Investigating the effect of mechanical loading in a total reversed shoulder implant

Abstract

The shoulder joint is a multi-axis synovial ball and socket joint, by having a loose connection it provides a wide degree of freedom; however this means the joint lacks robustness and is prone to damage most commonly from shoulder dislocations. A rotator cuff tear causes major problems in allowing the arm to be lifted beyond a 90˚ abduction position. It is common that this insufficiency aggravates arthritis problems that may have occurred due the rotator cuff tear problem. The study focuses on investigating, describing and quantifying the implant geometric properties to evaluate the joint contact characteristics and use the outcome in redesign the implant. The investigation presents results of finite element analysis on a heavy loading condition on a Verso (reverse) shoulder implant which is validated using experimental data on the same prosthesis. The results are validated within a 5% error margin. A Verso implant is modelled using MIMICS (materialise) and imported into ABAQUS (Simulia, Providence, USA) to analyse the distribution of stress, strain and displacement across the Humerus and Scapula. Details of interaction, boundary conditions, loads and material properties are all obtained from research and applied to the model to portray realistic behaviour. The resulting stress, strain and displacement from this simulation are indicated to show the magnitude and distribution across the entire bone region. This validates the benefits of a Verso implant compared to conventional and long stemmed reverse shoulder implants, as well as provide a basis from which improved designs can be built upon and allow further accurate methods to be developed in analysing shoulder implants effectively.