  Reconstructive surgeries often use topological manipulation of tissue to
minimize post-operative scarring. The most common version of this, Z-plasty,
involves modifying a straight line cut into a Z-shape, followed by a rotational
transposition of the resulting triangular pedicle flaps, and a final
restitching the wound. This locally reorients the anisotropic stress field and
reduces the potential for scarring. We analyze the planar geometry and
mechanics of the Z-plasty to quantify the rotation of the overall stress field
and the local forces on the restitched cut using theory, simulations and simple
physical Z-plasty experiments with foam sheets that corroborate each other. Our
study rationalizes the most typical surgical choice of this angle, and opens
the way for a range of surgical decisions by characterizing the stresses along
the cut.
