Primum non Nocere Demands Knowledge of the Related Anatomy
The technique first required carrying out anatomical dissections to determine both the pathway and also the depth of the branches of the temporal division of the facial nerve and specifically of the frontal ramus (which according to Baker and Conley [2] is a terminal branch in 85% of cases) to prevent its damage. The other branches (two to the upper orbicularis muscle; the upper zygomatic branch to the lower orbicularis muscle; the lower zygomatic branch, which reaches the major zygomatic muscle from its deep surface and proceeds to the levator labii superioris, buccinator and levator anguli oris [6]) as well as the usually two buccal branches, which cross the masseter muscle beneath its fascia, present, according to our dissections, frequent anastomosis with the neighbouring branches before reaching their respective muscles. The buccal branches also communicate with the homonymous of the mandibular division. Freilinger et al. [6], who quoted four anatomosis of each branch, proved that the facial muscles are situated in four planes of depth, of which the zygomatic major muscle is situated on the second plane beneath the more superficial level of the orbicularis oculi muscle.
According to our dissections, performed in the Departments of Anatomy at the universities of Madrid and Cordoba (Ramon Ribes), in Barcelona (Alfonso Rodriguez Baeza), as well as with Rodrigo Vildosola (Mexico), and at the ISAPS anatomy courses in Nice in 1986 and the ISAPS/LSNA meeting in San Diego, 1991, the branches of the temporal division leave the protection of the parotis, depending on its size, at approximately 1.5 cm in front of the tragus. The frontal branch then crosses an area of approximately 0.8 cm2 around the midpoint between the lateral canthus and the facial helix implantation and is always located below the anterior branch of the superficial temporal artery. Subdivisions occur after this point and are spread fanlike between 1 and 5 cm above the vertical level of the lateral canthus.
Concerning the depth, when leaving the protection of the parotis, the frontal ramus as well as the branches to the orbicularis muscle including the upper zygomatic branch ascend and are embedded in the deep fibro-fatty tissue of the SMAS to reach the respective muscles at an angle of approximately 90° angle (Fig. 41.2).
- 41.2. Left: Dissection of the main branches of the facial nerve [23], when emerging from the protection of the paro-tis: From top downward: the frontal ramus; the branches to the upper orbicularis muscle; the superior and inferior zygomatic branches; the buccal branches of the temporal division and of the inferior division running beneath the masseter fascia; the mandibular branch with a proximal and distal division. Right: The terminal frontal branch has been dissected from the deep
- 41.2. Left: Dissection of the main branches of the facial nerve [23], when emerging from the protection of the paro-tis: From top downward: the frontal ramus; the branches to the upper orbicularis muscle; the superior and inferior zygomatic branches; the buccal branches of the temporal division and of the inferior division running beneath the masseter fascia; the mandibular branch with a proximal and distal division. Right: The terminal frontal branch has been dissected from the deep fibro-fatty tissue of the superficial musculo-aponeurotic system (SMAS) (the latter held by two forceps). The black point corresponds to the midpoint between the lateral canthus and the facial helix implantation. Close to the forceps is the anterior branch of the superficial temporal artery running on the surface of the SMAS. Beneath the proximal part of the frontal ramus are the next branches of the temporal division of the facial nerve
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