[Biomechanical evaluation of TiNi shape-memory sawtooth-arm embracing plate and its effect on fracture healing].

Objective: To investigate the detailed biomechanics of TiNi shape-memory sawtooth-arm embracing plate (TiNi SMA) by comparing with limited-contact dynamic compression plate (LC-DCP) and static interlocking intramedullary nail (SIiN), so as to provide theoretical evidence for clinical application.

Methods: Eight paired cadaveric femurs immersed in formaldehyde were harvested from eight specimens of adults. After making X-ray films and modeling midpiece transverse fracture, one side randomly was fixed by TiNi SMA (group A) and SIiN (group C) orderly, the other side was fixed by LC-DCP (group B). The axial compression, three-point bending (pressed from plate side and opposite side both of group A and group B, from inside of group C), and torsion were tested, and the stress shielding rate was compared.

Results: At every classified axial compression load, the strains of group A were greater than those of group B and group C (P < 0.05), the displacements of group A were greater than those of group B and group C (P < 0.05) except 100 N. At every classified three-point bending moment, the displacement of group A were greater than those of group B and group C pressed both from two sides, but there was no difference when pressing from two sides under the same load of group A (P > 0.05). At every torsion moment, the torsion angels of group A were greater than those of group B (P < 0.05), but equal to those of group C (P > 0.05). At 600 N of axial compression load, the stress shielding rates of groups A, B, C were 48.30% +/- 22.99%, 89.21% +/- 8.97%, 95.00% +/- 3.15%, respectively, group A was significantly less than group B and group C (P < 0.01).

Conclusion: The anti-bending ability of TiNi SMA is weaker than LC-DCP and SIiN; the anti-torsion ability of TiNi SMA is weaker than SIiN, but TiNi SMA is a center-type internal fixation, the superior stress shielding rate and micromovement promote the stress stimulation of fracture, which makes it an ideal internal fixation device.