Neuromodulation: Technology at the Neural Interface | 2019
Response to “Spinal Cord Stimulation—The Implantable Systems Performance Registry”
Abstract
To the Editor: We read with great interest the article by Schultz et al (1) on real-world safety of implantable spinal cord stimulation (SCS) systems. In their implantable systems performance registry (ISPR), 1116 non-product performance Events (non-PPE) and 640 product performance events (PPE) were reported in 2605 patients. A majority of devices (56%) included rechargeable IPGs. In figure 1, the authors illustrate that 5.7% of reported events (N = 100) were related to a failure of the recharge process (non-PPE), and that 0.9% (N = 7) did not recharge due to a product-related problem (PPE). In table 2, they mention 16 cases of ‘recharging unable to recharge’ as PPE. In the discussion, one recharging issue attributed to the neurostimulator is reported. In 2016 Medtronic product performance report (2), we identified product-related recharge problems in 1.3% of patients and non-product related issues in 4,65% of subjects. Based on these data, we conclude that a recharging problem can be expected in over 5% of patients with a rechargeable IPG. Energy transfer between the recharger and the IPG can be very effectively established by resonant inductive coupling but is highly dependent on the distance between the charger and the stimulator. Therefore, the IPG should not be placed in a deep subcutaneous location, which can be challenging in obese patients. A too superficial position on the other hand can lead to pocket pain and wound complications. The current trend toward rechargeable devices (3) due to the use of higher frequency stimulation, especially in failedback surgery syndrome, makes the subject of recharging-related issues all the more actual. Recharging issues related to the distance between the recharger and the IPG have been largely neglected in the literature. As mentioned, having a layer of subcutaneous fat on top of the IPG is desirable but an excess of subcutaneous fat can cause difficulties recharging. Therefore, the optimal distance between the epidermal surface and the IPG has a very limited range, a problem that seems more apparent in overweight patients, and in patients gaining weight after the implantation of the battery. When confronted with this problem, we mostly perform a local wound revision in an attempt to place the IPG in a more superficial position. In a recent case, we opted for an alternative and novel approach where we performed very local liposuction. After placing the IPG in a deeper position due to local skin irritation and accompanying pain, a connection between the recharger and the battery could barely be established. Under general anesthesia, a minimal stab incision was made 4 cm lateral and inferior to the scar of the IPG (near the inguinal fossa), adrenaline was infused in the area around the IPG and liposuction was performed until the battery could be easily recharged, which was confirmed on the operating table. When performing this quick procedure, specific attention has to be paid to the leads and to the location of the recharging part of the IPG. In rare and selected cases, we believe that local liposuction can represent a very elegant procedure to facilitate recharging. However, long-term efficiency of this technique remains uncertain and needs further evaluation.