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

Area of Science:

• Biomechanical engineering
• Orthopedic surgery
• Computational modeling

Background:

• Stress shielding is a clinical concern after total shoulder arthroplasty, potentially leading to bone resorption.
• Relative stem size (RSS) is a known factor influencing stress shielding, but population-level modeling requires further development.

Purpose of the Study:

• To develop a population-level finite element modeling approach to simulate stress shielding after total shoulder arthroplasty.
• To reproduce the clinical effect of relative stem size (RSS) on stress shielding.

Main Methods:

• A population-level finite element model was created using 35 bone models.
• Surgical variability (stem sizing, alignment) and patient variability (bone quality, loading) were incorporated, resulting in approximately 300 unique models.
• Stress shielding was assessed in four diaphyseal regions.

Main Results:

• The model accurately predicted the highest stress shielding in the proximal lateral stem region, consistent with clinical findings of cortical thinning.
• A larger RSS and varus stem tilt significantly increased stress shielding across all assessed regions.
• Inclusion of muscle forces enhanced bone resorption prediction in the lateral proximal aspect, further validating the model.

Conclusions:

• The developed in silico approach can simulate stress shielding and enrich clinical trials.
• This method allows for the identification of surgical conditions and implant designs that may increase the risk of stress shielding, contributing to an in silico clinical trial (ISCT).