The purpose of this study is to determine if the ProAdjuster system of analysis can be used to determine cervical spine instability using the Penning system of radiographic marking as a standard of comparison.

This study will utilize the ProAdjuster Device as a method of assessing the motion of the cervical spine in participants with instability as determined by a Penning Radiographic analysis. Only participants with existing radiographic studies will be included in the study. No additional Radiographic will be required.

Inclusion Criteria: Logan student, staff, or faculty with no history of ankle injury; 2. Age 18 - 60 yoa.

Exclusion Criteria: 1. Logan student, staff, or faculty ; 2. Local infection, injury or other malignancy affecting the cervical spine; 3. Any unstable joints of the cervical spine than require immobilization ; 4. Any manipulation to cervical spine within 48 hours; 5. Pregnancy.