Friction Blisters of the Feet: A New Paradigm to Explain Causation

Abstract

Friction blisters on the feet commonly occur when individuals engage in active pursuits such as running, hiking, and military training. The high prevalence of blisters in active individuals underscores the fact that the pathomechanics of this condition are not fully understood. The traditional blister causation paradigm revolves around heat, moisture, and friction. In reality, foot friction blisters are caused by repetitive shear deformation. The 3 fundamental elements of blister-inducing shear deformation are (1) motion of bone, (2) high friction force, and (3) repetition of the resulting shear events. Rubbing at the skin surface is not a mechanism for friction blister formation. To that end, prevention of the friction blister continues to be an elusive quest for both the patient and the treating clinician. In this article, we aimed to highlight the limitations of the long-held blister-causation paradigm and offer a new explanation.

Keywords: foot injury; shear; skin injury.

Figure 1

A schematic representation of the 5 layers of the epidermis of “thick skin” present on the plantar and palmar surfaces, from deep to superficial: stratum basale, stratum spinosum, stratum granulosum, stratum lucidum (absent in “thin skin”), and the stratum corneum.

Figure 2

Initial contact creates anterior-directed shear force. Illustration courtesy of Kevin Rosenbloom, CPed. Reproduced with permission from SNCSC.

Figure 3

Push-off creates posterior-directed shear force. Illustration courtesy of Kevin Rosenbloom, CPed. Reproduced with permission from SNCSC.

Figure 4

Pressure and shear (AP) curves of a representative diabetic subject obtained by a single transducer. Peak-to-peak AP shear was determined by adding the absolute values of maximum anterior and posterior shear magnitudes for each transducer. Abbreviations: AP, anteroposterior; pp, peak-to-peak. Used with permission of Elsevier; permission conveyed through Copyright Clearance Center, Inc.

Figure 5

Simple shear diagram showing the critical influences of friction force and bone movement to the development of shear deformation.