Ankle ROM
The main motions which occur at the talocrural, or ankle joint are dorsiflexion and plantarflexion. There is some contention as to the normal range of dorsiflexion that should be available at the ankle, however, most of the literature states that there should be a minimum of 10 degrees available for normal gait. There are several different ways of assessing dorsiflexion range of motion. The first is to position your patient supine with their knee fully extended. Position the subtalar joint in its neutral position by palpating the talar head and then, stabilizing the leg above the ankle and push the ankle in dorsiflexion by applying pressure to the plantar forefoot. Take note of the end feel - whether bony or spongy, as well as the general range and quality of motion.
This test should then be repeated with the knee in a flexed position to eliminate the influence of the gastrocnemius muscle. It may be easier to perform this test with your subject in a prone position.
Ankle plantarflexion can be assessed with the knee flexed and extended also. Note that you would expect there to be around 50 degrees of ankle plantarflexion range of motion.