Electrical Bone Growth Stimulators
Both invasive and noninvasive electrical bone growth stimulators have been investigated as an adjunct to spinal fusion surgery, with or without associated instrumentation, to enhance the probability of obtaining a solid spinal fusion. Noninvasive devices have also been investigated to treat a failed fusion.
Electrical and electromagnetic fields can be generated and applied to bones through surgical, noninvasive, and semi-invasive methods.
Invasive devices require surgical implantation of a current generator in an intramuscular or subcutaneous space, with an accompanying electrode implanted within the fragments of bone graft at the fusion site. The implantable device typically remains functional for six to nine months after implantation, and although the current generator is removed in a second surgical procedure when stimulation is completed, the electrode may or may not be removed. Implantable electrodes provide constant stimulation at the nonunion or fracture site but carry increased risks associated with implantable leads.
Noninvasive electrical bone growth stimulators generate a weak electrical current within the target site using either pulsed electromagnetic fields, capacitive coupling, or combined magnetic fields. In capacitive coupling, small skin pads/electrodes are placed on either side of the fusion site and are worn for 24 hours a day until healing occurs, or for up to 9 months. In contrast, pulsed electromagnetic fields are delivered via treatment coils that are placed into a back brace or directly onto the skin and are worn for six to eight hours a day for three to six months. Combined magnetic fields deliver a time-varying magnetic field by superimposing the time-varying field onto an additional static magnetic field. This device involves 30 minutes of treatment daily for 9 months. Individual compliance may be an issue with externally worn devices.
Semi-invasive (semi-implantable) stimulators use percutaneous electrodes and an external power supply, obviating the need for a surgical procedure to remove the generator when treatment is finished.
Either invasive or noninvasive methods of electrical bone growth stimulation may be considered medically necessary as an adjunct to lumbar spinal fusion surgery in individuals at high risk for fusion failure, defined as any one of the following criteria:
Noninvasive electrical bone growth stimulation may be considered medically necessary as a treatment for individuals with failed lumbar spinal fusion surgery.
Failed spinal fusion is defined as a spinal fusion that has not healed at a minimum of 6 months after the original surgery, as evidenced by serial radiographs over a course of 3 months.
Semi-invasive electrical bone growth stimulation is considered investigational as an adjunct to lumbar spinal fusion surgery and for failed lumbar fusion.
Invasive, semi-invasive, and noninvasive electrical bone growth stimulation are considered investigational as an adjunct to cervical fusion surgery and for failed cervical spine fusion.
Practice Guidelines and Position Statements
North American Spine Society
The North American Spine Society (2016) issued a coverage recommendation for electrical bone growth stimulators, which stated the following:
American Association of Neurological Surgeons and Congress of Neurological Surgeons
Updated guidelines from the American Association of Neurological Surgeons and the Congress of Neurological Surgeons (2014) indicated that there was no evidence published after their 2005 guidelines that conflicts with the previous recommendations on bone growth stimulation.
Based on a single-level II study (2009), the routine use of direct current stimulation in individuals older than age 60 years was not recommended. Use of direct current stimulation was recommended as an option for individuals younger than 60 years of age, based on level III and IV studies showing a positive impact on fusion rate. However, concerns about the level III study were that it was a poorly designed and poorly conducted cohort study consisting of an exceedingly small heterogeneous population of individuals, and the overall recommendation was level C. There was insufficient evidence to recommend for or against the use of pulsed electromagnetic field stimulation as a treatment alternative to revision surgery in individuals presenting with pseudoarthrosis following posterolateral lumbar fusion (single-level IV study). No additional studies investigating the efficacy of capacitively coupled electrical stimulation were identified.
The 2 medical associations also issued guidelines in 2005 that stated there was class II and III evidence (non-randomized comparative trials and case series):
“…to support the use of direct current stimulation or [capacitive coupled stimulation] for enhancing fusion rates in high-risk individuals undergoing lumbar PLF. A beneficial effect on fusion rates in individuals not at ‘high risk’ has not been convincingly demonstrated, nor has an effect been shown for these modalities in individuals treated with interbody fusion. There is limited evidence both for and against the use of PEMFS for enhancing fusion rates following PLF. Class II and III medical evidence supports the use of PEMFS for promoting arthrodesis following interbody fusion. Although some studies have purported to demonstrate functional improvement in some individual subgroups, other studies have not detected differences. All of the reviewed studies are significantly flawed by the use of a four-point individual satisfaction scale as the primary outcome measure. This outcome measure is not validated. Because of the use of this flawed outcome measure and because of the conflicting results reported in the better-designed studies that assess functional outcome, there is no consistent medical evidence to support or refute use of these devices for improving individual outcomes.”