Electrical bone growth stimulators are a supplemental form of therapy to help enhance the body’s bone healing process… a process that is absolutely essential for the success of any type of spinal fusion surgery.

The first stage includes the inflammatory phase, which lasts for about five days. In this stage, a blood clot is formed at the site of the surgery. This clot provides a protective barrier for the treated area and helps propagate healing through the infiltration of several proteins and enzymes that promote the growth of new bone.

The second stage includes the repair phase, which lasts for about a month. In this stage, new bone tissue is generated through a process called osteogenesis, which bridges the gap between the fused vertebrae. Specialized cells, such as osteoblasts and chondroblasts, produce new bone and cartilage, which gradually solidify and fuse with the surrounding bone tissue. The bone graft used in the surgery also serves as a scaffold for new bone growth.

The third and final stage is called bone remodeling, which lasts anywhere from the 18th day of surgery to several months or years after the surgery. In this stage, the new bone tissue is gradually reshaped and strengthened, as it responds to the stresses placed upon it by movement and weight bearing in the spine.

During these stages, it's important to follow the doctor's instructions for post-surgical care, including physical therapy and activity modification to ensure proper bone healing and avoid complications.

Human bone is a living tissue and, like skin, has the inherent ability to heal itself when broken or injured. When bone is broken, it creates its own electrical field to help promote the body’s bone healing process.

In the same way, application of an electrical stimulator can enhance the body’s natural bone healing process.

Based on the surgeon’s preference, or if the patient has risk factors for fusion, an electrical bone growth stimulator may be used as an adjunct to spinal fusion surgery to help enhance the chances of achieving a successful bone fusion.

See Postoperative Care for Spinal Fusion Surgery

The Bone Healing Process of Spine Fusion

In the case of a spinal fusion, it is necessary for multiple bone fragments to heal together, or “fuse” together, to create one solid bone.

The repair phase of bone healing from a fusion.

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The repair phase of bone healing from a spinal fusion.

A fusion does not occur immediately at the time of surgery, but rather the surgery sets up the environment for the bone to fuse together over the months following the surgery.

During surgery, the surgeon lays down bone fragments (usually taken from iliac crest in the patient’s hip) in the segment of the spine to be fused.
After the surgery, a process called "osteogenesis" starts, which is the body's way of growing bony tissue.
The goal of this bone growth process is to unite the bone graft pieces into a solid union of bone.
This process takes a few months to one year to complete, and may take as long as 18 months

The fusion of these bone fragments into one solid bone that connects two vertebrae stops the motion in the affected segment of the spine, and thereby eliminates or reduces the pain that was created by the motion.

Risk of Failed Spine Fusion

However, there is always a risk that the bone will not grow together and fuse in a normal period of time.

The medical term for failure to fuse is pseudoarthrosis.
In common parlance, it is referred to as non-fusion, failed fusion, or failed back surgery syndrome.

The failure for a solid fusion to form following a spine fusion procedure may result in an increase in pain, functional limitations. A failed fusion may also necessitate repeat surgery or other medical interventions, along with the concomitant risks and adverse effects.

To mitigate this risk, an electrical bone growth stimulator is sometimes used to help enhance the body's bone healing process.

The use of an electrical bone growth stimulator is more likely to be recommended when a patient has risk factors that impeded bone healing and the likelihood of achieving a successful bone fusion.

Indications for Electrical Bone Growth Stimulation

It is reasonable to consider bone growth stimulator treatment when there is potential for bone healing problems, such as patients with:

A previous failed spine fusion
Surgery that involves more than one level of the spine. A multi-level spine fusion includes 3 vertebrae, such as L3-L4-L5, or L4-L5–S1 levels of the spine.

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X-ray of a two and three level spinal fusion.

Patients who smoke, vape, chew tobacco, or any type of nicotine intake.
Patients with a diagnosis of Grade II (or worse) spondylolisthesis
Patients with osteoporosis or osteopenia
Anyone with long term steroid use

There are many additional factors that may lessen the chance of obtaining a solid fusion, such as vascular disease, obesity, diabetes, renal disease, alcoholism, and any medications that deplete calcium.

This is not a complete list of indications, and some surgeons may be more inclined to recommend electrical stimulation for a broader range of patients.

Types of Electrical Stimulation after Spinal Fusion

There are two general types of bone stimulators:

Internal bone growth stimulators – a small device, like a pacemaker, that is implanted under the skin at the time of the fusion surgery
External bone growth stimulators – a device that is worn externally, like a back brace (for lumbar fusion) or a neck brace (for cervical fusion or ACDF)

The choice or which type to use is based on the surgeon’s preference, the patient’s preference, and the patient’s individual condition.

If in the weeks or months following the fusion is not setting up as expected, external bone growth stimulation therapy may be introduced at that time to better stimulate the fusion process.

Success Rates for Bone Growth Stimulators

An analysis of research to determine the success rates for bone growth stimulators found that use of bone growth stimulators had the following outcomes:

Significant pain reduction
Significant improvement in achieving a solid spinal fusion
Inconclusive results on improvement in patient ability to function¹Aleem, I. S. et al. Efficacy of Electrical Stimulators for Bone Healing: A Meta-Analysis of Randomized Sham-Controlled Trials. Sci. Rep. 6, 31724; doi:10.1038/srep31724 (2016).

Another review of 13 clinical studies conducted by The Johns Hopkins School of Medicine showed a two-fold increase in fusion rates when electrical bone growth stimulation therapy was used.²Journal of Neurosurgery: Spine. 2020;32(1):106-126. Doi:https://doi.org/10.3171/2019.5.SPINE19465

There are more research studies demonstrating the effectiveness of bone growth stimulators in helping long bone fractures heal than for spine fusion. More research is needed to understand the effectiveness and role of bone growth stimulation in modern spinal fusion techniques.

1 Aleem, I. S. et al. Efficacy of Electrical Stimulators for Bone Healing: A Meta-Analysis of Randomized Sham-Controlled Trials. Sci. Rep. 6, 31724; doi:10.1038/srep31724 (2016).
2 Journal of Neurosurgery: Spine. 2020;32(1):106-126. Doi:https://doi.org/10.3171/2019.5.SPINE19465

Dr. Larry Parker is an orthopedic surgeon at the Spine Center at TOC in Huntsville, AL. Dr. Parker has specialized in spine surgery for more than 25 years. He has given several scientific presentations and published numerous papers in medical journals.