Is Shear The New Peak Plantar Pressure?
- Volume 25 - Issue 6 - June 2012
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• Total weight of the cast limits activity. The fact is that the weight of the cast itself is a great deterrent to fast walking. Simply put, it just is not easy to get around in the cast. However, by slowing the speed of walking, the rate of tissue deformation and the duration of load are reduced.
Simply put, shear is likely to play just as significant a role in the development of diabetic foot ulcers as peak plantar pressures. However, due to the difficulties associated with measuring shear, it is harder to know where the thresholds for injury exist. Remember that all mechanical forces consist of vectors that normally contain components in both the vertical and horizontal directions. If you understand the nature of the damage caused by each component, you can take precautions to offset these forces.
Not all wounds require a total contact cast. However, if your current plan for reducing vertical loads is not resulting in wound healing, then consider the effect that shear forces may have as well. Utilize protective footgear that limits the excursion of the foot against the insole during walking. The patient can wear boots and fixed ankle walkers to limit motion in the ankle and lower leg.
Finally, clinicians should reassess at each visit so no detrimental loads sneak through to impede the patient’s wound healing progress. Inspect the condition of the shoe and the insole to make sure patients are able to achieve the level of correction needed.
Dr. Landsman is an Assistant Professor of Surgery at the Harvard Medical School. He is the Chief of the Division of Podiatric Surgery with the Cambridge Health Alliance in Cambridge, Mass. Dr. Landsman is a Fellow of the American College of Foot and Ankle Surgeons.
1. Yancey P, Brand P. The Gift of Pain: Why We Hurt & What We Can Do About It. Zondervan Publishing House, Grand Rapids, Michigan, 1993.
2. Coleman WC, Brand PW, Birke JA. The total contact cast. A therapy for plantar ulceration on insensitive feet. J Am Podiatry Assoc. 1984; 74(11):548-52.
For further reading, see “Can Smart Orthotics Have An Impact In Preventing Ulceration?” in the June 2010 issue of Podiatry Today.