On December 16, 1993 - Eric Harris had surgery on the pectus excavatum (his chest) at the Fitzsimons Army Medical Center.
It's located in Aurora, Colorado.
He suffered from a sunken chest.
It was corrected by removing the costal cartilage.
It's located along the sternum and placing a steel strut, behind the sternum to support it.
The strut is later removed, following a second surgery.
The second surgery took place on June 9, 1994 - at the same location, with the removal of the steel strut.