The Serratus Anterior Subslip: Anatomy and Implications for Facial and Hand Reanimation

Abstract

The ideal donor muscle for facial and hand reanimation has yet to be found. Donor muscles commonly used today, such as the gracilis and pectoralis minor, are limited by bulkiness and the number of force vectors they can provide. In the authors' study of 50 fresh cadaver serratus anterior muscles, they further describe neurovascular anatomy of the muscle slip (i.e., the portion of the muscle that inserts on a rib) and subslip (superficial or deep subdivision of the slip after division along a loose areolar plane). All 260 slips could be separated into a deep and a superficial subslip, yielding a total of 520 subslips. A branch of the serratus artery (a terminal branch of the thoracodorsal artery serving the lower five to seven slips of the muscle) and a branch of the long thoracic nerve were identified for each of these. Deep subslips were thinner than superficial subslips, both at the origin of the slip on the rib periosteum (2.4 mm versus 3.0 mm, p < 0.0001) and centrally at the serratus artery (3.3 mm versus 4.0 mm, p < 0.0001). In addition, the subslips of the most inferior slip were thinner than those of more superior slips, both at the origin of the slip (2.3 mm versus 2.8 mm, p < 0.0001) and at the serratus artery (3.0 mm versus 3.8 mm, p < 0.0001). Fine anastomosing vessels were present between the slips and the subslips. The average number of anastomosing vessels present between adjacent slips was 1.7, and 2.1 anastomosing vessels were present between the subslips of a given slip. Given the thinness of these vessels (all less than 0.2 mm) compared with those of the vascular pedicle of the subslip (mean, 0.7 mm; all greater than 0.4 mm), the authors believe these can be safely divided without compromising subslip vascularity. After division of these vessels, a mean length of 9.6 +/- 1.5 cm is available to allow independent orientation of each subslip. When the serratus muscle flap is separated into its component subslips, a maximum of 10 possible force vectors may be transferred on a single vascular pedicle. Subslips are significantly thinner than donor muscles commonly used today. These two advantages offer the potential for significant functional and aesthetic improvement when the serratus anterior muscle flap is used for face and hand reanimation. Mimetic muscles such as the orbicularis oculi and orbicularis oris could possibly be reconstructed in their proper anatomical positions.

Modification of Tension on Muscle Insertion Improves Smile in Free-Muscle Transplantation

“…Its parallel fiber orientation is also another advantage which enables it to generate the contractile force of the mimetic muscles. 15,22,23 The serratus anterior muscle free flap was first used for facial reanimation by Buncke et al 10 in 1982. They secured the seventh slip into the corner of the mouth, the eighth slip into the outer third of the upper lip, and the ninth slip was directed through the upper and lower eyelid after splitting.…”

“…14 The serratus anterior flap with multiple thin slips of muscle on a single neurovascular pedicle offers potential for the development of a more complex multivector functional muscle. 15 Current methods for reanimation of the mouth are overly simplistic. A muscle usually is transplanted subcutaneously between the corner of the mouth or around the modiolus and the body of the zygoma, simulating the zygomaticus major muscle, to acquire elevation of the corner of the mouth when smiling, and the muscle fibers run to the mouth under an angle of about 45 degrees.…”

Application of lateral thoracic flap in maxillofacial defect reconstruction: Experience with 28 cases

“…5,6 The two supplying vessels have variable positions in the lateral thorax, which may be responsible for inconsistencies in blood supply to the overlying skin. The presence of these two vessels and their variable positions has been shown in previous case series reports describing application of free and pedicle LT flaps.…”

“…Recent anatomical study of cadavers have demonstrated that the LT flap is supplied mainly by these two arterial networks running in the subcutaneous plane. 5,6,8 Surgical techniques for harvesting the lateral thoracic flap…”

“…2 Meanwhile, the lateral thoracic (LT) flap has rarely been reported for head and neck reconstruction and has been used primarily as a pedicle flap for the reconstruction of limb and chest wall defects. 3,4 Although prior extensive cadaveric study of the vascular anatomy of the LT flap found it to have reliable vessels, 5,6 other free flaps such as the anterolateral thigh, forearm and rectus are favored over application of free LT flaps for oral and maxillofacial reconstruction. 7 A reliable free flap for oral and maxillofacial reconstruction would ideally have multiple muscle segments that could be oriented independently, producing different force vectors to more effectively restore facial reanimation.…”