Sciatic, Femoral, and Lateral Femoral Cutaneous Nerve Ultrasound-Guided Percutaneous Peripheral Nerve Stimulation

Abstract

Objective

With advances in peripheral nerve stimulation technology, there has been an emergence of new minimally invasive techniques to provide neurostimulation therapies for chronic pain. This technical note describes the utilization of ultrasonography for percutaneous placement of peripheral nerve stimulation leads at the sciatic, femoral, and lateral femoral cutaneous nerves.

Methods

Ultrasound can be utilized to localize a specific nerve, view neighboring soft tissue anatomy, and plan a needle trajectory. Various ultrasound techniques and transducer orientations allow for multiple options for lead placement relative to the targeted nerve.

Conclusions

The option of ultrasound-guided percutaneous technique for neurostimulation lead placement allows this treatment modality to be made available to more patients with chronic pain in specific nerve distributions.

Introduction

Technological advancements in the 21st century have rapidly expanded the scope of peripheral nerve stimulation (PNS) as a treatment modality for acute and chronic pain management [1]. Conventional surgical PNS lead placement methods are now being replaced by minimally invasive, ultrasound-guided percutaneous techniques [2].

Similar to other neurostimulation techniques, sciatic, femoral, and lateral femoral cutaneous nerve (LFCN) stimulation is broadly indicated in patients with chronic pain that is refractory to conventional management. This includes patients with intractable nerve neuropathy, nociceptive/neuropathic postamputation lower extremity pain, and complex regional pain syndrome type 2 (direct trauma to the nerve or its branches) [3–5].

Technique

For percutaneous PNS lead placement, ultrasonography is utilized to localize the targeted peripheral nerve and plan the needle trajectory. Ultrasound-guided percutaneous lead placement techniques allow for parallel or perpendicular lead orientation in reference to the targeted nerve. Once the final needle path is determined, the skin and the anticipated proximal needle track are anesthetized with local anesthetic under ultrasound visualization using a proper aseptic technique. Infiltration of local anesthetic near the targeted nerve and nearby muscles must be avoided, as it will interfere with nerve and muscle stimulation during testing before final lead placement.

First, a percutaneous sleeve with a stimulating probe is inserted using an in-plane technique and directed along the planned trajectory to within a 5–15-mm proximity of the targeted nerve. Then, electrical stimulation is used to identify the ideal position to achieve comfortable paresthesia at the region of the patient’s pain. Once the optimal stimulation site is determined, the stimulating probe is replaced with the lead with the tip positioned at the same site under ultrasound guidance. Lastly, the lead should be once again tested to confirm appropriate coverage of the distribution of the patient’s pain. Depending on the specific device recommendations, the lead can be placed subcutaneously or secured externally.

Sciatic Nerve

The sciatic nerve arises from the ventral rami of L4-S3 and is composed of Tibial and common peroneal nerve components. These fibers provide coverage to the distal femur, knee, leg, ankle, and foot (expected of the medial aspect of the leg and foot). The sciatic nerve after its origin passes through the greater sciatic foramen below the piriformis. It then descends down in an inferolateral direction and is located midway between the greater trochanter of the femur and the ischial tuberosity in the gluteal region [6]. Further down in the posterior thigh, it is located deep to the long head of the biceps femoris before it ultimately divides into its terminal branches in the popliteal fossa.

The sciatic nerve can be targeted via anterior, transgluteal, subgluteal (infragluteal), and popliteal approaches. Anterior and transgluteal approaches are not ideal for PNS placement due to longer needle trajectory, traversing several muscle layers, awkward lead location, and increased patient discomfort.

For the subgluteal approach, the patient is placed in a prone position and a curvilinear ultrasound probe is placed in short axis at the subgluteal fold. The sciatic nerve is identified deep to the gluteus maximus muscle and superficial to the quadratus femoris muscle with the ischial tuberosity medially and the greater trochanter laterally. The sciatic nerve can be thin and wide at this location and is not always visibly distinct. The nerve can be traced distally and proximally or viewed in long axis to verify the location. The needle is inserted laterally to medially using an in-plane technique (Figure 1).

Figure 1.

Subgluteal approach to the sciatic nerve with in-plane ultrasound technique, where the nerve is identified deep to the gluteus maximus muscle (GMM) and superficial to the quadratus femoris muscle (QF) with ischial tuberosity (IT) medially and greater trochanter (GT) laterally. *Sciatic nerve; arrows, needle.

The sciatic nerve can also be targeted more distal or proximal to the popliteal fossa. Using a linear ultrasound probe in short axis, the tibial and peroneal components can be traced cephalad as they combine into the sciatic nerve, which is found lateral to the semitendinosus and semimembranosus muscles and medial to the biceps femoris muscle (Figure 2A). The needle is inserted laterally to medially and can be directed superficial or deep to the nerve. At this site, the sciatic nerve can also be visualized in long axis (Figure 2B and C), and the stimulation lead can be placed parallel to the nerve by translating the ultrasound probe medially or laterally for preferential stimulation of the posterior tibial or common peroneal nerve fibers, respectively (Figure 2D).

