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Clin Biomech (Bristol, Avon). 2019 Aug 16;70:89-96. doi: 10.1016/j.clinbiomech.2019.08.008. [Epub ahead of print]

Locking plate constructs benefit from interfragmentary lag screw fixation with decreased shear movements and more predictable fracture gap motion in simple fracture patterns.

Author information

1
Centre for Musculoskeletal Surgery, Charité-Universitätsmedizin Berlin, Augustenburger Platz 1, 13353 Berlin, Germany. Electronic address: sven.maerdian@charite.de.
2
Department of Trauma Surgery, Medical University Innsbruck, Anichstraße 35, 6020 Innsbruck, Austria.
3
UniversitätsCentrum für Orthopädie & Unfallchirurgie, Universitätsklinikum Carl Gustav Carus Dresden, Fetscherstraße 74, 01307 Dresden, Germany.
4
Julius Wolff Institute for Biomechanics and Musculoskeletal Regeneration, Charité - Universitätsmedizin Berlin, Augustenburger Platz 1, 13353 Berlin, Germany.

Abstract

BACKGROUND:

A mechanical characterisation of lag screw fixation plus locking plate - although clinically widely used as either "mixed fixation concept" or absolutely stable fixation - is so far missing. This study aimed to evaluate the influence of an interfragmentary lag screw on the resulting motion at the fracture site of locking plate constructs using a simple fracture at the distal femur.

METHODS:

Human cadaver femora were in vitro loaded in torsion and axial bending-compression with and without lag screw fixation next to a locking plate fixation. In addition, two plate working lengths were tested. Interfragmentary movement was measured optically.

FINDINGS:

Axial interfragmentary movement is reduced with lag screw (102 mm plate working length, 1000 N, mean): 0.28 mm versus 0.82 mm. With lag screw, the fracture gap stays closed with mean normal interfragmentary movement ≤0.03 mm. Fracture gap tends to open without lag screw: normal interfragmentary movement up to -0.29 mm. Reduction of shear interfragmentary movement was observed throughout all tested loads and groups. Mean true shear remains generally low with lag screw (≤0.42 mm) compared to without lag screw (≤1.46 mm). We also found that interfragmentary movement variance decreases with lag screw, especially for longer plate working length.

INTERPRETATION:

An interfragmentary lag screw next to locking bridge plating reduces fragment motion in vitro for a simple fracture pattern and provides a sufficient tool to decrease detrimental shear movements. Prospective clinical trials with interfragmentary lag screw fixation should prove these findings in wide clinical use to treat simple fracture patterns.

KEYWORDS:

Hybrid fracture fixation; Locking bridging plate; Long bone fracture; Minimal invasive plate osteosynthesis; Plate independent lag screw

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