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Transplantation of Olfactory Ensheathing Cells to Evaluate Functional Recovery after Peripheral Nerve Injury

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Muscles of the Lower Lip: Functional Anatomy, Innervation Patterns, and Nerve Injury Prevention.

Lior Har-Shai¹, Christine F Johansen, Sahejbir S Bhatia

¹Department of Plastic Surgery, The University of Texas Southwestern Medical Center, Dallas, Texas.

Plastic and Reconstructive Surgery

|January 22, 2026

Summary

Injury to the marginal mandibular nerve (MMn) rarely affects lower lip position. The depressor labii inferioris (DLI) is primarily innervated by cervical branches, and platysma myotomy can prevent abnormal lip elevation.

Keywords:

Cervical Nerve Branch Deep Plane Depressor Labii Inferioris Face Lift Facial Nerve Functional Anatomy Lower Lip Muscles Marginal Mandibular Nerve Neck Lift Platysma Myotomy Synkinesis

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Published on: February 23, 2015

Area of Science:

Anatomy
Neurology
Plastic Surgery

Background:

The depressor labii inferioris (DLI), depressor anguli oris (DAO), mentalis, and platysma muscles are crucial for lower lip position and oral function.
These muscles are vulnerable during facial reconstructive and aesthetic surgeries.
Previous studies suggested significant contribution of the marginal mandibular nerve (MMn) to lower lip depression via DLI innervation, lacking functional analysis.

Purpose of the Study:

To systematically assess the functional anatomy and innervation of the DLI, DAO, mentalis, and platysma muscles.
To evaluate the impact of MMn injury on lower lip position.

Main Methods:

Retrospective cohort study of adult synkinesis patients undergoing selective neurectomies and myectomies.
Intraoperative facial nerve mapping via nerve branch stimulation and muscle activation pattern categorization.
Sub-analysis of lower lip position changes in patients who underwent MMn neurectomy without platysma myectomy.

Main Results:

DAO and mentalis muscles showed mixed innervation patterns.
DLI and platysma muscles were predominantly innervated by cervical branches; 95.5% of DLI branches were cervical.
MMn neurectomy did not worsen lower lip position in the sub-analysis (n=24).

Conclusions:

DAO, mentalis, and platysma muscles are poly-innervated by various facial nerve branches.
DLI is mostly mono-innervated by cervical branches.
Isolated MMn injury rarely worsens lower lip position; injury to cervical branches to DLI can cause abnormal lip elevation, preventable by caudal platysma myotomy.