Are there any long-term studies on the safety of electrical stimulation for patients with metal implants?
All medical devices have indications and contraindications, and the manufacturer always states these clearly. However, not all electrical stimulation devices on the market are classified as medical devices, so the manufacturer may not clearly describe when they might be unsafe to use.
A very common situation we face when dealing with clients is the presence of metal implants such as joint replacements, fracture fixation plates and spinal instrumentation near where we wish to apply electrodes. The concern has been that the energy generated by electrical stimulation over metal implants would cause local, damaging heating within the tissues. We consider this below.
We must follow the manufacturer's recommendations. However, you might wonder about the real risks. Do the benefits of using electrical stimulation outweigh the risks? This article explores this topic.
Indications for safety?
Contraindications might be stated as "absolute" or "relative." An absolute contraindication says the risks in such a situation outweigh any potential benefit. In contrast, a relative contraindication acknowledges that some risks exist, but clinical opinion may consider that the benefits may outweigh the risks for a particular individual.
We all realise this situation is not so unusual; consider every medication you have ever taken. When you read the instructions with the tablets, you will usually see a long list of possible "side" effects you should be aware of. Electrical stimulation as we apply it is generally a safe approach, but it is important to note that it is not one "thing"; it comes in many different forms. We need to know something about the specific energy form applied to the body to see if it will be safe.
Absolute contraindications often cited by medical device manufacturers are as follows
Active Electronic Implants
• Cardiac pacemakers
• Implanted cardioverter defibrillators (ICDs)
• Neurostimulators
• Pain pumps
Medical Conditions
• Active phlebitis or thrombophlebitis
• Active cancers/malignant tumors
• Pregnancy
• Undiagnosed pain conditions
Skin Conditions
• Open wounds or lesions in the treatment area
• Active skin infections
Safe use with metal implants?
The safety of electrical stimulation for patients with metal implants has been studied in controlled experiments, but long-term clinical data remain limited.
Passive metal implants (pins, plates, screws, joint replacements) are not generally contraindicated for certain forms of electrical stimulation when using:
• TENS (transcutaneous electrical nerve stimulation)
• Interferential current
• Neuromuscular electrical stimulation (NMES)
The presence of metal implants will likely distort the current pathway but won’t cause harmful heating effects with these modalities. However, high-frequency heating modalities like shortwave and microwave therapy should be avoided over metal implants.
Key findings from existing research include:
Short-Term Safety Evidence
1. In vitro experiments with titanium, stainless steel, and copper implants showed:
- No significant temperature rise (<3°C) during therapeutic electrical stimulation (TENS, high-volt stimulation, galvanic current)[3][4][12].
- No corrosion or surface roughness changes under accelerated iontophoresis conditions (70 V for 30 minutes)[1].
2. Passive metal implants (e.g., orthopaedic plates, screws):
- Do not contraindicate TENS, NMES, or interferential current when applied at therapeutic intensities[6][13].
- Titanium implants showed no heating even under extreme galvanic current conditions (40 minutes at 10x typical current density)[3][12].
Gaps in Long-Term Data
Repeated exposure: Most studies tested single or short-term sessions. No trials have evaluated cumulative effects over months/years[1][12].
Real-world variability: Existing work uses simplified models; clinical conditions (e.g., tissue conductivity, implant positioning) may alter outcomes[1][3].
Human trials: Preliminary reports focus on in vitro or animal models. Long-term human studies are absent[12][16].
Clinical Recommendations
Avoid high-frequency heating modalities (shortwave, microwave) near implants[13].
Use biphasic waveforms to minimize charge accumulation and improve safety[1][3].
Biphasic rectangular pulses are considered safer for clinical use because they: • Are charge-balanced, avoid toxic charge accumulation, reduce risk of skin reaction and provide better patient comfort. We use biphasic waveforms with the RehaMove, Stim2Go and the RISE stimulatorMonitor patients with sensory deficits or implants in conductive pathways (e.g., near electrodes)[2][14].
Implant Location and Risk Considerations. The safety of electrical stimulation near metal implants depends critically on implant location, with three key factors determining risk.
1. Proximity to Sensitive Structures such as the Brain, Chest and Neck
Brain/Skull: Transcranial stimulation near DBS leads or skull plates increases peak electric fields by 10-100x, potentially causing unintended neuromodulation.
