Micromotion of plasma spray versus grit-blasted radial head prosthetic stem surfaces

Background: Initial stability of a textured surface prosthetic stem is necessary for bone in-growth. Surfaces currently used for radial head prostheses include titanium plasma spray and grit-blasted titanium. Hypothesis: Plasma spray radial head prosthetic stems are less dependent than grit-blasted stems on a tight press fit. Good initial press-fit stability, with acceptable micro-motion, can be achieved with a greater range of stem sizes using a plasma spray than grit-blasted surface. Methods: Paired cadaveric radii were implanted with plasma spray or grit-blasted radial head prosthetic stems. Micromotion at the stem tip was measured under circumstances simulating eccentric loads. Results: Micromotion in the plasma spray (PS) stems (49 +/- 37) mm was not better than that in the grit-blasted (GB) stems (28 +/- 10) mu m (P = .13). Micromotion of less than 100 mu m was measured in all 12 GB stems that were maximum or 1 mm less than maximum size, versus 5/6, and 4/6 PS stems, respectively. Discussion: Micromotion in plasma spray prosthetic radial head stems was not better than that seen in grit-blasted stems, contrary to our initial hypothesis. Conclusion: Grit-blasted prosthetic radial head stems confer initial press-fit stability that is as good as, or slightly better than, corresponding plasma spray stems. Acceptable amounts of micromotion can be achieved with 2 grit-blasted stem sizes and probably with 2 plasma spray stem sizes. Level of evidence: Basic Science, Biomechanical Laboratory Study. (C) 2011 Journal of Shoulder and Elbow Surgery Board of Trustees.