title: No functional benefit of larger femoral heads and alternative bearings at 6 months following primary hip replacement.
abstract: OBJECTIVE
  There has been a recent trend towards the use of greater femoral head sizes in an attempt to improve function and enhance stability after primary hip replacement. This has been associated with the use of alternative bearings, theoretically to reduce wear and improve implant longevity.
  
  
  METHODS
  We examined the influence of these variables on patient-reported outcome measures (PROMs) for a consecutive series of primary hip replacements using National Joint Registry (NJR) and PROMs-linked data. To minimize the confounding influence of implant design factors, the single most commonly used brand in England and Wales (DePuy Corail Pinnacle) was examined. Improvement in patient hip-specific outcomes (Oxford hip score, OHS), general health outcomes (Euroqol, EQ-5D), and rates of self-reported complications (bleeding, wound problems, re-admission, and reoperation) were compared for different head sizes (28-mm, 32-mm, and 36-mm) and bearings (metal-on-polyethylene (MoP), ceramic-on-polyethylene (CoP), and ceramic-on-ceramic (CoC)), adjusting for differences in case mix.
  
  
  RESULTS
  At a mean follow-up of 7 months, improvements in OHS and EQ5D index were similar for 28-mm and 36-mm heads. A 32-mm head was associated with poorer function (OHS: 20, 99% CI: 19-21, p = 0.002; EQ5D index: 0.39, 99% CI: 0.36-0.42, p = 0.004), although these small differences may not be of clinical importance. There were no statistically significant benefits of either CoP or CoC bearings compared to a MoP bearing. Complication rates were similar within comparisons of head sizes or bearings.
  
  
  CONCLUSIONS
  In this short-term study, we did not find any functional benefits of larger head sizes or alternative bearings, after adjusting for other influences. We question their use in routine primary hip replacement given the lack of evidence of improved long-term survival in the literature.
authors.affiliation: The National Joint Registry for England and Wales.
authors.forename: Simon S
authors.initials: SS
authors.lastname: Jameson
authors.forename: James M
authors.initials: JM
authors.lastname: Mason
authors.forename: Paul N
authors.initials: PN
authors.lastname: Baker
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Gregg
authors.forename: David J
authors.initials: DJ
authors.lastname: Deehan
authors.forename: Mike R
authors.initials: MR
authors.lastname: Reed
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D019644:Arthroplasty, Replacement, Hip / Q000379:methods*; D002516:Ceramics; D015331:Cohort Studies; D004739:England; D005260:Female; D006622:Hip Prosthesis; D006801:Humans; D008297:Male; D008670:Metals; D008875:Middle Aged; D015207:Osteoarthritis, Hip / Q000601:surgery*; D063868:Patient Outcome Assessment; D020959:Polyethylene; D011474:Prosthesis Design; D012042:Registries; D016896:Treatment Outcome; D014852:Wales
chemical_list: D008670:Metals; D020959:Polyethylene