The Effects of Extracorporeal Shock Wave Therapy in Different Stages of Scar Formation in Postsurgical Scars Especially After Abdominplasty and Breast Reduction.

1. State of the art Every year 80 million scars develop in the world and 40-70% of these will develop into hypertrophic or problematic scars. Moreover, fibrosis and scar formation of the skin pose a substantial physiological and psychological burden on patients. Scars can be caused by physical trauma, surgical incisions, burn injuries and even acne. Most superficial injuries, that do not reach the dermis, do not leave significant scars. However, deep cutaneous injuries can induce pathological scars. Such scars often result in pain, itching, functional impairment, aesthetic disadvantages, anxiety, depression and poor quality of life of the affected person. All these aspects may cause poor functioning during ADL (4). Other aspects, such as uncontrolled mechanical loading, prolonged inflammation, overactive proliferation, bacterial colonization, and foreign-body reaction are potential factors thought to underlie human hypertrophic and keloid scar formation or contractures.

Recent studies have identified that under influence of mechanical load scar proliferation will be prolonged and will even prohibit full maturation of the scar within the foreseen timeframe of two years of wound healing. Mechanical loading can be regarded as any mechanical stress applied to a healing wound, for example imposed forces during physical therapy or tensile forces during activities of daily living. It has been proven that specific sites that are frequently subjected to mechanical load during daily activities have more risk to develop into hypertrophic scars.

Interestingly, mechanical loading cannot only be regarded as a negative predictive factor in scar formation. Under controlled conditions, mechanical load can activate a process called 'mechanotransduction'. Once activated inflammation, proliferation and thereby fibrosis and hypertrophic scarring can be regulated/controlled. Thus, mechanotransduction can be defined as the intracellular conversion of mechanical stimuli into internal chemical signals resulting in gene transcription. This has an effect on the cytoskeleton and the ECM. Signaling pathways are activated or modulated resulting in modification of the affected (scar) tissue.

Various non-invasive mechanical interventions of physical scar management (e.g. extracorporeal shock wave therapy or ESWT, pressure therapy, vacuum massage,..) apply mechanical load and thereby initiate mechanotransduction. Controlled physical scar management can have a beneficial influence on wound healing and prevention of pathological scars. Therefore, this study will focus on the application of mechanical forces in the form of ESWT application. ESWT considerably improves the appearance and symptoms of hypertrophic scars. However, the mechanisms underlying the observed beneficial effects in scar management is not well understood.

To date, there is no consensus concerning the optimal standard of care in scar treatment. Therefore, there is a need to study the underlying mechanism of scarring and the related influence of controlled mechanical forces. 2. Rationale of the study The heterogeneity in causes of scars, the complicated histology of scarring and the numerous intervention possibilities make late-stage clinical research in this field a search for a needle in a haystack. Moreover, it is always difficult to control variables such as location, demographics and genetics in studies.