Prefabricated or custom orthoses are frequently utilised to reduce plantar heel pressures, particularly in the “At Risk Foot”. The design of these insoles often differs between health professionals, NHS Trusts and individual preferences rather than following set scientific guidelines. Although this paper isn’t particularly recent, it gives a thought-provoking insight into the most effective essentials for insole design through finite element analysis.
Reduction of plantar heel pressures: Insole design using finite element analysis.
Goske, S., Erdemir, A., Petre, M., Budhabhatti, S. & Cavanagh PR. (2006).
Journal of Biomechanics 39(13):2363-70.
“The aims of this study were to develop a finite element model of the heel pad and footwear and to explore the insole design space in order to quantify the effects of insole conformity, insole thickness, and insole material on pressure relief”.
What it all means:
This research found that conforming insoles had the biggest effect, possibly because they have a bigger contact area which could decrease overall pressure (Pressure = Force / Area). Material thickness also had a bearing on pressure reduction while insole material choice showed the least effect.
- “Finite element analysis provides an efficient computational framework to investigate the performance of a large number of designs for optimal plantar pressure reduction”.
- 2D plane strain finite element modelling was utilised to investigate 27 insole designs
- Combinations of the following were stimulated during the early support stage of gait:
- 3 insole conformity levels (flat, half conforming, full conforming),
- 3 insole thickness values (6.3, 9.5 and 12.7 mm)
- 3 insole materials (Poron Cushioning, Microcel Puff Lite and Microcel Puff)
- Conformity of the insole was the most important design variable
- Peak pressures were relatively insensitive to insole material selection
Putting it into practice:
- Rather than issuing a flat cushioning material cut out for elderly and “At Risk” patients, try using a contoured orthotic which supports the natural structures of the foot.
- For more complex patients or those with complex foot deformities, a custom made “Total Contact Insole” (TCI) can work very well. Maximising the surface area with a custom orthotic means that high pressure areas are reduced because the load is spread over a greater area.
- Bio-Soft-Plus is an excellent choice if using a prefabricated orthotic because the memory foam top cover conforms to the shape of the individual patient’s foot, while the polyurethane base provides cushioning and shock attenuation.