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A B M P m e m b e r s e a r n F R E E C E a t w w w. a b m p . c o m / c e b y r e a d i n g M a s s a g e & B o d y w o r k m a g a z i n e 89 A B M P m e m b e r s e a r n F R E E C E a t w w w. a b m p . c o m / c e b y r e a d i n g M a s s a g e & B o d y w o r k m a g a z i n e 89 PRIMARY CAUSES Overpronation occurs when the body moves too far or too fast through the pronation movement during gait and may lead to dysfunctional biomechanics and various pain complaints. Causes vary, but there are a number of important factors that may increase the risk of overpronation. One of the most common causes of overpronation is functional weakness of the tibialis posterior muscle, which is in the posterior compartment of the leg deep to the gastrocnemius and soleus. It plays a critical role in foot mechanics. Anatomy texts will often say that its primary actions are plantar flexion and inversion of the foot. However, one of the most important things it does is control the amount of foot pronation during gait, essentially putting on the brakes (eccentric action) for the pronation movement. When a person overpronates, it is often because the tibialis posterior is not doing an adequate job of resisting the pronation movement. In these cases, there may be an excessive load on the muscle that is transmitted to its attachment site along the tibia, and this can produce medial shin splints (periostitis) because of constant pulling on the periosteal tissue at the attachment site. 2 3 While the tibialis posterior is certainly a key factor in resisting overpronation, it doesn't work alone. Ligaments of the ankle complex also restrain excessive movement between bones and contribute to foot stability and prevention of overpronation. There is a group of ligaments on the medial side of the ankle that are collectively referred to as the deltoid ligament because they create somewhat of a triangle (the Greek letter delta) in their shape. These ligaments have an important role in resisting excessive calcaneal eversion, which is a significant component of overpronation. Calcaneal eversion is explained later in this article. Previous sprains or genetic factors of ligamentous laxity may cause the deltoid ligament group to be looser than normal, thereby producing hypermobility of the foot and ankle complex. This hypermobility can easily contribute to overpronation. The deltoid ligament complex is not sprained as frequently as the ligaments on the lateral side of the ankle, but they can certainly be involved in ankle injuries and become overstretched and contribute to overpronation. Excessive weight is another factor that may lead to overpronation. The architecture of the foot and ankle is designed to distribute body weight across Genu valgum (knock-knees). Image courtesy Wikimedia Commons. Pronation in a nonweight-bearing position.