Anatomical Features in Lower-Lip Depressor Muscles for Optimization of Myectomies in Marginal Mandibular Nerve Palsy

Myectomies of the lower-lip depressor muscles, with the aim to improve facial balance in unilateral facial paralysis, have unexplained high recurrence rates. A potential explanation is that these recurrences are due to inadequate resection through the muscle width, leaving lateral muscle fibers intact.

Revisit the anatomy of the lower-lip depressor muscles and suggest an optimization of the surgical technique. Perform a literature review to identify recurrence rates and surgical technique of the procedure.

Ten fresh hemifaces were dissected. The following measurements of depressor labii inferioris and depressor anguli oris were made: the widths of the muscles, the distance from the mandibular midline to the lateral borders of the muscles, and the intraoral distance from the lateral canine to the lateral border of depressor anguli oris. A literature review was performed.

The width of depressor labii inferioris was 20 ± 4 mm and depressor anguli oris 14 ± 3 mm. The distance from the midline to the lateral border of depressor labii inferioris was 32 ± 4 mm and 54 ± 4 mm for depressor anguli oris. The literature review revealed a mean recurrence rate of 21%.

A potential optimization of the surgical technique in lower-lip depressor myectomies is to extend the muscle resection laterally. To ensure inclusion of the whole width of the depressor muscles and decrease the recurrence rates of the procedure, the measurements presented in this study should be kept in mind during surgery.