FLEXIBLE INTRAMEDULLARY NAILS IN PEDIATRIC SUBTROCHANTERIC FEMUR FRACTURE: BIOMECHANICAL STUDY.

Objective: Evaluate the stability provided by two flexible intramedullary nails (FINs) in a simulation of fractures at the proximal levels in pediatric femur models.

Methods: Two FINs were inserted in 18 synthetic models of pediatric femurs. Fractures were simulated at one of three levels, and the models were divided into the following groups (n=6): diaphysis (control), subtrochanteric and trochanteric. Flex-compression tests were performed with force up to 85 N. Relative stiffness and the average deformation was obtained. Torsion tests were performed by rotating the proximal fragment until 20°, to obtain the average torque.

Results: At flex-compression, the set's average relative stiffness and average deformations were: 54.360x10³ N/m and 1.645 mm in the control group, respectively. In the subtrochanteric group, the relative stiffness was 31.415x10³ N/m (-42.2%) and the deformation was 2.424 mm (+47.3%) (p<0.05). For the trochanteric group, the relative stiffness was 30.912x10³ N/m (+43.1%) and the deformation was 2.508 mm (+52.4%) (p<0.05). In torsion, the average torque was 1.410 Nm in the control group; 1.116 Nm in the subtrochanteric group (-20.8%), and 2.194 Nm in the trochanteric group (+55.6%) (p<0.05).

Conclusion: FINs do not seem to be biomechanically competent for the treatment of proximal femoral fractures. Level of Evidence I; Therapeutic Studies - Investigating the results of treatment.