title: The influence of body mass index on functional outcome and quality of life after total knee arthroplasty.
abstract: OBJECTIVE
  This study investigated the influence of body mass index (BMI) on the post-operative fall in the level of haemoglobin (Hb), length of hospital stay (LOS), 30-day re-admission rate, functional outcome and quality of life, two years after total knee arthroplasty (TKA).
  
  
  METHODS
  A total of 7733 patients who underwent unilateral primary TKA between 2001 and 2010 were included. The mean age was 67 years (30 to 90). There were 1421 males and 6312 females. The patients were categorised into three groups: BMI < 25.0 kg/m(2) (normal); BMI between 25.0 and 39.9 kg/m(2) (obese); and BMI ≥ 40.0 kg/m(2) (morbidly obese).
  
  
  RESULTS
  Compared with the normal and obese groups, the mean LOS was longer by one day (95% confidence interval (CI) 0 to 2) in the morbidly obese group (p = 0.003 and p = 0.001 respectively). The 30-day re-admisison rate was also higher in the morbidly obese group compared to the obese group (OR 2.323, 95% CI 1.101 to 4.900, p = 0.024); and showed a higher trend compared to the normal group (OR 1.850, 95% CI 0.893 to 3.831, p = 0.100). However, the morbidly obese group had a smaller drop in post-operative Hb level by a mean of 0.5 g/dl (0.3 to 0.6) and 0.3 g/dl (0.1 to 0.5), when compared with the normal and obese groups respectively (both p < 0.001). Furthermore, the mean improvement in Oxford Knee Score (OKS) and Knee Society Knee Score (KSKS) at two years follow-up was three points (two to four) and five points (two to seven) more in the morbidly obese group than in the normal group (both p < 0.001). The mean improvement in Knee Society Function Score, and Physical and Mental Component Scores of Short Form-36 were comparable between the three BMI groups (p = 0.736, p = 0.739 and p = 0.731 respectively). The ten-year rate of survival was 98.8% (98.0 to 99.3), 98.9% (98.5 to 99.2) and 98.0% (95.8 to 100), for the normal, obese and morbidly obese groups, respectively (p = 0.703).
  
  
  CONCLUSIONS
  Although morbidly obese patients have a longer LOS and higher 30-day re-admission rate after TKA, they have a smaller drop in post-operative Hb level and larger improvement in OKS and KSKS at two years follow-up. The ten-year rate of survival of TKA was also comparable with those with a normal BMI.
  
  
  CONCLUSIONS
  Morbidly obese patients should not be excluded from the benefits of TKA. Cite this article: Bone Joint J 2016;98-B:780-5.
authors.affiliation: Singapore General Hospital, 20 College Road, Academia Building Level 4, 169856, Singapore.
authors.forename: J Y
authors.initials: JY
authors.lastname: Chen
authors.affiliation: Singapore General Hospital, 20 College Road, Academia Building Level 4, 169856, Singapore.
authors.forename: N N
authors.initials: NN
authors.lastname: Lo
authors.affiliation: Singapore General Hospital, Outram Rd, 169856, Singapore.
authors.forename: H C
authors.initials: HC
authors.lastname: Chong
authors.affiliation: Singapore General Hospital, 20 College Road, Academia Building Level 4, 169856, Singapore.
authors.forename: H R
authors.initials: HR
authors.lastname: Bin Abd Razak
authors.affiliation: Singapore General Hospital, 20 College Road, Academia Building Level 4, 169856, Singapore.
authors.forename: H N
authors.initials: HN
authors.lastname: Pang
authors.affiliation: Singapore General Hospital, 20 College Road, Academia Building Level 4, 169856, Singapore.
authors.forename: D K J
authors.initials: DK
authors.lastname: Tay
authors.affiliation: Singapore General Hospital, 20 College Road, Academia Building Level 4, 169856, Singapore.
authors.forename: S L
authors.initials: SL
authors.lastname: Chia
authors.affiliation: Singapore General Hospital, 20 College Road, Academia Building Level 4, 169856, Singapore.
authors.forename: S J
authors.initials: SJ
authors.lastname: Yeo
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D019645:Arthroplasty, Replacement, Knee; D015992:Body Mass Index; D005260:Female; D005500:Follow-Up Studies; D006454:Hemoglobins / Q000032:analysis; D006801:Humans; D007902:Length of Stay / Q000706:statistics & numerical data; D008297:Male; D008875:Middle Aged; D009765:Obesity / Q000453:epidemiology; D009767:Obesity, Morbid / Q000453:epidemiology; D010359:Patient Readmission / Q000706:statistics & numerical data; D011183:Postoperative Complications; D011788:Quality of Life; D012189:Retrospective Studies; D012846:Singapore / Q000453:epidemiology
chemical_list: D006454:Hemoglobins
keywords: Body Mass Index; Functional outcome; Quality of life; Revision Rate; Total knee arthroplasty