I Stood Erect For Approx. 2 Hrs. Afterward Had Pain

I stood erect for approx. 2 Hrs. Afterward had pain in outer thigh on left leg and pain on outer side of shin bone same leg. Knee joint would collapse when leg bent ( like walking up stairs , I had to use my right foot only to step up stairs )My pain subsided after a couple of days. The knee joint is still weak and when walking I have to keep the left leg locked or the knee will give away thus depositing me on the floor , What is your opinion ?