[Biomechanical test of intramedullary controlled dynamic nailing]

To explore the biomechanical properties of a new intramedullary controlled dynamic nailing (ICDN).

Ten pairs of specimens of adult femurs, with the age of 18 to 55 years, were divided into two groups (groups Al and B2, n = 10). The length of the specimens was (438 +/- 10) mm , and the external diameter was (26.4 +/- 1.5) mm. The specimens of the two groups were osteotomized transversely after the biomechanical test. ICDNs and GK nails were randomly implanted into the femurs, respectively (groups A2 and B2). Torsional, bending and axial compressive tests were made in each group, and the effect of dynamic compression between the fracture fragments was tested.

The resistance to compression of groups A1, B1, A2 and B2 were (0.19 +/- 0.18) x 10(6), (0.22 +/- 0.12) x 10(6), (1.67 +/- 0.68) x 10(6) and (0.86 +/- 0.32) x 10(6) N/mm, respectively. There was statistically significant difference between groups A2 and B2 (P < 0.01). The bending stiffnesses of coronal section of groups A1, B1, A2 and B2 were (0.94 +/- 0.25) x 10(3), (1.10 +/- 0.21) x 10(3), (0.70 +/- 0.22) x 10(3), (0.64 +/- 0.21) x 10(3) N/mm, respectively. The bending stiffness of sagittal plane of groups A1, B1, A2 and B2 were (1.06 +/- 0.26) x 10(3), (0.96 +/- 0.25) x 10(3), (0.67 +/- 0.25) x 10(3), (0.61 +/- 0.18) x 10(3) N/mm, respectively. There were no statistically significant differences between groups A1 and B1 or between groups A2 and B2 (P > 0.05). When the torque was 5 Nm, the torsional stiffness of groups A1, B1, A2 and B2 were (4.00 +/- 2.54), (4.76 +/- 1.93), (0.50 +/- 0.63), (0.35 +/- 0.31) Nm/degrees, respectively. When the torque was 8Nm, the torsional stiffness of groups A1, B1, A2 and B2 were (4.30 +/- 3.27), (3.94 +/- 2.01), (0.42 +/- 0.52), (0.36 +/- 0.18) Nm/degrees, respectively. There were statistically significant differences between groups A1 and A2 or between groups B1 and B2 (P < 0.05), and no statistically significant difference between between groups A2 and B2 (P > 0.05). The average maximal pressure generated between the fracture fragments which were fixed with ICDN was 21.6 N, and the pressure between the fracture fragments which were fixed with GK nailing could not be tested.

The design of ICDN conforms to the special anatomical structure of the femur. ICDN could provide a completely different structure, a different fixation principal and a more balanced fixation than GK nail. ICDN incorporates the flexible and rigid fixation, which is likely to be the trend of the fracture fixation.