Flexible Intramedullary Nails in Pediatric Subtrochanteric Femur Fracture: Biomechanical Study

Abstract

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.

Estabilidade de osteotomias proximais em modelos do fêmur pediátrico fixadas por hastes intramedulares flexíveis e avaliadas pelo método dos elementos finitos

“…Therefore, the fixation must counteract the mechanical moments generated by local forces, providing adequate stability to maintain the reduction and allow consolidation. Thus, elastic rods may not meet these criteria, as already shown by clinical reports 3 and mechanical tests, 6 not being indicated for fractures in the most proximal regions.…”

“…The preparation of the specimen was described earlier. 6 In summary, two flexible titanium rods ( Titanium Elastic Nail - TEN®, TiGa 114v, DePuy Synthes®, Oberdorf, Switzerland) with a diameter of 3.5 mm were inserted retrograde into the spinal canal. Radiography were performed to confirm proper positioning, followed by computed tomography of the entire bone model, archived in the DICOM communication protocol ( Digital Imaging and Communications in Medicine ).…”

“…O preparo do espécime foi descrito anteriormente. 6 Em resumo, duas hastes flexíveis de titânio ( Titanium Elastic Nail - TEN®, TiGa 114v, DePuy Synthes®, Oberdorf, Suíça) com diâmetro de 3,5 mm foram inseridas retrogradamente no canal medular. Radiografias foram realizadas para confirmar o posicionamento adequado, seguidas por tomografia computadorizada de todo o modelo ósseo, que foram arquivadas no protocolo de comunicação DICOM ( Digital Imaging and Communications in Medicine ).…”

“…1 2 However, when a fracture occurs in the trochanteric or subtrochanteric regions, the use of flexible rods is questioned due to possible insufficiency of mechanical stability to maintain the reduction and provide consolidation. 3 4 5 6 Under these conditions, it is interesting to simulate the mechanical behavior of an implant in order to anticipate whether it depends on clinical conditions.…”

“…1 2 No entanto, quando ocorre uma fratura nas regiões trocantérica ou subtrocantérica, o uso de hastes flexíveis é questionado devido a possível insuficiência da estabilidade mecânica para manter a redução e propiciar a consolidação. 3 4 5 6 Nestas condições é interessante simular o comportamento mecânico de um implante a fim de antecipar sua dependência ou não em condições clínicas.…”