Effect of hoop stress fracture on micromotion of textured ingrowth stems for radial head replacement

Background Successful bone ingrowth around cementless implants requires adequate initial stability. Hoop stress fractures during stem insertion can potentially hinder prosthesis stability. Hypothesis We hypothesized that an oversized radial head prosthetic stem (1 mm “too large” and causing a hoop stress fracture during insertion) would result in an unacceptable amount of micromotion. Materials and methods Grit-blasted radial head prosthetic stems were implanted into cadaveric radii. Rasp and stem insertion energies were measured, along with micromotion at the stem tip. The sizes were increased until a fracture developed in the radial neck. Results Prosthetic radial head stems that were oversized by 1 mm caused small cracks in the radial neck. Micromotion of oversized stems (42 ± 7 μm) was within the threshold conducive for bone ingrowth (