Answer:
Explanation:ll scars tell a story. A childhood fall, an adult fight, an accident, an assault—all will leave their mark. In modern times, the elective scar of a surgical incision has gone from the large heroic scars (the bigger the better) of general surgery, to the carefully planned, minimally invasive incisions of modern times. Once the sign of a great surgeon, the prestigious elective scar is now the nearly invisible scar. The contributions of war-related medical advances represent an important chapter in medical history. Survival from the complex blast/burn/bullet injuries of modern weapons is nearly assured and provides new challenges for recovery. Thus, the history of scars, from ancient wounds to the horrendous scars that signify survival from grievous injury, tells the story of not only human resilience, but of medical miracles.
Scars result from healing without regeneration through the deposition of collagen and fibrous connective tissue. Why the salamander can regenerate a leg and other tissue, but a human cannot, is an evolutionary conundrum. A common laboratory regeneration model is the Mexican axolotl (Fig. 1-1). This endangered species regenerates entire limbs as well as nervous tissue. Mammals are known for some specific regenerative capacities, like antlers in the deer family, which are shed and regrown annually. Humans may be able to regenerate the endometrium, liver, and kidney, but only minimal segments of fingers or toes. In general, humans heal after injury by the formation of scar tissue as a means of bridging the defect, whether it involves only skin or larger chunks of skin muscle and bone.
What is the evolutionary advantage of healing by scar versus regeneration? Energy requirements for wound healing in humans are well documented. For a simple femur fracture, the bedridden patient who normally requires 2,500 calories per day may require up to 6,000 calories per day.1 Burns, in particular, result in high caloric requirements during recovery and are significant scar-forming injuries.2 Burns involving less than 20% of the total body surface and wartime amputations were frequently fatal until nearly the end of the 19th century, and only slightly larger burns until well after 1950. The relative efficiency in time and energy requirements for scar healing compared to regeneration after major injury is likely an evolutionary advantage for the species, if not for the modern individual.
As the complex biology of wound healing becomes increasingly understood, greater insights into the modulation of healing and vertebrate regeneration are emerging. Genetic manipulation in one mouse species has even restored regenerative capacity. The Lin28a gene, silenced in maturing vertebrates, restores regenerative ability when turned on in mouse infancy, but not in maturity.3 Another species, the African spiny mouse, can heal full-thickness skin injuries without scarring. Current intensive research on the use of stem cells for regeneration is widespread, as are clinical practices promoting their use, despite limited documentation in controlled clinical trials. The identification of the Lin28a and b genes and their role in stem cell regeneration is also being rapidly elucidated.4 These concepts offer the promise of future transformative approaches to healing human tissues.
Scars are destined to become part of medical lore if the full potential of current research on genetic manipulation, embryonic healing, and stem cell applications is achieved. The management of scars to date has depended on the prevention of injury, the optimization of wound healing, and the direct treatment of scars after they have formed. This chapter will explore the progress in scar care through history, as well as the meaning scars have had in medicine, law, and literature. So many different individuals have contributed to our knowledge of wounds, their management, and the diagnosis and treatment of scars that not all of them can be introduced in this chapter. Table 1-1 provides an outline of the more important events in the years preceding the modern era of wound care and scar management. I have chosen not to focus on events of this modern era. Rather, I have offered my own view of some of the key people and events prior to the last 60 years. More recent advances are the province of other authors in their respective chapters.
