Biomechanical comparison of two fixation methods for pediatric femoral neck fractures: an in vitro study using ovis aries lambs.

Objective: In pediatric patients, femoral neck fracture is a relatively rare injury with a high complication rate despite proper diagnosis and treatment. Fixation of femoral neck fractures is usually performed with screws placed along the neck axis. In this study, we aim to compare two different implants and methods in terms of biomechanics.

Materials and methods: Twenty-eight right-left fresh femur bones of 6-month-old male Ovis aries lambs grown on the same farm were used. Bones were randomly divided into 4 groups (n=7). In group 1, the Delbet type III femoral neck fracture model was fixed with two 4.5 mm cannulated screws, one screw crossing the physis. In group 2, two 4.5 mm cannulated screws, which did not cross the physis, were used. In group 3, Delbet type III femoral neck fracture model was fixed with a 3.5 mm proximal femoral anatomical plate and five screws, one screw crossing the physis. Finally, in group 4, Delbet type III femoral neck fracture model was fixed with one 3.5 mm proximal femoral anatomical plate and five screws that did not exceed the physis.

Results: Biomechanical tests were performed using a Zwick/Roell AllroundLine 100 kN device. While axial failure burden (F = 6.819, p<.05, d = .46) and axial stiffness (F = 3.576, p<.05, d = .30) have been found to be significantly different between the independent treatment groups, axial failure displacement (F = .622, p>.05) and axial failure energy (F = .727, p>.05) have been found not to be significant between the independent groups. The effect sizes of the axial failure load and axial stiffness variables were 0.46 and 0.30, respectively, suggesting a moderate clinical effect. The highest axial failure load was recorded in group 3, while the smallest load was recorded in group 2. Similarly, the axial stiffness level in group 3 was statistically higher than the axial stiffness measurement recorded in group 2, p<.05.

Conclusions: Consequently, we found that the biomechanical fixation success was the highest with a 3.5 mm proximal femoral anatomical plate, a 3.5 mm locking screw crossing the physis, and five 3.5 mm screws.