The effect of implant misalignment on shoulder replacement outcomes

Abstract

Total shoulder arthroplasty is a well-established treatment to relieve pain and restore joint function particularly in arthritis patients. The damaged shoulder joint is replaced with humeral and glenoid components. For success, all replacement components must be aligned properly. However, errors in glenoid component alignment particularly in version is not infrequent due to the complexities such as limited monitoring available during the surgical procedure and glenoid posterior wear, commonly observed in glenohumeral osteoarthritis. Glenoid component version has been found to induce eccentric load and may result in component loosening which is the main indicator for revision surgery. The overall aim of this thesis is to gain the in-depth understanding of how the component version affects the fixation loosening in both cementless and cemented shoulder arthroplasty. Early loosening in cementless arthroplasty is associated with failed biological fixation due to excessive micromotion at the implant-bone interface. To measure interface micromotion, this thesis developed an in-vitro technique based on the application of digital volume correlation (DVC) and micro-computed tomography (μCT). This technique was validated and verified the use of the finite element (FE) method as a tool for investigating the effect of glenoid component version on micromotion. The FE predicted micromotion during a full range of shoulder abduction confirmed that 60° of abduction was the critical position inducting the largest micromotion and large micromotions were shown to be related to increased component retroversion. The condition of the bone was also found to be an important parameter as less stiff bone caused large micromotions.