Sex Differences in the Temporalis Tendon-Aponeurotic Complex: An in vivo MRI Macroscopic Analysis in Children and Adolescents.

The tendon-aponeurosis complex (TAC) of the temporalis dissipates forces produced during function. Abnormally reduced temporalis TACs have been found in individuals with chronic muscular temporomandibular disorders - a painful musculoskeletal condition that is more frequent in women than men. Whether there are sex differences in the temporalis TAC in healthy individuals is currently unknown. Here, we characterized and measured the temporalis TAC in healthy male and female young individuals between 5 and 15 years old to determine whether the volume of the temporalis TAC and the TAC-to-muscle ratio are different between males and females. We collected MRI studies from 90 healthy individuals, including equal numbers (15 M and 15 F) of young children (ages 5-7), children (9-11), and adolescents (13-15) and segmented the right temporalis and its TAC using software. Using general linear models, we tested the effect of sex, age, and their interaction on the volumes of the temporalis and its TAC, and the TAC-to-muscle ratio. The volumes of the temporalis and its TAC increased with age (both p < 0.001) and were not affected by sex (p = 0.252 and p = 0.179) or by the interaction sex-by-age (p = 0.079 and p = 0.095, respectively). The TAC-to-muscle ratio did not change significantly with age (p = 0.655) and was not affected by sex (0.438) or by the interaction sex-by-age (0.524). We provide, for the first time, volumetric data of the temporalis TAC in children and adolescents. The volumes of the temporalis TAC and the TAC-to-muscle ratio are not different between male and female individuals until the age of 15.