Systems and methods for performing neurophysiologic monitoring during spine surgery

This disclosure describes a surgical instrument comprising a combination femoral nerve localizer and needle placement guide instrument. The instrument may be used with a neuromonitoring system to localize and monitor the femoral nerve during a spinal procedure.

FIELD OF INVENTION

The present application pertains to devices and methods in the field of surgery, and more particularly spine surgery.

BACKGROUND

The spinal column is a highly complex system of bones and connective tissues that provide support for the body and protect the delicate spinal cord and nerves. The spinal column includes a series of vertebral bodies stacked one atop the other, each vertebral body including an inner or central portion of relatively weak cancellous bone and an outer portion of relatively strong cortical bone. Situated between each vertebral body is an intervertebral disc that cushions and dampens compressive forces exerted upon the spinal column. A vertebral canal containing the spinal cord is located behind the vertebral bodies.

There are many types of spinal column disorders including scoliosis (abnormal lateral curvature of the spine), excess kyphosis (abnormal forward curvature of the spine), excess lordosis (abnormal backward curvature of the spine), spondylothesis (forward displacement of one vertebra over another), and other disorders caused by abnormalities, disease or trauma, such as ruptured or slipped discs, degenerative disc disease, fractured vertebra and the like. Patients that suffer from such conditions usually experience extreme and debilitating pain, as well as diminished nerve function.

A noteworthy trend in the medical community is the move away from performing surgery via traditional “open” techniques in favor of minimally invasive or minimal access techniques. Open surgical techniques are generally undesirable in that they typically require large incisions and high amounts of tissue displacement to gain access to the surgical target site, which produces concomitantly high amounts of pain, lengthened hospitalization (increasing health care costs), and high morbidity in the patient population. Less-invasive surgical techniques (including so-called “minimal access” and “minimally invasive” techniques are gaining favor due to the fact that they involve accessing the surgical target site via incisions of substantially smaller size with greatly reduced tissue displacement requirements. This, in turn, reduces the pain, morbidity, and cost associated with such procedures. One such minimally invasive approach, a lateral trans-psoas approach to the spine, developed by NuVasive, Inc., San Diego, Calif. (XLIF®) has demonstrated great success in reducing patient morbidity, shortening the duration of hospitalization, and speeding recovery time if it is employed.

One example of a surgical retraction system and methods of use in a lateral trans-psoas approach to the spine is described in commonly owned U.S. Pat. No. 7,905,840, issued on Mar. 15, 2011 and entitled “Surgical Access System and Related Methods,” the entire contents of which are incorporated by reference into this disclosure as if set forth fully herein. To create the lateral access corridor to the lumbar spine, the patient is positioned on his or her side and a surgical access system is advanced through an incision, into the retroperitoneal space, and then through the psoas muscle until the target spinal site (for example, a disc space between a pair of adjacent vertebral bodies) is reached. The surgical access system may include a sequential dilation assembly of increasing diameter and a tissue retraction assembly. The sequential dilation assembly is advanced to the target site first and the retractor assembly is then advanced to the target site over the sequential dilation system. One or more stimulating electrodes may be provided on the distal tip of each component of the surgical access system. Nerve monitoring may be performed while advancing each of the dilation and retraction assemblies to the target site to detect the presence of, and thereby avoid, nerves lying in the trans-psoas path to the target site.

Once the retractor assembly has been docked at a target site however, a nerve situated near any location along the length of a retractor blade (for example, a center (posterior) blade) might come into inadvertent contact with the blade which could cause the nerve to become compressed over the course of the surgical procedure. As such, information regarding the proximity, health, and status of nearby nerves (e.g., the ipsilateral femoral nerve, which is a “mixed” nerve) during maintenance of a lateral access corridor is desirable. Such information may include neurogenic responses (e.g. compound nerve action potential (CNAP) responses) obtained in response to stimulation of the sensory branches of the nerve and myogenic responses (e.g. compound muscle action potential (CMAP) responses or neuromuscular responses) obtained in response to stimulation of the motor branches of the nerve. Changes in these sensory and motor responses from baseline (i.e., prior to positioning of the retractor) could indicate that the nerve is potentially compromised at the location of the surgical site. A quick, reliable means of obtaining these sensory and motor responses could provide an advanced neuromonitoring capability that may further reduce the risk of neural compromise during spine surgery.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIGS. 1-4illustrate an example of one embodiment of a combination femoral nerve localizer and needle placement guide instrument10(hereinafter “localizer/guide10”) for use in reliably localizing the femoral nerve for stimulating and recording purposes during neuromonitoring of a spinal surgical procedure, preferably a minimally-invasive lateral spine procedure. By way of example only, the localizer/guide10includes a handle12and a body14separated by a shaft16extending between the handle12and body14. The handle12is sized and dimensioned to allow a user to comfortably position the localizer/guide10on the surface of a patient's body (e.g., at the ilioinguinal ligament). The body14is attached to the distal end of the shaft16and includes a pair of transcutaneous stimulation electrode units18and a pair of needle guides20. One electrode unit18and needle guide20pair is provided on each side of the midline M (FIG. 3) as defined by the handle12and shaft16. In the first embodiment shown, the electrode unit18and needle guide20pairs are arranged in a minor image orientation, however other configurations are possible without departing from the scope of this disclosure. Preferably, the body14is positioned offset from the handle12to enhance visibility of the patient's anatomy during femoral nerve localization and placement of the subdermal needles as will be described in greater detail below. To accomplish this, the shaft16may be provided as other than linear, for example the shaft16may be curved or may have a pair of linear portions connected by an angled joint portion as shown inFIG. 1.

