Purpose
Surgeons confronted with a long spiral metacarpal fracture may choose to fix it solely
with lagged screws. A biomechanical analysis of a metacarpal spiral fracture model
was performed to determine whether 3 1.5-mm screws or 2 2.0-mm screws provided more
stability during bending and torsional loading.
Methods
Second and third metacarpals were harvested from 12 matched pairs of fresh-frozen
cadaveric hands and spiral fractures were created. One specimen from each matched
pair was fixed with 2 2.0-mm lagged screws whereas the other was fixed with 3 1.5-mm
lagged screws. Nine pairs underwent combined cyclic cantilever bending and axial compressive
loading followed by loading to failure. Nine additional pairs were subjected to cyclic
external rotation while under a constant axial compressive load and were subsequently
externally rotated to failure under a constant axial compressive load. Paired t tests were used to compare cyclic creep, stiffness, displacement, rotation, and peak
load levels.
Results
Average failure torque for all specimens was 7.2 ± 1.7 Nm. In cyclic torsional testing,
the group with 2 screws exhibited significantly less rotational creep than the one
with 3 screws. A single specimen in the group with 2 screws failed before cyclic bending
tests were completed. No other significant differences were found between test groups
during torsional or bending tests.
Conclusions
Both constructs were biomechanically similar except that the construct with 2 screws
displayed significantly less loosening during torsional cyclic loading, although the
difference was small and may not be clinically meaningful.
Clinical relevance
Because we found no obvious biomechanical advantage to using 3 1.5-mm lagged screws
to fix long spiral metacarpal fractures, the time efficiency and decreased implant
costs of using 2-2.0 mm lagged screws may be preferred.
Key words
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Article info
Publication history
Published online: September 07, 2017
Accepted:
July 21,
2017
Received:
November 7,
2016
Footnotes
Materials for fracture fixation and cadavers for the experiments were provided by Medartis (Exton, PA).
Identification
Copyright
© 2017 by the American Society for Surgery of the Hand. All rights reserved.
