Purpose
Implant design parameters can greatly affect load transfer from the implant stem to
the bone. We have investigated the effect of length or material of distal ulnar implant
stems on the surrounding bone strains.
Methods
Eight cadaveric ulnas were instrumented with 12 strain gauges and secured in a customized
jig. Strain data were collected while loads (5–30 N) were applied to the medial surface
of the native ulnar head. The native ulnar head was removed, and a stainless steel
implant with an 8-cm–long finely threaded stem was cemented into the canal. After
the cement had cured, the 8-cm stem was removed, leaving a threaded cement mantle
in the canal that could accept shorter threaded stems of interest. The loading protocol
was then repeated for stainless steel stems that were 7, 5, and 3 cm in length, as
well as for a 5-cm–long titanium alloy (TiAl6V4) stem. Other stainless steel stem lengths between 3 and 7 cm were tested at intervals
of 0.5 cm, with only a 20 N load applied.
Results
No stem length tested matched the native strains at all gauge locations. No significant
differences were found between any stem length and the native bone at the 5th and
6th strain gauge positions. Strains were consistently closer to the native bone strains
with the titanium stem than the stainless steel stem for each gauge pair that was
positioned on the bone overlying the stem. The 3-cm stem results were closer to the
native strains than the 7-cm stem for all loads at gauges locations that were on top
of the stem.
Conclusions
The results from this study suggest that the optimal stem characteristics for distal
ulnar implants from a load transfer point of view are possessed by shorter (approximately
3 to 4 cm) titanium stems.
Key words
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Article info
Publication history
Accepted:
March 19,
2007
Received:
November 28,
2006
Footnotes
No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article.
Identification
Copyright
© 2007 American Society for Surgery of the Hand. Published by Elsevier Inc. All rights reserved.
