With long standing unilateral facial paralysis hyperactivity of the contralateral depressor muscles of the lower lip result in significant asymmetry during function and rest.
Resection of the depressor angularis muscle can be a permanent solution.
2. Planning and surgical preparation
The location of the depressor angularis muscle can be determined by observing the vector of pull of the lower lip when the patient is asked to smile and show their lower teeth.
The location of the muscle is marked on the lower lip and chin, prior to the operation.
This procedure can be performed either under local or general anesthesia.
An intraoral incision is performed in the vestibule of the lower lip corresponding to the location of the skin markings.
The muscle is identified intraorally and resected entirely from the mandible to the orbicularis oris muscle.
Note: care should be taken to avoid injury to the branches of the mental nerve during muscle excision.
The oral mucosa is closed with resorbable sutures.
4. Alternative 1 – Botulinum toxin injection
Lower lip asymmetry can be managed non-surgically with botulinum toxin injections into the muscle every 3-4 months.
Advantages of botulinum toxin injection:
Reversible if patient not happy with result
Can be used as a test prior to muscle resection
Disadvantage of botulinum toxin injection:
Case example: botulinum toxin injection
a) Patient presented with irreversible paralysis of the left marginal mandibular branch of the facial nerve. b) Botulinum toxin was injected into the contralateral depressor angularis oris muscle (patient's right side) in order to give symmetry during function.
5. Alternative 2 – Marginal nerve division
This procedure is rarely indicated.
Advantages of marginal nerve division:
Disadvantages of marginal nerve division:
May paralyze adjacent muscles causing worsening asymmetry and function
A 2-3 cm incision is made below the border of the mandible, centered over the facial vessels.
Marginal nerve identification
The marginal branch of the facial nerve is predictably found deep to the platysma muscle and superficial to the facial vessels at the jaw.
A nerve stimulator can be used to identify the branches of the nerve and assess muscle function.
The branches that stimulate the depressors of the lip can be divided. This may require division of the entire marginal branch of the facial nerve.
Routine wound care is all that is necessary for the majority of the procedures.