My Husband Has Severe Pain On The Outside Side Of

My husband has severe pain on the outside side of his left knee. He is able to walk but finds driving very painful because of having yo use the clutch. Going upstairs is very difficult and extremely painful. He has problems sleeping due to the pain and screams with pain if he moves his knee into certain positions although he is able to straighten and bend his knee. This is getting progressively worse by the day.