Ultrasound-Guided Peripheral Nerve Stimulation

Michael Gofeld

Background and indications: Peripheral nerve stimulation (PNS) was the first attempted method for neuromodulation in chronic neuropathic pain. The PNS effect is based on the gate control theory, wherein a stimulation of thick A-beta fibers blocks the nociceptive input of spinal neurons conducted via small A-delta and C fibers. Even before development of the gate control theory, Sweet and Weptik experimented with PNS by inserting stimulating electrodes onto the infraorbital nerve and eliciting a paresthesia. Notably, they performed experiments on each other. In the ensuing decades, multiple case series and observational clinical studies were published reporting variable but overall significant effectiveness of this method. Mononeuropathies, stump neuroma pain, and the complex regional pain syndrome have been tagged as indications. Because PNS is based on surgical implantation and the achievement of paresthesia as sine qua non for pain relief, randomized control studies are deemed impossible. This notable drawback is typical not only for PNS but also for other complex health interventions in which no pharmacotherapy-like research is possible.

Given the necessity to surgically explore the target nerve, often accompanied by a need to perform external neurolysis and transposition, PNS had been belonged to the neurosurgical domain until it became apparent that ultrasound may help in localizing peripheral nerves and neuromas. Ultrasonography may also facilitate preoperative localization, planning of the access, and guiding dissection. Development of percuTaneous methods has been delayed because of regulatory difficulties and insufficient interest amongst neurosurgeons and pain physicians.

PNS can be arbitrary divided into two methods. The first method is a stimulation of a definite nerve by either surgical or percuTaneous lead placement onto the nerve. The author prefers a surgical technique because it is easier to suture the lead next to the nerve. The second method can be best described as a stimulation of a painful skin region that may or may not be outlined within cuTaneous distribution of a specific nerve. This method received the name peripheral field nerve stimulation (PFNS).

Anatomy

1. PNS is performed according to the anatomical pathway of the target nerve.

2. PFNS is performed based on pain distribution and only the lead position is defined by the anatomical site of the pain.

Patient position: Variable and related to the specific target.

Probe: Broadband high-frequency linear transducer, low-frequency curvilinear probe or a small (25-mm) linear probe for intraoperative ultrasound.

Equipment: Either percuTaneous or surgical (paddle) sTandard spinal cord stimulation leads. In the past, custom-made leads (e.g., spiral, sandwich-type) were used, but they are not commercially available. Special PNS leads are currently under development.

Technique

Peripheral Nerve Stimulation

PercuTaneous (cylindrical) lead placement technique: This is essentially the same technique that is used for peripheral nerve continuous catheter placements described elsewhere in the text. It is unclear which nerve-lead configuration—parallel or perpendicular—should provide better and more consistent stimulation. However, given peripheral nerves’ mobility and inability to anchor the lead in soft tissue, lead migration is likely to happen. When this occurs, stimulation will be lost. A purely percuTaneous approach is most suitable for a PNS trial before implantation. Even during a percuTaneous trial, the limb must be completely immobilized.

Paddle (surgical) lead placement technique: Paddle placement is a neurosurgical approach that requires a cut down and mobilization of the nerve. Ultrasound is an invaluable technique in all stages of implantation and for postoperative management. A proximal segment of the intact nerve of either upper or lower extremity is usually suited for the PNS implantation. This allows avoiding both unnecessary excessive exploration of a damaged nerve and crossing moving joints with lead extensions. For the upper limb, typically the midarm is used for ulnar, median, and radial nerve stimulation. Surgical access and stimulation of the nerves of the lower limb are more complicated and less sustainable. The femoral nerve is accessed below the inguinal crease. The saphenous nerve can be found in the subsartorial space. The sciatic nerve and its branches can be approached via different sites, such as the posterior thigh, the popliteal, distal leg, and the proximal tarsal canal.

Planning of the pulse generator implantation is also challenging and influenced by patient habitus, preferences, and local anatomy.

A preoperative ultrasound is performed in both the short (Fig. 72.1)

Only gold members can continue reading. Log In or Register to continue