Can Foot Orthoses Help Improve Postural Control?

Emphasizing an increased awareness of those who may be at risk for fall injuries, this author discusses key elements in facilitating one's balance and reviews key studies to assess the potential impact of foot orthoses in improving balance. Balance is defined as “the act of maintaining an upright posture in standing or locomotion.” Until recently, human balance was not a function normally evaluated or treated by podiatric physicians. Yet it is now understood that many of the pathologies we treat are accompanied by significant balance disorders. If you have not noticed this already, try asking your next patient presenting with posterior tibial tendon dysfunction to do a modified Romberg test, namely standing on one foot with the eyes closed and his or her arms crossed over the chest.    Perform a similar test of any patient with diabetic neuropathy, any patient who has recently suffered an ankle sprain or any patient over the age of 70. These patients may be surprised to discover they cannot stand on one foot and keep their balance for only a few seconds, even with their eyes open.    Podiatric physicians have a responsibility to screen for and direct treatment for any patient whom they suspect of having a balance disorder. Within the multidisciplinary team approach, the podiatric physician has the knowledge and skill to implement a new, innovative approach to the treatment of balance disorders. This approach utilizes a modality that previously has not been thought of as useful in the treatment of balance disorders. What is this modality? Custom functional foot orthoses.

Understanding The Gravity Of Fall Injuries

When we “lose our balance,” we are in the process of sustaining a fall. Accidental falls have become a significant public health issue around the world, particularly among the aging population. The following statistics emphasize the importance of preventing fall injuries in the elderly population.    * One-third to one-half of the population age 65 or older will experience a fall each year.1-3    * Falls are the leading cause of injury in older adults.4-7    * Falls are the leading cause of accidental death in people over age 85.6,7    * The medical cost for treatment of fall-related injuries in the United States exceeds $20 billion annually, and is expected to climb to $32 billion by 2020.8,9    * Falls cause approximately 350,000 hip fractures per year at a treatment cost of $35,000 per patient.7,10    * Most of the falls resulting in hip fracture are related to balance disorders.10    * Fear of falling causes a compensation strategy which actually impairs postural control, causing a vicious cycle.9    * Researchers have shown that elderly patients with diabetes, especially women, have a higher risk of sustaining an injurious fall.11,12    An increased risk of falling is not a normal part of aging. Studies have shown that elderly patients with a history of falling are different than their similarly aged counterparts without a history of falling.13-17 Patients at increased risk of falling have consistently shown deficits in balance control.18-23

A Closer Look At Key Factors In Balance Control

Balance control utilizes two systems: the gaze stabilization system, which ensures that the head remains upright and oriented to the body; and the postural stabilization system, which keeps the body upright while an individual stands or ambulates. The two systems are interdependent in their function to maintain overall body balance.    Researchers have recognized that over 50 percent of falls in the elderly are the result of vestibular problems.13 The vestibulo-ocular reflex stabilizes gaze during both head and body movements, and can be affected by a myriad of pathologies. Podiatric physicians should be aware of this important component of balance control and should make a specialty referral when appropriate.    In regard to the postural stabilization component of balance control, the postural stabilization system receives sensory input from three sources: the visual system, the vestibular system and the somatosensory system.24 Foot orthoses interact with the somatosensory system and the motor process of the lower extremity to maintain postural control during stance and gait.    The roles of the somatosensory system and postural control have been studied extensively during the past 20 years. Postural control is the ability of a human to maintain his or her center of mass over the supportive foot. Postural control is the mechanism and balance is the end result whereby a person is able to remain upright during stance and gait. Postural sway is the deviation of the center of mass determined during quiet stance on both feet or on a single foot.    A consistent finding among patients with chronic ankle instability is a deficit in postural control. Accordingly, most of the information we have to date about identifying and correcting deficits in postural control has been gained from studies of athletes with chronic ankle instability.25-31    In comparing sensory and motor deficits found among young athletic patients with chronic ankle instability and elderly patients with an increased risk of falling, there are several findings common to each group.32-39 (See “What Deficits Are Associated With Risk For Falls And Ankle Sprains?” below.)    In evaluating the neuromuscular deficits associated with increased risk of falling or suffering ankle injury, several functions appear amenable to treatment with foot orthoses. Indeed, over the past 15 years, seven papers have been published, studying the effects of foot orthoses on balance and postural control. In a past issue of Podiatry Today, I provided a detailed review of these papers and their relevance to the use of foot orthotic treatment of chronic ankle instability.40    Studies of the effects of foot orthoses on patients with chronic ankle instability have relevance to other patient populations with balance disorders (i.e. patients with PTTD, diabetic neuropathy, Parkinson’s disease, multiple sclerosis and certain segments of the elderly population).

Understanding The Patient’s Compensation For Balance Perturbation

When balance is perturbed, a human being utilizes several mechanisms to ensure that the body remains upright. In the lower extremity, two critical compensations occur to correct body sway. The ankle strategy utilizes muscular contraction of the lower leg to pull a falling body back over the fixed foot. Mergner, et. al., describe this mechanism as an “inverted pendulum” in which the entire body rotates over the fixed foot at the ankle joint.24    When ankle joint proprioception is diminished or when neuromuscular control of the ankle is lost, patients may use a “hip strategy” to correct body postural alignment for balance control. Studies of postural control in patients with diabetic neuropathy have shown that these patients use a hip strategy rather than an ankle strategy.12    It has been speculated that an ankle strategy is more efficient than a hip strategy for maintaining postural control during single leg stance. An ankle strategy requires finely tuned short range corrections while a hip strategy requires gross movements in a larger range of motion. A hip strategy uses more energy and is less efficient in correcting body sway than an ankle strategy.

