We know that orthotics work for pain related to disorders of the foot in 70 to 80 percent of cases. There has been numerous studies which always arrive at this percentage of successful interventions for orthotics, which in the world of evidence based medicine is a very good success rate, and high enough for podiatrists to prescribe devices with confidence that they have a good chance of reducing their patient’s pain.
How do they work? There has been a number of theories and paradigms over the years, and the reality is that we are still not exactly sure how they work, but lets have a look at some of the current theories.
Foot orthotics have 3 variables, being the topography (shape), stiffness of the material and the friction of the surface. Podiatrists can change the prescriptive value of a device by changing any of these variables.So, what does a podiatrist want to change, is it skeletal alignment, neurological stimulus, pressure? The answer lies in a combination of these, current thinking lies in thinking that orthotics change the stimulus on a foot, which in turn changes the amount of work a structure has to do. All of the tissues in a body have a zone in which they can work, and if the load exceeds that zone an injury can occur. All materials have this zone in which they can be stressed, whether it is wood, steel, muscle, tendon or bone. By reducing forces to injured structures we can facilitate rest and subsequent healing.
Current theories include:
- Tissue stress model (each tissue in the body has a zone of stress that it can take).
- Centre of pressure theory
- Sagittal plane theory
- Windlass mechanism
- Rootian theory
- Preferred pattern of movement theory
A google search of any of these theories in relation to orthotics will give more details for those who have a yearning for greater understanding.
The prescription of orthotics is a skilled work, requiring a knowledge of the evidence base of theories of biomechanics, detailed anatomical knowledge and experience of treating injured patients Theories as to how orthotics work will continue to develop over time, and along with this the success rates will continue to rise. Orthotics will also continue to embrace new materials, and reflect the demands of modern living and athletic performance.
A unified theory is still elusive, and will probably remain so due to the complexity of the human body and gait.