Ask the doctor: How can I stop my knee from suddenly locking up?

A few weeks ago my knee completely locked, leaving me in excruciating agony and unable to straighten or stand on it for quite a few hours.

http://www.dailymail.co.uk/health/article-2478488/Ask-doctor-How-I-stop-knee-suddenly-locking-up.html?ITO=bookmark-chromeext&ns_mchannel=rss&ns_campaign=bookmark-chromeext