Reformatted CT Evaluation Of Lower Cervical And Thoracic Pedicle For Transpedicular Screw Placement

BackgroundWith the development of the society, there are more traffic accidents, industrial and architectural accidents, sports trauma, there are more traumatic cervical injury. And with the coming aged society, there are more cervical spondylosis patients. Dealing with cervical diseases with surgery, there are several ways, anterior approach AO plate fixation and spinous process wire fixation, lateral mass screw fixation and pedicle screw fixation. Pedicle screw fixation was generally accepted because of its three collumn fixation.Cervical pedicle fixation has better biomechanics stability than the other internal fixations. It has the advantage of best biomechanics stability, high rate of bone graft fuse and need not outer fixation after operation. In all the cervical internal fixations, only pedicle fixation can keep the movement of near segments. It is better than wire fixation and lateral mass fixation.Cervical pedicle has special anatomy and adjacent structure: spinal cord medially, vertebral artery latterly, nerve roots superiorly and inferiorly, variation of pedicle anatomy. Surgeons must know the anatomy of pedicle well before surgery, and it necessary to evaluate the morphology of cervical pedicle. There are reports about the anatomy of cervical pedicle of cadaver and patients by using caliper and general CT scan. Both of them could not evaluate pedicle accurately. Three-dimensional CT evaluation can provide accurate parameters of pedicle. By using reformatted CT, we can get the transverse view paralleling pedicle axis and coral view vertical to pedicle axis. We can get accurate parameter of pedicle from these views which are very useful information for surgeon to decide the direction, diameter and length of screw. ObjectsEvaluate the adult lower cervical pedicles by using reformatted CT,pursuit a better way to evaluate the morphology of cervical pedicle and measure the relative parameters. Provide the parameters of cervical pedicle for surgeons to decide the direction, diameter and length of screw.Materials and MethodsThe study consisted of 40 patients of Chinese origin, who were chosen randomly from the patients'registry. The patients were aged from 18-83 years (mean age was 46 years), including 20 males and 20 females. There was no statistical difference in the mean ages of male and female patients. Those who had thoracic spinal abnormalities (congenital deformity, trauma, infection, primary or secondary tumor) were excluded.A Lightspeed Vct CT scanner system was used. C3-C7 vertebrae were scanned continuously with a thickness of 0.625 mm. Advantage Workstation AW 4.3₀5 and Reformat Software were applied to reformat the transverse view of the image by MPR to get the sagittal section of the pedicles. From these sagittal images, the authors'cut paralleled the pedicle axis with a thickness of 0.4 mm to obtain the transverse view which paralleled the pedicle axis. Thus in the transverse view, the reformatted CT cuts were made vertical to the pedicle axis and get the coronal section. We choose the smallest side pedicle section to measure all the parameters. The authors performed the statistical analysis using SPSS for windows 11.0. Means and standard deviations of every parameter were calculated for the groups of male and female individuals. Statistical differences of the parameters were compared between right and left pedicles and between male and female patients at every level using the independent T test.Results1. PH, PSH, PW and PSW: PH is larger than PW, coronal plane are oval-shape like and become near round from C3 to C7. PW and PSW in male are smallest at C4 and in female at C3. PW decide the diameter of pedicle screw. 2. PCS, PCI, PCM, PCL: PCS and PCI become smaller from C3 to C7. PCS are larger than PCI. PCM are larger than PCL. PCM are easer to be injuried during pedicle screw fixation. 3. La, Lb and PD: All the length very near in different vertebral. They decide the length of pedicle. 4. TA and SA: Both become smaller form C3 to C7 and have no statistics difference between male and female.Conclusions1. Evaluate the cervical pedicle by Reformatted CT can provide accurate parameters for surgeon to perform pedicle screw fixation before surgery. 2. Most of the cervical pedicles can accept 3.0 mm crews. It is safe to perform pedicle screw fixation with precise entrance point, exact direction and proper length. 3. Pedicle side in female in smaller than male, some female patients are not suitable to be performed pedicle screw fixation, especially in C3. 