Smas

SMAS is the acronym for "Superficial Musculo-Aponeurotic System".

The platysma, the SMAS and the fascia temporalis superficialis are found in one layer and originate from the mesenchyme of the 2nd pharyngeal arch. The"Superficial Musculo-Aponeurotic System", SMAS, consists of the mimic muscles and a thin layer of fascia. This fascia connects the facial muscles and ensures that complex facial expressions can develop. The fascial portion arises from the superficial cervical fascia, wraps around the platysma, and inserts on the mimic musculature from the lower face to the forehead.

The fascia inserts at the mastoid process and at the superficial parotid fascia one to two centimeters anterior to the tragus. Other insertion points are found on the zygomatic arc and the sternocleidomastoid fascia. The SMAS ends medially from the nasolabial fold.

The SMAS has its own vascular plexus, usually described as the subdermal plexus, which is formed from the transversa faciei artery, the lacrimal artery, and/or the infraorbital artery. The trunks of the facial arteries lie superficially in the SMAS or at the border of the SMAS with the subcutaneous adipose tissue.

The SMAS separates the superficial tissue from the deep portions and thus serves as a barrier to infection. The SMAS divides the fat compartments of the face into subcutaneous and deep fat compartments. With age, the distance between the skin surface and the SMAS decreases, and with an increasing BMI, the distance increases. The sensory nerves are located above the SMAS and the motor nerves below the SMAS.

Dermatosurgical significance: In case of a dissection in the temporal region above the SMAS, the temporal ramus of the facial nerve is spared.

A plication of the SMAS is part of many facelift techniques and can also be used during wound closure to reduce the tension of the layers above.

Knowledge of the SMAS is essential for "liquid face-lift" with hyaluronic acid preparations.

1. Jonathan Kantor (2018) Dermatologic Surgery. McGraw-Hill Education / Medical.
2. June K. Robinson MD et al (2014) Surgery of the Skin: Procedural Dermatology. Saunders.
3. Casabona, Gabriela et al (2019) Influence of Age, Sex, and Body Mass Index on the Depth of the Superficial Fascia in the Face and Neck. Dermatol Surgery 45: 1365-1373
4. D'Arpa S et al (2011) The face lift SMAS plication flap for reconstruction of large temporofrontal defects: reconstructive surgery meets cosmetic surgery. Plast reconstruction surgery 127:2068-2075.