The main issue to sort out with you is to achieve full extension. If not this will cause you to walk with an altered gait and may cause other pains to occur. An exercise to avhieve this increase in movement is to have your foot up so your leg is out straight and try and push you knee down.This may cause some discomfort, but this is normaly when tryign to increase range. If it is too painful to do I would suggest a visit to a physio to make sure you are not causing more damage.