Bone stimulators are devices that deliver ultrasound or electrical signals to injured bones. They stimulate bone cells and mimic natural stress. The FDA approves them for certain bone conditions. Patients use them under doctor’s guidance. In orthopedics, clinical uses of bone stimulator devices include accelerating fracture healing and supporting spinal fusion.
How Bone Stimulator Devices Work
Bone stimulators produce signals that affect bone cells. Ultrasound units emit low-intensity pulses that create micro-stress in bone, delivering tiny pressure waves that mimic natural loading. Electrical stimulators use weak currents or magnetic fields that osteocytes detect, enhancing bone formation and calcification. These signals upregulate growth factors (e.g., BMPs) in bone and speed repair.
Types of Bone Stimulator Devices
Bone stimulators work in different ways using ultrasound or electrical fields. Each method has its own devices. Ultrasound units send pulsed waves through the skin, while electrical units use coils or electrodes to send current. Both aim to jumpstart bone growth.
Ultrasound (LIPUS)
Low-intensity pulsed ultrasound devices (LIPUS) apply sound waves to the fracture through the skin. For example, Exogen is a handheld LIPUS unit worn on the skin. The FDA cleared Exogen in 1994 for tibial and wrist fractures after trials showed faster healing.
Pulsed Electromagnetic Field (PEMF)
PEMF devices apply magnetic pulses via an external coil placed over the bone or fusion site. Examples include Orthofix SpinalStim and CervicalStim. In one trial, a PEMF device raised cervical fusion success by 22% compared to controls. These stimulators often require daily use for many hours to be effective.
Capacitive Coupling
Capacitive coupling uses electrodes on the skin on each side of the fracture. The electrodes connect to a portable generator, letting patients stay mobile during treatment. One example is the Zimmer OrthoPak capacitive stimulator (FDA-cleared in 1986). Patients usually wear electrodes in their casts.
Direct Current Implants
Direct-current (DC) devices were the first stimulators approved (1979). Surgeons implant a battery-powered electrode at the fracture site. It provides continuous current but requires two surgeries (implantation and removal). DC implants are less common today, replaced mostly by noninvasive systems.
Combined Magnetic Field (CMF)
Combined magnetic field stimulators (e.g. OrthoLogic OL1000) use both static and oscillating magnetic fields. The OrthoLogic 1000 was FDA-cleared in 1994. It only needs short daily use (around 30 minutes) instead of hours.
Semi-Invasive
Some early devices were semi-invasive, using percutaneous leads through the skin. These delivered current directly but are now mostly obsolete.
Conditions Treated with Bone Stimulator Devices
In orthopedics, the clinical uses of bone stimulator devices include healing fractures, improving spinal fusions, and treating certain bone defects. They are especially used for long-bone fractures (tibia, femur) that are slow to heal or have failed to unite. Doctors also treat delayed unions and congenital pseudarthrosis with stimulators.
Fractures and Nonunions
One main clinical use of bone stimulator devices is enhancing the healing of nonunion fractures (where bones fail to heal). In one trial, daily LIPUS reduced tibial shaft healing time from 154 to 96 days. Stimulators allow some fractures to heal without surgery. They are used when X-rays show little progress after months.
Spine Fusion
Surgeons use stimulators after spinal fusion surgery to promote bone union. For example, a PEMF device improved cervical fusion success by 22% in one study. In fact, the FDA approved a PEMF stimulator (CervicalStim) specifically as an adjunct in high-risk cervical fusions. Studies also suggest electrical stimulators can aid lumbar spine fusion healing.
Foot and Ankle
Foot and ankle surgeons may use stimulators in tough cases. For example, a bone stimulator for foot may be prescribed for a complex diabetic foot fracture or Charcot osteoarthropathy (a neuropathic joint). Stimulators may enhance bone formation in these neuropathic feet by boosting osteoblast activity. Electrical stimulation has also been tried in ankle or hindfoot fusion cases to promote healing.
