Biomechanical analysis of titanium elastic nail fixation in a pediatric femur fracture model.
BACKGROUND
Increasing weight in relation to total diameter of implanted titanium elastic nails has been found to be significantly associated with increasing sagittal angulation. However, the biomechanical literature has not well established the load at which failure of titanium elastic nails in the sagittal and coronal planes occurs. The purpose of this study was to determine load to failure in sagittal and coronal plane bending of transverse midshaft femur fractures stabilized with titanium elastic nails and correlate this with the maximum patient weight.


METHODS
Ten synthetic, pediatric-sized femurs 35 cm in length with an intramedullary canal diameter of 9.5 mm were used. Transverse midshaft fracture patterns were created with a handheld saw. Two 4.0-mm titanium elastic nails were then placed in a retrograde fashion through medial and lateral insertion sites in the distal metaphysis of the femur to stabilize the simulated fractures. A 4-point bending load to failure test was performed on each of the femurs. Five femurs were tested in the sagittal plane, and 5 femurs were tested in the coronal plane. Yield load, bending stiffness, and bending moments for both testing configurations were determined.


RESULTS
For the sagittal plane bending tests, the yield load was 628 +/- 29 N. For the coronal plane bending tests, the yield load was 596 +/- 20 N. The resulting bending moments in the sagittal and coronal planes were 20.4 +/- 0.9 and 19.4 +/- 0.6 Nm, respectively. From these data, we correlated bending moments with in vivo gait data to find a patient weight cutoff of 40 to 45 kg.


CONCLUSIONS
With the increasing rate of childhood obesity and tendency for sagittal and coronal angulation of femur fractures treated with titanium elastic nails, it is necessary to determine the load at which permanent sagittal and coronal deformation of the nails occurs because this may result in an unfavorable outcome.


CONCLUSIONS
Our study provides biomechanical evidence that patients weighing more than 40 to 45 kg who undergo stabilization of a transverse midshaft femur fracture with titanium elastic nails are at risk for loss of reduction in the sagittal and coronal planes.
Li
Ying
Y
Department of Orthopaedic Surgery, Wake Forest University Baptist Medical Center, Winston-Salem, NC 27157, USA. yli@wfubmc.edu
Stabile
Kathryne J
KJ
Shilt
Jeffrey S
JS
D001696:Biomechanical Phenomena; D001835:Body Weight; D001858:Bone Nails / Q000009:adverse effects; D002648:Child; D004867:Equipment Design; D005264:Femoral Fractures / Q000601:surgery*; D005594:Fracture Fixation, Intramedullary / Q000295:instrumentation*; D006801:Humans; D008422:Materials Testing; D009765:Obesity / Q000150:complications; D011183:Postoperative Complications / Q000209:etiology* / Q000517:prevention & control; D014025:Titanium; D016896:Treatment Outcome
D014025:Titanium