Factors contributing to pressure injuries in traumatic spinal cord injury

Pressure and shear

Pressure and shear forces, especially over bony prominences or due to medical devices or other objects, are the principal factors associated with the development of PI. As a result of these forces, the loaded soft tissues will deform, causing strains and stresses which, if sustained, may lead to tissue damage ( ). Sustained soft tissue deformation leads to hypoxia, reduced lymphatic flow as well as reduced nutrient supply and removal of metabolic waste products which in turn causes cell death and tissue damage ( ; ; ). Pressure intensity and duration as well as tissue tolerance and vascular perfusion also play a significant role ( ).

Both low mechanical load for a long period and high load for a short period of time may result in tissue damage ( ; ; ). To date, no universal safe tissue interface pressure threshold has been established, thus highlighting the importance of evaluating and addressing all possible PI risk factors as tissue interface pressure measurement alone is insufficient ( ; ; ).

Tissue tolerance

Different tissue types have varying degrees of tolerance to deformation with muscle tissues being more susceptible to damage than fat and skin ( ). The orientation of shear forces is also important as skin is more resistant to forces occurring in alignment with collagen fiber bundles than when they are applied perpendicular to fiber bundles ( ).

In addition, soft tissue tolerance may be affected by many factors such as perfusion, micro-climate as well as patients and tissue characteristics ( ). For example, trauma victims have an increased risk of developing PI, with 45.8% of them developing within 48 h of admission ( ). Because of the risk factors inherent to their condition, such as immobility, decreased autonomic control, hyper catabolic responses, and lack of protective response due to sensorimotor deficits ( ; ), patients with traumatic spinal cord injury (TSCI) are almost 14 times more likely to develop a PI than other trauma patients ( ).

Most common locations and severity

During acute care and rehabilitation, when patients spend more time in a supine position, the most commonly affected areas include the ischium (28%), the sacrum (17%–27%), trochanters (12%–19%), and heels (9%–18%) ( ). During the chronic stage, when patients spend more time in a sitting position, the ischium or perineum (48.3%), sacrum (37.2%), and trochanters (14.5%) are more susceptible to PI ( ).

Molano et al. have shown that in their cohort, the majority of PIs occurring during acute care were stage 2 and 3 ( ). For their part, Powers et al. have shown a predominance of stages 1 and 2 ( ). In a recent study, Ham et al. suggested that the number of stage 1 PI may be underestimated due to the absence of skin loss, making their identification sometimes more difficult and by the fact that they rapidly progress to more severe stages if not addressed ( ).

Impact

Patients with TSCI who develop a PI during acute hospitalization have higher complication rates, significantly longer length of stay, and higher risk of recurrence ( ; ; ). Complications of PI such as wound infection, cellulitis, septic arthritis, osteomyelitis, sepsis, and malignant transformation (Marjolin’s ulcers) may also occur ( ). In some cases, PI can lead to surgical procedures, amputation, and sometimes even death due to an infection ( ). Indeed, 7%–8% of patients with TSCI who develop a PI die from associated complications ( ). PI also limit long-term functional outcome by interfering with rehabilitation ( ; ). Following the acute hospitalization, patients are at higher risks of developing a PI during the first year post-SCI or more than 25 years post-injury ( ). After urinary tract infections, PI represent the second most common cause of re-hospitalization during the first year post-TSCI as well as in the following years, accounting for 11.3% of re-hospitalizations at 1 year, 14.6% at 5 years, 17.5% at 10 years, and 21.3% at 20 years post injury ( ).

Cost

It has been estimated that one-quarter of the cost of care for patients with SCI is associated with PI and thus represent a significant preventable financial burden. In 2013, in Canada, the occurrence of PI resulted in an additional $18,758 to the cost of acute hospitalization following TSCI ( ). In the United Kingdom, PI treatment ranges from $2000 to $18,000 ( ) while in the United States, annual health care costs per patient was estimated to be $73,021 higher for patients with PI when compared to patients without PI ( ). Finally, a recent systematic review showed that interventions to prevent PI occurrence were considerably less expensive than the interventions for their treatment ( ).