The Effect of Radial Head Hemiarthroplasty Geometry on Proximal Radioulnar Joint Contact Mechanics

Abstract

To compare the joint contact area and peak contact stress of different radial head (RH) hemiarthroplasty articular profiles for the proximal radioulnar joint (PRUJ) to the native radial head with the hypothesis that the side radius and side angle closest to the native mating ulnar articular profile would provide the best contact mechanics. Finite element models generated from the computed tomography geometry of 14 native elbows (73 ± 17.5 years) were subjected to 12 different RH profiles having varying side radii (flat [r= ∞ mm], 16.25, 8.12, and 4.50 mm) and side angles (0°, 5°, and 10°) under a constant compressive 20-N medial load. Contact areas and peak contact stresses were computed and compared with the native joint. On average, RH implants significantly reduced PRUJ contact area by 55% ± 16% and increased peak contact stress by 337% ± 241% compared with the native RH. The prosthesis side radius had significant effects on both contact area and stress, but side angle did not. The 16.25-mm radii produced the largest contact areas, and the 4.50-mm radius model generated the smallest contact areas. As the side radius was decreased, peak contact stress was reduced as the contact migrated toward the center of the native ulnar articulation, although the 8.12-mm radius achieved the lowest peak contact stress. Whereas RH hemiarthroplasty side radius can affect both contact area and peak contact stress, the magnitude of the effect on contact area is relatively small compared with that of the peak contact stress. Furthermore, although a flat RH side profile with a side angle of 5° more closely matched the side profile of the native ulnas used in the present study, the optimal profile was found to be a smaller radius of 8.12 mm. Optimizing PRUJ contact mechanics after metallic RH hemiarthroplasty may contribute to better clinical outcomes by reducing the potential for native cartilage degeneration.