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Effect of screw position on single cycle to failure in bending and torsion of a locking plate–rod construct in a synthetic feline femoral gap model

Simone K. Niederhäuser DVM1, Slobodan Tepic DIPL ING, DR SCI2, and Urs T. Weber DVM3
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  • 1 Tierärztliches Überweisungszentrum, Small Animal Referral Practice, CH-4456 Tenniken, Switzerland.
  • | 2 Kyon AG, Technoparkstrasse 1, CH-8005 Zurich, Switzerland.
  • | 3 Tierärztliches Überweisungszentrum, Small Animal Referral Practice, CH-4456 Tenniken, Switzerland.

Abstract

OBJECTIVE To evaluate the effect of screw position on strength and stiffness of a combination locking plate–rod construct in a synthetic feline femoral gap model.

SAMPLE 30 synthetic long-bone models derived from beechwood and balsa wood.

PROCEDURES 3 constructs (2 locking plate–rod constructs and 1 locking plate construct; 10 specimens/construct) were tested in a diaphyseal bridge plating configuration by use of 4-point bending and torsion. Variables included screw position (near the fracture gap and far from the fracture gap) and application of an intramedullary pin. Constructs were tested to failure in each loading mode to determine strength and stiffness. Failure was defined as plastic deformation of the plate or breakage of the bone model or plate. Strength, yield angle, and stiffness were compared by use of a Wilcoxon test.

RESULTS Placement of screws near the fracture gap did not increase bending or torsional stiffness in the locking plate–rod constructs, assuming the plate was placed on the tension side of the bone. Addition of an intramedullary pin resulted in a significant increase in bending strength of the construct. Screw positioning did not have a significant effect on any torsion variables.

CONCLUSIONS AND CLINICAL RELEVANCE Results of this study suggested that, in the investigated plate-rod construct, screw insertion adjacent to the fracture lacked mechanical advantages over screw insertion at the plate ends. For surgeons attempting to minimize soft tissue dissection, the decision to make additional incisions for screw placement should be considered with even more caution.

Contributor Notes

Dr. Niederhäuser's present address is BolligerTschuor AG, Fachtierärzte für Kleintiere, Kieferstrasse 2, CH-4665 Oftringen – Zofingen, Switzerland.

Address correspondence to Dr. Niederhäuser (s.niederhaeuser@gmail.com).