Phase 2 Heel Pop: The Target to Achieve by 6 Weeks
In Phase 2, the single most important range-of-motion goal is getting your knee fully straight — matching your other leg. The trouble is, it's surprisingly hard to tell at home whether you're truly there or just nearly there. A few missing degrees don't look like much, but they're enough to change the way you walk.
That's why I like the heel pop test. It takes ten seconds, needs no equipment, and gives you an honest answer every day between physiotherapy sessions. Watch this video to understand more:
How to Do the Heel Pop
Most of us have a few degrees of natural hyperextension — the knee can straighten slightly past flat. When you tighten your thigh hard, that last bit of straightening pushes the back of the knee down and lifts the heel up. That little lift is the "pop".
- Sit on a firm surface — a bed, the floor, or a mat — with both legs straight out in front of you. Lean back on your hands if that's more comfortable.
- Start with your good leg. Tighten your thigh muscle as hard as you can, pushing the back of your knee down into the surface.
- Watch your heel. It should lift a little off the surface. That's your target.
- Now do the same with your operated leg, and compare.
If both heels lift by a similar amount, you have symmetrical extension. If your good heel pops and your operated heel stays down, you're still missing some extension — and that's what we work on next.
The goal is always to match your other knee. Not everyone has a big pop, and that's fine. Don't force the operated knee further than your good side goes.
Why It Matters Now
Phase 2 (2–6 weeks) is your window to regain full range of motion, and extension comes first. A knee that can't fully straighten can't lock out when you stand. You end up walking with a bent knee, often on your toes, and the muscles and capsule at the back of the knee slowly tighten to match.
The longer a missing few degrees are left alone, the harder they are to win back. Phase 3 is about walking normally without crutches or a brace — and you can't walk normally on a knee that won't straighten. Getting your heel to pop in Phase 2 sets up everything that follows.
Can't Pop Your Heel Yet? Find Your Limiter
When the heel won't lift, it's usually one of three things holding it back. Each needs a slightly different fix, and many patients have a bit of all three.
1. Your quads aren't firing fully. After surgery, swelling and pain switch the quadriceps off reflexively. You may be trying hard, but the muscle simply isn't contracting all the way. How you'll know: the thigh feels soft when you squeeze, or your kneecap barely moves. What helps: keep up your NMES twice daily and practise quad sets — tighten, hold for 5–10 seconds, relax, repeat. There's a bonus here too. When your quads contract, your hamstrings reflexively relax — this is reciprocal inhibition. So every good quad squeeze also loosens the muscles holding your knee bent.
2. The back of your knee is tight. If you've spent weeks walking or sitting with the knee bent, the hamstrings, calves and the posterior capsule (the lining at the back of the joint) shorten to match. How you'll know: you feel a strong pull behind the knee as you try to straighten. What helps: heel props — rest your heel on a rolled towel or low stool with nothing under the knee, and let gravity gently straighten it for several minutes. Add gentle hamstring and calf stretches, and do the heel slides your physiotherapist has taught you.
3. There's still swelling in the knee. A swollen knee is most comfortable slightly bent, and fluid physically limits how far it can straighten. How you'll know: the knee looks puffy, or the dimples around your kneecap have disappeared. What helps: ice, compression, and elevation — with your leg raised straight, never with a pillow under the knee.
Little and often wins. Check your heel pop a few times a day rather than one long session, and you'll see it come back gradually.
When to Let Us Know
Most extension deficits improve steadily with consistent work. Please tell your physiotherapist or myself if:
- your heel still doesn't pop by around 6 weeks, despite doing the work;
- you had a heel pop and then lose it again;
- the knee feels blocked — a firm stop rather than a stretch — when you try to straighten it.
These can be signs of something in the joint physically stopping the knee from straightening, and they're far easier to sort out when caught early.
A heel that lifts a centimetre off the bed may not feel like much of a victory. But it's one of the clearest signs that your knee is ready for what comes next.
If you'd like to see where you are in your recovery, you can start here: 
This article was clinically narrated by Dr. Mok Ying Ren, with AI assistance limited to language editing and formatting.