Now showing 1 - 5 of 5
  • Publication
    Development of a Hip Joint Model for Finite Volume Simulations
    This paper establishes a procedure for numerical analysis of a hip joint using the finite volume method. Patient-specific hip joint geometry is segmented directly from computed tomography and magnetic resonance imaging datasets and the resulting bone surfaces are processed into a form suitable for volume meshing. A high resolution continuum tetrahedral mesh has been generated, where a sandwich model approach is adopted; the bones are represented as a stiffer cortical shells surrounding more flexible cancellous cores. Cartilage is included as a uniform thickness extruded layer and the effect of layer thickness is investigated. To realistically position the bones, gait analysis has been performed giving the 3D positions of the bones for the full gait cycle. Three phases of the gait cycle are examined using a finite volume based custom structural contact solver implemented in open-source software OpenFOAM.
    Scopus© Citations 13  949
  • Publication
    Preparation of Morselised Bone for Impaction Grafting using a Blender Method
    Impaction bone grafting is a method of restoring bone stock to patients suffering significant bone loss due to revision total hip surgery. The procedure requires morselised bone (MB) to be impacted into the site of bone loss in order to stabilise the prosthesis with the aim of the long term resorption and reintegration of the impacted bone graft. Currently, the method for producing MB requires the use of expensive surgical bone mills or manually-intensive rongeurs that can produce a limited variety of particle sizes and may have a low throughput. This study examines the potential to produce suitable MB using a domestic blender. The method produces a wide range of particle sizes without the need for an adjustment of the system. It was found through packing modelling that this particle distribution resulted in reduced initial graft porosity and thus a theoretical potential to increase the graft stiffness and ability of the graft to stabilise a prosthesis in comparison to a manually prepared roughly cut morselised bone samples. Mechanical testing confirmed the increased mechanical performance of the graft through both impaction testing and subsidence testing. The blended MB was found to exhibit greater graft stiffness under the same impaction conditions. The graft was also found to have subsided less in comparison to the rough cut, less well graded MB. Scanning electron imaging also confirmed the retention of the trabecular structure necessary for revascularisation and host bone ingrowth. In conclusion, the blender method offers a rapid and cheap way of obtaining morselised bone with favourable particle size distribution, particle morphology and mechanical properties with preservation of the bone trabecular structure. 
    Scopus© Citations 1  365
  • Publication
    The Use of Hardened Bone Cement as an Impaction Grafting Extender for Revision Hip Arthroplasty
    Impaction bone grafting is a method of restoring bone stock to patients who have suffered significant bone loss due to revision total hip surgery. The procedure requires morsellised cancellous bone (MCB) to be impacted into the site of bone loss in order to stabilise the prosthesis with the aim of long term resorption and reintegration of the impacted bone graft. Due to financial cost and the potential to transmit disease, the use of supplementary material, known as an extender, is frequently used to increase the graft material volume. This study investigates the use of hardened Hydroset (Stryker Corp, MA, USA), an injectable bone cement (IBC), as an extender material and compares the performance of the IBC in different weight percent inclusions to a commercially available bone graft extender (GCP, BoneSave, Stryker Corp, MA, USA). The surgical impaction procedure was standardised and samples were evaluated in terms of graft stiffness and height. It was observed that 30 wt.% IBC extended samples had significantly improved graft stiffness (p = 0.02) and no significant different in height (p = 0.067) over a 100% MCB control sample. Cyclic loading, representative of gait, found that the IBC subsided similarly to the commercial bone substitute in wt.% above 10%. Shear testing of the impacted grafts showed no significant differences between GCP and IBC with impaction forces determining the shear parameters of impacted grafts. The effects of the impaction and cyclical loading procedures on extender particle sizes was assessed via particle size analysis. It was found that the IBC extended samples demonstrated reduced friability, evident in the better retention of particle size as a result of both impaction and gait representative loading compared to that of the GCP samples. This indicates a potential reduction in issues arising from small particle migration to joint surfaces. Scanning electron microscopy of the MCB particles with both GCP and IBC as extenders showed retention of the porous trabecular structure post-testing which is essential for revascularisation and bone growth into the graft.
      253Scopus© Citations 3
  • Publication
    Development of mapped stress-field boundary conditions based on a Hill-type muscle model
    (Wiley Blackwell (John Wiley & Sons), 2014-04-07) ; ; ;
    Forces generated in the muscles and tendons actuate the movement of the skeleton. Accurate estimation and application of these musculotendon forces in a continuum model is not a trivial matter. Frequently, musculotendon attachments are approximated as point forces; however, accurate estimation of local mechanics requires a more realistic application of musculotendon forces. This paper describes the development of mapped Hill-type muscle models as boundary conditions for a finite volume model of the hip joint, where the calculated muscle fibres map continuously between attachment sites. The applied muscle forces are calculated using active Hill-type models, where input electromyography signals are determined from gait analysis. Realistic muscle attachment sites are determined directly from tomography images. The mapped muscle boundary conditions, implemented in a finite volume structural OpenFOAM (ESI-OpenCFD, Bracknell, UK) solver, are employed to simulate the mid-stance phase of gait using a patient-specific natural hip joint, and a comparison is performed with the standard point load muscle approach. It is concluded that physiological joint loading is not accurately represented by simplistic muscle point loading conditions; however, when contact pressures are of sole interest, simplifying assumptions with regard to muscular forces may be valid.
      638Scopus© Citations 4