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Vet Comp Orthop Traumatol 2015; 28(02): 95-103
DOI: 10.3415/VCOT-14-06-0093
Original Research
Schattauer GmbH

The effect of intramedullary pin size and monocortical screw configuration on locking compression plate-rod constructs in an in vitro fracture gap model

T. Pearson
1   College of Veterinary Medicine, Murdoch University, Perth, Australia
,
M. Glyde
1   College of Veterinary Medicine, Murdoch University, Perth, Australia
,
G. Hosgood
1   College of Veterinary Medicine, Murdoch University, Perth, Australia
,
R. Day
2   Department of Medical Engineering & Physics, Royal Perth Hospital, Perth, Australia
› Author Affiliations
Further Information

Publication History

Received:20 June 2014

Accepted:15 January 2014

Publication Date:
26 December 2017 (online)

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Summary

Objective: To investigate the effect of intramedullary pin size in combination with various monocortical screw configurations on locking compression plate-rod constructs.

Methods: A synthetic bone model with a 40 mm fracture gap was used. Locking compression plates with monocortical locking screws were tested with no pin (LCP-Mono) and intramedullary pins of 20% (LCPR-20), 30% (LCPR-30) and 40% (LCPR-40) of intramedullary diameter. Locking compression plates with bicortical screws (LCP-Bi) were also tested. Screw configurations with two or three screws per fragment modelled long (8-hole), intermediate (6-hole), and short (4-hole) plate working lengths. Responses to axial compression, biplanar four-point bending and axial load-to-failure were recorded.

Results: LCP-Bi were not significantly different from LCP-Mono control for any of the outcome variables. In bending, LCPR-20 were not significantly different from LCP-Bi and LCP-Mono. The LCPR-30 were stiffer than LCPR-20 and the controls. The LCPR-40 constructs were stiffer than all other constructs. The addition of an intramedullary pin of any size provided a significant increase in axial stiffness and load to failure. This effect was incremental with increasing intramedullary pin diameter. As plate working length decreased there was a significant increase in stiffness across all constructs.

Clinical significance: A pin of any size increases resistance to axial loads whereas a pin of at least 30% intramedullary diameter is required to increase bending stiffness. Short plate working lengths provide maximum stiffness. However, the overwhelming effect of intramedullary pin size obviates the effect of changing working length on construct stiffness.

Keywords

Plate-rod - intramedullary pin size - monocortical - screw configuration - working length
 

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