D jones norway2012
•
1 like•453 views
Diabetes is a global public health problem. In particular, type 2 diabetes is imposing a growing burden on health care systems as the number of people affected continues to grow. The economic and human costs are high. We see, for example, that foot problems due to diabetes account for more hospital inpatient days than any other diabetes related complication. Prevention of ulceration is a key aspect of care but it isnʼt always easy to achieve. Diabetic foot problems can develop extremely quickly, with tissue breakdown often complicated by infection. Everything possible must be done to prevent tissue breakdown though good medicine and effective therapeutic footwear prescribed according to the personʼs individual level of risk. An individualʼs risk of ulceration determines the strategy for prevention or treatment and also influences the nature and extent of the resources that must be committed. 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 discuss why this is so. We examine the terms used to describe this complex mechanical environment. However, 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. These models are imperfect - they are simplifications that we can hold to be true for a while or just for certain specific situations. When we use terms like force, pressure, stress and strain we should do so acknowledging the inherent limitations of our viewpoint. There is a lot of confusion on the topic of shoes for persons with diabetic foot disease. We seem to lack clarity about exactly how shoes for diabetic patients should be designed, manufactured and prescribed. The principles of biomechanics imply that it is nonsense to suggest that there is such a thing as a “diabetic shoe” or that what is needed is footwear that is “soft and roomy.” In the minds of many, especially administrators and budget holders, there is a belief that prescription shoes can't be all that complicated. Health care systems strive to treat things often as a commodity so that they can be bought at the lowest cost. As in many aspects of life the subject is much more complex than we might like. In the UK, and perhaps many other countries professionals in our field have a responsibility to educate budget holders on the true complexity of foot care for persons with diabetes and establish approaches that recognise the natural limitations of biomechanics
Recommended
More Related Content
Similar to D jones norway2012
Similar to D jones norway2012 (20)
More from Derek Jones
More from Derek Jones (19)
Recently uploaded
Recently uploaded (20)
D jones norway2012
- 1. Biomechanical Considerations of the Diabetic Foot Derek Jones PhD, MBA
- 3. Life as we knew it ...
- 4. Life as we know it ...
- 5. A drop in the ocean? Diabetes Expenditure 10% of the UK NHS Budget £9 Billion per Year
- 6. A drop in the ocean? Diabetes Expenditure 2.9 million10% of the in the UK affected UK NHS Budget £9 Billion per Year Lifetime risk of foot ulceration - 25%
- 7. Total Expenditure Approximately £1.8 Billion per year in the UK Attributable to the Diabetic Foot
- 8. 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.
- 10. Diabetic Foot Ulceration Three Great Pathologies Neuropathy Ischemia Infection
- 11. Improved Survival of the Diabetic Fot The role of a specialised foot clinic ME Edmonds et al QJ Med 1986; August; 60(232):763-71
- 12. ” Sh oes iabe tic t and R oomy “D Sof Up pers Pressure Relief? toc k? eorS ok esp Rock B er Sol We Must S e? ave Money .. But Who Has the Skills? Relieve Pressure? How Complicated Can Shoes Be..?
- 13. Your shoes caused my ulcer!
- 15. Prevention “becomes cost effective if we reduce incidence of foot ulcers and amputation by 25%” Boulton et al; Lancet Nov 2006
- 16. Prevent Ulceration Strategy according to individual risk Ulcerated High Risk Moderate Risk Low Risk
- 17. Prevent Ulceration Strategy according to individual risk Ulcerated Improve Extrinsic Influences High Risk Moderate Risk Low Risk
- 18. Problem is one of Mechanics Paul Brand "The whole problem is one of mechanics, not of medicine. The biological responses to these denervated limbs are qualitatively similar to those of normal limbs. It is the permitted pattern of mechanical stress that is different"
- 19. Extrinsic Factors Repeated “Trauma” At Chronic Risk Wound Acute Wound Ischaemia Infection
- 20. Extrinsic Factors Repeated “Trauma” At Chronic Risk Wound Acute Wound Ischaemia Infection
- 21. Preventing Trauma Means Controlling the Mechanical “Environment” su re on ics ati an es ns ch Pr Se Me y ed ue r s at om lte is A T An d ctur al Friction re ru lte St A d an She ar F orce
- 22. Elevated Plantar Pressure Causative Factor in Ulceration and Ulceration is often a Precursor to Amputation
- 23. High Pressure is Bad Friction & Shear are Very Bad
- 24. Everything I tell you Is a “Lie”
- 25. Pres sure Not Just a Surface Effect
- 26. Pres sure Not Just a Surface Effect
- 27. Interface Effects Stress Strain(%)
- 28. Pressure Tissue Damage is Likely “Safe” Reswick & Rogers Time
- 29. r ea Sh Fr ict io n
- 30. Friction.. Good or Bad?
- 31. Friction Force that resists the relative motion of two objects in contact OR The Action of one object rubbing against another
- 32. Shear Stress Results from a force parallel to the tissue which causes Tissue Deformation The AMOUNT of deformation is known as Shear Strain
- 33. Understand “Cause” & “Effect” “dynamic, quasi-linear, viscoelastic, structural model”
- 34. NO
- 35. NO Due to Complexity of Factors
- 36. Mechano-transduction Mechanisms by which cells convert mechanical stimulus into physiological activity - anabolic and catabolic
- 39. The Stiffness of the Upper needs to match the stiffness of the sole
- 41. • Shoe and Contact Surface (footbed) Designed to 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” • “Soft” Uppers not Necessarily Best - Match to the Ambulatory Status and Load Expectations
- 42. Remember .. Biomechanics can provide insight. It should support every choice. Confusion of Terminology
Editor's Notes
- 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.\nWe 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.\n\n
- \n
- \n
- \n
- \n
- \n
- \n
- \n
- \n
- \n
- \n
- \n
- \n
- \n
- \n
- \n
- \n
- \n
- \n
- \n
- \n
- 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.\n\n
- \n
- \n
- \n
- \n
- \n
- \n
- \n
- \n
- 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.\n\n
- \n
- 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.\n\n\n
- 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.\n
- 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.\n
- 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. \n\n
- \n
- 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.\n\n
- \n
- \n
- \n
- 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.\n\n
- \n
- \n
- 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.\n\n
- \n
- \n
- \n
- Here is a short list of principles that should guide us.\nFirst 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.\nThe 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. \nTake 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.\nOf 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.\n\n
- \n