Can Orthoses And Insoles Have An Impact On Postural Stability?
In recent years, there has been a growing interest in the neurophysiological effects that orthoses can have on the foot. Accordingly, these authors review the literature and offer their perspectives on the ability of orthoses and insoles to enhance postural stability.
Podiatrists frequently prescribe foot orthoses to treat and prevent overuse running injuries, as well as enhance comfort, cushioning, realignment, redistribution of forces and stability for chronic conditions such as diabetes and rheumatoid arthritis. However, the exact biomechanical mechanism of the action of orthoses remains unknown. Researchers have attempted to understand the biomechanical and anatomical factors associated with the prescription of foot orthoses. Only recently has there been an interest into the neurophysiological factors.
There is evidence that neurophysiological factors can affect lower limb biomechanical alignment. This evidence suggests that disrupting the function of intrinsic foot muscles, via induced fatigue, results in excessive foot pronation. The evidence also suggests that impact forces during daily physical activity produce a reaction in the muscles to minimize soft tissue vibration.1,2 Orthoses can augment the medial longitudinal arch, thus altering the muscular work required to maintain foot posture. Foot orthoses also may act to dissipate and absorb this impact, subsequently affecting levels of fatigue, the intensity of muscular work, performance and comfort.2
In addition, when one places orthoses under the midfoot and forefoot, they may provide biofeedback by enhancing afferent feedback from cutaneous receptors on the plantar surface of the feet and reducing eversion due to contraction of the inverting muscles.3 Furthermore, anatomical factors can affect lower limb biomechanical alignment. Research has shown that induced excessive foot pronation significantly increases internal tibial rotation, internal hip rotation and anterior pelvic tilt.4 Correcting anatomical malalignment at the foot with orthotic devices may indirectly realign the lower limb more superiorly.
Nigg postulated that by inserting a corrective interface between the plantar aspect of the foot and sole of a shoe, orthoses can counteract abnormal biomechanics, support natural joint motion and alter muscle activation patterns.2 The foot orthotics filter information generated by the ground reaction force and this information transfers to the central nervous system, which elicits a subject specific dynamic response.
The central nervous system controls upright posture and integrates visual, vestibular and somatosensory information. The somatosensory system is a diverse sensory system, which comprises the receptors and processing centers to produce the sensory modalities such as touch, temperature and pain. This initiates appropriate motor and muscle responses at the trunk and lower limbs.
Current evidence suggests that orthotic devices may affect lower limb muscle activity while patients are walking and participating in physical activities. Three recent literature reviews have been published on the subject.4-6 Recently, there has been exponential growth in the use of orthoses and insoles to help enhance postural stability or balance. Although it is essential to understand the muscle activity that includes strength, range of motion and muscle tone, let us take a closer look at orthoses, footwear and insoles that may facilitate improved postural stability.
Researchers have explored the effects of balance-facilitating, noise-enhanced, textured and functional orthoses on postural stability. The relevance of these studies centers around postulations that improved balance performance with such interventions may be due to alterations in sensory information at the plantar surface of the foot.