Neuromuscular patterns in hemifacial microsomia.

This study was designed to establish the extent of neuromuscular abnormalities in different types of hemifacial microsomia and to relate these findings to the existing skeletal malformations. Neuromuscular recruitment patterns were established in twenty-three normal subjects. These patterns served as baselines for comparison with recruitment patterns obtained from forty-eight subjects with hemifacial microsomia. The anterior and posterior temporalis, masseter, suprahyoid, buccinator, platysma, mentalis, and upper and lower lips were studied electromyographically. Consistent presence or absence of recruitment for a given task was considered a significant finding with which the hemifacial microsomia data were compared. The subjects with hemifacial microsomia were divided into five groups according to type of mandibular malformation. Abnormal recruitment was found in all recorded muscles except the lips, mentalis, and buccinator muscles. There were variations in recruitment patterns within each group as well as among the groups. A relationship was found between the development of the gonial angle area and the recorded masseter activity. Muscle activity was recorded in the area of the temporal muscle, even in the absence of a coronoid process. It was found that after insertion into a new coronoid process the temporal muscle developed mass and palpable contraction. This study shows that in persons with hemifacial microsomia certain neuromuscular patterns may differ from the norm because of missing or underdeveloped muscles and because of the different relationship between the mandible, its attached muscles, and other structures.