TRAUMA SURGERY The Humerusblock NG: a new concept for stabilization of proximal humeral fractures and its biomechanical evaluation Alexander Brunner • Herbert Resch • Reto Babst • Susanne Kathrein • Johann Fierlbeck • Alfred Niederberger • Werner Schmo ¨lz Received: 28 November 2011 Ó Springer-Verlag 2012 Abstract Background The Humerusblock NG represents a new semi-rigid angular stable fixation device for minimally invasive stabilization of proximal humeral fractures. This study evaluates the function and stability of the Humer- usblock NG and its biomechanical properties on the basis of two different fracture models under cyclic loading. Methods Six fresh frozen human humeri were tested in a dynamic shoulder joint abduction motion test bench, sim- ulating abduction between 15° and 45°. A stable wedge fracture with intact medial hinge and an unstable fracture with 5-mm gap were loaded for 500 cycles. Radiological measurement of implant migration was performed. Results The stable fracture model showed a slow constant fracture settling. The unstable fracture model showed ini- tial fracture settling with closure of the medial fracture gap during the first 20 cycles. Thereafter, a slow constant settling of the fracture was measured comparable to the stable fracture model. Maximum varus tilt was 3.17° for the stable and 3.68° for the unstable fracture pattern. Radiological analysis showed no change in the tip apex distance and a significant settling of the implants fixation pins in the unstable fracture model. None of the specimen failed during the testing. Conclusion The Humerusblock NG allows for angular stable dynamic fixation of two-part proximal humeral fractures. It enables closure of the fracture gap and main- tains fracture compression during loading, a concept already established in the stabilization of femoral neck fractures (dynamic hip screw). Clinical trials will be nec- essary to evaluate the value of this device in daily practice. Level of evidence Basic science study. Keywords Proximal humerus Á Fracture Á Percutaneous Á Minimally invasive Á Semi-rigid Á Fixation Introduction Fractures of the proximal humerus are common injuries and represent approximately 5 % of all fractures of the human skeletal system [1, 2]. The majority of these frac- tures occur in patients over 65 years of age [3] and because the proportions of elderly people in developed societies are rising, this pathology will result in a significant health care burden in the years to come. During the last decade, open reduction and fixation with angular stable anatomically pre-shaped plates [4–6] and intramedullary nailing [7, 8] have become widely accepted methods of treatment. Both implant types have biomechanically proven their fixation stability [9–15] and a number of clinical trials have reported satisfactory results after the use of these devices A. Brunner Á S. Kathrein Á W. Schmo ¨lz (&) Department for Trauma Surgery and Sports Medicine, Medical University Innsbruck, Anichstrasse 35, 6020 Innsbruck, Austria e-mail: werner.schmoelz@uki.at A. Brunner e-mail: a-r.brunner@web.de H. Resch Department of Traumatology and Sports Injuries, University Hospital Salzburg, Mu ¨llner Hauptstrasse 48, 5020 Salzburg, Austria R. Babst Department of Trauma Surgery, Cantonal Hospital Lucerne, Spitalstrasse 16, 6000 Lucerne, Switzerland J. Fierlbeck Á A. Niederberger Synthes Innovation Workshop, Strubergasse 21, 5020 Salzburg, Austria 123 Arch Orthop Trauma Surg DOI 10.1007/s00402-012-1503-x