title: A biomechanical assessment of modular and monoblock revision hip implants using FE analysis and strain gage measurements.
abstract: BACKGROUND
  The bone loss associated with revision surgery or pathology has been the impetus for developing modular revision total hip prostheses. Few studies have assessed these modular implants quantitatively from a mechanical standpoint.
  
  
  METHODS
  Three-dimensional finite element (FE) models were developed to mimic a hip implant alone (Construct A) and a hip implant-femur configuration (Construct B). Bonded contact was assumed for all interfaces to simulate long-term bony ongrowth and stability. The hip implants modeled were a Modular stem having two interlocking parts (Zimmer Modular Revision Hip System, Zimmer, Warsaw, IN, USA) and a Monoblock stem made from a single piece of material (Stryker Restoration HA Hip System, Stryker, Mahwah, NJ, USA). Axial loads of 700 and 2000 N were applied to Construct A and 2000 N to Construct B models. Stiffness, strain, and stress were computed. Mechanical tests using axial loads were used for Construct A to validate the FE model. Strain gages were placed along the medial and lateral side of the hip implants at 8 locations to measure axial strain distribution.
  
  
  RESULTS
  There was approximately a 3% average difference between FE and experimental strains for Construct A at all locations for the Modular implant and in the proximal region for the Monoblock implant. FE results for Construct B showed that both implants carried the majority (Modular, 76%; Monoblock, 66%) of the 2000 N load relative to the femur. FE analysis and experiments demonstrated that the Modular implant was 3 to 4.5 times mechanically stiffer than the Monoblock due primarily to geometric differences.
  
  
  CONCLUSIONS
  This study provides mechanical characteristics of revision hip implants at sub-clinical axial loads as an initial predictor of potential failure.
authors.affiliation: Department of Mechanical and Industrial Engineering, Ryerson University, Toronto, ON, M5B-2K3, Canada. zderor@smh.toronto.on.ca.
authors.forename: Habiba
authors.initials: H
authors.lastname: Bougherara
authors.forename: Rad
authors.initials: R
authors.lastname: Zdero
authors.forename: Suraj
authors.initials: S
authors.lastname: Shah
authors.forename: Milan
authors.initials: M
authors.lastname: Miric
authors.forename: Marcello
authors.initials: M
authors.lastname: Papini
authors.forename: Paul
authors.initials: P
authors.lastname: Zalzal
authors.forename: Emil H
authors.initials: EH
authors.lastname: Schemitsch
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