Hi again
Here's an update for those interested.
I saw my surgeon last night and will have surgery on Friday to remove my plica. The OS said it was pretty rare to have symptoms as extreme as mine but everything that I've read matches how I've felt post op - locked knee, collapsing knee, pain at the front of my knee and aches at night and whenever I stand up.
So, the plica was a red herring. I needed a partial meniscectomy but it was the plica all along giving me the pseudo-locked knee.
Hopefully, after Friday I'm on the road to recovery and will be walking in no time. I'll let you know...