Three checks, one for each link from the foot to the hip. Do them in this order and write down what you find.
The checks below take ten minutes. If you'd rather have the whole routine on video, QUAD CORE is the four moves I start with, from the big toe up to the hip. $27 once.
Foot. The big toe

Toes against a wall, heel flat on the floor. Drive the knee forward over the toes without letting the heel lift. Then press the big toe into the wall.
If the toe will not bend back, the foot rolls in to get around it. The shin turns in with it. The knee takes a twist it was never built for.
Knee. Sit back on your heels

Kneel and sit all the way back on your heels.
If your hips do not reach, it is rarely the knee itself. The tissue behind the joint is not making room, so the joint runs out of space first.
Hip. Turn the knee in

Sit on the floor, knees bent, feet apart. Let one knee drop inward toward the floor while the foot stays where it is. Then the other side.
The side that will not go is the one your knee has been covering for.
Most people find one link that is clearly worse than the rest. That is your link.
Why it started there
I had three knee surgeries before anyone said the word rotation. Every one of them aimed at the place that hurt.
The arch collapses. The shin rotates in. The knee follows. The hip loses control. The load goes where it was never meant to go.
The knee sits between two joints that decide for it. When the foot or the hip stops doing its job, the knee does not get a vote. It absorbs the twist. Thousands of times a day.
That is why the scan can come back clean and the knee still hurts. The tissue is fine. The path of the force is wrong.
For me, pain usually pointed to a part of the chain that wasn't moving well. That was my experience. Pain can also mean something that needs a clinician, so don't ignore it.
Four minutes for your link
Pick the link that failed. Do only that one.
Ankle or big toe. Toes against a wall, heel flat. Drive the knee forward over the toes without letting the heel lift. Press the big toe into the wall and hold two seconds. Twenty slow reps each foot. Every day. A joint that stiff needs frequency, not intensity.
Knee. Kneel. Put a soft ball in the crease behind the knee. Sit back onto it, only as far as it stays comfortable. Five slow breaths. Move the ball one thumb width toward the outside of the knee and take five more. Two minutes each side.
Hip. Sit on the floor, knees bent, feet apart, band around the feet. Let one knee drop inward while the foot stays where it is. Go to the edge of the range, hold two breaths, come back. Ten each side, two rounds.
Then repeat the check. What changed is your answer.
Open the range first. Only then strengthen it.
How I stay capable
Three knee surgeries later. My week, my food, my checks. Five checks that build on the three here, with my training week and the mobility and release layer.
Keep going
The checks are the start. QUAD CORE is the next step. The four I start with, from the big toe up to the hip, on video, with a one page PDF. $27 once.
Get the four for your link, $27
You're welcome
Educational content, not medical advice. These are movement screens and exercises, not a diagnosis or treatment. They may help. If a check hurts, stop. If something gets worse, see a clinician where you live.