Decoding foot wounds: Pressure injury vs. diabetic foot ulcer (DFU)

Foot wounds

How often have you found yourself in the conundrum of deciding whether a wound on the foot of a diabetic patient is a diabetic foot ulcer or a pressure injury? 

Probably more than once. This is a hotly debated issue among wound care clinicians.

In this post, we’ll dissect the facts and provide a clear understanding of how to differentiate the two types of foot wounds.

Let’s start with some basic understanding behind the etiology of each wound type. 

Pressure injury foot wounds

A pressure injury results from intense and/or prolonged pressure at sufficient levels to create ischemia in the tissue that ultimately leads to tissue necrosis. 

This occurs when the pressure becomes greater than the capillary closing pressure (usually 32 mmHg in healthy people) and tissue perfusion stops. Bony prominences are some of the highest risk areas; friction and shear can also be contributing factors.

Diabetic foot ulcer (DFU) foot wounds

A diabetic foot ulcer (DFU), or technically a diabetic neuropathic ulcer (since neuropathy can occur for other reasons as well), has several potential causes. These include:

  • Neuropathy (85% of all DFUs)
  • Infection
  • Peripheral arterial disease (large and/or small vessel disease)
  • Trauma from inappropriate footwear, penetrating injuries and repetitive pressure

With neuropathy being the most common, the diabetic does not feel the pain/discomfort associated with the different forms of trauma. 

The common definition of a diabetic/neuropathic ulcer is that it is located below the ankle and the patient has diabetes. Ulcers located on the plantar surface of the foot and toes are most often related to neuropathy (and ischemia as well) in conjunction with trauma, infection and/or high, repetitive pressures. 

DFUs and infections

Infection often occurs as the ulcer progresses. Ulcers located along the lateral side of the foot are most often related to poor fitting footwear and ulcers on the dorsum are most commonly trauma induced.2 

A diabetic ulcer can start as a trauma wound, however, when the diabetes creates conditions in which the wound does not heal in the normal manner, it then becomes classified as a diabetic ulcer.

Note that it would not be called a diabetic ulcer from the onset. For example, if a patient steps on a nail that penetrates into the foot, how would diabetes have caused that? It obviously didn’t initially.

Diagnosing diabetic foot wounds

An area where there is much controversy and debate is the posterior aspect of the heel. As we know, this is a top 5 location for pressure injuries due to the large bony prominence (calcaneus) and the risk of pressure when in bed.

It is not a weight-bearing surface subject to high, repetitive pressures like the plantar heel, nor is it a common area for trauma other than superficial damage from poor fitting shoes. Thus, diabetics are less likely to develop significant neuropathy in that particular area vs. the plantar surface of the foot.

So how should one classify a wound located to the posterior heel? 

When diagnosing and/or classifying the wound type, it should always be based first and foremost on the predominant “cause.” Additional contributing factors that affect healing may exist, but unless they played a notable causative role (mixed etiology), one would not use that as the diagnosis. 

There are basically 11 wound diagnoses:

  • Pressure
  • Venous insufficiency
  • Arterial insufficiency
  • Lymphedema
  • Trauma
  • Surgery
  • Infection
  • Malignancy
  • Autoimmune (systemic)
  • Neuropathy
  • Mixed (multiple causes)

Additionally, in analyzing the posterior heel wound, one should ask some key questions.

  • Were the heels properly offloaded in the bed? 
  • Was the damage associated with improper footwear?
  • What created either ischemic conditions in the tissue or could have traumatized the tissue to lead to this wound?

To simply call it a diabetic wound because it is below the ankle and the patient has diabetes when we know it was because the patient’s heels were not properly offloaded in bed for many hours would be medical malfeasance.

That is not to say that diabetes cannot be the cause of a wound on the posterior heel or be a significant contributing factor to how quickly it will heal in the long term. 

Conclusion

To sum up: do your due diligence and determine the most significant (and likely) causative factor or factors for your patients’ foot wounds. Then diagnose accordingly. 

This is not the time to play the “Hide the PI Game” because we do not want an in-house acquired pressure injury on the record. Your best approach is always intellectual honesty and integrity. 

We wouldn’t call a penetrating wound through the foot from a nail in a diabetic patient a diabetic wound initially. We would call that a traumatic wound. Only when it failed to heal in a timely manner due to the diabetes would we reclassify the wound.

We all are probably familiar with the old saying “Call a spade a spade.” This applies to pressure injuries and diabetic foot ulcers as well.

Until next time, heal on!

Learn more about foot wounds in diabetic patients in our Live Online Diabetic Wound Care Course!

wound care

Bill Richlen, PT, WCC, DWC, is a clinical instructor for the Wound Care Education Institute. As a licensed physical therapist, Richlen 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 more than 17 years. His expertise in diverse settings enhance his role as a clinical instructor. His dynamic and captivating teaching style keeps attendee’s attention throughout each course.

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