Biomechanical analysis of stresses occurring in vertical and transverse scars on the lower leg

Background: The processes involved in wound healing differ depending on wound tension. However, biomechanically, little is known about how mechanical stimulation actually works on wounds. Methods: Six isotropic lower leg models were generated from computed tomographic findings with computer-aided design. Two types of scar were generated in the posterior calf: scars parallel to the limb axis (vertical scars) and scars perpendicular to the limb axis (transverse scars). Two types of elastic modulus were assigned to each scar: one for the early wound and one for the hypertrophic scar. A force of 10 N was applied at the ankle to imitate dorsiflexion, and stresses occurring in the scars were investigated using the finite element method. Results: In early wound models, the mean maximum stress was threefold higher in the transverse scars than in the vertical scars, and the difference was statistically significant. In hypertrophic scar models, however, the mean maximum stress was fourfold higher in the vertical scars than in the transverse scars, and the difference was statistically significant. Conclusions: In the early healing phase when the wound is weak, transverse scars are unfavorable because articular movement is consistent with the wound-opening direction. However, after wounds become stiff, the vertical scars are exposed to higher stresses than transverse scars. Therefore, from the long-term point of view, vertical scars are unfavorable in the lower leg. If high stresses in the wound inhibit scar maturation, the authors' results were consistent with the clinical observation that vertical leg wounds take a longer time to mature than transverse wounds.