Contact analysis of the native radiocapitellar joint compared with axisymmetric and nonaxisymmetric radial head hemiarthroplasty
Journal of Shoulder and Elbow Surgery
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© 2015 Journal of Shoulder and Elbow Surgery Board of Trustees. Background: Radial head (RH) implants are manufactured from stiff materials, resulting in reduced radiocapitellar contact area that may lead to cartilage degeneration. Although the native RH is nonaxisymmetric, most implants are axisymmetric, potentially contributing to altered contact mechanics. This study compared the joint contact area (Ac) and maximum contact stress (σmax) of axisymmetric and nonaxisymmetric RH implants to the native radiocapitellar joint. Methods: The contact mechanics of intact elbows derived from cadaveric computed tomography data (n=15) were compared with axisymmetric (size: 18, 20, 22mm) and nonaxisymmetric (size: 16 × 18, 18 × 20, 20×22mm) RH hemiarthroplasty reconstructed elbows using Abaqus finite element software. Under a100 N load, Ac and σmax were computed for ±90° pronation-supination and 0°, 45°, 90°, and 135° flexion. Results: Compared with native, both hemiarthroplasty models produced significantly lower Ac and higher σmax (P<.001). In the best orientation, the nonaxisymmetric RH provided significantly larger Ac at 0° and 135° flexion (P=.03, P=.007) and reduced levels of σmax at 45° and 90° flexion (P=.003, P<.001). However, there was also a worst orientation that reduced Ac and increased σmax for all flexion angles (P<.003 for all). The native RH was less sensitive to rotation than the nonaxisymmetric RH in terms of σmax (P<.001). The axisymmetric RH was not sensitive to rotation. Conclusions: Whereas a nonaxisymmetric RH can provide improved contact mechanics at certain forearm rotations and flexions, there are also orientations where Ac is reduced and σmax is increased. Axisymmetric designs are more consistent throughout forearm rotation and therefore may be more forgiving than the nonaxisymmetric RH implant design used in this study.