Short answer: a plate, screw, rod or joint replacement under the skin is almost never a reason to avoid an electric heat pad. The warning people half-remember comes from a different machine entirely.
A pacemaker or implanted defibrillator is the one worth checking, and the check is simple.
Where the warning came from
Physiotherapy departments have long carried a rule about metal implants, and it’s a real rule. It applies to shortwave diathermy and some ultrasound therapy: machines that drive energy deep into tissue, which metal can concentrate.
An electric heat pad does nothing of the sort. It warms the skin, and the warmth spreads a centimetre or two below it. See what heat actually does under your skin. Hardware sits deeper than that, wrapped in tissue with a blood supply carrying heat away.
So the plate in your wrist isn’t going to heat up. People worry about this a great deal and it isn’t the thing to worry about.
What to actually watch: the skin over the metal
The risk moved, it didn’t disappear. Skin over a surgical site is often not normal skin.
- Numb patches around a scar are common, and numb skin burns without warning you. Check sensation with something warm from the tap before a pad goes anywhere near it.
- Scar tissue is thinner and tolerates less than the skin beside it.
- Hardware close to the surface, such as a plate on the shin, collarbone or the back of the hand, leaves very little padding between pad and bone. Shorter sessions there.
- Nothing until the wound is fully healed. See after surgery: when is heat allowed?
Same rules as everywhere else, applied more carefully: lowest setting, cover on, 15 minutes, look at the skin afterwards. The full exclusion list is in who should not use a heating pad.
Metal that comes through the skin is different
External fixators, pins and K-wires that pass through the skin are a firm no while they’re in place.
Exposed metal conducts heat straight into tissue, the pin sites are broken skin, and infection risk is already the thing everyone is managing. Ask the surgical team what they want done for stiffness instead.
Rings, bracelets and piercings sitting under a pad heat up the same way. Take them off first, particularly on a stiff hand or wrist: hand arthritis, a stiff wrist after a cast.
Pacemakers and defibrillators
Two separate questions here, and only one of them is about electronics.
Don’t put a pad over the device itself. It sits in a pocket under the skin below the collarbone, with very little tissue over it. That’s a skin question, not an interference one, and it’s the straightforward rule.
Ask your cardiologist or device clinic about anything else. They know your device, and it takes one message. Device makers publish guidance on household electrical items, and the people who manage yours can tell you what it says without you having to interpret it.
Worth knowing separately: chest pain is not something to treat with a heat pad while you work out what it is. See rib and chest wall strain, which starts with the symptoms that mean calling 995.
Joint replacements and spinal hardware
Once everything has healed, heat over a replaced knee, hip or shoulder, or over rods and screws in the spine, is treated like heat anywhere else. The implant is inert as far as a warm pad is concerned.
In the months after the operation the timing is what matters, not the metal: a stiff knee after a knee replacement and after surgery: when is heat allowed?
One thing heat won’t do is loosen scar tissue around hardware or improve a stiff joint on its own. It makes the exercises more comfortable, and the exercises are what change the range: “my physio said use heat” — but how, exactly?
Ask before using heat if…
- You have a pacemaker, defibrillator, spinal cord stimulator or any other implanted electronic device
- Your wound isn’t fully closed, or there’s any discharge
- You have numbness anywhere near where you want the pad
- Hardware is prominent enough to feel through the skin
See a doctor if…
- The area around an implant becomes red, hot, swollen or painful, or you develop a fever. Infection around hardware needs treating quickly.
- A previously settled implant starts hurting again
- You see skin changes over hardware: darkening, thinning, or a patch that doesn’t settle
- A joint replacement becomes unstable, or gives way
The heat pad we use
We’ve supplied the Bremed BD7800 since 2010. It holds a steady temperature, covers a whole lower back and has a machine-washable cotton cover. Physiotherapy clinics in Singapore use it with their patients.
Clinically reviewed by: Nigel Chua (Hand Occupational Therapist) & Louise Yow (Physiotherapist). This article is general information, not a diagnosis. electricheatpad.com sells electric heat pads.
