title: Improving stability of elastic stable intramedullary nailing in a transverse midshaft femur fracture model: biomechanical analysis of using end caps or a third nail.
abstract: BACKGROUND
  Elastic stable intramedullary nailing (ESIN) is accepted widely for treatment of diaphyseal femur fractures in children. However, complication rates of 10 to 50 % are described due to shortening or axial deviation, especially in older or heavier children. Biomechanical in vitro testing was performed to determine whether two modified osteosyntheses with end caps or a third nail could significantly improve the stability in comparison to classical elastic stable intramedullary nailing in a transverse femur fracture model.
  
  
  METHODS
  We performed biomechanical testing in 24 synthetic adolescent femoral bone models (Sawbones®) with a transverse midshaft (diaphyseal) fracture. First, in all models, two nails were inserted in a C-shaped manner (2 × 3.5 mm steel nails, prebent), then eight osteosyntheses were modified by using end caps and another eight by adding a third nail from the antero-lateral (2.5-mm steel, not prebent). Testing was performed in four-point bending, torsion, and shifting under physiological 9° compression.
  
  
  RESULTS
  The third nail from the lateral showed a significant positive influence on the stiffness in all four-point bendings as well as in internal rotation comparing to the classical 2C configuration: mean values were significantly higher anterior-posterior (1.04 vs. 0.52 Nm/mm, p < 0.001), posterior-anterior (0.85 vs. 0.43 Nm/mm, p < 0.001), lateral-medial (1.26 vs. 0.70 Nm/mm, p < 0.001), and medial-lateral (1.16 vs. 0.76 Nm/mm, p < 0.001) and during internal rotation (0.16 vs. 0.11 Nm/°, p < 0.001). The modification with end caps did not improve the stiffness in any direction.
  
  
  CONCLUSIONS
  The configuration with a third nail provided a significantly higher stiffness than the classical 2C configuration as well as the modification with end caps in this biomechanical model. This supports the ongoing transfer of the additional third nail into clinical practice to reduce the axial deviation occurring in clinical practice.
authors.affiliation: Department of Paediatric Surgery, Hospital of Kassel, Mönchebergstr. 41-43, 34125, Kassel, Germany.
authors.forename: Marion
authors.initials: M
authors.lastname: Rapp
authors.affiliation: Department of Paediatric Surgery, University of Lübeck, Ratzeburger Allee 160, 23538, Lübeck, Germany.
authors.forename: Nina
authors.initials: N
authors.lastname: Gros
authors.affiliation: Department of Biomechatronics and Academic Orthopaedics, University of Lübeck, Ratzeburger Allee 160, 23538, Lübeck, Germany.
authors.forename: Gregor
authors.initials: G
authors.lastname: Zachert
authors.affiliation: Department of Paediatric Surgery, University of Lübeck, Ratzeburger Allee 160, 23538, Lübeck, Germany.
authors.forename: Maaike
authors.initials: M
authors.lastname: Schulze-Hessing
authors.affiliation: Department of Paediatric Surgery, University of Lübeck, Ratzeburger Allee 160, 23538, Lübeck, Germany.
authors.forename: Christina
authors.initials: C
authors.lastname: Stratmann
authors.affiliation: Department of Biomechatronics and Academic Orthopaedics, University of Lübeck, Ratzeburger Allee 160, 23538, Lübeck, Germany.
authors.forename: Robert
authors.initials: R
authors.lastname: Wendlandt
authors.affiliation: Department of Paediatric Surgery, University of Lübeck, Ratzeburger Allee 160, 23538, Lübeck, Germany. kaiser@uni-luebeck.de.
authors.forename: Martin Michael
authors.initials: MM
authors.lastname: Kaiser
mesh_terms: D000293:Adolescent; D001696:Biomechanical Phenomena / Q000502:physiology; D001858:Bone Nails / Q000592:standards / Q000706:statistics & numerical data*; D004548:Elasticity / Q000502:physiology*; D004867:Equipment Design / Q000379:methods / Q000592:standards; D005264:Femoral Fractures / Q000473:pathology / Q000601:surgery*; D005594:Fracture Fixation, Intramedullary / Q000295:instrumentation / Q000379:methods*; D006801:Humans