Electrical stimulation for spinal fusion

Electrical stimulation is sometimes used as an adjunctive therapy to enhance the chances of obtaining a solid spinal fusion. A solid fusion between two vertebrae eliminates the motion at a painful motion segment, helping reduce or eliminate the back pain associated with motion at that spinal segment.

The earliest reported use of electrical stimulation to improve the efficacy of spinal fusion was over 25 years ago. At that time, a study showed that adjunctive electrical stimulation improved the fusion rate of a diagnostically varied group of patients undergoing both anterior and posterior spinal fusion.¹

Bone growth stimulators are most typically employed for patients who have a lower likelihood of obtaining a solid spine fusion, such as for patients with the following risk factors:

• Multi-level fusions

• Revision surgery (after a failed fusion)

• Smokers

• Diagnosis of Grade III or worse spondylolisthesis

• Other risk factors, such as obesity or diabetes

Electrical bone growth stimulation devices costing between $3,000 and $5,000 have been shown to be cost effective as they increase the percentage for success of a solid fusion.

A 1996 study analyzed a large database of patients and the costs incurred in caring for patients over a two-year follow-up after a posterolateral spinal fusion performed with and without pedicle screw instrumentation and with and without direct current electrical stimulation. Those patients having a fusion with and without pedicle screw instrumentation but with internal bone stimulators showed significant long term cost savings over those patients fused without the use of internal bone stimulators.²

Before assessing the scientific and clinical efficacy of these devices to aid spine fusion, it must be appreciated that not all electrical stimulation devices work in the same manner, and, all spinal fusions do not physiologically or biomechanically heal in the same manner.

• Anterior interbody spine fusions are revascularized primarily through the vertebral bodies themselves and the bone graft is under compressive forces. Bone responds well to compression and this helps stimulate a healing response.

• Posterolateral spine fusions are revascularized primarily from the surrounding muscle tissue. There is little or no compressive force on the graft material.

The three most common types of bone growth stimulation used as adjuncts to spinal fusion are: a surgically implanted stimulator (“Internal bone stimulator”) that delivers a direct current (DC) at the fusion site and two different types of external stimulation (“External bone stimulators”).

• Internal bone stimulators—are implantable devices that utilize direct current (DC) electrical stimulation and are implanted at the time of the spinal fusion.

• External bone stimulators—are external devices worn outside the skin and are either worn as a brace type stimulator or are attach to the skin with pads. One common type of external device utilizes pulsed electromagnetic fields (PEMF). The newest type of non-invasive stimulation is a capacitive coupling device (CC) that delivers a constant current to the fusion site.

This article includes a review of both internal and external bone stimulators, including how they work and reviews of clinical studies about their efficacy in enhancing spinal fusion.