Increasing stability by pre-bending the nails in elastic stable intramedullary nailing: a biomechanical analysis of a synthetic femoral spiral fracture model.

Elastic stable intramedullary nailing (ESIN) is generally acknowledged to be the treatment of choice for displaced diaphyseal femoral fractures in children over the age of three years, although complication rates of up to 50% are described. Pre-bending the nails is recommended, but there are no published data to support this. Using synthetic bones and a standardised simulated fracture, we performed biomechanical testing to determine the influence on the stability of the fracture of pre-bending the nails before implantation. Standard ESIN was performed on 24 synthetic femoral models with a spiral fracture. In eight cases the nails were inserted without any pre-bending, in a further eight cases they were pre-bent to 30° and in the last group of eight cases they were pre-bent to 60°. Mechanical testing revealed that pre-bending to 60° produced a significant increase in the stiffness or stability of the fracture. Pre-bending to 60° showed a significant positive influence on the stiffness compared with unbent nails. Pre-bending to 30° improved stiffness only slightly. These findings validate the recommendations for pre-bending, but the degree of pre-bend should exceed 30°. Adopting higher degrees of pre-bending should improve stability in spiral fractures and reduce the complications of varus deformity and shortening.

Biomechanical analysis of a synthetic femur spiral fracture model: Influence of different materials on the stiffness in flexible intramedullary nailing.

BACKGROUND: Flexible intramedullary nail fixation of dislocated diaphyseal femur fractures has gained wide acceptance for children and adolescents with open physes. Studies with a special emphasis on complications reveal frequent problems regarding stability, usually in complex fracture types such as spiral fractures and in older children weighing >40kg. This biomechanical study analyses how much the material of the nails influences the stiffness in a synthetic bone model. METHODS: Twenty-four composite grafts (Sawbones®, 4th generation, medullar canal of 10mm) with an identical spiral fracture were used in three configurations of eight grafts. Elastic stable intramedullary nailing was performed in a retrograde C-shaped manner with two nails of equal size (2×3.5mm). Close contact of the fragments could be achieved. We compared Group A (steel nails) with Group B and C (two types of titanium nails). All specimens underwent 4-point bending, torsion and axial compression in the 0° and 9° positions, and the results were analysed. FINDINGS: Group A (steel nails) revealed a significantly higher stiffness in all directions than Group B. Apart from compression in the 9° position this steel nail fixation showed significant higher stiffness than titanium nails of Group C. Comparing Group B and C did not show an systematic difference. INTERPRETATION: In this biomechanical study with composite artificial bones the use of steel Nails demonstrated the highest stiffness in our model when compared to two different titanium nail configurations. Apart from in cases of known allergy or planned MRI-examinations our results and data from the literature question the use of titanium nails.