The Experimental Study Of Making Screw Pilot Hole Placement In Atlas-axis Pedicle Using Free-hand Technique

Objective: Successful placement of a pedicle screw in thecervical spine requires a sufficient three-dimensional understanding ofpedicle morphology to allow accurate identification of the ideal screwaxis. Variability in cadaveric based morphometric measurements usedto guide the surgeon in the placement of a Altar-axis pedicle screw hasraised legitimate concerns as to whether transpedicle fixation can beapplied without significant neurovascular complications. It issuggested that only those cervical spine surgeons who are experiencedin transpedicle screw fixation can carry out the performance. Thevariability in unique pedicle size and morphometry demands carefulassessment of the angle and placement of Altar-axis pedical screws.Incorrect insertion of pedicle screws can cause damage to adjacentvital structures such as the nerve roots, and vertebral arteries. Thepedicle isthmus is the narrowest spot extended on the pedicle axisthread. How large diameter screw the pedicle can withstand is to bedecided by this plane. Therefore, it appears especially important to getfamiliar with and grasp anatomical morphology characteristics of thepedicle isthmus in pedicle screw implanting technology. The securityand accuracy of screw trajectory drilling, especially before placement,becomes the key to surgery success. So, we apply the interrelatedvariable data concerning Atlas-axis pedicle isthmus acquired from theCT scanning to the drilling of screw trajectory by free-hand, and toexamine its security and accuracy. This is a promethean researchwhich has not been reported in documents domestic and abroad.Material & Methods:Fourteen adult cadaver specimens ofcervical spine (C1~C2) with intact structures including ligaments andperivertebral muscles are well reserved and used. To gain pedicleisthmus department CT reconstruction data C1~C2 pedicle CTscanning are performed separately, to reconstruct the Atlas-axisisthmus. Measuring the variable parameter of the pedicle isthmus axisposition, the data gained will be used as the guidance for surgeryoperation. Atlas –axis pedicle screw trajectory drilling is performed byfree-hand technique. Through X-rany measuring and CT scanning ofthe screw trajectory is carried out after the operation to evaluate theresult of the placement of screw so as to improve the security andaccuracy of the pedicle screw insertion trajectory by free-handtechnique.Results:1. There is no distinct difference between the left andthe right side of atlas pedicle isthmus, high and width of medial andlateral from Atlas axis specimen measurement. 2. There is no distinctdifference between the left and the right side of axis pedicle isthmus,high and width of medial and lateral, and compared with the left andright side from the range of safety angle from CT survey data. 3.Results from the screw placement trajectory drilling: Observe theposition of screw trajectory by the way of CT scanning and bydissecting the pedicle. (That is, to observe the infraction degree whichthe screw infract pedicle cortex cliff ) It is divided into Ⅰ, Ⅱ, Ⅲ,Ⅰ: The screw trajectory is inside the pedicle. Ⅱ: The screwtrajectory is inside the pedicle. There is default of cliff;Ⅲ: The screwtrajectory is outside the pedicle. The screw penetrates through thespinal channel, vertebral artery or intervertebral foramina. Altogether56 trajectories are made, 85.7% of atlas is Ⅰ (23/28), 96.4% of axisof Ⅰ (27/28);14.3% of atlas is Ⅱ (5/28), 3.6% of atlas is Ⅱ(1/28);Ⅲ: Infraction (penetrating through) is 0% (0/56).Conclusion:Results show that pedicle screw is allowed to usingfrom direct measurement of Atlas axis pedicle trajectory cadaverspecimen and the results of CT survey data. In the experiment, thepedicle screw is placed by free-hand technique. There is no obviousdestruction inside the spinal channel and vertebral artery. And thesafety for the placement of pedicle screw can be highly improved. Theresult is of important reference to ensure the accuracy rate and successrate to the spine surgeons who can not utilize the pilot technique in theoperation.