Friction vs. Shearing in Wound Care: How Do You Tell the Difference?

Published on August 20, 2015 by Bill Richlen, PT, WCC, DWC

Friction vs. Shearing: What's the Difference?

Content updated in 2021

In my many years as a wound care clinician, I have frequently heard other clinicians use the words “friction and shearing” interchangeably. 

However, truth be told, the forces are not exactly same, and when involved in creating tissue damage, the outcome from each is much different. Our goal here is to parse and differentiate these two terms — forces and the manifestations observed in a wound. 

What is Skin Friction in Wound Care?

Let’s begin with “friction.” According to Dictionary.com, friction is “surface resistance to relative motion, as of a body sliding or rolling” and “the rubbing of the surface of one body against that of another.” An example related to our patients would be their skin against the sheets on the bed. 

Another term to understand is “coefficient of friction,” which is defined as the ratio of the force required to move two sliding surfaces over each other and the force holding them together. 

Basically, the higher the coefficient of friction, the more aggressively the two surfaces will adhere to each other. The lower the coefficient of friction is, the more easily the two surfaces will slide across each other. 

In order for tissue damage to occur, the coefficient must be at a level high enough to create drag that will injure the superficial layers. Decreased levels of friction allow the surfaces to easily slide across each other. Too much friction and there is no movement at all. 

Ultimately, the damage to the tissue can and will only be limited to the superficial layers (i.e., skin) thus resulting in partial thickness damage. Single movements cannot cause full thickness damage when friction is the only force involved.  And friction alone cannot cause a pressure injury, but rather a traumatic wound, such as a skin tear. 

What is Skin Shearing in Wound Care?

“Shear” is an entirely different subject that incorporates friction and another force, usually gravity, (leading to pressure injuries) or inertia (leading to trauma injuries). 

Shear is often described as an internal opposing motion of tissue and bone created when a patient is sitting up in bed or in a chair. Gravity affects all tissues/layers pulling them down in a slow, gradual manner. 

Simultaneously, the skin interacts with the sheets creating friction. As the bone is pulled down by gravity and the skin is in essence “pulled up” by the sheet, the subcutaneous tissue and muscle are caught in between, literally pulled in opposite directions, leading to shear. 

This pulling creates stress on the soft tissue layers (fat and muscle) and potentially could lead to a tearing of the tissue depending on how high the shearing force becomes.

The greatest stress is also now applied to the two tissues that are the least tolerant of ischemia from the concurrent pressure from sitting. Shearing forces are greatest over the sacrum, gluteal and ischial areas of the body. 

When you put this together, the subcutaneous and/or muscle layer will be the first to succumb to pressure damage leading to full thickness wounds often with tunneling and/or undermining. 

However, shearing can only contribute to and compound the damage created by pressure, it cannot cause a pressure injury in and of itself. A purely shear-based injury is a traumatic wound that requires enough inertia to keep the body moving in one direction. This occurs while the coefficient of friction is high enough to limit the tissue in contact with the other surface from sliding across but rather “grabbing” the surface. This results in a violent shearing force that tears tissue apart such as in an avulsion. 

Keeping Things Straight

As we discussed above, friction and shearing are not the same. Each affects tissue differently when applied to the body and how the resultant damage manifests itself. 

Implementing surfaces and devices that can reduce both forces also will reduce the risk of pressure injuries.

Interested in wound care certification courses? Kickstart your career and explore course today!

wound care

Bill Richlen, PT, WCC, DWC, is a licensed physical therapist and has experience in advanced wound care consultations in long-term care, outpatient, skilled rehabilitation and home health. He has served as a clinical instructor for physical therapy students, been the director of several large rehabilitation departments, and has been providing multi-disciplinary wound care education to nurses and therapists for over 17 years. His expertise in diverse settings enhance his role as a clinical instructor. Bill’s dynamic and captivating teaching style keep’s attendee’s attention throughout the course.

Wound Care Education Institute® provides online and onsite courses in the fields of Skin, Wound, Diabetic and Ostomy Management. Health care professionals who meet the eligibility requirements may sit for the prestigious WCC®, DWC® and OMS national board certification examinations through the National Alliance of Wound Care and Ostomy® (NAWCO®). For more information see wcei.net.

What do you think?

comments

  • Don’t miss the latest wound care news! Subscribe to receive our newsletter to your inbox.

    *By submitting this form you consent to receive communication via email from the Wound Care Education Institute®. Check out our privacy policy for more information. You can unsubscribe at any time.