title: Surgical site infection and transfusion rates are higher in underweight total knee arthroplasty patients.
abstract: BACKGROUND
  Underweight (UW) patients undergoing total hip arthroplasty have exhibited higher complication rates, including infection and transfusion. No study to our knowledge has evaluated UW total knee arthroplasty (TKA) patients. We, therefore, conducted a study to investigate if these patients are at increased risk for complications, including infection and transfusion.
  
  
  METHODS
  A case-control study was conducted using a prospectively collected institutional database. Twenty-seven TKA patients were identified as UW (body mass index [BMI] < 18.5 kg/m2) from 2000-2012 and were matched for age, gender, date of surgery, age-adjusted Charlson comorbidity index, rheumatoid arthritis, and diabetes. These patients were compared to 81 normal weight patients (BMI 18.5-24 kg/m2). Demographic variables were compared, along with wound complications, surgical site infection (SSI), blistering, deep vein thrombosis, pulmonary embolism, transfusion, revision, flexion contracture, hematoma formation, and patellar clunk.
  
  
  RESULTS
  The average BMI was 17.1 kg/m2(range 12.8-18.4) for UW and 23.0 kg/m2(range 19.0-25.0) for normal weight patients (P< .001). UW TKA patients were more likely to develop SSIs (3/27, 11.1% vs 0/81, 0.0%,P= .01) and were more likely to require transfusions (odds ratio = 3.4, confidence interval 1.3-9.1;P= .02).
  
  
  CONCLUSIONS
  Our study demonstrates that UW TKA patients have a higher likelihood of developing SSI and requiring blood transfusions. The specific reasons are unclear, but we conjecture that it may be related to decreased wound healing capabilities and low preoperative hemoglobin. Investigation of local tissue coverage and hematologic status may be beneficial in this patient population to prevent SSI. Based on the results of this study, a prospective evaluation of these factors should be undertaken.
authors.affiliation: Rothman Institute at Thomas Jefferson University, Philadelphia, PA, USA.
authors.forename: Jorge
authors.initials: J
authors.lastname: Manrique
authors.affiliation: Rothman Institute at Thomas Jefferson University, Philadelphia, PA, USA.
authors.forename: Antonia F
authors.initials: AF
authors.lastname: Chen
authors.affiliation: Rothman Institute at Thomas Jefferson University, Philadelphia, PA, USA.
authors.forename: Miguel M
authors.initials: MM
authors.lastname: Gomez
authors.affiliation: Rothman Institute at Thomas Jefferson University, Philadelphia, PA, USA.
authors.forename: Mitchell G
authors.initials: MG
authors.lastname: Maltenfort
authors.affiliation: Rothman Institute at Thomas Jefferson University, Philadelphia, PA, USA.
authors.forename: William J
authors.initials: WJ
authors.lastname: Hozack
keywords: Arthroplasty, replacement, knee; Body mass index; Perioperative complication; Prosthesis-related infections; Underweight