Chapter 3 - Computational modeling of the thin muscle layer, panniculus carnosus, demonstrates principles of pressure injury and prophylactic dressings

Abstract

Pressure injuries or pressure ulcers (PUs) are wounds that arise from sustained mechanical loading, and people who lack mobility are at high risk of developing chronic PUs. Prevention of PUs is a labor-intensive burden for caregivers, and there is growing interest in protective devices and prophylactic dressings to prevent PU formation. This motivates us to ask what biomechanical structures exist in nature for mechanical protection of soft tissues. The panniculus carnosus (PC) is a thin muscle present under the skin of many mammals, and it is present to some extent in humans as a so-called vestigial organ. Most people have some PC muscle present in discrete regions of the body, such as the neck and the base of the palm, while other regions may have no PC or sparse strands of muscle fiber. A thin layer of PC muscle has been documented in the plantar region of human heels, and we ask whether a similar PC layer at the dorsal heel would affect biomechanical load and soft tissue stress during mechanical loading and/or PU formation. To answer this question, we constructed simplified biomechanical models of the heel, with and without a 1.5mm PC layer beside the dermis. We then performed finite element calculations to simulate the weight of the foot being applied from the calcaneus bone onto the dorsal heel. The model with PC showed broader distribution of load and decreased peak stress, compared with the model without PC, suggesting that the PC serves naturally to protect skin and soft tissues from mechanical injury. Taking inspiration from the natural properties of PC, we propose future work should engineer PC-like dressings for adhesion to epidermis. Biomimetic dressings with firm elasticity resembling a PC muscle might be beneficial for prevention of pressure-related injuries in a variety of locations and contexts.