Frontalis midline dehiscence: an anatomical study and discussion of clinical relevance.

Abstract

The frontalis muscle has a midline dehiscence that has not been well described. The anatomic characteristics of the muscles of the central forehead are important to effectively treat rhytids in this area, e.g. with botulinum toxin. Anatomical dissections of 21 cadaver foreheads. For males, the midline attenuation point occurred in a range from 1.4 to 6 cm above the horizontal orbital rim plane, with the mean being 3.5+/-1.6 cm. The mean angle of the left muscle belly in the male cadavers was 26.0+/-17.4 degrees off the midline, while the right was 36.4+/-14.9 degrees. Overall average angulation was 62.4 degrees (Figure 4). The mean distances between left and right muscle bellies at 4 cm, 5 cm and 6 cm superior to the orbital rim were 1.2 cm, 1.9 cm and 3.1 cm, respectively. The mean distance of dehiscence in the midline from the horizontal reference plane of the female cadavers was 3.7+/-1.8 cm, with a range of 1.3 to 6.0 cm. The left frontalis belly formed an angle with the midline of 15.9+/-16.6 degrees, while the right belly formed an angle of 22.3+/-20.1 degrees, with an overall average angle of 38.2 degrees. The interbelly distances at 3, 4, 5 and 6 cm were 0.4 cm, 0.9 cm, 1.7 cm and 2.6 cm, respectively. One third of females had no midline frontalis dehiscence at 6 cm above the orbital rims. The anatomic characterization of the midline frontalis muscle dehiscence permits more intelligent placement of chemotherapeutic agents when treating forehead rhytids.