The Development of New Surfaces for Orthopaedic Implants to Enhance Osseointegration
The number of joint replacement procedures continues to increase year-on-year with approximately 160,000 hip and knee replacements performed in England and Wales in 2010, representing an increase of 6% and 5.7%, respectively from 2009 [1]. These recent data also indicate that there is a trend away from using cemented fixation of such devices to press-fit type implants. Although total joint replacement is one of the most successful orthopaedic procedures, the revision rates for younger patient’s remains unacceptably high. Given that cementless fixation is favoured in this patient group in particular, there is an urgent need to augment the surface properties of press-fit orthopaedic implants to induce more rapid osteointegration and thereby improve implant stability and attendant long-term survival.
The use of plasma sprayed hydroxyapatite (HA) coatings for fixation of press-fit cementless orthopaedic implants is well established. However, control of the key surface parameters in plasma spraying (e.g, phase purity and crystallinity) is recognised as being less than ideal. One of the disadvantages of plasma spraying is that the addition of various different ions into the HA lattice namely silicon, zinc, titanium and more recently, strontium to address the obvious deficiencies of the standard coatings, is difficult given the nature of the deposition process. An alternative strategy, as presented here, is to develop HA coatings with a upper surface layer that targets rapid bone formation while still utilising the clinically proven benefits of the base HA.
This project will use a sub-micron strontium-doped HA (Sr-HA) layer to augment and enhance clinical grade HA coatings with the aim of achieving direct cell response that leads to better osteointegration in vivo. Strontium containing HA has been shown to promote oseteoblast response and stimulate new bone formation more readily than pure HA, both in vitro and in vivo. However, to date strontium’s mechanisms of action on osteoblasts are not fully understood. Studies of strontium in connection with cementless arthroplasty are very limited and still at the experimental stage.
Physical deposition methods will be employed here to create a well controlled Sr-HA layer at the uppermost surface of plasma sprayed HA coatings. Recent unpublished work by the applicants has shown that Sr-HA layers that maintain active at the interfacial region can be created effectively. In this regard, the PhD student recruited will investigate the role of processing conditions on the properties of novel Sr-HA surface augmentation to attain optimal compositions. Suitable candidate surfaces will be subjected to a rigorous characterisation schedule, including physical, chemical and in vitro testing methods in line with relevant standards. It is envisaged that the major outcome of the study will be a cost-effective method to augment HA coatings with a strontium rich layer that targets the more rapid establishment of a stable bone-implant interface leading to provided implant fixation and a reduction in need for revision surgery.
1 - National Joint Registry 8th annual report (2011).
Personnel Involved
First Supervisor: Boyd, AR Dr
Second Supervisor: Meenan, BJ Prof
Collaboration: This project does not involve collaboration with another establishment