Figure 2.

A) Short-axis ultrasound view of the distal sciatic nerve immediately proximal to its branch point at the popliteal fossa. B) Long-axis view of the distal sciatic nerve. C) Caudad-to-cephalad needle trajectory to place the stimulator lead superficial and parallel to the sciatic nerve. D) Sagittal view at the thigh immediately lateral to the long-axis view of the sciatic nerve is used to place the stimulator lead lateral and parallel to the sciatic nerve. *Sciatic nerve; arrow = needle. BF = biceps femoris muscle; Sm/St = semimembranosus and semitendinosus muscles.

Femoral Nerve

The femoral nerve originates from the anterior rami of the L2, L3, and L4 nerve roots at the lumbar plexus and traverses through the psoas major muscle, exiting at the inferior lateral border. The femoral nerve then passes deep to the inguinal ligament into the femoral triangle, where it travels lateral to the femoral vessels for ∼4 cm before branching into anterior and posterior divisions [7].

Using a linear ultrasound probe in short-axis orientation, the femoral nerve can be visualized lateral to the femoral vessels, deep to the fascia iliaca, and superficial to the iliopsoas muscle (Figure 3). It can be targeted with a lateral-to-medial in-plane approach.

Figure 3.

Short-axis ultrasound view of the femoral nerve at the femoral triangle inferior to the inguinal ligament. *Femoral nerve. FA = femoral artery; FV = femoral vein; IPM = iliopsoas muscle; SM = sartorius muscle.

Lateral Femoral Cutaneous Nerve

The LFCN provides sensation to the lateral thigh and arises from the dorsal division of L2-3. It courses inferiorly and laterally toward the anterior superior iliac spine (ASIS). Located between the fascia lata and iliaca, it passes under the inguinal ligament and over the sartorius muscle into the thigh [8].

To locate the LFCN, the clinician can place a high-frequency linear ultrasound probe in short axis at the ASIS and slowly scan inferiorly and medially. The nerve can be found subfascial to and above the sartorius muscle (Figure 4A). The nerve can also be located a few centimeters distally between the sartorius (medial) and tensor fascia lata muscles (lateral) (Figure 4B). At both locations, it can be targeted at a shallow angle with a lateral-to-medial in-plane approach.

Figure 4.

A) Proximal lateral femoral cutaneous nerve (*) can be located deep to the fascia lata (FL) and superficial to the sartorius muscle (SM). B) It can also be located distally between the sartorius muscle (SM) and tensor fascia lata muscles (TFL).

Discussion

Similar to peripheral nerve catheters, PNS leads can now be reliably placed at common sites with ultrasound-guided, minimally invasive percutaneous techniques. Some clinicians also elect to use fluoroscopic guidance in conjunction with stimulation to direct lead placement.

Limited data are currently available to support the long-term efficacy of PNS in chronic pain patients. Mobbs et al. did a retrospective study that included 38 patients who had implantable peripheral nerve stimulators. In their study, they followed the patients for a mean of 31 months, and 61% of patients reported >50% pain relief. Improvement in activity was seen in 47% of patients [9]. However, further studies are required to specifically determine the efficacy of minimally invasive percutaneous PNS techniques.

Various complications exist in percutaneous PNS. Lead migration is commonly seen in 0–100% of cases and can be readily diagnosed with a radiograph [10]. Lead fracture, infection, erosion, hemorrhage, nerve injury, and malfunction can also occur [10]. When looking at PNS performed using devices developed for spinal cord stimulation applications, studies have shown lead infection rates in up to 15% of patients, who required removal of stimulators [9]. With newer PNS devices and techniques, there may be a reduction in complication rates, which will need to be reassessed in the future.

In conclusion, advances in technology and improvement in existing electrode designs have greatly increased the feasibility and use of lower extremity PNS for treatment of chronic pain patients.

 

Funding sources: This work was supported, in part, by the National Cancer Institute Cancer Center Support Grant P30CA008748.

Conflicts of Interest: Harmandeep Singh: There are no disclosures to report. Akshat Gargya: There are no disclosures to report. Tiffany Lin: There are no disclosures to report. Amitabh Gulati: Medical Advisor for AIS. Consultant for Medtronic, Flowonix, Bausch Health, SPR Therapeutics and Nalu Medical.

Supplement sponsorship: This article appears as part of the supplement entitled “Peripheral Nerve Stimulation: Update for the 21st Century” sponsored by Bioness and by SPR Therapeutics, Inc.