Definition and Causes
Treatment of the paralyzed face requires a specialized compilation of surgeries. Often, these surgeries require sequencing in stages. The cause of facial nerve paralysis includes congenital defects, acquired defects such as tumor resection, bells palsy or trauma. The facial nerve is the seventh cranial nerve and innervates the muscles of facial expression. There are five main branches: cervical, marginal mandibular, buccal, zygomatic, and frontal. Each provides innervation to specific facial muscles allowing them motor function (contraction). Functionally, the buccal and zygomatic branches have the greatest importance as these innervate the muscles that control oral competence (prevent drooling), voluntary eye closure, and smiling.
Patients who have inability to control their mouth not only cannot smile, but often have difficulty with drooling and chewing/eating food. Lack of innervation of the eye muscles leads to reduced eyelid tone, causing droopiness of the lower eyelid and excessive dryness. This dryness can be very debilitating and have adverse effects on vision. Options for treatment are generally categorized into either static or dynamic reconstructions. Static procedures such as facial slings that do not produce any restoration of movement. They are supsensory surgeries that hold in position the corners of the mouth and the lower eyelid to improve closure (or competence).
Surgical Procedures
Dynamic procedures involve substituting lost mobility of facial muscles with a transplanted and innervated muscle (typically from the inner thigh – gracilis muscle). Patients who undergo dynamic reconstructions not only improve the resting tone of their mouth and face, but can animate voluntarily, re-creating a smile. Dr. Ha overwhelmingly prefers dynamic facial reanimation for patients with facial paralysis, due to its superior results.
Previously, the most common dynamic reconstruction that Dr. Ha performed involved a 2-stage facial reanimation. The two surgeries were spaced approximately one year apart. The first surgery involved placement of a Cross-Face Nerve Graft utilizing harvested sural nerve (from the posterior calf). A facial nerve dissection was performed on the normal, non-paralyzed side. Mapping of the nerve branches helped identify the specific functions of the 5 branches. One of the branches would be sacrificed to attach the nerve graft. Because of alternate crosspaths, sacrificing one branch did not affect the normal side significantly. The nerve graft would then be tunneled through the facial soft tissue and out in front of the ear on the paralyzed side. This graft would sit for a year, while re-innervation occurred. To provide an analogy, a cable was attached to the power source and then routed to the paralyzed side. Time elapsed until the charge was adequate. It was now ready to receive the motor, or the muscle. In the second stage, a surgery was performed to attach the gracilis muscle to the cross facial nerve graft. Microsurgical attachment of the blood vessels and the nerve was required for transplantation. The muscle reinnervated after 8 to 12 months and motion was regained.
Presently, Dr. Ha has employed a newer technique for muscle transplantation that is performed in one stage. The same muscle, the gracilis, is utilized for the transfer, but instead of attaching its nerve to a graft placed 12 months prior, the nerve is attached to the motor nerve of the masseter. The masseter muscle is one of several that controls jaw movement. It is dissected free from the masseter’s undersurface and used to “power” the gracilis. Microsurgical attachment of the blood vessels is performed in usual fashion.
Experience
Dr. Ha has found tremendous advantages in this newer technique:
• One stage reconstruction (instead of 2)
• Faster time to reinnervation (4 to 6 months from the surgery to begin motion,
• and about 1 year for optimal strength)
• Stronger excursion (or pull) along the corner of the mouth – creates a more balanced smile
• High consistency and reproducibility
One potential advantage of the traditional 2 stage technique is that from the outset of innervation, there is “spontaneous” function of the muscle (or smile). If a smile is being created on the non-paralyzed side, the gracilis muscle on the reconstructed side will automatically contract – this is because the cross facial nerve graft is connected directly to one of the branches of the facial nerve.
With the technique involving the motor nerve of the masseter, smiling has to be gradually developed. The transplanted muscle will initially work when chewing/biting movements are mimicked. With some training and therapy, patients learn to activate the muscle (smile) without having to actively bite down. Eventually, patients can train the muscle to work spontaneously and in concert with the normal side so that a spontaneous and symmetric smile can be achieved. This process can take several months to a couple of years.
Dr. Ha does offer both types of procedures and will tailor the reconstructive plan to each patients’ specific goals and degree of facial paralysis.