Tension and flap advancement in the human scalp.

The aim of the present study was to evaluate quantitatively the change in stiffness of scalp flaps determined by increased loads of tension. Data were collected by stepwise loading 20 scalp flaps, created by a reversed-Y incision down to and through the galea aponeurotica together with undermining. In the layer between the galea and the pericranium, to within 1 cm of the external auditory canal. The biomechanical properties of the tested scalp flaps were significantly influenced by increased extents of tension. The tissue's stress response to displacement was visualized as a three-phase characteristic. Initially linear (indicative load range, 0 to 500 g), the scalp's compliance gradually reduced (indicative load range, 500 to 1,500 g) and eventually demonstrated an exponential stress/strain characteristic of rapidly increasing stiffness (indicative load range, 1,500 to 5,000 g). The Young's modulus, E, of the stress/strain curve was found to be equal to 49.2 g per millimeter. The obtained data suggest that a reasonable approach should consist of closing a scalp defect within the tension range of 500 to 1,500 g. This will take full advantage of the plasticity of the scalp flap. The gain obtained with a closing tension above this range would be minimal, with a presumably increased complication rate.