The superficial plane just under the skin with a thin layer on facial fat of the skin flap does not correspond to a proper anatomical plane. Too many vessels especially of the subdermal plexus are divided.
Anatomically the subadipose dissection encounters and damages far fewer of the important vascular elements and separates the two anatomical leaflets without injuring either of them (Fig. 44.6).
A Trepsat dissector in different sizes (Fig. 44.7a, b) may be helpful to perform a wide undermining with spreading movements, blunt-tipped scissors allowing atraumatic separation of the various anatomical layers. The deep plane undermining is extended to the nasolabial fold, the modiolus and the mandibular osteocutaneous attachments (Fig. 447c, d). All the fat remains on the flap (Fig. 44.7e).
The deepening of the nasolabial fold with aging is due to progressive thickening and ptosis of the lower portion of the cheek fat and skin but not to any remarkable change in the fibromuscular plane (SMAS) [12, 16].
Attention must be paid to a localized thickening of the following areas of fat pads: submental, buccal, na-solabial (midcheek) and malar. The deep subcutane ous undermining over the SMAS/platysma layer allows the surgeon the directly address these fat collections for contouring. In addition to that, the deep subcutaneous approach (supra-SMAS) provides a complete release of the osteocutaneous ligaments described by Furnas  for better mobilization and even distribution of tissues: malar (McGregor's patch), parotid, masseteric, infra-inferior-distal-zygomatic, mandibular (Fig. 44.8).
The more advanced the situation of jowling and sagging of the facial skin and fat, the more extended epi-fascial undermining is necessary to provide access to all zones of drooping, accumulated fat and the release of osteocutaneous ligaments (Figs. 44.9, 44.10).
Fig. 44.7. a, b Trepsat dissecting instrument for spreading movements. c, d Wide undermining in the deep plane between fat and fibromuscular tissue (superficial adipo-cutaneous system, SACS, lifting). e, f All the fat is kept on the flap
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