Evolving the design of unicondylar knee replacement to improve post operative function

Lead Research Organisation: Imperial College London
Department Name: Dept of Mechanical Engineering

Abstract

The aim of this project is to evolve current unicondylar knee replacement (UKR) design paradigms based on contemporary knowledge of natural knee kinematics. The design concepts shall consider implants specific for knees with varus and valgus deformity, and an all polymer configuration that would remove metal from the replaced joint entirely. To achieve these aims, a large dataset of computed tomography scans of normal, varus and valgus knees will be generated. The geometry and morphology of these data will be analysed using principal component analysis and multivariate statistical methods such that key relationships are identified. These data shall be used to generate implant design concepts for normal, varus and valgus knees that can recreate the natural anterioposterior constraint of the medial tibiofemoral articulation during flexion. Design concepts shall be assessed for implant stress, bone strains and interface micromotion using an experimentally validated finite element (FE) protocol previously generated in our group. Once the FE gives acceptable values, rapid prototypes of the designs shall be manufactured and implanted in cadaver knees by an experienced surgeon. The kinematics during flexion shall be measured using established methods in our laboratory and compared to the natural knee to prove the concept of the prototype design. Successful delivery of the proposal will lead to the development of a UKR with significant advantages over existing devices including more natural kinematics and soft tissue tension, morphology to suit common deformities, and potentially lower cost materials and manufacturing methods. By supporting the final design concepts, the proposed research can be used to support clinical trials of the device or any subsequent regulatory submission. The proposed research is highly likely to succeed due to the close relationship our lab has with orthopaedic surgeons, our track record of commercialising concepts and the support of a well respected industry partner. The environment in which the proposed research will be conducted will therefore allow the project to thrive.

Planned Impact

Successful delivery of the proposal will lead to the development of a new unicondylar knee replacement (UKR) concept and the IP will be protected through Imperial's technology transfer company. Licensing of this IP to an industrial partner will allow the development of the prototypes to continue in an industrial setting. A successful commercial launch of the device would create jobs associated with the regulatory surveillance of the device and those associated with selling and marketing the device. It would also provide the industrial partner with a device that is notably different to others on the market, supported by sound research at an independent institution. Upon completion of the proposed research, the industrial partner could complete development of the device and, depending on the regulatory strategy, commence either clinical trials or commercial activity within a year. The principal investigator and the team at Imperial have a vast collective experience in developing novel designs and bringing them to market. Involving an industrial partner in the proposed research project is part of this strategy and maximises the likelihood of a successful transfer to industry.

Another benefactor of the proposed research is the governmental agency responsible for the safety and performance of medical devices (Medicines and Healthcare Regulatory Agency (MHRA)). The regulatory pathway for developing medical devices is changing due to several recent high profile device recalls. The proposed research may benefit the MHRA by presenting a model in which new design concepts are refined by an independent party in a transparent manner before being adopted and developed by industry. Our group has close links with the British Orthopaedic Association and the Institution of Mechanical Engineers, through whom we are able to present the proposed model to the MHRA.

The ultimate benefactor of the proposed research is the patient. Post operative knee function has limitations and typically less than half of UKR/TKR patients are completely satisfied with their replaced joint. The new UKR design will be based on the latest knowledge of knee function and promises to improve the post operative function compared to conventional devices. UKR is an early interventional device, typically implanted into younger patients who still work, have active lifestyles and young families. Improving the function of their knee post-operatively will allow these patients to return to their active lifestyles with benefit to their personal health and family life. After a successful commercial launch, the number of patients treated with the device could conservatively reach 5,000 within five years.

Publications

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Puthumanapully PK (2014) A morphometric study of normal and varus knees. in Knee surgery, sports traumatology, arthroscopy : official journal of the ESSKA

 
Description We have demonstrated that for bow-legged knees (a common deformity in active people), the joint alignment can change, but there are specific landmarks that do not change with the deformity, and this can be very useful to make sure knee replacements are aligned properly in this patient population.
Exploitation Route We have published key geometrical relationships for the bow-legged knee (varus) that could be used in knee replacement design
Sectors Leisure Activities, including Sports, Recreation and Tourism

 
Description Patient satisfaction after knee replacement is poor, and this is a function of the replaced joint not replicating the biomechanics of the natural knee. One aspect of this is the morphology of the replaced surfaces, which partly define the stability and movement of the knee. Our study presented new data on the morphology of the varus (bow legged) knee, and this data will be used in improved implant design.
 
Description Research grant
Amount £70,000 (GBP)
Organisation Defence Science & Technology Laboratory (DSTL) 
Sector Public
Country United Kingdom
Start 01/2015 
End 01/2016