Other Indications
Some clinicians use stimulators in challenging cases beyond fractures. For example, doctors have applied stimulators in hip avascular necrosis (osteonecrosis) to support bone health. They may also be considered for stress fractures or difficult revision fusions, acting as an adjunct when standard methods have failed.
Use in Children
Stimulator use in children is limited. The effects on growing bones (growth plates) are unknown, so doctors use stimulators with caution in paediatric patients. No major studies exist on long-term effects in children, so use is generally restricted.
Benefits of Bone Stimulator Devices
- They accelerate healing and shorten recovery time in many cases.
- Healing succeeds in about 80–90% of properly selected patients.
- They often eliminate the need for bone graft surgery, avoiding additional operations.
- They work locally at the fracture, avoiding systemic drug side effects.
- Typical LIPUS sessions are short (∼20 minutes daily) and can be done at home.
- Portable stimulators allow patients to remain active and do light activity during treatment.
Risks and Limitations of Bone Stimulator Devices
- No serious systemic side effects have been reported.
- They require daily use for several weeks to work. Patient adherence is essential.
- They do not correct mechanical problems like malalignment or major bone loss; proper fixation is still needed.
- They are not indicated for very large fracture gaps or for flat bones (pelvis, skull).
- Implanted stimulators need a minor surgery to insert and later remove the device.
- Cost and insurance coverage can limit access; not all insurers pay for them without strict criteria.
Insurance Coverage and Guidelines
Most insurers (including Medicare) consider bone stimulators covered when strict criteria are met (for example, a documented nonunion).
Cost and Guidelines
One UK report noted that treating a nonunion can cost ~£7,000–79,000 per patient, far more than a stimulator (about £1,425). This suggests stimulators could save costs in suitable cases. However, NICE guidelines caution that evidence is of low quality and recommend using stimulators only under formal audit or research conditions.
FDA Approvals and Regulation
Class III Device: Bone stimulators are Class III (high-risk) medical devices, requiring full FDA Premarket Approval (PMA) with clinical trials.
- 1979: FDA first approved pulsed electromagnetic field (PEMF) stimulators for nonunions and congenital pseudarthrosis.
- 1986: FDA cleared the Zimmer OrthoPak (capacitive coupling) and Orthofix SpinalStim (PEMF) systems.
- 1994: The FDA approved the Exogen LIPUS ultrasound device for fresh tibial shaft and wrist fractures.
- 2000: FDA expanded Exogen approval to treat established nonunions.
- 2022: OrthoFix’s AccelStim ultrasound device received FDA approval for fracture healing.
- 2024: XStim (a wearable PEMF patch for spine fusion) gained FDA PMA approval.
Emerging Trends and Developments
Looking ahead, new stimulators and research trends are emerging. Wearable devices, advanced ultrasound, and market growth are key trends.
Wearable and Connected Stimulators
New devices are wireless and connect to smartphones for tracking compliance. For example, XStim is a wearable patch that links to an app and was FDA-cleared in 2024. Such systems let doctors monitor use remotely.
Ultrasound Technology Advances
Ultrasound stimulators remain an active area. Bioventus (maker of Exogen) acquired Misonix in 2021 to advance ultrasound research. Future ultrasound units may become more efficient or user-friendly and may integrate sensors.
Market and Research Trends
Market analysts project steady growth in global stimulator use. This reflects the rising demand for noninvasive orthopedic treatments as populations age. Researchers are also exploring combination therapies (e.g., ultrasound plus biomaterials) to further boost bone repair.
Conclusion
In summary, we reviewed the clinical uses of bone stimulator devices in healing fractures, spine fusions, and other bone conditions. These devices stimulate bone cells and have FDA clearance for selected uses. Used properly, they can avoid additional surgeries and reduce healthcare costs. Emerging technology is expanding its applications and making devices easier to use, which may broaden the role of bone stimulators in orthopedics.