Does the Extent of Prebending Affect the Stability of Femoral Shaft Fractures Stabilized by Titanium Elastic Nails? A Biomechanical Investigation on an Adolescent Femur Model

Abstract

Elastic stable intramedullary nailing (ESIN) is a common procedure for stabilization of femoral shaft fractures in childhood. Prebending of the nail is generally recommended to achieve optimal nail tension at the fracture site. To our knowledge there are no published data on the effects of prebending on stability. The purpose of this biomechanical study was to compare the effects of different degrees of prebending on the stability of transverse femoral fractures after ESIN using a bone model. Standardized transverse midshaft fractures were created in 20 synthetic, biomechanically validated adolescent bones (4th Generation Composite Femur--Sawbones Europe AB, Sweden) that were stabilized with 2 titanium nails (TEN) each (4 mm diameter, Synthes) and inserted in standardized retrograde technique. The 4 test series addressed nail prebending at 0 degree, 30 degrees, 45 degrees, and 60 degrees. The models were tested biomechanically in 4-point bending in the coronal and sagittal planes, relative stiffness was determined and analyzed statistically. The level of significance was set at P < 0.05. Comparison of the individual groups showed no significant differences in stiffness for different degrees of prebending in the coronal plane. Significantly reduced stiffness was found in the sagittal plane for the group with 60-degree prebending compared with the 0-degree, 30-degree, and 45-degree prebending groups. Intragroup comparison in the coronal and sagittal planes yielded a significantly reduced stiffness in the sagittal plane compared with the coronal plane in the group with 60-degree prebending. The 45-degree prebending group showed a similar tendency and in the 0-degree and 30-degree prebending groups there were no significant differences. On a synthetic bone model, prebending of TEN was found to affect the stability of transverse fractures of the femoral shaft, whereby indiscriminate prebending will reduce stability in the sagittal plane.Despite limited extrapolation of the findings to the in vivo situation, it can be stated that prebending of TEN by 0 to 30 degrees offers the greatest stability in the coronal and sagittal planes for transverse fractures of the femoral shaft.