Presentation at Otto Bock Scandinavia - focusing on the diabetic foot and covering screening, biomechanics and orthotic management for ulcer prevention and treatment
5. A drop in the ocean?
Diabetes Expenditure
•
10% million affected inaffected world
2.9 of the UK NHS BudgetBudget
285 million UK NHS UK
10% of the people the
£9 Billion per Year
wide - 6.4% of population
• £9£286 per per Year
Billion Second
Lifetime risk of foot ulceration - 25%
• £286 per Second
6. Cost Burden for
Patients
Varies with Country
Cost of treating diabetic foot ulcers in five different countries.
Cavanagh P, Attinger C, Abbas Z, Bal A, Rojas N, Xu ZR.
Diabetes Metab Res Rev. 2012 Feb;28 Suppl 1:107-11. doi: 10.1002/dmrr.2245.
11. Screening Is..
The Starting Point
for Effectiveness
Quick & Simple
Assess Patient’s
Risk Level
Not the Same as
Assessment
12. What Do We
Screen For?
Previous Amputation
Significant deformity
Significant callus
Active ulceration
Previous ulceration
Vascular insufficiency
Neurological insufficiency
Able to self care?
14. Risk Stratification 5 % Active Ulcers or
5 % Active Ulcers or
Infection --
Infection
revascularisation or
revascularisation or
amputation
amputation
Multidisciplinary
Multidisciplinary
management
management
15 % High Risk
15 % High Risk
Intensive foot
Intensive foot
protection
protection
Ulcerated
20 % Moderate
20 % Moderate
High Risk Risk
Risk
60% Low Risk
60% Low Risk Regular foot
Regular foot
Routine annual
Routine annual protection
protection
screening
screening
Moderate Risk
Low Risk
15. Match the Strategy & Activity to the
Individual’s Level of Risk
LOW RESULT is...
• Most Effective Use of
MEDIUM Resources
• Ulcer Prevention
HIGH • Keep the Individual at
Lowest Risk of
Ulceration
ACTIVE
21. Sho es
abe tic” and R oomy
“Di Soft
U ppers
Pressure Relief? Sto ck?
or
o ke
esp Rock
B er Sol
W e M us t S e?
ave Money
.. But Who Has the
Skills?
Relieve Pressure?
How
Complicated
Can Shoes Be..?
25. Prevent Ulceration
Strategy according to individual risk
Ulcerated
Improve
Extrinsic
Influences High Risk
Moderate Risk
Low Risk
26. Problem is one of
Mechanics
Paul Brand
"The whole problem is one of mechanics, not of medicine.
The biological responses of these denervated limbs are
qualitatively similar to those of normal limbs.
It is the permitted pattern of mechanical stress that is different"
28. Preventing Trauma Means
Controlling the Mechanical
“Environment”
sure
Pr es
on chan ics
. nsati e
s . Se y
a
h d e M natom
ot re su A
Fo lte d Tis al Friction
A e re
✓ Alt truct ur
✓ and S She
ar
✓ For
ce
29. Elevated Plantar Pressure
Causative Factor
in
Ulceration
and Ulceration is often
a
Precursor to
Amputation
30. High Pressure is Bad
Friction & Shear
are Very Bad
But do we understand
these terms?
Are we using them
correctly?
41. Mechano-transduction
Mechanisms by which cells convert mechanical stimulus
into physiological activity - anabolic and catabolic
A field holding the keys to progress?
46. • Shoe and Contact Surface
(footbed) Must Work Together
• Materials & Structures Chosen &
Positioned for BOTH Control
and Tissue Matching
• Shoes Need to act like the
“Skeleton” as well as the “Soft
Tissues” - Support as well as
protect
• “Soft” Uppers not Necessarily
Best - Match to the Ambulatory
Status and Load Expectations
Preserving and protecting the diabetic foot has been described as a mechanical challenge - a problem of mechanics as much as medicine - and in this presentation we touch upon why this is so. We are going to point out some of the complexity behind terms such as pressure, friction and shear stress and the implications for footwear design. We conclude by listing some of the principles to keep in mind when designing shoes for the diabetic foot.
Preserving and protecting the diabetic foot has been described as a mechanical challenge - a problem of mechanics as much as medicine - and in this presentation we touch upon why this is so. We are going to point out some of the complexity behind terms such as pressure, friction and shear stress and the implications for footwear design. We conclude by listing some of the principles to keep in mind when designing shoes for the diabetic foot.
There is certainly a lot of confusion on the topic of shoes for persons with diabetic foot disease. We seem to have a general lack of clarity about exactly how shoes for diabetic patients should be designed, manufactured and prescribed. There is certainly confusion - even an abuse of terminology. In the minds of many, there is a belief that prescription shoes can't be all that complicated. However this is a mistaken belief. As in many aspects of biomechanics, the subject is much more complex than we might like.
