| Objective: to compare the biomechanic effect of the commonly used internal fixations, including: dynamic hip screw (DHS); cannuiated screw (CS); Smith-petersen nail screw (SPN); Double heads empty compression screw (DECS), to the femoral neck fracture, and choose the ideal internal fixation. Material and method: In this present study, The DHS is made in ShangHai, and is composed of three parts; the screw, the plate and the compression nail. the cannuiated design is engaged in this screw-plate system which is very easy for the surgeon to use. Another spongy-bone screw is attached to this system. The DECS is from TianJing and made of 317-L stainless steel. The double circle shaped epmty space in the screw is the character of this system, and the bolts are hexagonal shaped. The experiment instruments emploied in this study were: the CSS1101 omnipotent experimemt device made in ChangChun; the electric resistance adaptor; the electric resistance migration measurement device; the electric resistance adaptor plate; the electric saw; the statistic SAS software package. Sixteen adult cadaver femora were used as the sample, the Puwel 70°and adduction base farctur was made to each sample. After the facture model were achieved, the reduction was applied to each model using the following internal fixation the DHS; CS; SPN and DECS. Adjust the screw positon to the standard demand. The two DHS fixations were used as the controlling group and the other fixations were used as the experiment groups. Each group was tested on the CSS1101 omnipotent experimemt device, the axis compression was applied. In this study, the 0-500N level linear load was chose and the loading speed was 1.5mm/min. The strain curve, the load-migration curve, the torque, and the shelter rate were recorded, and then the achived data were put into the SAS package to do the variance analysis. Result: There was strain discrepancy in the lateral and medial siade of the internal fixation, and the less the strain was, the stronger the fixation was. From the load –strain curve (figrue 1), we can see whatever in the lateral or the medial side, the strain of DHS was less than CS and SPN, There was obvious difference between each groups (P<0.05) between the DHS and the SPN the P value was less than 0.01 The horizontal and perpendicula migration can lead to the movement between the femoral neck frature parts. Tthe load – strain curve (figrue 2) tells that the maximum movement of the DHS is 3.96mm, the CS's is 4.92mm, the SPN's is 7.52mm.The P value was obvious and less than 0.01. The compression screw in the DHS played an key role in the compression effect, especially the long-lasting dynamic compression effect of the screw can compact the fracture parts into each other firmly, therefore the movement of the femoral head was the least and DHS was the best fixation to the frature in the groups. From the torque curve (figur 3), we can see the anti-torque rigid degree of DHS is 55.39N.cm/deg; 40.34 N.cm/deg in CS; 24.42 N.cm/deg in SPN. The anti-torque rigid degree of DHS was the best within these groups. it was 1.37 times of CS and 2.27 times of SPN. There were obvious difference between each group (P<0.01). Therefore the DHS fixation to femoal head fracture was the ideal one. The formular of shelter rate is ηï¼(1-σ1/σ2)×100%. σ1 is the stress recorded when there was not a fixation to the femoral head fracture. σ2 is the stress recorded when there was a fixation to the fracture. The different shelter rate of these internal fixation can be found in the fig.8.It is shown in the fig.8 that theηvalue of DHS is the less than the others . Theηvalue of SPN is bigger than the others. The obvious difference appeared in comparing DHS group with the other groups (P<0.01). From aspect of the recent advocated concept of elasrtic fixation, DHS can achieve the relatively ideal fixation effect to the femoral head fixation, can also can compact the fracture pars, therefore the DHS is an ideal fixation which will facilitate the reunion of th...
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