What The Literature Reveals About Foot Orthoses And Balance

In the past 20 years, we have gained significant insight into the effects of functional foot orthoses on lower extremity function. From this research, we can speculate about how foot orthoses can improve balance in the standing and walking human. The model of balance corrections using the ankle strategy will allow us to focus on these possible treatment effects.    Previous studies of foot orthoses and their effects on postural control have lead investigators to propose several theories about how these devices achieve improvements in balance. The proposed mechanisms include: improved joint alignment of the rearfoot/ankle complex; reduced strain on the ligaments and tendons around the ankle; shifting of ground reaction forces (CoP) to a more optimal position; and enhanced sensory feedback from the plantar surface of the foot.    The term “ankle strategy” implies movement only at the talocrural joint. However, we recognize that medial-lateral sway of the body over the fixed foot would have to occur at the subtalar joint while anterior-posterior sway would occur at the talocrural joint. It is assumed that foot orthoses exert their primary influence on the subtalar joint and accordingly affect medial-lateral body sway.    In terms of the effects of foot orthotics on the alignment of the subtalar joint, several published studies have shown moderate but significant improvements.41-45 While these studies show that changes in alignment of the subtalar joint achieved with foot orthoses are only in the realm of a few degrees, such changes may be significant in improving proprioceptive function of the subtalar and ankle joints. Researchers have shown that proprioception is diminished when a joint is positioned at end range-of-motion. This is presumably due to tension placed upon ligament mechanoreceptors. By changing joint position and reducing strain on ligaments, foot orthoses may be able to improve joint proprioception.    Foot orthoses also have the ability to shift the center of pressure (CoP) under the feet of standing and walking subjects. Studies conducted on walking patients that measured changes in the migration of the center of pressure have shown similar results to the single leg stance studies. McPoil, et. al., found that foot orthotics would limit pronation and migration of the center of pressure in a population of people with forefoot varus deformities.46    In one of the previous studies cited, Hertel and colleagues concluded that reduction of pronation was the primary mechanism by which foot orthotics could improve postural control. However, they gave no explanation of this cause-effect relationship.47 While several studies have shown no benefit of foot orthoses to improve postural control in healthy people, one study did demonstrate benefit in healthy people with excessively pronated feet.48    Recently, Paton and Spooner showed how foot orthoses with rearfoot posts could shift the CoP in walking patients.49 They speculated how this shift in CoP could improve the lever arm for ground reaction forces to affect the supination/ pronation moment to the subtalar joint. Changing joint moment to the subtalar joint could reduce strain on the surrounding ligaments and muscles necessary to correct body sway using the ankle strategy. Studies have already demonstrated significant effects of foot orthoses to affect moments at the subtalar and ankle joints.50,51    Realignment of the ankle and subtalar joints, and reduction of internal joint moments will reduce the demands on the stabilizing muscles of the ankle joint complex. Lundin, et. al., showed how fatigue of the lower leg muscles adversely affected balance and postural control.52 Ochsendorf and co-workers showed how foot orthoses could significantly offset the negative effects of fatigue of the lower leg muscles on postural control.53    Many authorities have speculated that foot orthoses can have a positive effect on the mechanoreceptors located on the plantar surface of the foot to improve proprioceptive feedback for balance and postural control. There are three distinct types of mechanoreceptors on the sole of the foot. These include Merkel cell complexes (responding to pressure), Meissner corpuscules and Pacinian corpuscules (both responding to pressure). A molded, conforming orthotic footplate will increase the size of the receptor field on the plantar surface of the foot by providing a “total contact” effect.    The hardness or surface configuration of the orthotic foot plate may also have an effect on the plantar mechanoreceptors. In their study of improvements in postural control with foot orthoses, Rome and co-workers speculated that the positive effects were partly due to the hardness or rigidity of the devices tested.48    Okubo and coworkers showed how one can reduce postural sway when a patient stands barefoot on a surface covered with shotgun pellets.54 Priplata, et. al., showed the application of sub-sensory noise to the plantar surface of the foot, via nylon bristles, could significantly improve postural control in elderly subjects.55 Studies using these types of tactile enhancements with foot orthoses have not been performed. Future research may show how foot orthoses can be modified to improve stimulation of mechanoreceptors on the plantar surface of the foot.

In Conclusion

Balance disorders are extremely common among certain patient populations who receive treatment from podiatric physicians. These patients include those with PTTD, diabetes and Parkinson’s disease, as well as a significant proportion of individuals over the age of 70.    A loss of balance and postural control has been the single most common causative factor in traumatic falls in the elderly population. Functional foot orthoses offer an exciting new intervention for podiatric physicians to consider in the treatment of balance disorders that commonly accompany lower extremity pathology.    Dr. Richie is an Adjunct Associate Clinical Professor at the California School of Podiatric Medicine at Samuel Merritt College. He is in private practice at the Seal Beach Podiatry Group Inc., in Seal Beach, Ca. Dr. Richie can be contacted via e-mail at drichiejr@aol.com.    For related articles, see “Chronic Ankle Instability: Can Orthotics Help?” in the October 2006 issue of Podiatry Today, “Offloading The Plantar Fascia: What You Should Know” in the November 2005 issue or “Key Insights On Writing Orthotic Prescriptions” in the January 2006 issue.    Also be sure to visit the archives at www.podiatrytoday.com.
 

References:

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