Hi Bec, thanks for the informative post. As you can't see a Physio at this stage I would suggest that the best answer here is the stability. If you feel that the knee is now much more unstable than it was prior to the weekend then you may have strained the graft or caused it to fail. The crack would not be from the Wikipedia reference-linkmeniscus but more the joint line or the patellofemoral joint. A good meniscal tear will also swell over about 24hrs so that something to look for. There are manual tests for instability more than laxity which a PT can perform but as you say you feel that the knee was always lax post-operatively and so this may have been positive prior to the recent slip.

See how you go after a few days on the stability/instability front. You can definitely see the effect even a simple knee brace has on the proprioception about the joint. I would continue to only play with that. Worse case (or some might suggest even better) you could tape with some functional taping (kinesiotaping concepts) if the brace was left at home.