Which of the following is NOT a necessary size for rigid C-collars?

The category of "Senior" is not typically designated as a necessary size for rigid C-collars. C-collars, or cervical collars, are primarily categorized by the sizes of the most common patient demographics: adults, children, and infants. Each of these groups has specific anatomical considerations, necessitating different collar dimensions to ensure proper immobilization and support of the cervical spine.

In contrast, seniors are usually accommodated within the adult collar range, unless there is a need for specific considerations due to anatomical variances associated with aging, such as frailty or other medical conditions. Thus, while it’s essential to have appropriately sized collars for adults, children, and infants to cater to their unique body sizes and shapes, a separate size classification for seniors is unnecessary. Therefore, saying that "Senior" is not a necessary size designation is accurate in the context of rigid C-collars.