Assisted flexion involves assisting the bad leg to regain a few more degrees of flexion than it can manage on its own.

This video shows how you might achieve this by using your good leg as the 'assistant'.



In case you cannot see the video, here is a still sequence -

assisted flexion In this exercise you need to sit on the edge of a firm bed or chair with two legs out in front of you, and the feet touching the floor. The bad leg is encouraged to bend of its own volition.
assisted flexion And then the good leg is hooked around the front near the ankle and a little bit of extra flexion is gained with its help.
assisted flexion Then slide the two feet away again, as far as they will go, and ...
assisted flexion ...repeat the flexion, again with the good leg to assist in gaining maximum flexion. This can be done five times, and the whole sequence can be repeated five times a day.