[Development of static three dimensional screw-plate system and the biomechanic features thereof, a comparative study]

To develop a new internal fixation device and the matching tools for subtrochanteric fracture, investigate the biomechanical features thereof, and compare its effects with those of other instruments.A new internal fixation device, static three dimensional screw-plate system: (STDSP) was developed based on the anatomical parameters and the biomechanical characteristics of proximal femur and combined with the biomechanical advantages of the model of three-dimensional plate and multiple-screws plate fixation. Sixteen paired cadaveric adult femurs were randomly divided into 2 equal groups: fracture healing group undergoing insertion of implant and then taking out thereof with a nail left, and fracture group with a trapezoid defect to mimic subtrochanteric fracture 4 of which were fixed with dynamic hip screw (DHS) and STDSP or Gamma nail and STDSP. All the specimens underwent A-P position four point bending test, axial compression test, torsion test, and destroyable test.(1) In the fracture group, A-P position four point bending test showed that the stretch displacement of STDSP group was (0.221 +/- 0.089) mm, significantly smaller than that of the Gamma nails group [(0.506 +/- 0.086) mm, t = 38.278 P = 0.000]; Axial compression test showed that the inferior displacement of the STDSP group was (2.804 +/- 0.585) mm, significantly larger than that of the Gamma nail group [(1.874 +/- 0.549) mm, t = -5.454, P = 0.012]; Torsion test showed that the torque values at 50 and 100 of the STDSP group were (3.78 +/- 0.84) J and (2.3 +/- 1.08) J, both significantly larger than those of the Gamma nail groups [(2.3 +/- 1.08) J and (4.35 +/- 1.81) J, t = -4.729 P = 0.018, and t = -3.227 P = 0.048] and those of the DHS group [(7.3 +/- 1.273) J and (4.325 +/- 0.88) J respectively, t = -3.242 P = 0.048]; and torsion destroyable test showed that the torque values at 200 of the STDSP group was (21.88 +/- 2.51) J, significantly larger than those of the Gamma nail and DHS groups, [(14.36 +/- 5.01) J and (15.475 +/- 1.924) J and (12.075 +/- 1.179) J, t = -3.323 P = 0.048, t = - 3.732 P = 0.034]. (2) In the fracture healing specimens, A-P position four point bending test showed that the radial degree displacement of the STDSP group was (1. 050 +/- 0.316) mm, significantly smaller than that of the DHS group [(1.261 +/- 0.364) mm, t = 3.4 P = 0.042].More capable of resisting bending than DHS and less capable of resisting axial compression, STDSP is an excellent internal fixator with good biomechanical feature in treating subtrochanteric femoral fracture.