title: Body mass index is not a clinically meaningful predictor of patient reported outcomes of primary hip replacement surgery: prospective cohort study.
abstract: OBJECTIVE
  To describe whether body mass index (BMI) is a clinically meaningful predictor of patient reported outcomes following primary total hip replacement (THR) surgery.
  
  
  METHODS
  Combined data from prospective cohort studies. We obtained information from four cohorts of patients receiving primary THR for osteoarthritis: Exeter Primary Outcomes Study (EPOS) (n = 1431); EUROHIP (n = 1327); Elective Orthopaedic Centre (n = 2832); and St. Helier (n = 787). The exposure of interest was pre-operative BMI. Confounding variables included: age, sex, SF-36 mental health, comorbidities, fixed flexion, analgesic use, college education, OA in other joints, expectation of less pain, radiographic K&L grade, ASA grade, years of hip pain. The primary outcome was the Oxford Hip Score (OHS). Regression models describe the association of BMI on outcome adjusting for all confounders.
  
  
  RESULTS
  For a 5-unit increase in BMI, the attained 12-month OHS decreases by 0.78 points 95%CI (0.27-1.28), P-value 0.001. Compared to people of normal BMI (20-25), those in the obese class II (BMI 35-40) would have a 12-month OHS that is 2.34 points lower. Although statistically significant this effect is small and not clinically meaningful in contrast to the substantial change in OHS seen across all BMI groupings. In obese class II patients achieved a 22.2 point change in OHS following surgery.
  
  
  CONCLUSIONS
  Patients achieved substantial change in OHS after THR across all BMI categories, which greatly outweighs the small difference in attained post-operative score. The findings suggest BMI should not present a barrier to access THR in terms of PROMs.
authors.affiliation: Oxford NIHR Musculoskeletal Biomedical Research Unit, Nuffield Department of Orthopaedics, Rheumatology and Musculoskeletal Sciences, University of Oxford, Windmill Road, Headington, Oxford OX3 7LD, UK; MRC Lifecourse Epidemiology Unit, University of Southampton, Southampton General Hospital, Southampton SO16 6YD, UK. Electronic address: andrew.judge@ndorms.ox.ac.uk.
authors.forename: A
authors.initials: A
authors.lastname: Judge
authors.affiliation: Oxford NIHR Musculoskeletal Biomedical Research Unit, Nuffield Department of Orthopaedics, Rheumatology and Musculoskeletal Sciences, University of Oxford, Windmill Road, Headington, Oxford OX3 7LD, UK. Electronic address: rajbir.batra@ndorms.ox.ac.uk.
authors.forename: R N
authors.initials: RN
authors.lastname: Batra
authors.affiliation: Oxford NIHR Musculoskeletal Biomedical Research Unit, Nuffield Department of Orthopaedics, Rheumatology and Musculoskeletal Sciences, University of Oxford, Windmill Road, Headington, Oxford OX3 7LD, UK. Electronic address: geraint.thomas@ndorms.ox.ac.uk.
authors.forename: G E
authors.initials: GE
authors.lastname: Thomas
authors.affiliation: Oxford NIHR Musculoskeletal Biomedical Research Unit, Nuffield Department of Orthopaedics, Rheumatology and Musculoskeletal Sciences, University of Oxford, Windmill Road, Headington, Oxford OX3 7LD, UK. Electronic address: david.beard@ndorms.ox.ac.uk.
authors.forename: D
authors.initials: D
authors.lastname: Beard
authors.affiliation: Oxford NIHR Musculoskeletal Biomedical Research Unit, Nuffield Department of Orthopaedics, Rheumatology and Musculoskeletal Sciences, University of Oxford, Windmill Road, Headington, Oxford OX3 7LD, UK; MRC Lifecourse Epidemiology Unit, University of Southampton, Southampton General Hospital, Southampton SO16 6YD, UK. Electronic address: kassim.javaid@ndorms.ox.ac.uk.
authors.forename: M K
authors.initials: MK
authors.lastname: Javaid
authors.affiliation: Oxford NIHR Musculoskeletal Biomedical Research Unit, Nuffield Department of Orthopaedics, Rheumatology and Musculoskeletal Sciences, University of Oxford, Windmill Road, Headington, Oxford OX3 7LD, UK. Electronic address: david.murray@ndorms.ox.ac.uk.
authors.forename: D W
authors.initials: DW
authors.lastname: Murray
authors.affiliation: Peninsula College of Medicine and Dentistry, C420, Portland Square, University of Plymouth Campus, Drake Circus, Plymouth PL4 8AA, UK. Electronic address: p.dieppe@exeter.ac.uk.
authors.forename: P A
authors.initials: PA
authors.lastname: Dieppe
authors.affiliation: Institute for Muskuloskeletal Rehabilitation, Prevention and Health Service Research, Center for Sport Science and Sport Medicine (CSSB), Center for Musculoskeletal Surgery (CMSC), Charité Universitätsmedizin Berlin, Philippstraße 13, 10115 Berlin, Germany; Department of Orthopaedics, Traumatology and Sports Medicine, Medical Park Berlin Humboldtmühle, An der Mühle 2-9, D-13507 Berlin, Germany. Electronic address: karsten.dreinhoefer@charite.de.
authors.forename: K E
authors.initials: KE
authors.lastname: Dreinhoefer
authors.affiliation: Department of Orthopaedic Surgery, University Hospital Carl Gustav Carus, Medical Faculty of the Technical University of Dresden, Germany. Electronic address: klaus-peter.guenther@uniklinikum-dresden.de.
authors.forename: K
authors.initials: K
authors.lastname: Peter-Guenther
authors.affiliation: Elective Orthopaedic Centre, Dorking Road, Epsom, Surrey KT18 7EG, UK. Electronic address: richard.field@eoc.nhs.uk.
authors.forename: R
authors.initials: R
authors.lastname: Field
authors.affiliation: Oxford NIHR Musculoskeletal Biomedical Research Unit, Nuffield Department of Orthopaedics, Rheumatology and Musculoskeletal Sciences, University of Oxford, Windmill Road, Headington, Oxford OX3 7LD, UK; MRC Lifecourse Epidemiology Unit, University of Southampton, Southampton General Hospital, Southampton SO16 6YD, UK. Electronic address: cc@mrc.soton.ac.uk.
authors.forename: C
authors.initials: C
authors.lastname: Cooper
authors.affiliation: Oxford NIHR Musculoskeletal Biomedical Research Unit, Nuffield Department of Orthopaedics, Rheumatology and Musculoskeletal Sciences, University of Oxford, Windmill Road, Headington, Oxford OX3 7LD, UK; MRC Lifecourse Epidemiology Unit, University of Southampton, Southampton General Hospital, Southampton SO16 6YD, UK. Electronic address: nigel.arden@ndorms.ox.ac.uk.
authors.forename: N K
authors.initials: NK
authors.lastname: Arden
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D019644:Arthroplasty, Replacement, Hip / Q000706:statistics & numerical data*; D015992:Body Mass Index; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D015207:Osteoarthritis, Hip / Q000601:surgery*; D010146:Pain / Q000534:rehabilitation; D063868:Patient Outcome Assessment; D017060:Patient Satisfaction; D011184:Postoperative Period; D011446:Prospective Studies; D011788:Quality of Life; D012307:Risk Factors; D011795:Surveys and Questionnaires; D016896:Treatment Outcome
keywords: Body mass index; Decision making; Epidemiology; Hip replacement; Osteoarthritis; Patient reported outcome