly diminished pulse oximetry readings. Subsequent blood gas analysis demonstrated methemoglobinemia. Intravenous methylene blue administration led to an uncomplicated resolution of the condition. Surgeons and anesthesiologists who manage such patients should be aware of methemoglobinemia, a rare but potentially fatal complication related to topical airway anesthetics.