title: An In Vitro Comparison of the Primary Stability of 2 Tapered Fluted Femoral Stem Designs.
abstract: BACKGROUND
  Proximal bony deficiencies present a biomechanical challenge to achieving primary stability in revision hip arthroplasty. Long tapered fluted stems have been engineered to span these defects but concerns of early subsidence are well documented. This work aimed primarily to investigate the issue of subsidence with this design using a cadaveric model. A secondary aim was to compare the stability of 2 versions of this design.
  
  
  METHODS
  Seven pairs of cadaveric femora were obtained, dual emission x-ray absorpitometry scanned, with calibration radiographs taken for digital templating. Each bone was potted according to the ISO standard for fatigue testing and a Paprosky type 3 defect was simulated. The established cone-conical Restoration Modular (Stryker) system and a novel design with a chamfered tip and flute configuration (Redapt, Smith & Nephew) were examined. Movement at the stem-bone interface was measured using radiostereometric analysis and micromotion transducers.
  
  
  RESULTS
  All restoration stems and 85% of the Redapt stems achieved stability by recognized criteria, micromotion < 150 μm and migration less than 2 mm. A Fisher exact test comparing the proportion of stems which were stable or unstable was not significant, P = .055. Mean axial subsidence (SD) was 0.17 mm (0.32) and 0.1 mm (0.131) for the Restoration and Redapt stems respectively.
  
  
  CONCLUSIONS
  This study has demonstrated minimal subsidence in the immediate post-operative period using tapered fluted stems. Both designs achieved excellent stability despite simulation of Paprosky type 3 bony defects in the cadaveric model. This geometry appears satisfactory for use in revision surgery in the presence of significant proximal bony deficiencies.
authors.affiliation: John Scales Centre for Biomedical Engineering, Institute of Orthopaedics and Musculoskeletal Science, University College and Royal Free Medical School, Stanmore, Middlesex; Orthopaedic Surgery Department, University College London Hospital NHS Trust, London.
authors.forename: Ivor S
authors.initials: IS
authors.lastname: Vanhegan
authors.affiliation: John Scales Centre for Biomedical Engineering, Institute of Orthopaedics and Musculoskeletal Science, University College and Royal Free Medical School, Stanmore, Middlesex.
authors.forename: Melanie J
authors.initials: MJ
authors.lastname: Coathup
authors.affiliation: John Scales Centre for Biomedical Engineering, Institute of Orthopaedics and Musculoskeletal Science, University College and Royal Free Medical School, Stanmore, Middlesex.
authors.forename: Ian
authors.initials: I
authors.lastname: McCarthy
authors.affiliation: John Scales Centre for Biomedical Engineering, Institute of Orthopaedics and Musculoskeletal Science, University College and Royal Free Medical School, Stanmore, Middlesex.
authors.forename: Jay
authors.initials: J
authors.lastname: Meswania
authors.affiliation: John Scales Centre for Biomedical Engineering, Institute of Orthopaedics and Musculoskeletal Science, University College and Royal Free Medical School, Stanmore, Middlesex.
authors.forename: Gordon W
authors.initials: GW
authors.lastname: Blunn
authors.affiliation: Orthopaedic Surgery Department, University College London Hospital NHS Trust, London.
authors.forename: Fares S
authors.initials: FS
authors.lastname: Haddad
mesh_terms: D000368:Aged; D019644:Arthroplasty, Replacement, Hip / Q000295:instrumentation*; D005260:Female; D005269:Femur / Q000601:surgery*; D006622:Hip Prosthesis; D006801:Humans; D008297:Male; D008875:Middle Aged; D011474:Prosthesis Design; D059869:Radiostereometric Analysis; D012086:Reoperation
keywords: Dadaveric; Micromotion; Primary stability; Radiostereometric analysis; Revision hip arthroplasty