American Society for Peripheral Nerve

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Free Functional Muscle Transfer for Masseter Replacement in Patients with Hemifacial Microsomia
Alexander Cardenas-Mejia, MD; Erika De La Concha, MD; Lucas Lesta-Compagnucci, MD; Crisol Contreras-Molinar, DDS
Hospital General Dr. Manuel Gea Gonzalez, Mexico City, Mexico

Hemifacial microsomia is a congenital disorder that affects the development of the lower half of the face. It is characterized by asymmetrical growth of the face with several degrees of involvement of bone and soft tissues. Mandibular hypoplasia is the most common encountered anomaly. It has been established that the muscles that insert in the mandible play an important role in mandibular growth. The objective of our study was to describe the masticatory force and electrical activity of the masseter muscle in children with hemifacial microsomia and describe the impact of free functional muscle transfer for masseter replacement in these patients.Our study group involved 20 patients with hemifacial microsomia, they were divided in groups according to their classification of mandibular deficiency using Kabanís modification of Pruzanskyís grading system. We realized measurements of their maximum masticatory force (MMF) and electromyography of the masseter muscles were done in every patient.
The electromyographic (EMG) results showed a statistically significant difference with an average of 53.2 RMS (root-mean-square, a calculation on the amplitude of the EMG signal) in the underdeveloped side compared with 89.4 in the unaffected side of the patients (P=0.03). No differences were found in the maximum masticatory force in our group of patients. We realized a case of free functional muscle transfer using the gracilis for masseter replacement in a patient with hemifacial microsomia with Pruzansky-Kaban grade IIB. This was realized using a sural nerve graft connected to the masseter nerve in the unaffected side in the first-stage. Afterwards, in a second-stage surgery, we realized a free gracilis muscle transfer using the temporal vessels and anchoring the muscle to the mandibular angle. We did a follow-up of the patient for a period of 12 months with clinical pictures, orthopantomogram, maximum masticatory force and electromyography of the masseter and the gracilis muscle. Comparative results with the preoperative values; we demonstrated a greater maximum masticatory force in the postoperative period and an increase in the vertical height of the mandibular body. Our results show that patients with hemifacial microsomia have asymmetric masticatory forces and electrical activities in their masseter muscles. Free functional muscle transfer would strengthen masticatory forces with a more symmetric bite. This free functional muscle could also stimulate the bone for skeletal growth in the underdeveloped facial bones.


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