The biomechanics of advancement and rotation flaps.

An animal model (using piglets) has been developed to study the mechanical properties of simple advancement and rotation flaps. The effects of different length-width ratios and defect sizes on the tension required to close a rectangular advancement flap are described. Characteristic curves of force vs. advancement distance are presented and mechanisms discussed. The flaps should have a length-width ratio of a least 1:1; the mechanical advantage of lengthening the flap further is directly related to the measured closing tension. The distribution of tension in a standard 180 degrees rotation flap is analyzed. Maximum tension is found between 90 degrees and 135 degrees (opposite the site of defect closure); this is at variance with the vector commonly pictured. The force required to close a defect with rotation flaps of varying length (45 degree to 180 degrees) is measured. There is little mechanical benefit in extending the flap past 90 degrees.