Neuromodulation for Foot and Ankle Pain

Neuromodulation for Foot and Ankle Pain

Krishna B. Shah

Daniel J. Pak


Defined by the International Neuromodulation Society (INS) as the “alteration of nerve activity through targeted delivery of a stimulus, such as electrical stimulation or chemical agents, to specific neurological sites in the body,” neuromodulation therapies have become increasingly popular over the last several decades for the treatment of neuropathic and sympathetically mediated chronic pain.1 These therapies include noninvasive approaches, such as transcutaneous electrical nerve stimulation (TENS) units, as well as implantable devices, such as spinal cord stimulation (SCS).

Implantable neuromodulation therapies have particularly evolved since the introduction of the first SCS in the 1960s. Hardware advancements have led to the development of smaller implantable batteries with increased longevity, thereby improving patient comfort while extending the life of the power unit. The introduction of new technologies, such as dorsal root ganglion (DRG) stimulation and peripheral nerve stimulation (PNS), has also broadened the application of these devices to a vast array of chronic pain conditions, and the development of novel stimulation modes has improved the efficacy of the treatments. While these devices have traditionally been viewed as a salvage therapy, many providers are now implementing them earlier in the treatment algorithm to improve patient outcomes. This chapter aims to discuss the utility of neuromodulation therapies for the management of common chronic foot and ankle pain syndromes.


Traditionally, based on the gate control theory of pain proposed by Melzack and Wall in 1965,2 SCS devices generate electrical fields between metal contact points that are placed in the epidural space on top of the dorsal column of the spinal cord. Electrical stimulation of large diameter afferent sensory nerve fibers then inhibits the ascension of nociceptive signals and suppresses pain perception.3 The gate control theory continues to serve as the core conceptual principle behind SCS though recent studies suggest other potential contributing analgesic mechanisms that are beyond the scope of this chapter.

Conventional tonic SCS delivers electrical pulses at a frequency typically less than 200 Hz with above-sensory threshold amplitudes, providing therapeutic paresthesias in the distribution of the patient’s pain. The recent emergence of subsensory threshold therapies, such as high frequency and burst SCS, now provide paresthesia-free stimulation modes, thus eliminating the uncomfortable tingling or pricking sensations associated with tonic stimulation and the need for intraoperative paresthesia
mapping (Table 19.1). High frequency SCS utilizes frequencies up to 10 kHz (HF10) while burst SCS delivers packets of higher frequency stimulation separated by pulse-free phases. The mechanisms of action for these modalities remain unclear though the activation of inhibiting interneurons and attenuation of wide dynamic range (WDR) dorsal horn neurons have been implicated.3


SCS implantation is a 2-stage process and is initiated with a trial period where 1 to 2 cylindrical leads are placed percutaneously in the epidural space under fluoroscopic guidance. Epidural needle entry is typically achieved at the T12-L1 or L1-L2 interlaminar spaces, and the leads are advanced along the midline dorsal epidural space so that the electrical contacts span the T8-T12 vertebral bodies for lower extremity symptoms (Figure 19.1).11 Paresthesia mapping during the procedure may be utilized to verify proper coverage of the patient’s painful areas. The leads are then secured with adhesive dressings or sutures and attached to an external
pulse generator. Patients typically spend a trial period of 7 days to determine the efficacy of the therapy. At least 50% reduction in pain is desired in order to proceed with implantation of the permanent system.

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Sep 8, 2022 | Posted by in ORTHOPEDIC | Comments Off on Neuromodulation for Foot and Ankle Pain

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