A Comparative Study On The Effect Of The Self-tapping And The Nonself-tapping Pedicle Screw

Objective:Because of it's advantages such as: simple structure, convenientoperation, short fix segment and 3D stability, the pedicle screw insidefix system has been applicated more and more extensively in theclinical spine surge. At the same time, the first generation pediclescrew-non-self tapping pedicle screw (NSPS) has been displaced bythe second one-self tapping pedicle screw (SPS). However, it has notthe study about the safety and the withdrawal force of two type screws.This experiment is done in the thoracic vertebrae of corpse. Thesubject is studying the difference of the destructiveness and thewithdrawal force of the NSPS and the SPS.Materials and methods:The first experimentThe vernier caliper directly measure the distance of everythoracic pedicle the narrowest position. Then, we calculate the75%-80% of the distance as the diameter of the pedicle screw that willbe placed in this thoracic pedicle. We intentionally make everythoracic pedicle screw channel that closed to the pedicle wall-corticalbone. Place the Kirschner wire respectively in every pedicle screwchannel, then take the X-ray picture of every thoracic Y-axis to test theaccurate and symmetry of channels. Expand the channels and placerandomly the same diameter NSPS and SPS in the both pediclechannels of the thoracic. We observe the condition of attack anddestructive in specimens and the X-ray picture of every thoracicY-axis. By contrasting above condition, we can use statistics toanalysis the destructive degree of thoracic pedicle wall-cortical boneabout the NSPS and the SPS. In addition, using vernier caliper tomeasure the distance of every thoracic pedicle the most narrowposition after operation in specimens and the X-ray picture andcomparing with the relevant distance before operation, we may usestatistics to analysis the inflate degree of thoracic pedicle after theNSPS and the SPS been placed.The second experimentThe operative method is the same as the first experiment inmaking the pedicle screw channels, which is normal "e" angle. Weplace randomly respectively the same diameter NSPS and SPS in theboth pedicle channels of the thoracic, and the depth of the pediclescrews is the 80% of the thoracic vertebrae. After bundling andstabling the thoracic vertebrae by the dental base acrylic resin powder,the withdrawal force experiment is carry on along the pedicle screws`length-axis in the permanent velocity of 5mm/min in the AutographUniversal Testing Machine. The Automatic Recorder accounts thewithdrawal distance of pedicle screws, the change curve, and themaximum length-axis withdrawal force. Then, we use statistics toanalysis the withdrawal force of the NSPS and the SPS.Results :1. The X2-test is used in examining the destructive degree ofthoracic pedicle wall-cortical bone about the NSPS and the SPS.2. The matched-pairs design t-test is used in examining the inflatedegree of thoracic pedicle after the NSPS and the SPS been placed.3. The matched-pairs design t-test is used in examining thelength-axis withdrawal force of the NSPS and the SPS.Conclusion:1. The destructive degree of thoracic pedicle wall-cortical bone isnot clear difference in the NSPS and the SPS.2. The inflate degree of thoracic pedicle is not clear differenceafter the NSPS and the SPS been placed.3. The X-axis withdrawal force of the SPS is stronger than theone of the NSPS.