Tweet
PhD Studentship: Imaging and modelling of the interference fit in cementless joint replacement
Bioengineering Research Group
Engineering Sciences, Faculty of Engineering and the Environment
University of Southampton, UK
Earliest starting date: October 1st 2011
A PhD studentship is now available in the Bioengineering Research Group, Engineering Sciences Unit, which fully covers University tuition fees (at EU/UK level**) and provides a tax-free bursary of £13,900 per year, rising every October in line with the UK Government (EPSRC) recommended rate, for a 3-year duration. **EU/UK fees £3732 p.a., Overseas fee £16,120 p.a. (figures subject to annual increase).
This position is available to EU/UK applicants only, unless additional funding/scholarships are obtained by the student to cover the overseas fees difference (£12,388 for 2011/12).
** THE POST WILL BE ADVERTISED UNTIL THE POSITION HAS BEEN FILLED **
Cementless fixation relies on achieving good primary stability in order for osseointegration to occur. As well as the shape of the component, the degree of interference between the bone and the implant is key in determining the primary stability. Typical planned interferences between the bone and the implant of up to 1mm are routinely used in clinical practice for cementless hip stems and pegs/keels in cementless tibial trays. However, due to tolerancing of the implant and of the instrumentation and due to the variability in preparation during surgey, the true level of interference achieved is likely to be less than planned and potentially highly variable. Due to the viscoelastic nature of bone, the degree of interference is likely to decay in the first few days following surgery. Variations in bone quality are therefore likely to lead to significant variability in the true interference that will ultimately determine the primary stability required in the first 4-6 weeks for osseointegration to occur.
Various finite element studies have attempted model interference at the bone-implant interface [1, 2]. These studies have reported that relatively small interferences, of the order of 100-150 microns are all that are necessary to achieve primary stability and that higher interferences lead to substantial yielding of the supporting bone. This leads to two observations: (i) Current FE models are unable to capture the true nature of the interference and (ii) insertion of the device does not simply elastically/plastically the bone, but probably also continues to rasp the cavity.
The aim of this study is to perform a comprehensive investigation of interference fit in cementless fixation, with a view to providing recommendations for optimal performance. This will be achieved as follows:
- Develop an in-vitro model to assess the influence of interference of idealised cementless devices (femoral hip stems and tibial trays). Use micro-computed tomography to visualise the insertion process and to analyse the response of the bone at the bone-implant interface. Once inserted, perform mechanical tests to evaluate the primary stability of the bone-implant construct.
- Having developed the above protocol, use it to explore factors influencing the interference fit including: degree of interference, component/implant tolerancing, bone cavity preparation method and bone quality.
- Explore the influence of stress relaxation on the degree of interference as a function time. This is likely to be assessed through mechanical testing.
- Based on the observations from the in vitro study, develop suitable FE methodologies that are better able to capture the mechanics of interference at the bone-implant interface.
References:
1. Chong, D.Y.R., U.N. Hansen, and A.A. Amis, Analysis of bone–prosthesis interface micromotion for cementless tibial prosthesis fixation and the influence of loading conditions. Journal of Biomechanics, 2010. 43(6): p. 1074-1080.
2. Wong, A.S., et al., Effect of bone material properties on the initial stability of a cementless hip stem: a finite element study. Proceedings of the Institution of Mechanical Engineers Part H- Journal of Engineering in Medicine, 2005. 219: p. 265-275.
The School of Engineering Sciences at the University of Southampton has an international reputation for research excellence. In the 2008 UK Research Assessment Exercise, the School (in collaboration with the Institute of Sound & Vibration Research) ranked second in the total number of Unit 28 academics whose research was deemed world leading or internationally excellent.
The School is a diverse community which is committed to creating an inclusive working and learning environment in which all individuals are equally treated and valued, and can achieve their potential. The School considers all studentship applications in relation to academic criteria and regardless of the individual's race, nationality, gender, or belief.
ENTRY REQUIREMENTS
Candidates will have a first class or upper second class degree (or its equivalent) in relevant disciplines, for example:
• Bioengineering
• Physics
• Mechanical Engineering
• Computer Science
If you wish to discuss any details of the project informally, please contact Dr Martin Browne, Bioengineering Research Group, Email: doctor@soton.ac.uk , Tel: +44 (0) 2380 59 3279.
How to apply: An on-line application form (or hard copy version) with guidance notes can be accessed here: http://www.soton.ac.uk/ses/courses/pg/pgapply.html
Please read the notes carefully before applying. Applications will only be considered on receipt of a completed application form.
You can attach supporting documents to the on-line application. If unable to do this, please email to Jacqui Holmes J.Holmes@soton.ac.uk (copy to Martin Browne), or fax/post if unable to send them electronically:
Jacqui Holmes, Postgraduate Admissions, Graduate School Office, Engineering Sciences, Room 4009, Lanchester Building, University of Southampton, Highfield, Southampton, SO17 1BJ, UK.
Fax: +44 (0) 2380 59 5167.
Please ensure you include a personal statement in your application, stating why you particularly want to do a PhD, why you think you are suited to a research degree and what particularly attracts you to this project.
