To measure accurately the range of motion of the ankle joint, the subtalar joint must be in the neutral position. This serves as a reference position. It is the most stable bony position of the foot. Occurring at mid stance when the ankle is dorsiflexed and the midtarsal joint is pronated.
Method: Place patient prone (face-down) on the examining table. Feet extended over end. Flex contralateral hip. Using thumb and index finger of one hand palpate (feel) the head of the talus evenly bulges on both sides just anterior to the medial and lateral malleoli. The fully pronated position of the midtarsal joint is accomplished by locking the forefoot against the hindfoot. With the Subtalar joint in neutral, apply planter pressure to the 4th and 5th metatarsal heads Dorsiflex the ankle while fully pronating the forefoot. Measurement of degree of ankle dorsiflexion / plantarflexion by bisecting line from distal third of tibia, with line that runs from the planter surface of the heel to the plantar surface of the fifth metatarsal. Special attention given when measurement of dorsiflexion. In this case the forefoot can be inverted to maintain a neutral subtalar joint. Test with knee in both flexed and extended positions, to determine involvement of the Gastrocnemius muscle. May be tight due to Spasticity / Contacted / Congenitally short / Rapid bone growth exceed muscle growth.

Remember Foot must be in Subtalar Neutral


Open and Closed Kinetic Chain Motion

Description of how the lower extremity moves in non-weight-bearing and weight bearing phases.
Open kinetic chain motion is when the foot is non-wright bearing. The talus and leg
do not move while the calcaneus moves through three planes of motion and carries the foot with it. Calcaneal eversion, abduction and dorsiflexion. Opposite happens with supination.
Weight bearing is closed kinetic chain motion. The heel is in contact with the ground and is unable to move in the saggital / transverse planes. The head of the talus shifts and the tibia rotates along its longitudinal axis.
Closed chain pronation, the calcaneus everts and head of the talus adducts / plantarflexes, the forefoot is in contact with the ground. The knee flexes and the tibia internally rotates. Abduction  and inversion of the forefoot on the hind foot. The medial longitudinal arch flattens. These combined actions make the lower leg a shock absorber during the loading phase of weight bearing.
Closed chain supination, calcaneal inversion with abduction and dorsiflexion of the talus. The knee extends, tibia externally rotates, adduction and everxion of the forefoot.
The medial longitudinal arch elevates. These motions form a rigid lever arm for propulsion.


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Figure 17.     CLOSED CHAIN MOTION OF RIGHT FOOT

Upper drawings show the posterior view of calcaneal motion. The lower drawings show the anterior view of the mid – tarsal articulation illustrating the motion of the calcaneus and head of the talus.