• Stefano Brianza, Michael Plecko, Boyko Gueorguiev, Markus Windolf, and Karsten Schwieger.
• AO Research Institute, Clavadelerstrasse 8, 7270 Davos Platz, Switzerland. stefano.brianza@aofoundation.org
• Clin Biomech (Bristol, Avon). 2010 Nov 1;25(9):886-92.

BackgroundThe optimal surgical treatment for displaced proximal humeral fractures is still controversial. A new implant for the treatment of three-part fractures has been recently designed. It supplements the existing Expert Humeral Nail with a locking plate. We developed a novel humeral cadaveric model and the existing implant and the prototype were biomechanically compared to determine their ability in maintaining interfragmentary stability.MethodsThe bone mineral density of eight pairs of cadaveric humeri was assessed and a three-part proximal humeral fracture was simulated with a Greater Tuberosity osteotomy and a surgical neck wedge ostectomy. The specimens were randomly assigned to either treatment. A bone anchor simulated part of a rotator cuff tendon pulling on the Greater Tuberosity. Specimens were initially tested in axial compression and afterward with a compound cyclic load to failure. An optical 3D motion tracking system continuously monitored the relative interfragmentary movements.FindingsThe specimen stabilized with the prototype demonstrated higher stiffness (P=0.036) and better interfragmentary stability (P values<0.028) than the contralateral treated with the existing implant. There was no correlation between the bone mineral density and any of the investigated variables.InterpretationThe convenience of this new IM-nail and locking plate assembly must be confirmed in vivo but the current study provides a biomechanical rationale for its use in the treatment of three-part proximal humeral fractures. The improved stability could be advantageous in particular when medial buttress is missing, even in osteoporotic bone.Copyright © 2010 Elsevier Ltd. All rights reserved.

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