Does a Bone Growth Stimulator Cause Pain?

Bone growth stimulators, whether electromagnetic or ultrasound-based, are not typically a source of pain for most patients. The devices deliver energy at levels far below what you would consciously feel as heat or pressure. That said, a subset of users do report discomfort during or after treatment sessions, and the reasons range from nerve stimulation at old injury sites to heating effects near metal implants. The relationship between these devices and pain turns out to be more layered than a simple yes-or-no, partly because the same biology that drives bone repair also drives pain signaling.

What Most Patients Feel During a Session

Bone growth stimulators fall into two broad categories: electromagnetic devices (which use pulsed electromagnetic fields, or PEMF) and ultrasound devices (which use low-intensity pulsed ultrasound, or LIPUS). Both are designed to work well below the threshold of sensation. PEMF units are typically strapped on or worn over the injury site for several hours a day, and most users report feeling nothing at all from the device itself. LIPUS units involve applying a transducer to the skin with coupling gel for about 20 minutes a day. Again, most people feel little or nothing.

The ultrasound devices produce minimal thermal effects at therapeutic intensities. In laboratory measurements, the temperature rise at the low power output used clinically was undetectable, while even at much higher power levels the maximum temperature increase was only about 1.8°C, suggesting that the therapeutic action is primarily non-thermal rather than heat-based.¹ LIPUS has been described as a technology with minimal thermal effects in reviews of its clinical use.² So if you are picturing something that heats your bones or buzzes painfully against your skin, the reality is much milder.

When Electromagnetic Stimulators Trigger Pain

The exception worth knowing about involves PEMF devices and nerve stimulation. Electromagnetic fields do not just affect bone cells. They can also stimulate nearby nerve tissue. Because the electromagnetic signal increases local circulation and drives electrical activity through nerve pathways, some patients experience a flare-up of pain at the treatment site. This is especially common in people who have had previous fractures in the area. The stimulation can cause pain not only where the current fracture is healing, but also at a distant site that carries scarring from an older injury.³

This distal pain effect catches some patients off guard. You might be treating a spinal fusion site and notice aching in an ankle you broke years ago. The mechanism is straightforward: nerve cells that were sensitized by past trauma are being re-activated by the electromagnetic field. If you have a history of multiple fractures or chronic nerve irritation, this side effect becomes more plausible. It does not indicate that the device is causing new damage, but it can be unsettling and uncomfortable enough to make people want to stop treatment.

What Clinical Trials Say About Pain Outcomes

The clinical evidence on whether bone growth stimulators affect pain is mixed, and it depends heavily on study quality and the condition being treated. A Cochrane systematic review looking at electromagnetic field stimulation for delayed or non-healing fractures found no reduction in pain across two trials, with only two minor complications reported from the treatment itself.⁴ For LIPUS, a large systematic review in the BMJ found that in well-designed trials with low risk of bias, ultrasound stimulation did not reduce pain at four to six weeks compared to sham treatment.⁵ That BMJ review also noted something telling: trials that were poorly designed tended to show pain benefits from LIPUS, while rigorous trials did not. The gap between high-quality and low-quality studies was dramatic.

On the other hand, a meta-analysis of randomized sham-controlled trials found that electrical stimulation did produce a statistically significant improvement in pain, with a mean difference of about 7.7 points on a 100-point pain scale.⁶ That is a real but modest effect. Meanwhile, a study on PEMF for odontoid (upper cervical spine) fractures found that pain did not differ significantly between the stimulator group and the group that went without it.⁷

The bottom line from the clinical literature is that bone growth stimulators rarely make pain worse in controlled trials, but they also do not reliably make it better in the fracture-healing context. Any pain people experience during treatment tends to be a side effect of the underlying healing biology rather than something the device is directly inflicting.

Why Healing Bones Hurt Whether or Not You Use a Stimulator

One of the most important things to understand about pain during bone growth stimulator treatment is that fracture repair is inherently painful, and the biology of that pain runs in parallel with the biology of healing. Bone is richly supplied with sensory nerve fibers that respond to nerve growth factor (NGF), and these fibers play a direct role in skeletal repair.⁸ When a bone breaks, the nerve network around the fracture site does not sit quietly. Within about a week, sensory nerve fibers begin rapidly sprouting and branching into the repair zone, forming dense networks around the developing callus tissue.⁹

This nerve sprouting is not an accident or a side effect. The nervous system appears to be actively involved in regulating bone repair. But the same nerve growth that helps guide healing also sensitizes the area. Research in animal models has shown that NGF expression during bone regeneration directly contributes to localized tenderness and heightened pain sensitivity at the injury site. When researchers blocked NGF activity, the mechanical hypersensitivity dropped.¹⁰

This matters because patients using a bone growth stimulator are simultaneously going through this natural process of nerve proliferation and sensitization. It can be genuinely difficult to separate discomfort caused by the device from discomfort caused by healing itself. If your fracture site starts aching more around weeks two through six of treatment, that timing lines up both with nerve sprouting during repair and with the period when many people are actively using their stimulator. Blaming the device is a natural response, but the timing overlap may be coincidental.

PEMF and Pain Relief in Osteoarthritis

Interestingly, the same electromagnetic technology used for bone growth has shown much clearer pain-relief effects in a different context: osteoarthritis. A systematic review and meta-analysis of randomized placebo-controlled trials found that PEMF therapy produced a clinically significant reduction in pain for osteoarthritis patients, along with improvements in stiffness and physical function.¹¹ A pilot study in patients with early knee osteoarthritis found that PEMF treatment reduced pain scores by about half compared to baseline, starting from the very first day, and that reduction persisted through six weeks. The active treatment group improved roughly three times as much as the sham group.¹²

The distinction matters because it suggests PEMF devices are not inherently pain-causing. In degenerative joint conditions, the anti-inflammatory and tissue-modulating effects of electromagnetic fields may actually settle pain down. The difference between the osteoarthritis experience and the fracture experience likely comes down to what is happening in the surrounding tissue. A fresh or healing fracture involves active nerve sprouting and inflammation that the device may temporarily amplify, while an arthritic joint involves chronic low-grade inflammation that the device may help calm.

