What is a gracilis muscle transplant to masseter nerve?
The gracilis muscle transplant to masseter nerve is a single surgery designed to reanimate the smile. The gracilis is a long muscle located in the inner thigh. It is responsible for moving the hip inwards (or, adduction). It is a redundant muscle for this function.
In other words, there are several other muscles that accomplish the same goal; therefore, sacrificing the muscle results in no loss of function in the thigh. Only a small, thin segment of the gracilis muscle is taken from the thigh along with its blood and nerve supply. The muscle is then moved to the paralyzed side of the face where it is connected to local nerves and blood vessels. In this case, it is attached to the masseter nerve on the same side as the paralyzed face. After 3-6 months, the muscle becomes active and contracts to move the corner of the lip.
The masseter nerve is derived from a branch of the fifth cranial nerve (trigeminal nerve) and is responsible for activating the bite via the masseter muscle. The reason that it is used in facial reanimation surgery is because biting is an analogous function to smiling. In other words, to a certain degree human beings trigger their biting muscles when smiling.
There are several advantages to using the masseter nerve to power the gracilis muscle over a cross-face nerve graft. First, only a single surgery is required to achieve lip movement as opposed to two. Second, recent studies suggest that gracilis muscles connected to the masseter nerve deliver a greater contractile force over a cross-face nerve graft, making the corner of the mouth rise more aggressively. Third, the time to smile reanimation is significantly abbreviated (3-6 months vs 12-18 months). The main disadvantage to using the masseter nerve is that activation of the smile is not spontaneous, since stimulation is derived from the fifth cranial nerve used in biting. In other words, initially, a person would need to trigger a bite to create a smile. Physical therapy is required to re-train the gracilis muscle for smiling. However, this is achievable in the great majority of patients.
How is a gracilis muscle transplant to masseter nerve performed?
The gracilis muscle is harvested through a small incision measuring 3-4 inches in the inner thigh. The blood vessels and nerves are isolated. The muscle is measured for the exact length and width that is required in the paralyzed side of the face, from the corner of the lip to an area near the top of the ear. Once the dimensions are confirmed, the muscle is then split and divided. It is then transplanted to the face where it is anchored.
In preparing the face, an incision is placed in the pattern of a facelift with a small extension underneath the jaw. The skin is elevated, and the masseter muscle is identified. The nerve to the masseter muscle is then carefully dissected deep within the muscle. There are at least two branches of the masseter nerve, which allows the use of one for the purpose of smile reanimation without risking loss of biting force. The nerve is prepared and brought into position for connection to the nerve of the gracilis muscle. Anchoring sutures are placed at precise locations along the corner of the mouth and upper lip. The blood vessels are located and prepared. The blood vessels are then connected using a high-powered microscope (microsurgery). Next, the nerve is connected to the masseter nerve. All incisions are closed with absorbable sutures.
What is the recovery from a gracilis muscle transplant to masseter nerve?
Following surgery, patients remain in the hospital or aftercare facility for 3-6 days. The head is kept wrapped in a bulky soft dressing, and the thigh is wrapped with a mild compression dressing. There may be moderate swelling of the face and eyelids. Antibiotics are required for 10-14 days, and a soft diet is necessary for 3 weeks. A soft rubber drainage tube is left underneath the skin to relieve any fluid collection in the face. This is taken out 2-3 days following surgery. It is imperative to avoid any pressure or accidental blunt trauma to the cheek during this time. Contact sports and heavy lifting are avoided for 4-6 weeks. Adults will need to take between 3-4 weeks off for recovery before they return to light duty. Muscle activity then begins approximately 3-9 months after surgery.
What are the risks and complications of a gracilis muscle transplant to masseter nerve?
Bleeding, infection, and complications from anesthesia are possible during or after surgery, as with all types of surgical procedures. These are rare risks; however, other risks are related more specifically. For example, asymmetry is possible either in the resting position or with smiling. The amount of muscle movement is difficult to predict with accuracy at the time of surgery. Also, there may be contour issues such as increased cheek bulk or unwanted dimpling of the cheek with smiling. The creation of the lip-cheek fold (nasolabial fold) may also be unpredictable. In addition, there is a small rate of failure that may be related to lack of nerve regeneration or disruption of blood flow to the gracilis muscle. In this event, there may be no discernible movement.
To minimize your risk, pay close attention to instructions before and after surgery. Dr. Panossian’s staff is available at all times to clarify any pre- or postoperative instructions that you are given.