With the diabetic foot, we understand that each affected individual may well have neuropathy, tissues of the foot that have mechanical characteristics that differ from "normal" ranges - and altered anatomical structures. These mechanical characteristics will vary from person to person, and are modified by the disease process and even will vary in one person over time. As we move through our environment the interaction - the points of contact - we have with our environment has mechanical and therefore biological consequences. The forces generated, for example, manifest as changing patterns of pressure, friction and shear force at the foot-shoe interface and deep within the tissues of the foot.
Well at a simpler level - what do we know for sure? We know that high pressure is bad and that friction and shear are potentially very bad. We also know that localised pressure, creating pressure gradients and localised tissue deformation generates damaging shear stresses. But that level of knowledge isn't sufficient to help us with the ideal shoe design. In order to influence design we need to delve deeper and this is where biomechanics can be useful.
Now I'd better start with a confession. Everything I will tell you is a lie - but hopefully a useful lie. The reason for this comes down to how biomechanics - that is - engineering applied to gain an understanding of body systems - must rely on models of reality. And these models are never perfect - they are simplifications that we can hold to be true for a while or for certain specific situations. The fact is, sooner or later a better model - and improved understanding - comes along. So when we use terms like force, pressure, stress and strain we should do so acknowledging the inherent limitations of our viewpoint.
Most of us believe we have a good grasp of the physical meaning of pressure. After all, its simple to imagine how pressure is created though the application of load over an area - but its difficult to accurately measure. And its not just a surface effect when we apply load to tissue. The skin, muscle and soft tissues deform and experience these mechanical loads in different ways. Many of the strategies that are applied in the creation of footbeds and footwear aim to spread applied loads over a greater area - thereby reducing the local pressure gradients.
Using a mixture of measurement and mathematics we can predict for example how different interface materials will influence the surface pressures and shear stress. These approaches are always simplifications because we have to make assumptions about the conditions that prevail. Of course we wish to manage the performance of the interface between foot and shoe - knowing that in use the parameters that we need to fine tune that performance vary from situation to situation and from person to person.
Two of the terms we frequently hear are "Friction" & "Shear". Actually, strictly speaking, there are a number of different types of friction and shear. Friction is the force that resists the relative motion of solid surfaces in contact. It is in practical terms very difficult to calculate a value for friction - it generally has to be determined empirically. Friction and Shear Stress occur together and this is why we try to minimise them in footwear for diabetics. Shear Stress results when a force acts coplanar to a surface with the result that the tissues deform. And when the tissue deforms and flexes to extremes we have part of the precursor for ulceration.
If we take a look at tissue closely we see that it is not homogenous. There are actually multiple layers of skin, fat, muscle, bone and other structures - each with different behaviours under load. An of course the foot and ankle is a dynamic jointed structure that is meant to be rigid at some phases of gait and flexible at others. Engineers have studied areas of the foot such the heel pad to understand how such tissue behaves under dynamic loading conditions such as those experienced during gait. As we try to model this type of situation we truly discover it's inherent complexity. Notice that the dynamic behaviour of the tissue might be modelled using forms well understood by engineers.
When we have to make choices about shoe design for diabetics we have to be mindful of the need for foot protection and control. Just as we saw with tissue, we potentially have multiple layers that have individual mechanical characteristics and shapes with the potential to harm or protect. During walking and other activities the shoe will flex and twist and thought must be given to how the shoe and tissues will interact. By all means have materials that behave like tissue in contact with the plantar surface and high load bearing areas of the foot. But we need to be mindful about how the whole shoe and footbed work together. If the thickness and weight of the upper is not matched to the flexibility of the sole unit, for example, the shoe is likely to distort under the loads generated during walking - the result will be undesirable pressure, friction and shear.
Here is a short list of principles that should guide us. First of all we need accurate, reliable measurements of the foot. At present we have a plethora of techniques and beliefs about how measurement should be done. Clearly if measurements cannot be taken consistently and reliably we are off to a bad start. Some areas of the foot are particularly sensitive to localised pressure gradients and therefore prone to ulceration. The insole and components of the shoe should be designed to work together. It is not good enough to put a soft "tissue like" insole inside a shoe and hope for the best. Materials chosen to behave like tissue should go close to tissue if we are to minimise stress. However, these insole materials need to interface with the structure of the shoe. Take a look at the human body that has layers of tissue for good reason. The skeleton, ligaments and tendons transmit force whilst the soft tissues absorb dynamic stresses and strains. The shoes we design should act like the skeleton too - not just like the soft tissues. They should allow safe transmission of dynamic load and should allow control and protection to be imposed. To think that shoes should always have "soft roomy uppers" is very inaccurate and mechanically flawed thinking. Of course we should choose the materials carefully and position them within a shoe so that they have the desired effect of control or tissue matching.