The purpose of this two-part series is to explain the benefits of orthotics. Before, we proceed I wanted to state that it is my professional opinion that although orthotics are beneficial to some, not every patient needs them. I believe that for certain individuals, similar benefits can be achieved with rehab exercises (short foot). Short foot exercises and gait retraining has numerous benefits; however, the patient has to do the work. Nevertheless, we were taught in school that based on the initial complaint or diagnosis, 70%!!!! of people experience complete relief or great improvement with orthotics. In order to discuss the benefits of orthotics, it is imperative to cover the anatomy of the foot first.
Anatomy of the Foot
The ankle is comprised of a couple of joints. For a basic understanding of the material in this post, just the subtalar joint will be covered. The heel of your foot (calcaneus) sits on a bone called the talus. Together these bones form the subtalar joint (talocalcaneal articulation). The subtalar joint is responsible for moving the sole of the foot away from (eversion) or towards (inversion) the midline of the body. An example of inversion injury of the subtalar joint would be when someone twists their ankle.
Biomechanics of the Ankle.
Patients who over-pronate (flat feet) are often prescribed orthotics. Pronation is a combination of 3 movements of the foot. It involves the movement of the calcaneus away from the midline (eversion), the foot lifting towards the ceiling (flexion) and the balls of the feet move away from the midline (forefoot abduction). Patients with supinated feet have the opposite movement. One of the main components of flat feet or over pronators is the percentage of calcaneal eversion from the midline. This range is anywhere from 14-66%, with an average eversion of 20 degrees.
In addition to the calcaneal eversion, the talus also moves differently in patients that are over-pronators. The talus pitches down to the floor (dorsiflexion) and rotates towards the midline (internal rotation). The average degree of elevation of the subtalar joint is 42 degrees. Research has shown that if the axis of the joint is steeper (higher inclination – almost vertical) then there is more rotation of the subtalar joint. Increased rotation of the subtalar joint correlates with a higher predisposition to knee pain. Whereas, if the subtalar joint is more horizontal to the ground then the subtalar joint is more of rolling motion (eversion/inversion). Horizontal subtalar joint correlates with a higher predisposition to foot pain.
Why is over-pronation a problem?
Neutral pronation individuals toe-off with the weight evenly distributed among the toes with a slight emphasis on the big toe. The problem with over-pronation is that the foot is unable to supinate fully and toe-off occurs primarily on the first and second toe. This is a common predisposing method of bunions (hallux valgus), because over-pronation increases pressure on the inside of the big toe.
Is Some Pronation of the Foot Beneficial?
Yes, some pronation of the foot is necessary (approximately 7-9%). Pronation of the foot occurs because ground reaction force and body weight are even in magnitude, but the forces are not aligned to oppose each other. This cause the ankle to roll in a counter-clockwise direction (the design of the foot causes a natural pronation). This is the reason why running increases pronation because of the increased force, increases natural movement of the foot. Nevertheless, some pronation is necessary to dampen ground reaction forces.
What are the Benefits of Orthotics? Theory 1: Aligns the skeleton (Altering joint kinematics).
The immediate effect of orthotics is that they help to align the subtalar joint into a neutral position. A neutral subtalar position helps to reduce the degree of downward pitch and internal rotation of the talus. These accommodations help to prevent the foot from overpronating. It also ensures that toe-off of the foot happens with the weight evenly distributed with a slight emphasis on the big toe.
Is pronation a good indicator for predicting lower extremity injuries?
We have established that over-pronation is not ideal; however, is too much pronation a good indicator of lower extremity injury? The short answer is NO. Research has shown that 40-50% of runners with excessive pronation do not have overuse injuries; however, injured individuals typically pronate 4 to 5 degrees greater than those with no injuries. So as you can tell the information regarding over-pronation and lower extremity injuries is cloudy. So what is a better predictor of lower extremity injuries and the need for orthotics?
What are the Benefits of Orthotics? Theory 2: Altering the transfer of rotations up the kinetic chain.
Studies have found that it’s not so much the degree of over-pronation that warrants orthotics in patients, rather the coupled motion of over-pronation and rotation of the leg towards the midline (tibial internal rotation). As mentioned previously, the calcaneus moves away from the midline (everts) anywhere from 14 to 66%, with an average eversion of 20 degrees. Research has shown that 14 degrees of calcaneal inversion causes 3 degrees of tibial internal rotation. At the other end of the spectrum, 66 degrees of calcaneal eversion causes 13 degrees of tibial internal rotation.
This coupled motion is important because of the effect it has on the body going up the kinetic chain. Injuries such as bunions, shin splints (MTSS), Achilles tendinitis, plantar fasciitis, PFPS, ITB irritation are all associated with over pronation and tibial internal rotation. Increased rotation of the leg (tibia) towards the midline (internal), causes the knees to approximate towards each other (valgus loading). The hips also rotate towards the midline (internal rotation) and the pelvis tilts forward (anteriorly). When the pelvis tilts forward the low back compensates by arching backward (lumbar lordosis). This coupled motion of the feet, ankles, knees, hips, pelvis and low back is what orthotics are usually prescribed for.
It is important to mention that numerous studies show weak to no evidence for the association of increased curvature (lordosis) and low back and pain. Nevertheless, I have had patients state their chronic back pain improved when prescribed orthotics. My recommendation is for patients to first try treatment combined with exercises. If patients still have persistent irritation then looking at orthotics is an option.
Orthotics are beneficial for placing the subtalar joint into a neutral position and reducing the movement of the talus. This minimizes the unwanted movement of the foot and ankle. Correction of the feet and ankle help to better align the rest of the body (knees, hips and low back). Optimal alignment of these joints is thought to prevent and alleviates a number of repetitive strain injuries.
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