What Causes A Tight And Pulling Sensation Behind The Knees?

thank you. I had sustained a fall at work on Dec. 16th, 2016 resulting in a knee contusion and a sprained shoulder. I am presently receiving P.T. for my shoulder. My knee has been progressing nicely ; not requiring any treatment up to this point. I started with an immomobilzer, moved to a cane, and have walked unassisted for about 2 1/2 weeks now. Just this week I noticed a tightness or pulling behind my knee . I had worn a pair of flats one day and attributed to that, immediately returning to my sneakers. It hasn t gotten worse but it does not feel as good as it had been. I called the doctor who originally examined me and sadly have not gotten an response from him as yet. The good news for me is I have led a pain-free life for 63 years and have no reference point. I do not want to panic but at the same time do not want to ignore something which could result in further damage. What do you suggest?