Simon A Euler1,2,3, Maximilian Petri4,5,6, Melanie B Venderley5, Grant J Dornan5, Werner Schmoelz7, Travis Lee Turnbull5, Michael Plecko8, Franz S Kralinger9, Peter J Millett4,5. 1. Department of Trauma Surgery and Sports Traumatology, Medical University Innsbruck, Anichstr. 35, 6020, Innsbruck, Austria. simon.euler@tirol-kliniken.at. 2. The Steadman Clinic, 181 West Meadow Drive, Suite 400, Vail, CO, 81657, USA. simon.euler@tirol-kliniken.at. 3. Steadman Philippon Research Institute, 181 West Meadow Drive, Suite 1000, Vail, CO, 81657, USA. simon.euler@tirol-kliniken.at. 4. The Steadman Clinic, 181 West Meadow Drive, Suite 400, Vail, CO, 81657, USA. 5. Steadman Philippon Research Institute, 181 West Meadow Drive, Suite 1000, Vail, CO, 81657, USA. 6. Department of Trauma Surgery, Hannover Medical School, Carl-Neuberg-Str. 1, 30625, Hannover, Germany. 7. Department of Trauma Surgery and Sports Traumatology, Medical University Innsbruck, Anichstr. 35, 6020, Innsbruck, Austria. 8. Unfallkrankenhaus Graz, Göstinger Str. 24, 8020, Graz, Austria. 9. Department of Trauma Surgery, Wilhelminenspital, Montlearstr. 37, 1160, Vienna, Austria.
Abstract
PURPOSE: Varus failure is one of the most common failure modes following surgical treatment of proximal humeral fractures. Straight antegrade nails (SAN) theoretically provide increased stability by anchoring to the densest zone of the proximal humerus (subchondral zone) with the end of the nail. The aim of this study was to biomechanically investigate the characteristics of this "proximal anchoring point" (PAP). We hypothesized that the PAP would improve stability compared to the same construct without the PAP. METHODS: Straight antegrade humeral nailing was performed in 20 matched pairs of human cadaveric humeri for a simulated unstable two-part fracture. RESULTS: Biomechanical testing, with stepwise increasing cyclic axial loading (50-N increments each 100 cycles) at an angle of 20° abduction revealed significantly higher median loads to failure for SAN constructs with the PAP (median, 450 N; range, 200-1.000 N) compared to those without the PAP (median, 325 N; range, 100-500 N; p = 0.009). SAN constructs with press-fit proximal extensions (endcaps) showed similar median loads to failure (median, 400 N; range, 200-650 N), when compared to the undersized, commercially available SAN endcaps (median, 450 N; range, 200-600 N; p = 0.240). CONCLUSIONS: The PAP provided significantly increased stability in SAN constructs compared to the same setup without this additional proximal anchoring point. Varus-displacing forces to the humeral head were superiorly reduced in this setting. This study provides biomechanical evidence for the "proximal anchoring point's" rationale. Straight antegrade humeral nailing may be beneficial for patients undergoing surgical treatment for unstable proximal humeral fractures to decrease secondary varus displacement and thus potentially reduce revision rates.
PURPOSE:Varus failure is one of the most common failure modes following surgical treatment of proximal humeral fractures. Straight antegrade nails (SAN) theoretically provide increased stability by anchoring to the densest zone of the proximal humerus (subchondral zone) with the end of the nail. The aim of this study was to biomechanically investigate the characteristics of this "proximal anchoring point" (PAP). We hypothesized that the PAP would improve stability compared to the same construct without the PAP. METHODS: Straight antegrade humeral nailing was performed in 20 matched pairs of human cadaveric humeri for a simulated unstable two-part fracture. RESULTS: Biomechanical testing, with stepwise increasing cyclic axial loading (50-N increments each 100 cycles) at an angle of 20° abduction revealed significantly higher median loads to failure for SAN constructs with the PAP (median, 450 N; range, 200-1.000 N) compared to those without the PAP (median, 325 N; range, 100-500 N; p = 0.009). SAN constructs with press-fit proximal extensions (endcaps) showed similar median loads to failure (median, 400 N; range, 200-650 N), when compared to the undersized, commercially available SAN endcaps (median, 450 N; range, 200-600 N; p = 0.240). CONCLUSIONS: The PAP provided significantly increased stability in SAN constructs compared to the same setup without this additional proximal anchoring point. Varus-displacing forces to the humeral head were superiorly reduced in this setting. This study provides biomechanical evidence for the "proximal anchoring point's" rationale. Straight antegrade humeral nailing may be beneficial for patients undergoing surgical treatment for unstable proximal humeral fractures to decrease secondary varus displacement and thus potentially reduce revision rates.
Entities:
Keywords:
Humeral fracture; Proximal anchoring point; Stability; Straight antegrade nails
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