Kinematics

Lets begin with a few highlights about joint kinematics of particular importance.

Here is an animated review of all motions.

The closed chain animations for talocrural joint start at about 3 minutes. The closed chain animations for the subtalar joint run from 5:50-7 minutes:

 

Remember, the foot is built for weight bearing and it is the base of support for the ambulatory human body. Think about the muscles and the joint kinematics in terms of their function in closed chain positions.

The closed packed position is dorsiflexion and the open packed position of the ankle joint is plantar flexion. Open packed positions have the highest risk of ligamentous injury. In a closed chain plantar flexion at the ankle, the subtalar and transverse tarsal joints are closed packed. This puts a rigid lever designed to transmit forces at the distal end of an at risk joint complex (the open packed ankle). This is why inversion ankle sprains are so common place, and the most frequent mechanism of ankle sprain. Any footwear with an elevated heel increases ligament injury risk. The greater the heel elevation, the more danger of joint injury.

Pes planus, pronated foot, flat foot all mean decreased medial longitudinal arch.

Pes cavus or supinated foot means high-arched foot.

When the foot is weight bearing, subtalar motion and tibial motion are inseparable. External rotation of the tibia results in supination of the subtalar joint, or vice versa. Internal rotation of the tibia results in pronation of the subtalar joint.

In pronation, the ligaments of the forefoot and midfoot unwind allowing the bones more movement. This is so the foot can conform to the ground and better absorb forces, this happens during foot strike. In supination, the forefoot and midfoot ligaments are all wound tight, this allows for a rigid lever to push off of. This also has a very important effect on ROM. When stretching to increase dorsiflexion ROM, have the foot in supination. This transmits the force of stretching to the talocrural joint. If the foot is allowed to fall into pronation, a lot of midfoot dorsiflexion can occur. This both gives the false appearance of true ankle dorsiflexion, and prevents the desired stretch.

Functional ROM for gait purposes is 7 degrees of dorsiflexion, 25 degrees of plantar flexion and 40-50 degrees of toe extension. Make particular note of the dorsiflexion and toe extension measurements. These factors along with at least 3/5 dorsiflexion strength are required for adequate foot/toe clearance during swing phase of gait.