When the presence of tension adds to the diffi-culty of wound closure, the use of undercutting of the wound margins to allow a degree of advancement is frequently recommended. Before this can even be considered the vascular state of the skin has to be assessed, and the potential effect of tension on its viability, particularly if the injury has involved an element of degloving. Personal experience has been that the amount of advancement achieved in practice is often disappointingly small.
The levels at which such undercutting is car-ried out and its safe extent vary in the different body sites. In the face, the appropriate level is deep to the dermis, so that the plexus of subdermal vessels is included, while leaving undisturbed the branches of the facial nerve. The potential for advancement of facial skin depends very much on the degree of redundancy which was present previously.
In the child, there is an absence of skin redundancy, and the potential is virtually nil; in the ageing wrinkled face, it is considerable. In the scalp, the plane is between the galea aponeurotica and the pericranium, and the vascular anatomy of the scalp is such that extensive undercutting can be carried out with safety.
The galea rather than the skin is respons-ible for the inextensibility of the scalp, and it is multiple galeal ‘relaxation’ incisions which have been advocated to increase the amount of advancement. Experience indicates that the effectiveness of this manoeuvre has been greatly exaggerated. In the limbs and trunk, if undercut-ting is to be more than minimal, the plane between the superficial and deep fascia should be used.
Surgeons vary greatly in the extent to which they make use of undercutting in this way, but if more than minimal advancement is required to allow a wound to be closed, it is probably wiser to close the defect with a split skin graft.