Clin Orthop Surg.  2019 Sep;11(3):302-308. 10.4055/cios.2019.11.3.302.

Biomechanical Comparison of Fixed- versus Variable-Angle Locking Screws for Distal Humerus Comminuted Fractures

• Nourbakhsh A
• Hirschfeld AG
• Dhulipala
• Hutton W
• Ganey T
• Lozada L
• Schlatterer D
• Lourie GM

• KMID: 2462559
• DOI: http://doi.org/10.4055/cios.2019.11.3.302

Abstract

BACKGROUND
To compare the stability of fixed- versus variable-angle locking constructs for the comminuted distal humerus fracture (AO/OTA 13-A3).
METHODS
Eight pairs of complete humeri harvested from eight fresh frozen cadavers were used for the study. We fixed the intact humeri using 2.7-mm/3.5-mm locking VA-LCP stainless steel distal humerus posterolateral (nine-hole) and medial (seven-hole) plates. An oscillating saw was used to cut a 1-cm gap above the olecranon fossa. The specimens were loaded in axial mode with the rate of 1 mm per 10 seconds to failure, and stress-strain curves were compared in each pair. The mode of failure was recorded as well as the load needed for 2- and 4-mm displacement at the lateral end of the gap.
RESULTS
The stiffness of the constructs, based on the slope of the stress-strain curve, did not show any difference between the fixed- versus variable-angle constructs. Likewise, there was no difference between the force needed for 2- or 4-mm displacement at the lateral gap between the fixed- and variable-angle constructs. The mode of failure was bending of both plates in all specimens and screw pull-out in four specimen pairs in addition to the plate bending.
CONCLUSIONS
Our results did not show any difference in the biomechanical stability of the fixed- versus variable-angle constructs. There was not any screw breakage or failure of the plate-screw interface.

Keyword

Humerus; Fracture fixation; Bone screws

MeSH Terms

Bone Screws
Cadaver
Fracture Fixation
Fractures, Comminuted*
Humerus*
Olecranon Process
Stainless Steel
Stainless Steel

Figure

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  Fig. 1 (A) The distal and proximal configuration of the fixed- and variable-angle (VA) constructs. (B) Distal humerus dual plating is done and the specimen is mounted in the material testing system (MTS) Mini Bionix testing machine (MTS, Eden Prairie, MN, USA).

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  Fig. 2 The load-displacement curve of a fixed-angle construct.

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  Fig. 3 The load-displacement curve of a variable-angle construct.

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  Fig. 4 The posterolateral plate bent after biomechanical testing.

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  Fig. 5 The locking screws at the distal end of the medial plate broke out of the cortex.

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  Fig. 6 (A) The lateral X-ray of the distal humerus shows the bent posterolateral plate. (B) The anteroposterior view of the distal humerus shows the distal locking screws of the medial plate breaking out of the cortex.

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