Biomechanical analysis of a synthetic femoral spiral fracture model: Do end caps improve retrograde flexible intramedullary nail fixation?
1 Department of Paediatric Surgery, Medical Faculty of the University of Luebeck, Ratzeburger Allee 160, Luebeck, 23562, Germany
2 Department of Biomechatronics and Academic Orthopaedics, Medical Faculty of the University of Luebeck, Ratzeburger Allee 160, Luebeck, 23562, Germany
3 Department of Child and Adolescent Health, Medical Faculty of the University of Luebeck, Ratzeburger Allee 160, Luebeck, 23562, Germany
4 Department of Paediatric Surgery, University of Mannheim, Theodor-Kutzer-Ufer 1-3, Mannheim, 68167, Germany
5 Department of Traumatology, Orthopaedics and Sports Medicine, Trauma Center Hamburg, Bergedorfer Str. 10, Hamburg, 21033, Germany
Journal of Orthopaedic Surgery and Research 2011, 6:46 doi:10.1186/1749-799X-6-46Published: 18 September 2011
Elastic Stable intramedullary Nailing (ESIN) of dislocated diaphyseal femur fractures has become an accepted method for the treatment in children and adolescents with open physis. Studies focused on complications of this technique showed problems regarding stability, usually in complex fracture types such as spiral fractures and in older children weighing > 40 kg. Biomechanical in vitro testing was performed to evaluate the stability of simulated spiral femoral fractures after retrograde flexible titanium intramedullary nail fixation with and without End caps.
Eight synthetic adolescent-size femoral bone models (Sawbones® with a medullar canal of 10 mm and a spiral fracture of 100 mm length identically sawn by the manufacturer) were used for each group. Both groups underwent retrograde fixation with two 3.5 mm Titanium C-shaped nails inserted from medial and lateral entry portals. In the End Cap group the ends of the nails of the eight specimens were covered with End Caps (Synthes Company, Oberdorf, Switzerland) at the distal entry.
Beside posterior-anterior stress (4.11 Nm/mm vs. 1.78 Nm/mm, p < 0.001), the use of End Caps demonstrated no higher stability in 4-point bending compared to the group without End Caps (anterior-posterior bending 0.27 Nm/mm vs. 0.77 Nm/mm, p < 0.001; medial-lateral bending 0.8 Nm/mm vs. 1.10 Nm/mm, p < 0.01; lateral-medial bending 0.53 Nm/mm vs. 0.86 Nm/mm, p < 0.001) as well as during internal rotation (0.11 Nm/° vs. 0.14 Nm/°, p < 0.05). During compression in 9°- position and external rotation there was no statistical significant difference (0.37 Nm/° vs. 0.32 Nm/°, p = 0.13 and 1.29 mm vs. 2.18 mm, p = 0.20, respectively) compared to the "classic" 2-C-shaped osteosynthesis without End Caps.
In this biomechanical study the use of End Caps did not improve the stability of the intramedullary flexible nail osteosynthesis.