Knee Collapsing During Squats

I was playing basketball about 3 weeks ago when I landed on my left knee a little strangly, sort of on the outside of my foot. As a result, it felt like the landing torqued my knee towards the outside. Another perspective would be my body/thigh turning outward (to my left) while my lower leg remained stationary.

There was a short twinge of pain inside of the joint, but it did not last. There was no snapping or popping feeling or sound at the time of the injury. The joint did not dislocate or twist to the extent that anything felt like it “slipped”. I have been able to walk (even immediately after the injury) without any pain whatsover. There has also been no swelling, fluid, clicking, bruising, grinding, or anything else that I’ve experienced with previous knee injuries (to my right knee).

However, when trying to perform barbell back squats, I have noticed that at certain times, which remain relatively unpredictable, knee suddenly flares up (right at about parallel) and collapses, meaning that I suddenly have 0 power from the joint. This obviously causes me to fail the lift.

Prior to the “injury”, I was squating 315 for 6+ reps without any problems whatsoever. Now, the joint will collapse under even 135. It’s like I can’t even work my legs other than deadlifts, which don’t seem to cause a problem.

I’m confused as to what this may be. From what I’ve read, torn ACL’s and MCL’s would cause a lot more pain, swelling, fluid, etc. This only happens when I’m squatting. The worrying part is the joint “giving out” while I’m under the barbell. Otherwise, it hasn’t affected me at all. Does this sound like anything immediately familiar or should I not worry and just hope that it heals up?

The mehcnism of injury sounds more like it might be PCL related(and or LCL), i am gonna dig around a bit , just logically thinking though during the pivot shift test (for acl tears) the knee at a certain angle slides anteriorly. It sounds like this might be happening to you which would indicate laxity of the Anterior Cruciate Ligament. So my guess is that you may have some sort of damage to one of your cruciate ligaments which allows for too much laxity in your knee joint. At this point it’s just guessing but if you go see a doctor/physio they can perform the actual tests on you (lachmans, pivot shift anterior glide) and make a much better diagnosis

From a traditional biomechanical standpoint, there’s just no way of telling what is wrong without getting an exam.

It really makes no sense though if that your knee keeps giving out to keep squatting on it, talk about banging your head against a wall. If you insist on training legs, why not opt for a trap bar deadlift or rack pull until you can get an appointment?