A biomechanical study on flexible intramedullary nails used to treat pediatric femoral fractures

Abstract

Flexible intramedullary nails have been indicated to treat femoral fractures in pediatric patients. The purpose of this study was to examine the stability of simulated transverse fractures after retrograde intramedullary flexible nail fixation. Various nail diameter combinations were tested using composite femurs in bending, torsion, and a combined axiavbending test where a vertical cohpressive force was applied to the femoral head. The cross-sectional percent area fill of the nails within the femurs was also determined. In 4 point bending, the greatest repair stiffness was 12% of the intact stiffness. In torsion, the greatest stiffness was 1% of the intact stiffness for either internal or external rotation. The greatest repair stiffness was 80% of the intact stiffness for a compressive load applied to the femoral head. Nail combinations with single nail diameters greater than 40% of the mid-shaft canal width, as measured from an AP radiograph, prevented the fracture from being reduced and left a posterior gap. Flexible intramedullary nails may be of value in the treatment of pediatric femoral fractures, but care must be taken to insert nails that are correctly sized for the canal and to protect the healing fracture from high torsional and bending loads.

Differences in biomechanical stability of femur fracture fixation when using titanium nails of increasing diameter

“…The recommended use of two flexible nails each with a diameter, i.e., 40% of the medullary canal diameter will yield a ''canal fill'' of 80% [4,9,10]. A recent study found that an 80% canal fill improved the overall biomechanical stability of the fractured femur, but often resulted in malreduction with posterior gapping [18]. These authors advocated the potential use of multiple smaller nails (i.e., 2 mm) to achieve the dimension of a single larger rod (4 mm).…”

“…These authors advocated the potential use of multiple smaller nails (i.e., 2 mm) to achieve the dimension of a single larger rod (4 mm). However, the use of more than two nails, some of which may be dimensionally asymmetric, is not recommended by the manufacturer and has not gained clinical acceptance [18].…”

Increasing stability by pre-bending the nails in elastic stable intramedullary nailing

“…4,[6][7][8][9][10][11][12]16 Rapp, Albers and Kaiser The biomechanical properties of retrograde ESIN-osteosynthesis have already been described, 14,[24][25][26][27][28][29][30] but most published studies have considered only transverse or oblique fracture configurations, and most have tested only a limited combination of forces. In one of the few studies examining spiral fractures, Gwyn et al 27 performed biomechanical testing with different types of fracture in synthetic bone models using 4 mm diameter titanium elastic nails, but the testing was limited to rotational forces.…”

Osteossíntese das fraturas diafisárias da criança com hastes intramedulares flexíveis

“…Se hastes muito finas forem usadas, haverá angulação e perda de redução. A recomendação é usar hastes com os maiores diâmetros, mas que deixem um espaço para serem viradas e posicionadas (13) . Se forem usadas hastes com calibres diferentes, haverá a criação de desequilíbrio elástico que provocará deformidade (1) .…”