Effect of Humeral Stem Sizing and Alignment on Stress Shielding: A Virtual Cohort Study.

Abstract

Develop a population-level modeling approach that can reproduce the effect of relative stem size (RSS) on stress shielding as observed clinically after total shoulder arthroplasty. A population-level finite element modeling approach based on 35 bone models was developed accounting for surgical variability. Stress shielding was assessed in four diaphyseal regions following the clinical literature. Surgical variability was introduced for stem sizing and alignment resulting in 188 unique surgical intervention. Patient variability was introduced for bone quality and loading conditions, resulting in around 300 models overall. Consistent with clinical observations, the virtual cohort predicted the highest stress shielding in the proximal lateral stem region, in agreement with the location of cortical thinning, and the group with stress shielding showed a larger RSS as well as more stress shielding in all four regions compared to the no stress shielding group. Upsizing or tilting the stem in varus increased stress shielding significantly. Including muscle forces increased bone resorption in the lateral proximal aspect, again aligning with the clinical findings. The influence of bone quality on stress shielding was minimal. This in silico approach enables simulations of stress shielding to enrich clinical trial with virtual data as part of an in silico clinical trial (ISCT). ISCT allows to identify surgical conditions or implant designs that could lead to an increased risk of stress shielding.