4. Variation is common in pedicle morphology. It is necessary to evaluate the pedicle morphology before surgery by CT and X-ray. BackgroundPedicle screw has become popular since it was used to fix lumbosacral vertebrae in 1959. Pedicle fixation was used extensively in lower thoracic and lumbar pedicle because of its strong intensity and good reshaping ability. Three are special anatomic structure around thoracic pedicle including spinal cord medially, lung and thoracic membrane lately, artery and esophagus anterior. There will be serious results if the adjacent structure were injuried, including violating pedicle cortical, injury of spinal cord and nerve, breaking artery, rupture of spinal dura, leakage of cerebrospinal fluid. At the same time, it is reported that thoracic pedicles are smaller than cervical and lumbar pedicles and are not suitable for pedicle screw fixation. Therefore, it is controversial to use pedicle screw in thoracic pediclesBecause of high risk of middle thoracic pedicle fixation, researcher found a new way to take the place of pedicle screw fixation, that is extrapedicular screw fixation. Extrapedicular screw enter the vertebral beginning at the point of tip of transverse process, through costovertebral joint, laterally to the pedicle. It is far away from spinal column and has enough length. Later, research found that it is a safe and effective thoracic spinal fixation. Therefore, it is at the beginning to this technique in our country and we have no much relative parameters for clinic application. Our study is to evaluate the morphology of pedicle and pedicle rib units in the thoracic spine in normal thoracic human spines, and provide some anatomic information for extrapedicular screw fixation applied clinically. ObjectsEvaluate the morphology of pedicle and pedicle rib unit by reformatted CT. Make clear the difference of anatomic information of extrapedicular screw fixation and pedicle screw fixation. Provide anatomic parameters for extrapedicular screw fixation.Materials and MethodsThe study consisted of 40 patients of Chinese origin, who were chosen randomly from the patients'registry. The patients were aged from 18-73 years (mean age was 45 years), including 20 males and 20 females. There was no significant difference in the mean ages of male and female patients. Those who had thoracic spinal abnormalities (congenital deformity, trauma, infection, primary or secondary tumor) were excluded.A Lightspeed Vct CT scanner system was used. C3-C7 vertebrae were scanned continuously with a thickness of 0.625 mm. Advantage Workstation AW 4.3₀5 and Reformat Software were applied to reformat the transverse view of the image to get the sagittal section of the pedicles . From these sagittal images, the authors'cut paralleled the pedicle axis with a thickness of 0.7 mm to obtain the transverse view which paralleled to the pedicle axis. Thus in the transverse view, we choose the smallest pedicle section to measure. And then we cut the tranverse view vertically to the peidcle axis and get the coral view of the pedelce and measure. The authors performed the statistical analysis using SPSS for windows 11.0. Means and standard deviations of every parameter were calculated for the groups of male and female individuals. Statistical differences of the parameters were compared between male and female patients, between pedicle and pedicle rib unit at every level using the independent T test.Results1. PW and PRUW: Both in male and female, PW is smallest at T4( 4.44 mm and 3.91 mm respectively) and biggest at T1 (8.43 mm and 7.91 mm respectively). PRUW is biggest at T1 both in male and female (17.89 mm and 16.59 mm respectively), and is smallest at T5 in male(13.73 mm) and at T4 in female(12.00 mm). PW and PRUW are both become smaller from T1 to T4, T5 and become larger from T4, T5 to T12. 2. PL and PRUL: Both in male and female, PL is smallest at T1(35.54 mm and 32.85 respectively), largest at T11(45.19 mm and 42.39 mm respectively). PL becomes larger from T1 to T11, and then becomes smaller at T12. PRUL is smallest at T1 both in male and female(43.00 mm and 39.42 mm), but largest at T11 in male(59.90 mm) and at T12 in female(55.92 mm). Both of them become larger from T1 to T12.3. PA and PRUA: Both in male and female, PA is largest at T1(29.92°and 30.46°respectively), and becomes smaller at T12(-1.39°and -1.40°). Both in male and female, PRUA is biggest at T1(40.10°and 40.47°respectively), and becomes smaller at T12(9.68°and 9.55°).4. Of all the parameters except PA and PUR-A, are larger in male than in female.5. All the parameters of the pedicle rib unit were significantly larger than corresponding pedicle measurements at all levels.Conclusions1. Evaluate the morphology of pedicle and pedicle rib unit by Reformatted CT can provide accurate parameters for surgeon to perform pedicle screw and extrapedicular screw fixation before surgery.2. PW in female is smaller than that in male. PW is smallest in middle thoracic pedicle, most of the patients are not suitable to perform pedicle screw fixation.3. PRUW and PRUL are larger than PW and PL respectively. PRU can accept more longer and bigger screw, so PRU screw is safer than pedicle screw.4. Variation is common in pedicle and PRU morphology. It is necessary to evaluate the they morphology before surgery by CT and X-ray to clear the entrance point, direction, diameter and length of screw and to place screw individually.