The effects of temporalis muscle manipulation on skull growth: an experimental study

Craniofacial reconstructive procedures are frequently associated with some dissection or transposition of the temporalis muscle. During active growth, such muscle manipulations may influence craniofacial development. The purpose of this study was to determine the effects of surgical manipulation of the temporalis muscle on craniofacial skeletal growth and morphology. Twenty-five New Zealand White rabbits underwent temporalis muscle surgery at 6 weeks of age. Group I (n = 6) underwent a sham procedure and served as a control group. Group II (n = 6) underwent simple elevation of the left temporalis muscle and immediate reapproximation. Group III (n = 7) underwent complete transection of the left temporalis muscle. Group IV (n = 6) underwent elevation of the left temporalis muscle and transposition to the left zygoma. Growth alterations were evaluated by standardized cephalometric x-rays. Baseline anteroposterior skull x-rays were performed preoperatively and every 3 weeks for the duration of the study. The study was terminated at 24 weeks of age. At this point, dry skull preparations were analyzed quantitatively by direct cephalometric evaluation. Manipulations of the temporalis muscle produce changes in local skull morphology and affect craniofacial growth. Skull length increases when the action of the temporalis muscle is interrupted either transiently or permanently, while skull width decreases. Temporalis muscle transposition to the orbit resulted in altered orbital dimensions. Qualitative analysis of local skull morphology further revealed posterior displacement of the external auditory meatus, a depressed temporalis fossa, and multiple resorption cavities following elevation of the temporalis muscle.