Calluses harmful to foot health? Most people assume calluses protect the body from friction.
However, when diabetes and peripheral neuropathy enter the picture, there is increasing evidence that excessive callusing may indeed be harmful to foot health. A callus may hide and even worsen inflammation that occurs under the callus. The inflammation may be an early sign of a diabetic foot ulcer.
Diabetic foot ulcers can be devastating. Ulcers often lead to amputations. There are as many as 80,000 diabetes related amputations each year (Reiber 2002). The five-year mortality rate after amputation is 39 – 80% (Singh et al. 2005). The annual cost to the US health care system alone is between $ 1 and $ 9 billion (Reiber et al 2008; Frykberg et al. 2006; Ulbrecht et al. 2004).
Foot ulcers are difficult for the non-afflicted to understand. When the average person's foot hurts – when a blister forms for example – she or he hobbles and tries to stay off it. Pain is an effective communicator. For many people with diabetes, however, they have lost some or all sensation in their feet due to peripheral neuropathy. This compromised sensation can lead to excessive loading of and damage to the foot.
Callus formation precedes ulcer formation in over 82% of patients with diabetic foot ulcers (Sage et al. 2001). Murray and co-workers reported that a callus is "highly predictive" of ulcer development (Murray et al. 1996). Therefore the link between calluses and ulcer formation seems clear.
A group at the University of Tokyo recently looked at signs of inflammation under calluses on diabetic and non-diabetic feet (Nishide et al. 2009). The Tokyo group used ultrasonographic and thermographic imaging techniques to find evidence of traumatized tissue and elevated temperature. Even though the non-diabetic feet had more calluses, there were no signs of inflammation under the calluses on the non-diabetic feet. On the other hand, 10% of the calluses in the diabetic group had inflammation (Nashide et al. 2009).
Perhaps most concerning is that inflammation under calluses may be very hard to detect. In the Nishide study, experienced wound care nurses and specialists could not identify the latent inflammation in the calluses, even though three of the five inflamed calluses had tissue damage reaching down to the muscle layer.
If calluses obscure developing ulcers, it is even more critical that calluses be managed. One common way for calluses to be managed is shaving the calluses. The American Diabetes Association strongly recommends a professional caregiver such as a podiatrist perform any shaving or "debridement" procedure. Moreover, the procedure must be repeated regularly.
Can callus formation be prevented? Calluses form because of friction. This is well established in the scientific literature (Sanders et al. 1995; Carlson 2006). A reduction in friction should slow callus formation. One way to reduce friction is to lower the coefficient of friction (COF) between surfaces – ie, to make surfaces slide more easily in relation to each other.
Lubricating agents have been used to lower the COF in footwear. Lubricating agents such as oils, silicone, and powders may initially decrease the COF in footwear. However, in studies conducted by the US military, after 3 hours of use the lubrication agents an increase in COF of 35% above baseline occurred (Knapik et al 1995). Therefore lubricating agents can be very counterproductive in fighting the friction that causes calluses.
Materials such as moleskin have been used for a long time. However, the COF of moleskin when paired with commonly used materials such as a cotton sock is very high. (Carlson JM 2006). Socks can potentially reduce friction but the friction-relief is not targeted to the problem area.
ShearBan® and ENGO® patches provide long-lasting, targeted relief from the harmful effects of friction. They are patented products, developed and manufactured by Tamarack Habilitation Technologies, Inc. Unlike the typical bandage, however, ShearBan and ENGO apply to footwear or other pieces of equipment. ShearBan and ENGO have a surface made of a material of specially formulated material resembling Teflon® – the most slippery, friction fighting material known. ENGO or ShearBan's slippery surface should be placed opposite a callus, blister, or other hotspot to reduce friction and prevent harm to the skin.