ACL or PCL ?
Instability is a bit concerning.
Meniscus you would have pain.
I’d say if your knee gives out with instability again at some point…….. get an ortho to do their little shifting test and possibly confirm with MRI.

I’ve had the happy triad (x3).
So yes, tore my ACL, MCL, and meniscus twice in one knee and once in the other.

Let’s just say I played a LOT of sports on some fairly shitty knees.

Good luck!

I would definitely make a trip to your local ortho and get evaluated. It may be nothing or it could be a torn meniscus or damaged ACL. Had a friend squat down on his skis and heard a similar popping noise. It seemed like nothing at the time but he ended up with a torn ACL and a year’s worth of rehab to get back to high level skiing again.

If no pain and only a small amount of stiffness and no other symptoms but feeling a 'little unstable' it will more than likely settle itself. Does 'a little unstable' mean you don't fully trust putting all your weight on it, rather than it actually giving way?

Here is a very rough but simple guide on acute knee injuries and the likelihood based on your description.
Most of the time but not all of the time Ligaments when they tear bleed, so results in a big swollen knee (full of blood) within an hour or two and takes 2-4 weeks for the blood to absorb fully. The mechanism is usually a bad twist and the knee moving in a way it shouldn't. Lots of pain, stiffness and hobbling around. So unlikely!

Patellar tendon rupture will also bleed a lot into the joint but easy to assess. Usually you drop to the ground when it happens. If you can't hold the unsupported knee fairly straight and lower leg just drops then likely tendon rupture, or patella fracture. Your leg would also buckle when trying to walk. Unlikely!

Meniscal cartilage feels very little so when you tear it you may or may not notice. More common when the muscles around the knee are very tight, such as at the end of a day skiing or squatting/kneeling and can be a snapping sensation when it happens. Usually doesn't swell much as very little blood supply. Any swelling that does occur is usually felt the next day. The torn bit will only be sore if it moves and gets caught in the wrong place. Can feel like ' a pebble in the shoe' that comes and goes when the torn piece in the wrong spot as a result of twisting, catching your foot off a table leg, sitting with the knee bent in a long car journey. Definitely Possible!
Sudden locking, catching and giving way would warrant having something done about it, but the odd pinch would be managed through rehab.

Articular cartilage. If a piece breaks off it gives similar symptoms of sudden locking, catching or giving way which can unlock with a bit of a wiggle. If it breaks off that easily from just squatting down then it had lost it's blood supply and was already about to come off. If it rolls around the knee a lot it can causes damage over the medium to longer term. Possible but much less common than meniscal tear!

The patella can sometimes catch against the groove it runs in (trochlea), and the capsule around the joint can get pinched at the edges of the bones, like accidentally biting the inside of your cheek. Very possible!

The most likely 'snapping' culprits are IT Band suddenly flicking over the outside of the knee, kneecap subluxing and relocating also on the outside of the knee, or meniscus which can be inner or outer side, front or back depending on which meniscus and location of the tear.

Could also be a hamstring or calf muscle/tendon rupture but you'd have a very sore calf with noticeable bruising 3-5 days later down the back of the leg.
That's about it really.

Gradually do some quads and hamstring stretches, get on the bike and loosen things out. If you get a catch again then it's worthwhile having it looked at.

Joints click clunk and crack and most of the time means very little.

Hope this makes sense and helps. If I'm wrong I accept absolutely no responsibility :-) Good luck.

When I had that noise it was my meniscus.

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Went to the doctor and he said maybe an IT band snapping back into place. No swelling or bleeding, X-ray was normal and showed not a lot of space between the knee cap and other bones. Still feels a little funny a week out with something occasionally feeling out of place. Got the old list of exercises to strengthen everything around the knee.

Thanks for advice.

Every time I see this thread title I cross my legs, squirm and feel queasy inside.

Just bumping it up so others can share the same feeling.