Purpose
The goal of this study was to test the pullout strength of intramedullary (IM) screws
from within the humerus to establish their ability to seat an uncemented elbow arthroplasty.
Methods
Six humerus and 6 ulna Sawbones specimens were drilled with a drill bit diameter of
5/16 inches, and the inner cortex was hand tapped for a ⅜-16 thread. A ⅜-16 custom-made
titanium screw with an outer bolt diameter of 3/8 inches and 16 threads per inch was
inserted by hand into the tapped holes. The specimens were then axially tensile loaded
at a rate of 5 mm per minute until either the screw began to pull out from the bone
or a fracture was noted.
Results
Intramedullary screw fixation in the humerus achieved an average pullout strength
of 1,439 pound-force (6,401 N), and IM screw fixation in the ulna achieved an average
pullout strength of 882 pound-force (3,923 N). A fracture was noted in 3 humeral specimens,
with 3 screws pulling out. In the ulna, the IM axial load caused a fracture in 5 specimens,
and in 1 specimen, the screw pulled out.
Conclusions
Our findings demonstrate that IM screw fixation can create a tensile force within
the screw that is greater than that required to generate the calculated level of compression
between the implant and bone.
Clinical relevance
This may be beneficial in ensuring fixation between arthroplasty components and bone.
Key words
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Article info
Publication history
Published online: September 24, 2021
Accepted:
July 21,
2021
Received:
February 18,
2021
Footnotes
Robert A. Kaufmann owns Arrch Orthopedics. No benefits in any form have been received or will be received by the other authors related directly or indirectly to the subject of this article.
Identification
Copyright
© 2022 by the American Society for Surgery of the Hand. All rights reserved.
