Can Smart Orthotics Have An Impact In Preventing Ulceration?
Many studies that investigated the use of therapeutic footwear along with accommodative inserts have reported only moderate rates of efficacy in preventing diabetic ulcer recurrence. Can one attribute this to the oversimplification of the foot ulcer pathology?
As Metin Yavuz, PhD, notes, well-known scholars such as Cavanagh, Armstrong, Bakker and Bus classified the evidence to support the use of footwear for the ulceration as “meager.”1 Dr. Yavuz suggests that therapeutic footwear utilized in earlier studies may not have been tested for performance prior to researchers conducting the studies. He adds that all the footwear and orthotics in such studies focused on reducing plantar pressure and did not account for other factors such as shear forces or the activity level of patients. He says that may be why the footwear failed to prevent ulcer recurrence.
Ahmet Erdemir, PhD, also cites the importance of examining other factors such as the long-term performance of footwear, patient adherence and activity levels.
Brian Davis, PhD, concurs that one should not overlook shearing forces when noting the moderate success of therapeutic footwear. While it is likely frictional forces are a key variable, he acknowledges several other reasons for skin breakdown. These factors include alterations in collagen properties, autonomic nervous dysfunction that alters sweating responses, diminished microcirculation and superimposed aging.
Dr. Erdemir calls plantar pressure a “convenient candidate” that can identify the risk of ulceration and aid in testing the performance of footwear interventions since one can easily measure this variable for barefoot conditions and also via in-shoe testing. While he notes there is some association with peak plantar pressures and plantar ulceration, Dr. Erdemir adds the possibility of contact shear, pressure gradient and internal stresses as mechanical variables being responsible for foot ulceration.2-4 As he explains, it is not clear that interventions aimed at plantar pressure reduction also reduce these mechanical variables.
Dr. Yavuz notes that Lavery and colleagues called foot pressure a “poor tool” in predicting ulcers.5 As he explains, foot ulcers do not necessarily occur at peak pressure sites but may occur at sites that experience normal magnitudes of pressure.6,7 On the other hand, Dr. Yavuz has co-authored studies that suggest shear forces also play a major role in ulceration.2,8
Since the etiology of diabetic foot ulcers is multifactorial, Dr. Yavuz says focusing on only one or two factors will oversimplify the problem.
“I personally think it is time that we approach the problem from a broader perspective and try to understand the exact mechanism that leads to tissue breakdown. Once we know the exact pathology, we can then design optimal and more effective orthotics,” emphasizes Dr. Yavuz.
If frictional shear forces prove to be more important in the etiology of the diabetic foot lesions, can one design orthotics to reduce plantar shear effectively?
While it is possible to design orthotics to reduce plantar shear, there are some constraints, according to Dr. Erdemir. When it comes to tackling plantar pressures, Dr. Erdemir says the vertical force must be distributed evenly under the foot in order to support the foot during gait. When it comes to footwear, he tries to distribute pressure evenly so peak pressures will be close to mean pressure.
For plantar shear, Dr. Erdemir notes a horizontal force under the foot is necessary for adequate propulsion. He says physicians must also ensure even distribution of horizontal force to prevent high peak shear stress. Insole solutions to distribute plantar pressures may not necessarily have the same effect on contact shear. In addition, without in-shoe measurement capabilities to evaluate in-shoe shear, the performance of footwear on reduction of contact shear remains unknown, according to Dr. Erdemir.