A Stiff Knee After Knee Replacement: Heat or Cold?

The knee is swollen for weeks after a replacement, and it’s stiff at the same time.

That combination is why people get confused about heat and ice: the usual rule says cold for swelling, but the thing stopping you bending the knee is stiffness. The general version of that decision: heat or ice: a physio’s decision guide.

The short version: cold for the first few weeks and after every exercise session, heat later on and before exercises, and your surgeon’s or physio’s instructions beat anything on this page.

Timing

When	What the knee is doing	Heat or cold
Weeks 0–2	Wound healing, swelling and warmth around the joint	Cold only. No heat near the wound.
Weeks 2–6	Wound closed, swelling settling, stiffness is the main problem	Cold after exercise; heat before it, once the wound is fully healed and your team agrees
Beyond 6 weeks	Building range and strength	Heat before exercise, cold after a heavy session if it swells

The wider timeline for any operation is in after surgery: when is heat allowed?, and on managing the swelling itself, hot or cold compress for swelling.

A replaced knee often feels warmer than the other one for months. That’s normal and it isn’t a reason to hold off forever, but it does mean you can’t use warmth alone to judge readiness.

Rules that matter more here than usual

• Nothing on the scar until it’s fully healed. No scabs, no weeping, no gaps. Ask at your follow-up rather than deciding by eye. Once it is closed and tight, see tight scar tissue and scar massage.
• The skin around a new scar has altered sensation. Numb patches are common, and numb skin burns without warning you. Lowest setting, cover on, and check the skin afterwards every time. The same risk, from a different cause: heating pads and diabetes. Full list: who should not use a heating pad.
• The implant doesn’t care about a heat pad. Surface heat doesn’t reach or affect the metal. This worries people unnecessarily, and the full explanation is in heat pads with metal implants, plates and a pacemaker.
• Don’t strap a wrap tightly around a swollen knee. Pressure plus heat on compromised skin is how burns happen. See heated wraps vs a flat pad.

Using heat to get the bend back

Range of motion is the thing you’re racing for in the first three months. Stiff tissue moves better warm, so the sequence is:

1. 10 to 15 minutes of heat over the thigh and around the knee, cover on, lowest setting.
2. Straight into the exercises your physio gave you, while it’s warm. See “my physio said use heat” — but how, exactly?
3. Cold afterwards if the knee puffs up, 10 to 15 minutes with the leg elevated.

The heat is there to make the exercises possible. On its own it does nothing for range, and twenty comfortable minutes without the exercises afterwards is a wasted session.

The swelling that doesn’t mean trouble

Swelling that builds through the day and settles overnight is ordinary for months after surgery. Elevation, a walk, and cold at the end of the day handle it.

Call your surgeon’s team if…

• The knee becomes hot, very red, or increasingly painful rather than gradually better
• The wound weeps, opens, or smells
• You have a fever or feel unwell
• Your calf is swollen, warm and tender, or you’re breathless or have chest pain. Blood clots are a real risk after joint surgery and need same-day attention. An ordinary night cramp behaves differently: calf cramps at night.
• Your bend is going backwards rather than forwards

Never put heat on a swollen, tender calf while a clot is being ruled out.

More: after surgery: when is heat allowed?, knee arthritis and morning stiffness for the joint you had replaced, and heat for knee and joint pain generally. If you’re older and living alone with this, the extra precautions here apply.

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.