Motor Branch of Masseter for Innervation of Free Muscle Flap

Motor Branch of Masseter for Innervation of Free Muscle Flap

Michael J. A. Klebuc


  • The masseter nerve branches from the mandibular nerve and passes above the lateral pterygoid muscle where it runs through the mandibular notch to enter the substance of the masseter muscle.

  • Along its intramuscular path, the main trunk liberates a series of small proximal branches and terminates in a long descending branch that courses obliquely in posteroanterior, proximal-distal trajectory.

  • The main trunk of the masseter nerve can be identified at a point 3 cm in front of the tragus, 1 cm below the zygomatic arch, and 1.5 cm deep to the SMAS (FIG 1).1

  • The masseter muscle has three lobes (superficial, middle, and deep).

  • The motor nerve to the masseter (CN V) lies on the superficial surface of the deep lobe.2

  • The main trunk and descending branches contain approximately 2700 and 1550 myelinated motor fibers, respectively.1,3

  • The descending branch of the masseter nerve is usually selectively transected and employed to innervate free muscle flaps utilized for facial reanimation.

FIG 1 • Topographic landmarks for masseter nerve isolation. Main nerve trunk located 3 cm in front of the tragus, 1 cm below the zygomatic arch, and 1.5 cm deep to the SMAS.


  • The masseter nerve is frequently selected as a source of innervation in cases of bilateral facial paralysis and when the facial nerve is unavailable as a donor (ie, Moebius syndrome, Lyme disease, bilateral temporal bone fractures, brainstem cavernous malformation, Guillain-Barré).4

  • Often selected over cross face nerve grafts in older patients where the potential for nerve regeneration is diminished.5


  • Etiology of the facial paralysis:

    • Developmental

    • Traumatic

    • Post-tumor extirpation

    • Bell palsy

    • Ramsay Hunt syndrome

  • Patient age:

    • Peripheral nerve regeneration declines with advanced age.

    • There is no definitive age cutoff for cross face nerve grafting; however, after the age of 50 to 55 years, the ipsilateral motor nerve branch to masseter or other adjacent cranial nerves often provide a more reliable source of innervation to free muscle flaps with more powerful muscle flap contraction.

  • Comorbidities impairing nerve regeneration:

    • Smoking—higher risk of skin flap necrosis

    • Diabetes

    • Vascular disease

    • Previous radiation

    • Neurologic disorders

  • History of hypercoagulable state:

    • Patient or family history of pulmonary emboli or deep venous thrombosis signals the need for a hematologic workup prior to free, functional muscle flap reconstruction.

  • The patient’s level of motivation and willingness to comply with postoperative physical therapy is also important to ascertain.

  • History of temporomandibular joint dysfunction—consider alternative technique.


  • Imaging studies are seldom required in the presence of a normal physical examination.


Preoperative Planning

  • Smoking cessation and avoidance of nicotine

  • Discontinuation of oral anticoagulants

  • EMG

    • Concomitant activation of the masseter muscle with attempted smiling (may predict development of an effortless smile)6

  • Mark the nasolabial folds and smile vectors prior to entering the operating room.


Feb 27, 2020 | Posted by in Pediatric plastic surgery | Comments Off on Motor Branch of Masseter for Innervation of Free Muscle Flap
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