Why Compliance Changes the Pain Story

One of the more striking findings in the literature is how much compliance matters, not just for healing outcomes but for pain. A randomized double-blind study of PEMF for femoral neck fractures found that patients who were compliant with the stimulation protocol had significantly lower pain scores at every follow-up visit compared to the placebo group. But patients who did not follow the prescribed protocol showed no difference from placebo in either pain or healing rates.¹³ Compliant patients also achieved fracture healing at a rate of about 94%, compared to 69% in the placebo group.

This creates a practical consideration: if you are experiencing mild discomfort from the device and tempted to use it less often or for shorter periods, you may end up in the worst of both worlds. You get enough stimulation to trigger nerve irritation but not enough to push through the therapeutic benefit that comes with consistent use. The pain-relief advantage only showed up in patients who stuck with the full treatment schedule. If you are going to use a stimulator, using it as directed appears to be the difference between it helping with pain and it not doing much at all.

Metal Implants and Heating Concerns

Patients who have metal hardware from a surgical repair, such as screws, plates, rods, or joint replacements, sometimes worry about whether electromagnetic bone stimulators could heat those implants and cause pain. This concern is not unfounded, but the risk varies enormously depending on the type of implant. Laboratory testing of pulsed radio frequency energy near various metallic implants found that most orthopedic hardware (plates, screws, hip and knee components) produced only modest temperature changes. The heating rates near these standard implants ranged from roughly 0.04 to 0.69°C per second, well below the levels that would cause tissue damage or noticeable pain.¹⁴

The outliers were spinal cord stimulator electrodes and pacemaker leads, which produced heating rates roughly 4 to 60 times higher than standard orthopedic implants. If you have an implanted electronic device like a spinal cord stimulator or cardiac pacemaker, electromagnetic bone growth stimulators pose a real risk of uncomfortable or dangerous heating near those electrodes. This is a well-known contraindication, and your surgeon should screen for it before prescribing a PEMF device.

A separate study on induction heating of orthopedic implants found that while temperatures at the surface of an implant could reach high levels, the thermal dose dropped off rapidly with distance. For hip stems and intramedullary nails, the thermal dose just a few millimeters from the surface was well below the threshold for tissue damage. Fracture plates without nearby screws were the exception, with potentially elevated thermal doses extending up to about 5 millimeters from the plate surface.¹⁵ For most people with standard orthopedic hardware, the heating effect from a bone growth stimulator is negligible. But if you have exposed or superficial plates close to the skin surface, it is worth mentioning to your provider.

How Expectations Shape What You Feel

There is a well-documented psychological phenomenon that affects how patients experience any medical device, including bone growth stimulators. When people expect a treatment to cause pain or side effects, they are more likely to experience exactly that, even when the device is turned off or delivering a sham signal. This is called the nocebo effect, essentially the evil twin of the placebo effect. Research has shown that providers’ behaviors, environmental cues, and even the appearance of a medical device can create negative expectations that meaningfully alter pain perception.¹⁶

This is not about patients imagining pain or being told their discomfort is “all in their head.” The nocebo effect produces measurable changes in how the brain processes pain signals. Studies have found that nocebo responses are particularly easy to trigger and can be stronger than placebo responses in some experimental designs.¹⁷ Even the way a healthcare provider describes potential side effects of a bone stimulator can itself contribute to producing those side effects. Research on the nocebo response has found that information disclosure about potential adverse effects can increase the likelihood of patients reporting those exact effects, and that this influences quality of life and whether people continue treatment.¹⁸

For bone growth stimulator users, this has a practical implication. If you read online forums full of people describing pain from their devices, or if your doctor frames the device with heavy warnings about discomfort, you are primed to interpret normal healing pain or even neutral sensations as being caused by the stimulator. Being aware of this bias does not make you immune to it, but it can help you evaluate your own experience more objectively. Tracking your pain levels before, during, and after treatment sessions in a simple journal can help separate device-related discomfort from the background pain of fracture healing.

How Electrical and Ultrasound Stimulation Actually Work on Bone

Understanding the mechanism at a basic level can help explain why these devices rarely cause pain. Electromagnetic stimulators work by generating pulsed fields that trigger calcium channels on bone cells. Calcium flows into the cells, which activates growth-promoting pathways that encourage new bone formation and mineralization.¹⁹ The process is biochemical, not mechanical. The device is not physically pushing or vibrating bone tissue. It is nudging cells to behave as though they are receiving the electrical signals that naturally accompany bone loading and repair.

Ultrasound devices work through a different path. The LIPUS signal travels through soft tissue to the bone surface, where cells detect the micro-mechanical vibration through surface receptors called integrins.²⁰ Activation of these receptors triggers downstream signaling that promotes mineralization and the formation of new cartilage and bone at the fracture site.²¹ Again, the intensity is extremely low. You are not receiving a deep tissue ultrasound massage. The signal is subtle enough that cells respond to it but your conscious nervous system mostly does not.

Neither type of device is designed to produce sensation. They operate at energy levels chosen specifically to stay below the threshold of tissue heating or nerve activation. When pain does occur, it is typically because of the biological context surrounding the device, nerve-rich healing tissue, prior injuries, metal implants, or the patient’s own expectations, rather than the device’s energy output itself.