Rib Cap

Has anyone heard of a rib cap?  Client of mine came in for a session and had inflammation around intercostal on right side on the bottom of rhomboid area.  Client stated her chiropractor and personal trainer both stated she may have a rib cap. Client had no explanation for problem, injury or excessive training, ect. per chiropractor or trainer, but they suggested a rib cap?  Can anyone explain what this is?  I have been an LMT for 12 years and have not heard of this until my client came in for her session and told me what her Chiro and PT stated.  Can not find any research for this.