A spinal cord stimulator (SCS) manages chronic pain by delivering mild electrical pulses to the spinal cord. The system consists of thin wires, called leads, placed near the spinal cord, and a small, pacemaker-like power source known as the Implantable Pulse Generator (IPG), often called the battery. Although the system is designed to be permanent, patients often worry if the internal components, particularly the IPG, can move. While modern surgical techniques secure the device, IPG movement is a known, though infrequent, complication that can affect the system’s function.
The Spinal Cord Stimulator System
The SCS system has two main parts: the leads and the Implantable Pulse Generator (IPG). The leads contain electrodes that deliver electrical energy and are positioned in the epidural space near the spinal cord to interrupt pain signals. These leads connect to the IPG, which serves as the system’s power source and is housed inside a durable case.
The IPG is implanted beneath the skin in a soft-tissue area, usually the lower abdomen or upper buttocks. This location is chosen for patient comfort and accessibility, especially for rechargeable models requiring external charging. The generator provides the electrical power, and the leads are tunneled from the spine to the IPG pocket, ensuring the system functions as a single unit.
Understanding Battery Migration
The IPG, or battery, can move or rotate from its implanted position, though this is less common than lead movement. When the IPG shifts, it is called migration or, if caused by patient manipulation, ‘twiddler’s syndrome’. Since the IPG is a hard object placed in a surgically created pocket, any movement can cause mechanical irritation or discomfort.
Migration is primarily due to insufficient anchoring during surgery or excessive patient activity during the healing phase. Surgeons anchor the device using sutures, and if this anchoring is not robust, the device can shift before scar tissue fully encapsulates it. Strenuous activity, excessive twisting, or stretching too soon after implantation can overcome the initial surgical anchoring, causing the device to rotate or migrate.
Recognising Symptoms of Movement
IPG movement causes both physical and functional symptoms. Physically, a patient might notice a change in the device’s position or orientation under the skin, often feeling a sharp poking or tugging sensation at the implant site. The skin over the pocket may become red, swollen, or warm, and rotation can rarely lead to skin erosion as the device edges press against the skin.
The most significant functional symptom is the loss of stimulation effectiveness. Since the IPG is connected to the leads, its movement can pull on them, causing them to shift away from the targeted spinal nerve area. This shift results in a sudden return of chronic pain, decreased pain relief, or the sensation of stimulation in a new area. Any unexpected change in therapy effectiveness warrants an imaging assessment to check the position of the IPG and the leads.
Prevention and Correction
Preventing IPG migration starts with meticulous surgical technique, where the surgeon carefully anchors the device within a well-formed subcutaneous pocket. The leads and the IPG are secured using non-absorbable sutures to minimize movement until surrounding tissue naturally stabilizes the components. Surgeons may also create a mesh pocket or use specialized anchoring devices to further reduce migration risk.
Patient compliance during the initial post-operative period is equally important. Patients are advised to avoid excessive bending, twisting, or heavy lifting for the first six to eight weeks to allow for proper scar tissue formation. If the IPG migrates and causes symptoms, the standard correction is a minor revision surgery. This procedure involves reopening the incision, repositioning the device, and re-anchoring it securely to prevent future movement.