Very interesting… It looks like you might have an anatomical variation of the posterior arch of your atlas (C1 vertebra). On the 3D model it looks unfused.
Especially Case 5 looks like yours.
Could it be the source of upper back pain?..
Btw “broken” hyoid can be seen on many young people’s CT scans. The hyoid bone AFAIK is actually three bones that finish fusing by mid-late thirties.