The Effect of Tibial Varum on the Gait Cycle
The anterior tibialis tendon in (A) eccentrically contracts to decelerate the forefoot during the contact phase of gait.
However, in (B) the anterior tibialis is under excess tractional forces due to excess compensatory pronation, which is required to gain ground contact. This mechanism commonly results in the condition called: anterior tibialis tendonitis (anterior shin splints) and may have a bearing on the development of anterior compartment syndrome.
A. During the gait cycle we notice a lateral inverted heel strike position adopted by the foot as it strikes the ground. This is commonly represented by the natural shoe wear on the outside heel portion of your footwear.
The heel strike phase of gait is commonly represented by:
- Supination at the subtalar joint
- Inversion of the calcaneus
- External tibial rotation
- Abduction & dorsiflexion of the talus over the calcaneus
B. As the tibia internally rotates and adducts the talus over the calcaneus, it causes pronation at the subtalar joint to occur. This increases the transverse distance (T.D.) with internal tibial rotation and causes the calcaneus to evert which allows the talus to plantarflex and decrease vertical distance (V.D.) from the ground. Thus, absorbing shock by lowering the arch and elongating the foot. However, excess pronation causes an extreme increase in transverse (T.D.) rotation and excess unlocking and lowering of the arch structures. Therefore, increasing osseous instability and tractional forces on the soft tissue structures, commonly resulting in injury.