A Biomechanical Comparison of the Stiffnesses of Sacral Dressings Designed for Pressure Ulcer Prevention

Introduction: Sacral dressings are commonly used prophylactically to reduce the risk of tissue damage under the dressing. The protective mechanism relies on its capacity to absorb soft tissue deformation due to the patient’s weight and dampen the buttocks’ deep tissue pressure. Finite element analyses (FEA) demonstrated that dressing’s flexibility can affect its protective capacity and that a difference in stiffness in the medio-lateral and cranio-caudal directions, referred as anisotropy, could be an important design feature. The clinical relevance of FEA models relies on the input of real-life material properties. The objective of this study was to characterize dressings stiffness used in clinical practice to improve our understanding of dressings’ protective mechanism.

Materials and Methods: Tensile tests (ASTM D882) were performed on five sacral dressings, namely LQ, SA, EX, MP, and AL. Medio-lateral and cranio-caudal stiffnesses were characterized on six samples of each dressing respectively. Force-displacement curves were collected to extract the linear stiffness of each dressing. Mann Whitney statistical tests were performed to compare dressings’ stiffnesses and evaluate anisotropy.

Results: The stiffest dressing was almost four times stiffer than the most flexible dressing in the cranio-caudal direction. The SA dressing was the most flexible (1.9 N/m; p<0.05), compared to the EX (2.4 N/m) and LQ (2.5 N/m) that were equivalent (p>0.05), followed by the MP (3.3 N/m; p<0.05) and the AL (6.6 N/m; p<0.05). The EX, MP, LQ, and AL were anisotropic (p<0.05) with a reduction of stiffness in the medio-lateral direction of 85%, 79%, 47%, and 46%, respectively.

Conclusion: A large variability of stiffness exists between dressings used in clinical practice, with most dressings exhibiting an anisotropic behavior. The clinical impact of dressing stiffness is still under investigation, but the characterization of dressings’ mechanical properties is important to further assess the capacity of different designs to reduce pressure injury risks.