May 29, 2009
May 29, 2009
The foot provides dynamic stability for a person's entire body weight, while simultaneously maintaining flexibility for shock absorption and propulsion along uneven surfaces. As a result, there are unique biomechanical demands on the foot. One of the body's adaptations to these demands is through specialized movements in the foot, such as pronation. In order to fully understand pronation, let's look at some fundamentals of movement and mechanics.
Most joint movements of the body are described in one of the three cardinal planes: sagittal, frontal or transverse. While there are foot motions such as dorsiflexion and plantar flexion that occur in these standard planes, most foot and ankle motion is not adequately described by these planes. More commonly, motion of the foot at the ankle is in a diagonal or oblique plane. This oblique plane motion involves movement through all three planes. For example, pronation is a diagonal plane movement of the foot around an oblique axis that combines the primary cardinal plane movements of dorsiflexion, eversion and abduction of the foot.
The diagonal plane movement of pronation occurs normally during walking or running. Although the term pronation routinely is used to describe dysfunctional foot mechanics, a better description of the pathological problem is overpronation. Also called hyperpronation or excessive pronation, this biomechanical disorder involves too much pronation during gait. Overpronation results when an individual moves either too far, or too fast, through the phases of pronation, placing more weight on the medial side of the foot during gait.
Unless there is a severe, acute injury, overpronation develops as a gradual biomechanical distortion. Several factors contribute to developing overpronation, including tibialis posterior weakness, ligament weakness, excess weight, pes planus (flat foot), genu valgum (knock knees), subtalar eversion, or other biomechanical distortions in the foot or ankle. Tibialis posterior weakness is one of the primary factors leading to overpronation. Pronation primarily is controlled by the architecture of the foot and eccentric activation of the tibialis posterior.1 If the tibialis posterior is weak, the muscle cannot adequately slow the natural pronation cycle.
Another primary cause of overpronation is subtalar eversion, also called calcaneal valgus (Figure 1). When the calcaneus is everted, weight is forced onto the medial edge of the foot. The subtalar eversion of pronation is visible in a standing position and it's evident that increased weight is placed on the medial side of the foot (Figure 2). Obesity can cause overpronation because the additional weight produces subtalar eversion and forces the longitudinal arch to collapse.
Overpronation can be a contributing factor in other lower extremity disorders, such as foot pain, plantar fasciitis, ankle injuries, medial tibial stress syndrome (shin splints), periostitis, stress fractures and myofascial trigger points. Overpronation increases the degree of internal tibial rotation, thereby contributing to various knee disorders such as meniscal injury or ligament sprains. The effects of the postural deviation are exaggerated in athletes due to the increase in foot strikes while running and the greater impact load experienced. When running, three to four times the body weight is experienced with each foot strike.2 If overpronation exists, the shock force is not adequately absorbed by the foot and is transmitted further up the kinetic chain.
Overpronation is best viewed from the posterior while the individual is walking, such as on a treadmill. When viewed with the client in a standing position, the overpronated foot looks similar to calcaneal valgus, because subtalar eversion is a fundamental component of overpronation. Examine the shoes for evidence of excessive pronation. If the shoes have had sufficient use, there will be an exaggerated wear pattern toward the medial side of the shoe bottom.
Overpronation usually is corrected with orthotics and/or strengthening exercises for the tibialis posterior. Massage treatment can relieve myofascial trigger points in the tibialis posterior, and other muscles, and address any resulting neuromuscular dysfunction in the leg or foot. Biomechanical correction of overpronation might require orthotics, neuromuscular reeducation, or gait retraining methods, as well. Stretching the gastrocnemius and soleus muscles will reduce hypertonicity in these muscles and also is essential for effective treatment.1 Because of impacts throughout the remainder of the body, the detrimental effects of overpronation should not be overlooked.
- Stovitz SD, Coetzee C. Hyperpronation and foot pain. The Physician and Sportsmedicine 2004;32(8).
- Nordin MA, Frankel V. Basic Biomechanics of the Musculoskeletal System. 3rd ed. Baltimore: Lippincott Williams & Wilkins; 2001.