Initial mechanical stability of acetabular prostheses.
Secure initial stability is crucial for prostheses designed for biological ingrowth; without it, subsequent tissue ingrowth is impossible. Mechanical testing was performed in vitro to measure the interface shear stability of acetabular cup prostheses. Cemented, threaded, fined, and press-fit cups, both with and without supplemental screw fixation, were tested. A mechanically consistent polyethylene foam was used as a substrate to obviate the variations inherent in cadaver bones. Ramped, eccentric rim loads were applied using a servohydraulic materials testing system. Reaming, insertion, and loading variables were carefully controlled. Cups with external threads were significantly more stable than those fixed by fins or screws. Press-fit cups were significantly looser than all other tested designs. None of the uncemented prostheses approached the initial stability of cups secured with acrylic bone cement.
Litsky
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AS
Orthopedic BioMaterials Laboratory, Ohio State University, Columbus 43210.
Pophal
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SG
D000077:Acetabulum / Q000601:surgery*; D001696:Biomechanical Phenomena; D004867:Equipment Design; D006801:Humans; D019736:Prostheses and Implants