In free functional muscle transplantation, a functioning muscle is removed from another part of the body (e.g. thigh or chest) and transferred into the affected half of the face. The small muscle is connected to a suitable donor nerve and a vascular supply under the cheek skin with the surgical microscope. After healing and activation by the replacement (donor) nerve, the corner of the mouth function can be successfully restored, and improved symmetry of the face can be achieved. The tighter cheek tissues also have a positive effect on the previously often blurred speech and on the difficult food intake of those affected. However, it takes a few months for the missing facial expression to resume due to a newly gained dynamic in the face during which the patient already benefits from an improvement in facial symmetry at rest. The reappearance of a desired age-appropriate nasolabial fold (natural fold between the ala of the nose and the corner of the mouth) often indicates the spontaneous onset of muscle function.
In the setting of two-stage reconstruction, nerve fibers must first be diverted from the healthy, non-paralyzed half of the face: in the first surgical step, the patient receives an "extension" of the intact facial nerve with a nerve transplant from the lower leg into the paralyzed opposite side ("cross-face nerve").
In the second step, a small functioning muscle can be connected to the nerves before transplantation under the cheek skin. As illustrated here, it is simultaneously connected to small vessels in the face with the surgical microscope in order to be remain viable. After a phase of neural regeneration into the muscle, the opposite intact facial nerve can synchronously control the transplanted muscle in the paralyzed half of the face and restore a symmetrical smile.