Aim : several studies have shown that supracondylar fractures could be treated with two or three lateral pins. The aim of this study is to compare the stability of lateral pinning with two or three pins with two pins bridged with a small non-invasive device, which would allow the operator to use only two pins instead of three.
Methods : fifteen synthetic humerus were cut at the level of the center of the olecranon fossea to simulate supracondylar fractures. All the samples were fixed with parallel pins (Kirschner, diameter 1.6 mm) with lateral entry. Three different pins configurations were tested : two pins, two bridged pins and three pins. Each sample was tested in internal and external rotations using a MTS 809 axial / torsional Test System to measure the torsional stiffness and the torque needed to reach an angle of 10 degrees. A statistical analysis using the Student Law was performed.
Results : configurations with two pins, bridged with the non-invasive device or not, had identical mechanical properties. The configurations with three pins demonstrated the following change in mechanical properties, respectively over two pins and over two bridged pins : an increase in internal torsional stiffness of 21.2% and 25.3%, an increase in external torsional stiffness of 15% and 6.8% ; concerning the maximum torque needed to reach an angle of 10 degrees, the increase for internal rotation was 15.1% and 16.4% and the increase for external rotation was 12.4% and 13.3%.
The bridging device did not provide an increase in mechanical properties, which could have avoided the use of a third pin. However, this study showed that the third pin increased all four mechanical properties measured, increase that is needed to fix unstable reduced supracondylar fracture.
Our samples showed a statistically significant result (P<0.05) for the torsional stiffness in external rotation between two and three pins. No statistical difference was made between two pins configurations.
Clinical relevance : the opportunity to bridge two pins configuration with a small non-invasive device to reach a mechanical stability equivalent to a configuration with three pins would avoid one invasive pinning procedure and its iatrogenic complications.