Chest/Heart: Stimulation near pacemakers or ICDs risks electromagnetic interference, regardless of implant type.
Carotid Sinus/Neck: Current distortion near vascular or neural structures may trigger autonomic dysregulation
2. Implant Geometry & Tissue Interface Effects
Surface Area: Elongated implants (e.g., spinal rods) create stronger field distortions than compact ones (e.g., screws).
Depth: Superficial implants (e.g., subcutaneous plates) alter current pathways more than deep-bone implants.
Tissue Conductivity: Implants in fatty/avascular regions cause greater field distortions than those in muscle
3. Stimulation Modality
Electrical stimulation is not "one thing". The form of electrical stimulation is linked to the effects produced.
Conclusion
While short-term evidence supports the cautious use of non-thermal electrical stimulation over passive metal implants, no conclusive long-term safety data exist. Further research is needed to evaluate chronic exposure risks[1][12].
We always advise following the manufacturer’s recommendations when these are associated with a medical device.
Sources
[1] Alice V S Sinclair, Florence L R Garty, James R Smith, Alexa R Shipman, Is it safe for patients with metal implants to have iontophoresis treatment?, Clinical and Experimental Dermatology, Volume 48, Issue 7, July 2023, Pages 759–764, https://doi.org/10.1093/ced/llad074
[2] What Are the Contraindications Associated With Electrical Stimulation Therapy. https://www.occupationaltherapy.com/ask-the-experts/what-contraindications-associated-with-electrical-5702
[3] Thaler E, Toledo F, Korte H. Can Direct Current Electrotherapy Be Used for Patients With Orthopedic Implants? Geriatr Orthop Surg Rehabil. 2017 Mar;8(1):44-48. doi: 10.1177/2151458516681141. Epub 2017 Feb 15. PMID: 28255511; PMCID: PMC5315240. https://pmc.ncbi.nlm.nih.gov/articles/PMC5315240/
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[6] Is it safe to use TENS if I have a metal implant? - TensCare Ltd https://tenscare.co.uk/blogs/education-section/is-it-safe-to-use-tens-if-i-have-a-metal-implant
[7] Broderick BJ, Kennedy C, Breen PP, Kearns SR, Olaighin G. The influence of orthopaedic implants on patient tolerance of neuromuscular electrical stimulation (NMES). Annu Int Conf IEEE Eng Med Biol Soc. 2010;2010:5823-6. doi: 10.1109/IEMBS.2010.5627491. PMID: 21096915.
https://pubmed.ncbi.nlm.nih.gov/21096915/
[8] X. Cui, L. Wu, C. Zhang, Z. Li, Implantable Self-Powered Systems for Electrical Stimulation Medical Devices. Adv. Sci. 2024, 2412044. https://doi.org/10.1002/advs.202412044
[9] Is Electrical Stimulation Safe? - Anatomical Concepts https://www.anatomicalconcepts.com/articles/is-electrical-stimulation-safe
[10] TENS (transcutaneous electrical nerve stimulation) - NHS https://www.nhs.uk/conditions/transcutaneous-electrical-nerve-stimulation-tens/
[11] TENS unit: Benefits, side effects, and research - MedicalNewsToday https://www.medicalnewstoday.com/articles/323632
[12] (PDF) Can Direct Current Electrotherapy Be Used for Patients With ... https://www.researchgate.net/publication/315449256_Can_Direct_Current_Electrotherapy_Be_Used_for_Patients_With_Orthopedic_Implants
[13] FAQs | Electrotherapy On Th https://www.electrotherapy.org/faqs
[14] Contraindications and Precautions when using Electrical Stimulation https://www.pelvicfloorexercise.com.au/resources/post/contraindications-and-precautions-when-using-electrical-stimulation-nmes-and-tens
[15] [PDF] E-Stim Indications and Contraindications https://www.swrwoundcareprogram.ca/Uploads/ContentDocuments/HCPR%20-%20ESTIM%20Indications.pdf
[16] [PDF] Safety and best practice in neuromuscular electrical stimulation for ... https://thepogp.co.uk/_userfiles/pages/files/journals/124/gps89122ms.pdf