title: Higher Charlson Comorbidity Index Scores are associated with readmission after orthopaedic surgery.
abstract: BACKGROUND
  The Charlson Comorbidity Index (CCI) originally was developed to predict mortality within 1 year of hospital admission in patients without trauma. As it includes factors associated with medical and surgical complexities, it also may be useful as a predictive tool for hospital readmission after orthopaedic surgery, but to our knowledge, this has not been studied.
  
  
  OBJECTIVE
  We asked whether an increased score on the CCI was associated with (1) readmission, (2) an increased risk of surgical site infection or other adverse events, (3) transfusion risk, or (4) mortality after orthopaedic surgery.
  
  
  METHODS
  A total of 30,129 orthopaedic surgeries performed between 2008 and 2011 without any orthopaedic surgery in the preceding 30 days were analyzed. International Classification of Diseases, 9(th) Revision codes were used to identify diagnoses, procedures, surgery-related adverse events, surgical site infection, and comorbidities as listed in the updated and reweighted CCI. A total of 913 patients (3.0%) were readmitted within 30 days after discharge; in 393 (1.4%) patients adverse events occurred; 417 patients (1.4%) had a surgical site infection develop; 211 (0.7%) needed transfusions, and 56 (0.2%) died within 30 days after surgery. Ordinary least squares regression analyses were used to determine whether the CCI was associated with these outcomes.
  
  
  RESULTS
  The CCI accounted for 10% of the variation in readmissions. Every point increase in CCI score added an additional 0.45% risk in readmission for patients undergoing arthroplasty, 0.63% for patients undergoing trauma surgery, and 0.9% risk for patients undergoing spine surgery (all p < 0.01). The CCI was not associated with surgical site infection or other adverse events, but accounted for 8% of the variation in transfusion rate and 10% of the variation in mortality within 30 days of surgery.
  
  
  CONCLUSIONS
  The CCI can be used to estimate the risk of readmission after arthroplasty, hand and upper extremity surgery, spine surgery, and trauma surgery. It also can be used to estimate the risk of transfusion after arthroplasty, spine, trauma, and oncologic orthopaedic surgery and the risk of mortality after shoulder, trauma, and oncologic orthopaedic surgery.
  
  
  METHODS
  Level IV, prognostic study. See the Instructions for Authors for a complete description of levels of evidence.
authors.affiliation: Department of Orthopaedic Surgery, Massachusetts General Hospital, Yawkey Center, Suite 2100, 55 Fruit Street, Boston, MA, 02114, USA.
authors.forename: Timothy
authors.initials: T
authors.lastname: Voskuijl
authors.forename: Michiel
authors.initials: M
authors.lastname: Hageman
authors.forename: David
authors.initials: D
authors.lastname: Ring
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001803:Blood Transfusion; D015897:Comorbidity; D003661:Decision Support Techniques; D005260:Female; D006801:Humans; D016018:Least-Squares Analysis; D008297:Male; D008875:Middle Aged; D019637:Orthopedic Procedures / Q000009:adverse effects* / Q000401:mortality; D010359:Patient Readmission; D011183:Postoperative Complications / Q000175:diagnosis / Q000401:mortality / Q000628:therapy*; D019984:Quality Indicators, Health Care; D012042:Registries; D018570:Risk Assessment; D012307:Risk Factors; D013530:Surgical Wound Infection / Q000401:mortality / Q000628:therapy; D013997:Time Factors; D055815:Young Adult