51312-01549-Seizing of Ti6Al7Nb Orthopedic Constructs in vitro

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Product Number: 51312-01549-SG

ISBN: 01549 2012 CP

Author: Douglas C. Hansen

Publication Date: 2012

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It has been reported in the literature that Ti6Al7Nb screws can seize in Ti6Al7NB locked-plate fixation plates in vivo. As a consequence head stripping can occur upon explantation of the constructs thus causing further complications. One of the reasons cited in the literature for the occurrence of cold-welding has been the failure to use torque-limiting screwdrivers when final screw seating is performed. Another is the misalignment and cross-threading of locking head screws such as those used in Less Invasive Stabilization System (LISS) plate fixation constructs. It has also been reported (anecdotally) that internal fixation of LISS constructs longer than 1 year can result in galling or “cold welding” of the locking head screws to the fixation plate. To date there have been very few studies reported in the literature of attempts to understand the mechanism by which this galling occurs on biomedical titanium alloys or devices in vivo or the conditions required to reproduce this phenomenon in vivo. To better understand the parameters that lead to seizing by galling or other phenomena in these constructs the phenomena must first be reproduced in vitro. The objective of this preliminary study was to determine if it is possible to reproduce the galling of the locking head screws to the LISS plate in the laboratory under near physiological conditions (i.e. at 37° C in simulated body fluid) at different torque values for up to 12 month exposures as well as to see if there is any correlation of the galling with the electrochemical behavior of the constructs over time. An identical set of plate-screw constructs were immersed in Hanks Balanced Salt Solution (HBSS) and exposed under identical conditions as controls. Comparison between the two sets of constructs will be presented and discussed.