Table 2.

Codes of the ICD9MC used for selecting cases.

Procedure	ICD9CM codes	Observations
Appendectomy	47.0x; 47.1x	All appendectomies, including laparoscopic and incidentals.
Inguinal hernia repair	53.0x; 53.1x; 53.2x; 53.3x	Uni or bilateral repair, with or without mesh, of femoral or inguinal hernias.
Lower extremity amputation	84.10 to 84.17	Lower extremity amputation at any level.
Hip fracture	820.xx	Only emergency admissions.
Knee replacement	81.54; 81.55	Total or partial knee replacement
Pacemaker implant	37.80; 37.81; 37.82; 37.83	Pacemaker implant, permanent or not, in programmed or emergency admissions.

ICD9CM: International Classification of Diseases 9 revision Clinical Modification; The "x" indicates all the range of digits after the corresponding code.