Description

The application of traditional SSEPs and tcMEPs to lumbar nerve root monitoring during TLIF surgery is both challenging and problematic. When applied to lumbar nerve root monitoring, SSEPs and tcMEPs unfortunately suffer in specificity, sensitivity, or both. A surgeon thus cannot confidently rely on these techniques to monitor nerve root function and must guess the likelihood of dysfunction.

Spontaneous EMG (sEMG) is also used to monitor nerve root activity. While sEMG is an excellent indicator of spinal nerve root manipulation, it is a poor diagnostic indicator of dysfunction. 90-95% of sEMG alerts are not associated with dysfunction yielding a high false positive rate and poor specificity, and postoperative deficits are often not associated with sEMG alerts yielding many false negatives and poor sensitivity. The primary utility of sEMG is to use as an indicator of manipulation, which prompts the acquisition of tcMEPs to assess function.

There is a clear need to take the guesswork out of monitoring the functional status of nerve roots at risk during lumbar decompressions and select interbody fusions. During TLIFs, the exiting nerve root is at risk as it courses obliquely across disc space encroaching on the surgical corridor. Standardly, a hand-held retractor is used to retract and protect the nerve root during disc space preparation, implant insertion or even simple decompression. This maneuver and retraction place a particular nerve root at risk, but again, traditional SSEP and tcMEPs are not ideal for monitoring that risk.

The EARP Nerve Cuff Electrode (Retropsoas Technologies) is a novel, Class II, device that is 510(k) cleared by FDA. It conducts electrical signals as a component of intraoperative neuromonitoring, is used with commercially available neuromonitoring systems, and does not stimulate or record the signal itself. The standard connectors at the proximal end interface with the neuromonitoring equipment. The distal nerve cuff electrode partially encircles and contacts the target nerve root. It uses a bipolar configuration to limit current spread. It is available in several inner diameters to accommodate variability in patient nerve root size anatomy.

The EARP Retractor is a Class I device used with a commercially available Retractor system and is only used as an additional 4th blade.

In TLIF surgery, the exiting nerve must be retracted to allow for sufficient access to the intervertebral disc space. The retraction is applied at the medial portion of the nerve root. The application of this retraction may produce activity in the nerve root and/or conduction changes in the nerve root due to temporary manipulation, compression, or ischemia related to the retraction.1

The objective of the study is to demonstrate the ability to safely monitor lumbar nerve root activity and function during retraction using an Endoscopic Assisted Retropsoas (EARP) Nerve Cuff Electrode and an EARP Retractor system during a standard Transforaminal Lumbar Interbody Fusion (TLIF), with improved specificity and sensitivity over traditional monitoring techniques.