Anglia Ruskin University

PhD research student: Roger Mahadeo
Supervisory team: Prof Paul Ingle, Prof Kevin Cheah, Prof John Dowell, Mr Jeremy Tuite, Mr Tim Peckham
Funding body: Chelmsford Medical Education and Research Trust - £ 31,600

The total shoulder arthroplasty (TSA) procedure replaces the diseased articulating surfaces of the glenohumeral joint to treat degenerative arthritis. Failure of TSA reconstruction is attributed to glenoid component loosening commonly indicated radiographically. The aims of this study are to improve the fixation of the cemented keeled glenoid component and increase the longevity of the prosthesis. There has been little research carried out on keel design, cement mantle thickness and subchondral bone integrity.

3D homogeneous and heterogeneous finite element (FE) models of the reconstructed scapula were generated to investigate the effect that keel angle, in both the antero-posterior and supero-inferior planes, has on cement mantle fixation. Qualitative trends for keel angle design in both planes were assessed.

It was found that a keel angle invoking smaller keel geometry in the supero-inferior plane allows more of the glenoid bone stock to be preserved without compromising fixation with a confidence limit of 95%. A homogeneous FE model predicted the same comparative trend as a heterogeneous FE model employing muscle loading. Maintaining glenoid subchondral bone was found to lower cement mantle stresses. Increased cement mantle thickness around the keel of the component also predicted lower cement stresses.

A novel experimental test method involving both humeral head translation and rotation was devised to assess glenoid implant loosening. Cement mantle placement with or without cement on the back flange of the component was investigated. Results suggest that cement should be placed on the back flange of the component although the results must be treated with caution due to the variable bone material properties of the specimens used.

Publications:

• Mahadeo, R., Van Der Linde, I., Ingle, P., & Mootanah, R. 2002, "Accurate allocation of material properties to a three-dimensional scapula model with compensation for misalignment between CT scan and finite element representations", Proceedings of Biological and Medical Engineering, Singapore.