Abstract
Introduction: Uncemented humeral components rely heavily on initial stability and fixation as a function of the design of the implant. Concerns over initial torsional stability of humeral components have motivated the development of a variety of design concepts.
Aim: To investigate the torsional stability of two types of cementless humeral shoulder prostheses.
Methods: Twelve fresh-frozen cadaveric humeri were cleaned of all soft tissues and prepared for reconstruction with the two types of cementless humeral shoulder prostheses. The humeri were embedded in a low melting point alloy and tested in a servohydraulic-testing machine. The loading applied to the humeri was a controlled angle loading regime at ± 1.5 degrees for 150 cycles. Torque versus time was measured, and the exponential time constant was calculated.
Results: The Z implant displayed overall a tightening effect, and a positive time constant. Whereas the G implant displayed a negative time constant, i.e. a loosening of the implant.
Discussion: These differences reflect the initial stability achieved immediately following surgery and may have important implications for bone in-growth and long-term stability.
The abstracts were prepared by Professor A. J. Thurston. Correspondence should be addressed to him at the Department of Surgery, Wellington School of Medicine, PO Box 7343, Wellington South, New Zealand
