gms | German Medical Science

German Congress of Orthopaedics and Traumatology (DKOU 2019)

22. - 25.10.2019, Berlin

Biomechanical investigation of the effect of screw length on screw perforation in unstable 3-part osteoporotic proximal humerus fractures

Meeting Abstract

  • presenting/speaker Lisa Wenzel - Berufsgenossenschaftliche Unfallklinik Murnau, AO Research Institute Davos, Murnau, Germany
  • Daniel Ciric - AO Research Institute Davos, Flinders University, Australia, Davos, Switzerland
  • Dominic Mischler - AO Research Institute Davos, Davos, Switzerland
  • Feras Qawasmi - AO Research Institute Davos, Davos, Switzerland
  • Gueorguiev Gueorguiev - AO Research Institute Davos, Davos, Switzerland
  • Geoff Richards - AO Research Institute Davos, Davos, Switzerland
  • Markus Windolf - AO Research Institute Davos, Davos, Switzerland
  • Peter Varga - AO Research Institute Davos, Davos, Switzerland

Deutscher Kongress für Orthopädie und Unfallchirurgie (DKOU 2019). Berlin, 22.-25.10.2019. Düsseldorf: German Medical Science GMS Publishing House; 2019. DocAB30-188

doi: 10.3205/19dkou550, urn:nbn:de:0183-19dkou5509

Published: October 22, 2019

© 2019 Wenzel et al.
This is an Open Access article distributed under the terms of the Creative Commons Attribution 4.0 License. See license information at



Objectives: Locked plating of osteoporotic proximal humerus fractures remains challenging with 18-35% failure rate, indicating the need for improved solutions. Approximately 20-50% of all fixation failures are related to secondary screw tip perforation through the joint. The length of the proximal screws may affect the perforation risk; however, it remains unknown if the use of longer or shorter screws is more optimal to avoid fixation failure. Therefore, the aim of this biomechanical study was to investigate the effect of screw tip to articular surface distance (TJD) on screw perforation failure in unstable 3-part osteoporotic proximal humerus fractures.

Methods: Ten pairs of fresh-frozen human cadaveric proximal humeri were osteotomized to simulate a highly unstable malreduced 3-part fracture (AO/OTA 11-B1.1) with the head fragment unsupported from the greater tuberosity and the shaft. Following CT scanning, specimen-specific greater tuberculum fragments were segmented on the images and 3D printed with water-soluble polyvinyl alcohol to replace the osteotomized fragments during plating. The specimens were instrumented with PHILOS plate (DePuy Synthes, Switzerland) using screw rows A, B and E, randomising the bone pairs into either a long screw group (LSG) with 4 mm TJD, or a short screw group (SSG) with 8 mm TJD. Both distances were according to the recommended range limits of the surgical guide. Following instrumentation, the 3D printed tuberculum fragment was dissolved in water, leaving only the humeral head fragment; screws' purchase was unaffected by fragment removal. The specimens were cyclically tested to failure under sinusoidal loading at 4 Hz with constant valley load of 15 N and peak load progressively increasing from 50 N by 0.025 N/cycle. Construct failure was defined by the first screw to perforate through the articular surface and contact with an artificial acetabular cup. Additionally, initial screw thread loosening in the humeral head fragment was defined as 1 mm residual head fragment displacement.

Results and conclusion: The number of cycles to 1 mm residual displacement was significantly higher in the LSG (15860±4821) compared to the SSG (10230±4773, p<0.01). Failure mode was varus collapse combined with lateral-inferior displacement, with the calcar screws (row E) perforating first. Cycles to failure were 27849±5953 and 28903±7721 in the LSG and SSG, respectively (p=0.46). Screw thread loosening, accompanied by initiation of varus collapse, occurred later in the LSG compared to the SSG, due to purchase in stronger bone stock. However, the final failure event was not different between groups. The advantage of higher initial stability of the LSG was diminished, as the SSG screws had to perforate through a thicker bone region before reaching the joint surface. These results indicate that screw length is essential for achieving initial stability but may not be critical considering screw perforation when respecting the range of the surgical guidelines.