Implications of Radial Head Hemiarthroplasty Dish Depth on Radiocapitellar Contact Mechanics

Abstract

To investigate the effect of radial head implant dish depth on radiocapitellar joint contact mechanics. Computed tomography images of 13 fresh-frozen cadaveric humeri were reconstructed into 3-dimensional finite element models with accurate cartilage geometry. Native humeri were paired with the corresponding native radial heads and axisymmetric radial head prosthesis models of the following dish depths: 1.0 mm, 1.5 mm, 2.0 mm, 2.5 mm, and 3.0 mm. Radiocapitellar contact mechanics were quantified at 4 different flexion angles (0°, 45°, 90°, and 135°) with a 100-N axial load applied to the radial head using a modeling protocol previously validated by cadaveric studies. The radial head was permitted to translate freely to its optimal position while the humerus was fully constrained. Output variables were contact area and peak contact stress. All prostheses had significantly decreased contact area and increased peak contact stress at all flexion angles relative to the native radiocapitellar joint. Contact area increased with prosthesis dish depth until reaching a plateau with a predicted local maximum at a mean depth of 3.2 ± 0.7 mm. Peak contact stress was elevated for both the shallowest and deepest models and reached a predicted local minimum at a mean depth of 1.8 ± 0.3 mm. Contact area and peak contact stress were dependent on radial head prosthesis dish depth. There was an optimal implant dish depth for radiocapitellar contact mechanics at approximately 2 mm. Optimizing radiocapitellar contact mechanics using rigorous and systematic prosthesis design techniques may lead to better clinical outcomes due to reduced capitellar cartilage degradation.