Full off-loading v partial off-loading

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Any recent updated opinions on whether or not to include a poron / PPT plug in the apertures of (plantar ulcer) offloading insole. I do.

And for plantar hallucial lesions of functional hallux limitus etiology whether to use a full foot (forefoot) thickness aperture plantar pad or a forefoot valgus / rearfoot varus pad combination. I use the latter.

And for plantar 1st metatarsophalangeal lesions whether to use a full foot (forefoot) thickness aperture plantar pad of a forefoot valgus pad. I use the latter.

mark

 

I recall something from years ago that "total" off-loading was not as good as "partial' as 'total' encouraged oedema in the wound, so partial (ie poron plug in the cavity) would theoretically encourage less oedema.

 

I started this thread as I see a lot of the no plugs and full thickness pads been placed into post-surgical shoes and removable aircast walkers and wonder? It is a biomechanical topic after all (the latter two cases)

 

I think it will be interesting to see how the concept of spatial summation from ergonomics could be applied in the case of full off-loading vs partial off-loading !

Here is an abstract :
Contact Area Effects on Discomfort
Authors: Goonetilleke, Ravindra S.; Eng, Timothy J.
Source: Human Factors and Ergonomics Society Annual Meeting Proceedings, Industrial Ergonomics , pp. 688-690(3)
Publisher: Human Factors and Ergonomics Society

Abstract:

Most “ergonomic” products attempt to adopt a uniform force distribution strategy to improve comfort. The rationale being that force distribution over a large area reduces pressure and thereby enhances user comfort. However, sensory literature alludes to the concept of spatial summation, i.e. greater sensation by stimulating a larger surface area. Hence spatial summation would tend to suggest a greater discomfort when forces are applied over large surface areas. This study reports the effect of surface area on maximum discomfort causing pressure or maximum pressure tolerance (MPT). Two circular probes of different cross sectional area were used to stimulate the skin surface. The mean MPT with a probe of 5mm diameter was 3.3 times higher than the MPT with a probe of 13mm diameter. These findings suggest the following:
• Perceived discomfort and contact area seem to have a “U-relationship” above a critical force value. Traditional thinking of distributing forces is successful only in the first half of the U-curve or with forces below the critical value. The section with the monotonically increasing relationship between discomfort and contact area (i.e., second half of U) may not be seen at very low forces or forces below the critical value.
• “High” pressures in concentrated areas may cause less discomfort than “moderate” pressures over a larger area.
• The critical or threshold pressure to induce discomfort is force and contact area dependent.


More articles on this subject :
http://www-ieem.ust.hk/dfaculty/ravi/papers.html

Daniel

 

Full off loading versus parrtial off loading?

When the pads you give as examples of 'full off loading' are used, do they fully off load or do they just modify the time/load curve and stresses?

Bill

 

In this case is not a contradiction with Medicare : "A5513: For diabetics only, multiple density insert, custom molded from model of patient's foot, total contact with patient's foot, including arch, base layer minimum of 3/16 inch material of shore a 35 durometer or higher), includes arch filler and other shaping material, custom fabricated, each “ ? Are the "total off-loading" and "total contact" the same thing ?
Daniel

 

Hi Daniel?

I am taking "total off loading" to mean that the "traumatised/vulnerable" area has all the load removed from it, ie there is absolutely no force applied to the "wound".

I am sure Mark will be back soon to define terms.

Bill

 

Aloha,

I have had some decent clinical results using dynamic carbon fiber AFO's with at least 10 mm of soft top cover combination (ppt,poron,neoprene,plastizote etc). Otto bock makes the Walk On Brace. Using an energy efficient composite brace allows for a better transfer of pressure and shear off the high risk foot areas to the proximal leg and distal toe sections of the brace. The toughest thing is getting it in a standard shoe housing. Because the brace is light and provides some spring assist and proximal proproception to the upper leg neuropathic diabetics are willing to wear it even after wound closure.

A hui hou,
Steve

 

In this case is not a contradiction with Medicare : "A5513: For diabetics only, multiple density insert, custom molded from model of patient's foot, total contact with patient's foot, including arch, base layer minimum of 3/16 inch material of shore a 35 durometer or higher), includes arch filler and other shaping material, custom fabricated, each “ ? Are the "total off-loading" and "total contact" the same thing ?
Daniel


Total contact is not the same thing as total off-loading. Medicare wants the A5513 custom diabetic insert to interface completely to the foot from the heel, arch and ball of the foot. Any boney prominences will be cushioned by the Plastizote/Poron top cover and the arch fill will help decrease the pressure on the metatarsals during midstance.
Loading forces are present but the goal is to decrease them. Patients may also need a forefoot rocker applied to their shoes to help further decrease plantar pressures but the high risk are is still not totally off-loaded.

Steven

 

Hello Everyone,

I do not have any studies to refer to however I am able to comment on clinical experiences I have had over the past 12 months. We measure plantar pressures on lesions using Parotec dynamic in shoe pressure measurement. Fortunately we are also able to integrate the Parotec plantar pressure measurement with Paromed CAD CAM custom orthotic modelling and are able to model apertures around the peak plantar pressures.
As a general rule I use combinations of higher material densities to control/deflect biomechanical forces with lower densities for regions that require absorption of forces. Fortunately Paromed also allows apertures to be filled with material of choice such as Plastazote or Poron in an automated milling process.
I have found that for wounds on the apices of the lesser digits or on stumps of Metatarsals (post amputation) or effectively any “sagittal plane” pivot points that they are best suited to having no fill in the apertures. This is also reflected with measurement of these apertures with Dynamic in shoe pressure measurement and time taken to heal these wounds. I have found that with bony prominences that are situated around the mid foot, such as with a Charcot foot, they respond far better to poron filled apertures.

If anyone would like me to send a case study/examples please let me know, they were recently featured at the Australasian Podiatry Conference in Sydney this week. I can be reached via email or private message.

Andrew Barlow
Clinical Director
Paromed Australia