In vivo excursion of the temporalis muscle-tendon unit using electrical stimulation: application in the design of smile restoration surgery following facial paralysis.

IMPORTANCE: The temporalis muscle has the potential to substitute for the function of paralyzed facial muscles in a single-stage procedure when transferred as a muscle-tendon unit (MTU).
OBJECTIVE: To measure the available excursion of the temporalis MTU after release from the coronoid. DESIGN, SETTING, AND PARTICIPANTS Thirteen consecutive patients undergoing the temporalis MTU transfer procedure for facial reanimation participated in this study in an academic research setting. MAIN OUTCOMES AND MEASURES: Using transcutaneous electrical stimulation of the temporalis muscle, excursion of the temporalis muscle after its release as an MTU was recorded. Tension was varied on the released tendon during electrical stimulation of the muscle to determine the optimal muscle length at which the maximum excursion could be achieved. The tendon was inserted at the modiolus at the determined muscle length, and excursion of the oral commissure was recorded. Excursion data were then measured from the video recordings. RESULTS The mean excursion of the temporalis tendon after its detachment from the mandible and stimulation at an optimized passive tension was 20.6 mm (range, 14-30 mm) (n = 9). Following tendon insertion, the mean oral commissure excursion was 15.5 mm (range, 8-23 mm) (n = 13). CONCLUSIONS AND RELEVANCE: The temporalis MTU has adequate available excursion following mobilization for dynamic reanimation of the paralyzed face. Electrical stimulation of the released temporalis tendon gives useful information that is reproducible and can be an important intraoperative adjunct to setting the MTU at an optimal tension to maximize force generation and excursion. LEVEL OF EVIDENCE: NA.