title: Knee arthroplasty and bleeding: when to remove drainages.
abstract: OBJECTIVE
  The aim of this study is an attempt to clarify the productive time of drainages as we find that the use of drains in knee arthroplasty is controversial, and there is no consensus regarding their length-time maintenance. We analysed the survival curve of bleeding within three surgical techniques for knee arthroplasty and the effect of two variables on survival curve.
  
  
  METHODS
  One hundred and eighty-eight out of 234 knees were included in the study, and patients were divided into three groups according to the surgical technique: conventional total knee arthroplasty (TKA), subvastus TKA and unicompartmental knee arthroplasty. Variables of study were type of surgery, number and placement of drains.
  
  
  RESULTS
  Mean of survival curve for postoperative bleeding time was 16 h (95 % CI: 15.4; 16.6). The risk for longer bleeding increased 1.38-fold with each additional drain used (95 % CI 1.1; 1.8).
  
  
  CONCLUSIONS
  According to the present study, drains can be safely removed at around 17 h postoperative. Bleeding time reduces as less drains are applied.
  
  
  METHODS
  Therapeutic study, Level III.
authors.affiliation: Department of Orthopedic Surgery and Trauma, Hospital Clinic de Barcelona, C/Villarroel 170, Traumatologia, escalera 12-4, 08036, Barcelona, Spain. arestraumatologia@gmail.com
authors.forename: Oscar
authors.initials: O
authors.lastname: Ares
authors.forename: Roberto
authors.initials: R
authors.lastname: Seijas
authors.forename: Alberto
authors.initials: A
authors.lastname: Hernandez
authors.forename: Enric
authors.initials: E
authors.lastname: Castellet
authors.forename: Andrea
authors.initials: A
authors.lastname: Sallent
mesh_terms: D000368:Aged; D019645:Arthroplasty, Replacement, Knee / Q000009:adverse effects*; D004322:Drainage / Q000379:methods*; D006801:Humans; D008875:Middle Aged; D019106:Postoperative Hemorrhage / Q000209:etiology / Q000601:surgery*; D012189:Retrospective Studies; D013997:Time Factors; D016896:Treatment Outcome