Surgeons have constantly sought to achieve the most aesthetic scar. A major factor determining the final cosmetic appearance of a cutaneous scar is the tension acting on the wound edges during the healing phase. Since Theodor Kocher pioneered the alignment of skin incisions with Langer's lines in 1892, surgical techniques that attempt to overcome closing tension have become standard. Yet, no treatment has been available to minimize underlying muscle contractions, which are the major cause of this tension. Botulinum toxin A is a potent drug that produces temporary muscular paralysis when injected locally. It has proven to be safe and effective in the treatment of a variety of disorders, including hyperkinetic facial lines. The objective of this randomized, double-blind, placebo-controlled primate study was to investigate the efficacy of a single injection of botulinum toxin A to improve the cosmetic appearance of cutaneous scars. Symmetric pairs of standardized excisions were performed on either side of the forehead of six primates. The half foreheads were randomized to the botulinum toxin A treatment side versus the placebo injection side. A panel of three blinded facial surgeons assessed the cosmetic appearance of the mature scars 3 months postoperatively. The wounds that had been immobilized with botulinum toxin A were rated as significantly better in appearance than the control wounds (p < 0.01). Histologic examination confirmed that all scars were mature. Blinded, randomized, placebo-controlled human clinical trials are presently under way at the Mayo Clinic.
In 1816, Jules Cloquet reported that contraction of the underlying musculature creates ridges in the skin. 1 Nearly two decades later, Guillaume Dupuytren observed that circular cutaneous wounds inflicted with a round awl eventuated in linear clefts. 2 Using a similar technique, Karl Langer, a Viennese professor of anatomy, created a map of natural cutaneous lines in cadavers that reflect the tension created by underlying muscular contraction. 3 The modern concept of the relaxed skin tension lines advances Langer's works. In general, these lines lie perpendicular to the tension vector of the underlying muscular contraction. Scars aligned with them are subject to reduced tension and heal well, whereas scars oriented against relaxed skin tension lines are subject to repetitive tension, resulting in scar hypertrophy. 4,5 Standard surgical techniques attempt to avoid muscle pull on wounds by aligning them with the lines, undermining the wound edges or creating skin flaps. 6 A method to minimize rather than resist or avoid this muscle pull would be a desirable therapeutic modality in the treatment of cutaneous wounds.
Botulinum toxin A (Botox, Allergan, Irvine, Calif.) is a potent neurotoxin that produces a flaccid paralysis of striated muscle for a period of 2 to 6 months. For more than 30 years, its application has proven safe and efficient in the treatment of a variety of disorders, including hyperfunctional facial lines. 7 We hypothesized that local botulinum toxin A-induced paralysis of the musculature subjacent to a cutaneous defect would minimize the repetitive tensile forces on the wound edges, resulting in superior cosmetic outcome in the resultant scar. This study was thus designed to investigate the safety and efficacy of botulinum toxin A for temporary pharmacologic immobilization of a healing facial wound in a primate model.