A Closer Look At Foot Orthoses For Chronic Ankle Instability
While clinicians can understand mechanical instability from a physiologic standpoint, the notion of functional instability, particularly neuromuscular control of the ankle, is more complicated. At the same time, restoration of neuromuscular control is the mainstay of treatment for chronic ankle instability. As we will see, foot orthotic therapy can play a significant role in this treatment strategy.
Postural control describes the ability of humans to remain upright, keeping their center of mass within the borders of the support of the feet. Researchers have identified a loss of postural control as a causative factor of chronic ankle instability and repetitive sprains.9 Postural control requires an intact neuromuscular control mechanism, which foot orthoses can affect in several ways.
The visual, vestibular and somatosensory systems provide the sensory feedback to maintain upright balance and postural control. Of most interest to the podiatric physician, the somatosensory system provides feedback from the ligament mechanoreceptors in the ankle joint, the muscle spindle system of the lower leg and the cutaneous sensors on the soles of the feet. An ankle sprain disrupts the ligament mechanoreceptors but the other two levels of input from the leg muscles and the plantar surface of the foot are able to compensate adequately and provide essential proprioceptive input.9 Therefore, this challenges the notion that an ankle sprain causes loss of proprioception. While balance and postural control are compromised after an ankle sprain, the problem seems to lie beyond the sensory mechanisms.
There is mounting evidence that the disruption of neuromuscular control in chronic ankle instability is due to the “feed-forward” side of the system in which central processing, nerve activation and muscular contraction are not working properly.10 Instead of focusing on therapies to improve “proprioception” in patients with chronic ankle instability, new protocols now employ balance training, gait training, jump and landing training as well as muscular strengthening, which starts at the hip and works down to the feet.
Donovan and Hertel have proposed four specific symptom domains of chronic ankle instability: reduced range of motion, reduced strength, impaired proprioception and neuromuscular control, and altered gait patterns.11 They describe a systematic method of treating chronic ankle instability deficiencies to enable patients to return to full function. Foot orthotic therapy can provide an adjunct to treatment of chronic ankle instability in all four of the symptom domains that these experts describe.
How Can Foot Orthoses Treat Chronic Ankle Instability?
In 2006, I wrote an article on this same subject for Podiatry Today.12 At that time, seven studies had been published in the medical literature describing the effects of foot orthoses on postural control in both healthy patients and those with chronic ankle instability.13-19 Since that time, we have gained significantly more insight and verification of those previous studies.
While initial studies of foot orthoses and postural control focused on people with chronic ankle instability, more recent research has studied patient populations at risk for catastrophic falls. The findings continue to be quite remarkable given the simple nature of this treatment intervention.