Experimental Study On Accuracy Of Pedicle Screw Placement In The Thoracolumbar Spine With X-ray Monitoring Step By Step

[Objective]To explore the relation between the guide wire and the projection of thoracolumbar pedicle on the standard posteroanterior image of vertebrae and the depth of the guide wire on the standard lateral image of vertebrae, in order to improve the accuracy and quality of placing pedicle screws. [Methods]Ten human cadaveric thoracolumbar spines (T9-L5) were selected and anatomized into single vertebra. The standard lateral image was obtained when the guide wire was consistent with the pedicle axis and reached the anterior cortex of vertebrae. Withdrawing the guide wire, when the standard lateral image showed that it was located at the pedicle length and half of the length, the standard posteroanterior images were obtained respectively. The standard posteroanterior image was obtained when the guide wire was located at the pedicle posterior cortex. Analysing the following data: the percentage of the length of guide wire in vertebrae on the standard lateral image; the percentage of the length of guide wire in the pedicle projection when it was located at the pedicle length and half of the length on the standard posteroanterior image; the relation between the entry point and the projection of pedicle was recorded according to clock. Another 8 spinal specimens(T₉- L₅) were classified into group A and B randomly. The pedicle screws of group A were placed with x-ray monitoring step by step, while the ones of group B were placed with traditional x-ray monitoring.[Results]On the standard lateral image the length of the guide wire was from 71.53% to93.28% among T9-L5. There was no significant difference in Li.s(P>O.O5), T9> L4.5(P>0.05) , Tio-n(P>O.O5). There was greatly significant difference among others(P<0.001). On the standard posteroanterior image the percentage of the length of the guide wire in the pedicle projection when it was located at half of the pedicle length was from 49.16 % to 51.83 %. There was no significant difference among them (P>0.05). The percentage of the length of the guide wire in the pedicle projection when it was located at the pedicle length was from 61.13% to 74.68%. There was no significant difference between left and right pedicles (P>0.05), Ti0-i2(P>0.05), and T9> Li-5(P>0.05). However there was greatly significant difference between T10-12 and T^ L1-5 pedicles (PO.001). The entry point located at 9 to 10 o'clock of the pedicle projection in the left and at 2 to 3 o'clock in the right, while the point of the low thoracic vertebrae located at about inner 2 mm of the projection. Four of 72 (5.56%) pedicle screws were found to have perforated the pedicle wall in group A, and 19 of 72 (26.38%) pedicle screws perforated the pedicle wall in group B. The result of group A was better than the one of group B(P<0.001). [Conclusion]There is a rule of the relation between the guide wire and the projection of thoracolumbar pedicle on the standard posteroanterior image and the depth of the guide wire on the standard lateral image. According to the regularity, X-ray monitoring pedocle screw placement step by step can improve the accuracy and quality, and to some degree it can make bilateral pedicle screws place symmetrically.