Development Of Limited Reamed Dynamic Compress Intramedullary Nail And Biomechanic Study Of Fixation In Femoral Fractures

Objective To develop a new kind of intramedullary internal fixator-Limited Reamed Dynamic Compress Intramedullary Nail, and to study the biomechanic characteristics to provide experiment data for safe clinical application.Methods l)Base on the morphological study of femoral marrow cavity, a new kind of internal fixator-Limited Reamed Dynamic Compress Intramedullary Nail (LRDCIN) was developed. 2) 8 antisepticized femurs were obtained from adult cadavers. The fracture models with 2cm bone defect at the proximal, midshaft and distal of the femurs were produced and then fixed by LRDCIN according to its principle. So the nail-bone complex (NBC) were created. 3) The test platform at the two end of NBC which is parallel mutually were created to simulate single-leg stand. The NBC was then employed in the axis-compress, three-point bend and anti- torsion test. 4)The experiment data was analysed with SPSS statistics software (ver 11.0).Results 1) LRDCIN had a stronger capability of anti- compress in static fixation. The stiffness of anti- compress reached at 2974.03 + 100.31N/mm, which was almost equal to that of the G-K nail and a bit higher than that of the domestic interlocking nail. So it could be regard as a steady fixator. 2)The peak load of the NBC with LRDCIN was higher than that of G-K nail and reached 3429N, which is about 5.83 times of normal weight. So it would meet the strength requires of walk and exercises after operation. 3)In the non-static fashion, the "ill stress" such as torsion and bending could becontrolled. No axial stress shielding presented, which is beneficial to the bone healing. 4) LRDCIN provided stronger anti- torsion and bending forces in various fashions, which is up to the clinic internal fixation requirement.Conclusion l)No stress shielding or concentration presents in LRDCIN internal fixation, which is up to the biomechanic principle of bone healing. 2)The locking screws and the holes in cortex are reduced, so the missed locking rate is declined. 3)No image intensifier is needed intra-operatively and the operation time is shortened, so the surgical trauma is minimized and the radiological exposure is avoided. 4) The massive high speed ream complication is eliminated with the limited reamed technique. 5) The structure is reasonable and simple manipulation is required. No special equipment is requested. The physical, chemical and toxic characters are up to the demands of implant, so it can be used in clinic safely.