Please also visit www.soton.ac.uk/ses for further information about the Faculty and its research activities.
Bioengineering Research Group
Engineering Sciences, Faculty of Engineering and the Environment
University of Southampton, UK
Earliest starting date: October 1st 2011
A PhD studentship is now available in the Bioengineering Research Group, Engineering Sciences Unit, which fully covers University tuition fees (at EU/UK level**) and provides a tax-free bursary of £13,900 per year, rising every October in line with the UK Government (EPSRC) recommended rate, for a 3-year duration. **EU/UK fees £3732 p.a., Overseas fee £16,120 p.a. (figures subject to annual increase).
This position is available to EU/UK applicants only, unless additional funding/scholarships are obtained by the student to cover the overseas fees difference (£12,388 for 2011/12).
** THE POST WILL BE ADVERTISED UNTIL THE POSITION HAS BEEN FILLED **
Cementless fixation relies on achieving good primary stability in order for osseointegration to occur. As well as the shape of the component, the degree of interference between the bone and the implant is key in determining the primary stability. Typical planned interferences between the bone and the implant of up to 1mm are routinely used in clinical practice for cementless hip stems and pegs/keels in cementless tibial trays. However, due to tolerancing of the implant and of the instrumentation and due to the variability in preparation during surgey, the true level of interference achieved is likely to be less than planned and potentially highly variable. Due to the viscoelastic nature of bone, the degree of interference is likely to decay in the first few days following surgery. Variations in bone quality are therefore likely to lead to significant variability in the true interference that will ultimately determine the primary stability required in the first 4-6 weeks for osseointegration to occur.
Various finite element studies have attempted model interference at the bone-implant interface [1, 2]. These studies have reported that relatively small interferences, of the order of 100-150 microns are all that are necessary to achieve primary stability and that higher interferences lead to substantial yielding of the supporting bone. This leads to two observations: (i) Current FE models are unable to capture the true nature of the interference and (ii) insertion of the device does not simply elastically/plastically the bone, but probably also continues to rasp the cavity.
The aim of this study is to perform a comprehensive investigation of interference fit in cementless fixation, with a view to providing recommendations for optimal performance. This will be achieved as follows:
- Develop an in-vitro model to assess the influence of interference of idealised cementless devices (femoral hip stems and tibial trays). Use micro-computed tomography to visualise the insertion process and to analyse the response of the bone at the bone-implant interface. Once inserted, perform mechanical tests to evaluate the primary stability of the bone-implant construct.
- Having developed the above protocol, use it to explore factors influencing the interference fit including: degree of interference, component/implant tolerancing, bone cavity preparation method and bone quality.
- Explore the influence of stress relaxation on the degree of interference as a function time. This is likely to be assessed through mechanical testing.
- Based on the observations from the in vitro study, develop suitable FE methodologies that are better able to capture the mechanics of interference at the bone-implant interface.
References:
1. Chong, D.Y.R., U.N. Hansen, and A.A. Amis, Analysis of bone–prosthesis interface micromotion for cementless tibial prosthesis fixation and the influence of loading conditions. Journal of Biomechanics, 2010. 43(6): p. 1074-1080.
2. Wong, A.S., et al., Effect of bone material properties on the initial stability of a cementless hip stem: a finite element study. Proceedings of the Institution of Mechanical Engineers Part H- Journal of Engineering in Medicine, 2005. 219: p. 265-275.
The School of Engineering Sciences at the University of Southampton has an international reputation for research excellence. In the 2008 UK Research Assessment Exercise, the School (in collaboration with the Institute of Sound & Vibration Research) ranked second in the total number of Unit 28 academics whose research was deemed world leading or internationally excellent.
The School is a diverse community which is committed to creating an inclusive working and learning environment in which all individuals are equally treated and valued, and can achieve their potential. The School considers all studentship applications in relation to academic criteria and regardless of the individual's race, nationality, gender, or belief.
ENTRY REQUIREMENTS
Candidates will have a first class or upper second class degree (or its equivalent) in relevant disciplines, for example:
• Bioengineering
• Physics
• Mechanical Engineering
• Computer Science
If you wish to discuss any details of the project informally, please contact Dr Martin Browne, Bioengineering Research Group, Email: doctor@soton.ac.uk , Tel: +44 (0) 2380 59 3279.
How to apply: An on-line application form (or hard copy version) with guidance notes can be accessed here: http://www.soton.ac.uk/ses/courses/pg/pgapply.html
Please read the notes carefully before applying. Applications will only be considered on receipt of a completed application form.
You can attach supporting documents to the on-line application. If unable to do this, please email to Jacqui Holmes J.Holmes@soton.ac.uk (copy to Martin Browne), or fax/post if unable to send them electronically:
Jacqui Holmes, Postgraduate Admissions, Graduate School Office, Engineering Sciences, Room 4009, Lanchester Building, University of Southampton, Highfield, Southampton, SO17 1BJ, UK.
Fax: +44 (0) 2380 59 5167.
Please ensure you include a personal statement in your application, stating why you particularly want to do a PhD, why you think you are suited to a research degree and what particularly attracts you to this project.
Please also visit www.soton.ac.uk/ses for further information about the Faculty and its research activities.