Quantification of the mechanical properties of the plantar tissues of patients with diabetes is not extensively studied. Existing models typically favored linear or single-layer models of deformity. However, in a recently published study using a multilayer, non-linear model to assess plantar tissue stiffness in this high-risk population, Kwak and colleagues have provided great insights on this subject.1
The study involved 30 patients, 10 each in “healthy young,” “healthy old,” and “old diabetic” cohorts.1 After indenting two sites on the heel of these patients, researchers obtained computed tomography studies and proceeded to measure and analyze the thickness of fat and skin at each of the indentation sites. The shear modulus of the fat layer in old patients with diabetes was 4.68 MPa in comparison to 2.71 MPa in the healthy old cohort and 2.27 MPa in the healthy young group. The same measurements for the skin layer were 5.86, 7.05 and 14.58 MPa for the old patients with diabetes, healthy old and healthy young populations respectively.
The older cohort that had diabetes had a stiffer plantar fat layer while still having relatively softer skin, which alters stress conditions in comparison with younger and non-diabetic populations. Therefore, the same mechanical load could put older patients with diabetes at risk for ulceration.
All tissues in people with diabetes are prone to changes in viscoelasticity. In essence, the tissue (skin and fat) can turn from a tortilla to (if you will) a cracker because of (among other things) non-enzymatic glycation. It would be great if we could counter this. This is part of our philosophy and approach at the Southwestern Academic Limb Salvage Alliance (SALSA).
Although it seems age also plays a role in the stiffening of the plantar fat layer, diabetes effectively accelerates the process. As we know, offloading measures, including diabetic shoes, accommodative insoles and other interventions, play an important role. In our practice, we have begun to supplement some of these patients with plantar fat atrophy and stiffness with fat grafting. We especially perform fat grafting in patients with pre-ulcerative calluses. Our preferred technique uses both the patient’s own fat as well as donor fat grafting (Leneva® Allograft Adipose Matrix, MTF Biologics).
Overall, plantar tissue stiffness is one more facet we must understand to most effectively address faulty biomechanics in patients with diabetes and prevent ulcer occurrence or recurrence.
Dr. Armstrong is Professor of Surgery at the Keck School of Medicine at the University of Southern California. He is the Director of the Southwestern Academic Limb Salvage Alliance (SALSA).
Editor’s Note: This blog originally appeared at:
https://diabeticfootonline.com/2020/05/27/increase-of-stiffness-in-plantar-fat-tissue-in-diabetic-patients/?utm_sq=gh73unmxau&utm_source=linkedin&utm_medium=social&utm_campaign=davidarmstrong&utm_content=ownblogposts . It is adapted with permission from the author.
- Kwak K, Kim J, Lee KM, Koo S. Increase of stiffness in plantar fat tissue in diabetic patients. J Biomechanics. 2020:107:109857.