Highlights
- •Spinning a 6.5 mm cancellous screw results in 79.1% loss of pull-out strength.
- •Revising a spinning cancellous screw with a larger screw partially improves the pull-out strength.
- •Surgeons should consider the use of “two-finger tight” torque when inserting a screw to avoid stripping.
Abstract
Background
Cancellous screw fixation is often used in fracture fixation. When this screw is over-tightened,
damage to the bone and other non-linear processes such as fracture and construct failure
would be involved. The objectives of this study were (1) to determine the reduction
in pull-out strength when a cancellous screw spins and (2) to determine how much pull-out
strength can be restored by revising with a larger diameter screw.
Methods
A biomechanical study using synthetic polyurethane foam (320 kg/m3) was performed to assess (1) the pull-out strength of a 6.5 mm cancellous screw,
(2) the pull-out strength of a loosened 6.5 mm cancellous screw and (3) the pull-out
strength of a loosened 6.5 mm cancellous screw revised with a 7.3 mm cancellous screw.
Findings
The baseline pull-out strength of the 6.5 mm cancellous screw was 2213.91 ± 200.51 N.
There was a 79.1% (463.79 ± 99.95 N) reduction in pull-out strength once spinning
occurs (p = 0.027). When a spinning 6.5 mm cancellous screw was revised to a 7.3 mm cancellous
screw, the pull-out strength increased to 1313.65 ± 93.23 N, 59.3% of the baseline
pull-out strength (2213.91 ± 200.51 N) (p = 0.027).
Intepretation
A loosened 6.5 mm cancellous screw results in a 79.1% reduction in pull-out strength.
Revising a loosened cancellous screw by inserting a larger 7.3 mm diameter screw partially
improves the pull-out strength to 59.3% of the baseline. Surgeons should consider
the use of “two-finger tight” torque when inserting a screw to avoid stripping.
Keywords
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Article info
Publication history
Published online: August 24, 2021
Accepted:
August 20,
2021
Received:
February 19,
2021
Identification
Copyright
© 2021 Elsevier Ltd. All rights reserved.
