Early Detection of Pressure Injury Using a Forensic Alternate Light Source

Heather Hettrick, PT, PhD, CWS, CLT-LANA, CLWT; Cheryl Hill, PT, PhD, DPT; Patrick Hardigan, PhD


Wounds. 2017;29(8):222-228. 

In This Article


There are numerous factors associated with increased risk of pressure ulcer development, including people of African descent, of an older age, with a poor nutritional status, who are underweight or malnourished, with physical or cognitive impairment, with incontinence, and with specific medical comorbidities that affect circulation such as diabetes or peripheral vascular disease.[6] There are several instruments available to assess for the risk of pressure ulcers such as the Braden Scale, the Norton Scale, and the Waterlow Scale; however, there are no reliable tools to detect tissue trauma before visible manifestations are evident on the skin.

A study by Rowan et al[7] conducted within the field of forensic medicine has relevant implications within this study. Blunt force trauma may not show visual skin effects initially, but the subdermal breakdown may still be occurring.[7] This is similar to the pathophysiology that takes place with pressure ulcers. This study noted that these changes beneath the skin may be revealed by other tools, and Rowan et al[7] looked into the detection of previous blunt force injury after the resolution of skin changes were no longer visible to the naked eye. Just as with pressure ulcers, many times the damage is not visible to the naked eye. In their study,[7] the investigators used an adapted digital camera and a standard Nikon camera (Tokyo, Japan) to photograph 10 volunteers over a 6-month period. There was no statistically significant difference between groups of bruises photographed with both the IR digital camera adapted to capture only IR light and the standard camera with the same lens fitted to it. The 2 groups were not significantly different in regard to detectable skin changes. The use of the near-IR spectrum, with wavelengths longer than the human eye can detect, did not reveal significant evidence of bruising after it had faded from view to both the naked eye and to a standard camera.[7] While this was an innovative idea, it is implied that further work is needed to create a device that is more effective at detecting subdermal tissue destruction.

Also within the realm of forensic innovation in medicine is the study of ALS in crime scene investigations to detect soft tissue injuries not seen under visible light. In a study by Holbrook and Jackson,[8] ALS was used to determine its value as a tool for visualizing acute trauma in cases of suspected strangulation. The ALS emits UV, IR, and visible light wavelengths to enhance the visualization of marks on the skin and is also able to reveal bruising and pattern induced by, but not limited to, a shoelace or belt. The Holbrook and Jackson study[8] provides insight into the use of different wavelengths when utilizing ALS to detect injuries at various depths in the skin. It also presented evidence of use in individuals with darker skin tones, although specifics about the effects of the wound visualization in darker skin tones would be preferable.

In the methods of Holbrook and Jackson's study,[8] different wavelengths are discussed as beneficial in visualizing wound depth. For example, the study determined that most of the bruising caused by strangulation trauma was best seen using wavelengths 415 nm to 515 nm and multiple colored protection goggles. For subcutaneous wounds, the researchers recommend using IR light to best visualize the wound because of the depth of tissue involved. Ultimately, the wavelength used depends on the depth of the injury. Further research needs to be done to determine if different areas of the body affect the quality of the pattern that can be visualized under the ALS. Moreover, the researchers suggested using ALS in medical settings to aid health care providers in detecting tissue breakdown before the visible manifestation of a wound or injury becomes evident in white or ambient light.[8] Alternate light source has been used in autopsies and during crime scene investigations, and from this work,[8] it has been proposed to aid living patients as well. Based upon the findings of this study,[8] it appears that ALS could be an important tool for prevention and early detection of pressure ulcers.

Absorption occurs when light of a given wavelength is absorbed by a molecule's electrons, and thus the molecule appears darker than the surrounding environment; this absorbed light transfers its energy into the electrons of the molecule. Everyday colored objects, such as paint, cloth, human skin, and plastic, all absorb some wavelengths of light and reflect or transmit others. Without being bound to a particular theory, it is believed that tissue damage which has or may develop into a pressure ulcer/injury may damage deep tissue structures first, including bone, muscle, and tendon, before the skin is disrupted, given that skin has the highest resistance to hypoxia. Accordingly, it is expected that the damage from pressure and/or shear will cause microtrauma and myocutaneous infarction, leading to tissue death and the release of blood products into the tissues. The ALS, using one or more wavelengths, should detect this tissue trauma by the extravasated blood molecules absorbing the light. It is noted that the depth of the skin involved is typically between 3 mm and 7 mm and is therefore reachable at the greatest depth by, at least, IR light, and to varying depths by the shorter wavelengths generated by the forensic ALS as well.