The electrode unit18includes a transcutaneous stimulation electrode22in electrical communication with a lead receptacle24. Each transcutaneous stimulation electrode22is provided at the distal end of the electrode unit18and is configured to contact the skin S (FIG. 3) and send/receive electrical stimuli therethrough. Each lead receptacle24is configured to receive a male plug portion of an lead cable (not shown) that connects the surface electrode22to a control unit of a neuromonitoring system, for example of the type shown and described in commonly owned U.S. Pat. No. 8,255,045, issued Aug. 28, 2012 and entitled “Neurophysiology Monitoring System,” the entire contents of which is hereby incorporated by reference into this disclosure as if set forth fully herein. The two transcutaneous stimulation electrodes20function as a stimulation unit (i.e., one electrode acts as the anode, the other acts as the cathode) according to a preferred use. As the cathode is positioned directly over the femoral nerve, stimulation current is delivered from a neuromonitoring system (e.g. the neuromonitoring system of the above-referenced '045 patent) to the localizer/guide10which will activate the femoral nerve immediately deep to that electrode, and recording electrodes placed in muscle groups innervated by the femoral nerve will record neuromuscular responses on the neuromonitoring system.

The needle guide20is provided to accurately position a needle during the surgical procedure, for example a stimulating/recording needle electrode. The needle guide20includes a guide slot26positioned at a distal end of an arm member28extending laterally away from the midline M. The guide slot26is configured to receive a needle (not shown) therein. The distal end of the arm member28includes an angled distal surface30in which the guide slot26is formed. The angle of the distal surface30ultimately controls the angle (relative to the femoral nerve FN) at which the needle is inserted through the skin S. By way of example only, the angle may be a 30-degree angle. Other angles are possible without departing from the scope of this disclosure.

As previously mentioned, the electrode unit18and needle guide20pairs are positioned in a minor image orientation relative to one another. More specifically, the electrode units18are positioned between the needle guides20such that the angles of the angled surfaces30are convergent. This orientation not only maximizes the user's view of the anatomy, but it also enables the needles to be optimally placed distance from one another for recording purposes (for example, the distance between the needle tips may be 1 inch apart). The body14further includes a middle portion32extending between the electrode units18. The shaft16is connected to the middle portion32of the body14. In the example shown inFIGS. 1-4, the middle portion32has a generally concave curvature that also improves the view of the anatomy by the user.

FIGS. 5-7illustrate an example of one embodiment of a combination femoral nerve localizer and needle placement guide instrument40(hereinafter “localizer/guide40”) for use in reliably localizing the femoral nerve for stimulating and recording purposes during neuromonitoring of a spinal surgical procedure, preferably a minimally-invasive lateral spine procedure. By way of example only, the localizer/guide40includes a handle42and a body44separated by a shaft46extending between the handle42and body44. The handle42is sized and dimensioned to allow a user to comfortably position the localizer/guide40on the surface of a patient's body (e.g., at the ilioinguinal ligament). The body44is attached to the distal end of the shaft46and is generally a dual-pronged body is positioned offset from the handle12to enhance visibility of the patient's anatomy during femoral nerve localization and placement of the subdermal needles. The body44includes a pair of prongs47extending away from the shaft46in a generally arcuate manner. Each of the prongs47includes a transcutaneous stimulation electrode48and a needle guide50.

The two transcutaneous stimulation electrodes48function as a stimulation unit (i.e., one electrode acts as the anode, the other acts as the cathode) according to a preferred use. As the cathode is positioned against the patient's skin S directly over the femoral nerve FN (FIG. 6), stimulation current delivered from a neuromonitoring system (e.g. the neuromonitoring system of the above-mentioned '045 patent) to the localizer/guide40will activate the femoral nerve immediately deep to that electrode48. An electrode lead wire52extends from each electrode48, through the handle42of the localizer/guide40and is capable of electrical communication with the stimulation circuitry of a neuromonitoring system (not shown) as will be explained in greater detail below. The needle guide50includes a guide barrel54and a slot56extending through the needle barrel54configured to receive a needle therein, for example a stimulating/recording needle electrode. The needle barrel54is generally cylindrical in shape with a central aperture extending between two ends. However, it is to be noted that the needle guide barrel54is not a closed cylinder—there is an elongated slot56extending between its two ends which is sized and dimensioned to allow the localizer/guide40to be safely removed from the needles once the needles are securely positioned at a predetermined location. The needle guide barrels54are also not positioned perpendicular to the skin or parallel to the transcutaneous stimulation electrodes48. Instead, they are preferably angled, such that when a needle is inserted into the skin S through the barrel54, it does so at an angle (e.g., a 30 degree angle) relative to the femoral nerve.

For the sake of clarity, the various methods described herein will be described in relation to the localizer/guide10described above with respect toFIGS. 1-4. However, it should be understood that either example embodiment described herein (or any combination of the disclosed features) may be used without departing from the scope of this disclosure. Furthermore, it should be appreciated that while the localizer/guide10and nerve localization method will be described with respect to the femoral nerve, other nerves may be localized without departing from the scope of this disclosure. According to one method of femoral nerve localization, the transcutaneous stimulation electrodes22of the localizer/guide10are placed on the surface of the patient's skin S along the ilioinguinal ligament. The neuromonitoring system may then apply a stimulation current to the electrodes22until the control unit detects a significant neuromuscular response in one or more muscles innervated by the femoral nerve (e.g., adductor longus, vastus lateralis, vastus medialis). This is the stimulation threshold intensity. The stimulation threshold intensity may then be ascertained at one or more additional sites along the ilioinguinal ligament and compared to the previous locations to determine the optimal stimulation/recording location for the femoral nerve FN. By way of example only, the optimal location may be the location along the femoral nerve with the lowest stimulation threshold intensity value or the location with the most responses from the muscles innervated by the femoral nerve. According to one or more implementations, the neuromonitoring system may utilize a stimulating hunting algorithm to quickly ascertain the stimulation threshold intensities (e.g., the hunting algorithms described the above-referenced '045 patent). Once the ideal location for the femoral nerve recording/stimulating site is ascertained as described above, the subdermal needle stimulating/recording electrodes may be positioned using the needle guides20. Once positioned, the distal tip of each needle electrode will be directly beneath the transcutaneous stimulation electrode22at the idealized location for stimulating/recording from the femoral nerve.

With the location of the femoral nerve optimized and needle electrodes placed near the femoral nerve at that location, the neuromonitoring system may be used to 1) stimulate one or more locations inferior to the surgical site and record responses at one or more locations superior to the surgical site, and 2) stimulate one or more locations superior to the surgical site and record responses at one or more locations inferior to the surgical site.

According to a first example embodiment, the femoral nerve may be stimulated at the ilioinguinal ligament and the lumbar potential (LP) sensory responses may be recorded superior to the surgical site. According to a second embodiment, the femoral nerve may be stimulated at the ilioinguinal ligament and LP sensory responses may be recorded superior to the surgical site and/or AL, VL, VM responses may be recorded inferior to the surgical site. According to a third embodiment, the sensory tracts may be activated at the location of the LP electrodes and sensory responses may be obtained at the femoral nerve electrodes. According to a fourth embodiment, the sensory tracts may be activated at the location of the LP electrodes, the neurogenic potential may be obtained at the femoral nerve electrodes and motor responses may be recorded in the AL, VL, or VM. According to a fifth embodiment, a stimulation can occur at the surgical site (e.g., a stimulation signal can be elicited from an electrode integrated into or near a retractor blade, for example a retractor blade forming part of the retraction system in the above-referenced '840 patent) and the LP, FN, and neuromuscular responses may be obtained.

Optionally, the neuromonitoring system may either manually or automatically switch stimulating and recording capabilities from the inferior and superior locations, such that each stimulation site may also serve as a recording site.

It is to be appreciated that at least one and as many as all of the embodiments described in the preceding paragraph may be utilized in a given surgical procedure, alone or in combination. According to some implementations, the neuromonitoring system may automatically interleave stimulating and recording parameters between using each of the LP and FN sites as stimulating and recording sites. According to some implementations, a fixed stimulation threshold may be established and the amplitude and latencies of the neurogenic and/or myogenic responses may be tracked over time and compared to a baseline response (manually or automatically). By way of example only, if the amplitudes decrease below a pre-determined criteria or the latencies increase above a pre-determined criteria, it could be indicative of a change in the health and/or status of the femoral nerve across the surgical site. The user could be provided this information by the neuromonitoring system via one or more easy-to-interpret indicia. Further, according to yet other implementations, the neuromonitoring system may provide the user easy-to-interpret results as to the health and status of the femoral nerve. By way of example, this may be accomplished via one or more of color (e.g. R/Y/G), audio, visual, or textual indicators.

While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the invention to the particular forms disclosed, but on the contrary, the invention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined herein. For example, any of the features of a particular example described herein may be used with any other example described herein without departing from the scope of the present invention.