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Figure 2. Lateral view of coaxially placed K-wires in a human cadaveric cervical spine.

Figure 2 Lateral view of coaxially placed K-wires in a human cadaveric cervical spine.

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Figure 1. Posterior view of coaxially placed K-wires in a human cadaveric cervical spine.
Figure 1. Posterior view of coaxially placed K-wires in a human cadaveric cervical spine.
Figure 3. Schematic drawing of measured pedicle dimensions. PL = pedicle length, CL = chord length, TD = transverse diameter pedicle, SD = sagittal diameter Pedicle, TA = transverse angu- lation, SA = sagittal angulation, TW = transverse width, latera mass, SH = sagittal height, lateral mass, SO = sagittal offset TO = transverse offset. Dotted line represents the medial lamin- ofacet junctional line.
Figure 3. Schematic drawing of measured pedicle dimensions. PL = pedicle length, CL = chord length, TD = transverse diameter pedicle, SD = sagittal diameter Pedicle, TA = transverse angu- lation, SA = sagittal angulation, TW = transverse width, latera mass, SH = sagittal height, lateral mass, SO = sagittal offset TO = transverse offset. Dotted line represents the medial lamin- ofacet junctional line.
Table 1. Linear Morphometric Measurements
Table 1. Linear Morphometric Measurements
Figure 5. Graphic representation showing linear morphometric measurements of the subaxial cervical pedicles: pedicle length and cord length.
Figure 5. Graphic representation showing linear morphometric measurements of the subaxial cervical pedicles: pedicle length and cord length.
Table 2. Angular Morphometric Measurements Group 1: Topographic Guidelines. In group 1, the overall success rate for pedicle screw insertion (Figure 8), de- fined as containment of the screw completely within the cortical margins of the pedicle on the CT scan, was 5 screws successfully inserted out of 40 screws placed (12.5%). The overall rate of perforation was 35 in 40 (87.5%). Cortical perforations were divided further into noncritical (21.9%), and critical (65.6%) perforations. The rate of successful screw screw placement compared with the rate of perforation by level for group 1 is shown in Figure 9.
Table 2. Angular Morphometric Measurements Group 1: Topographic Guidelines. In group 1, the overall success rate for pedicle screw insertion (Figure 8), de- fined as containment of the screw completely within the cortical margins of the pedicle on the CT scan, was 5 screws successfully inserted out of 40 screws placed (12.5%). The overall rate of perforation was 35 in 40 (87.5%). Cortical perforations were divided further into noncritical (21.9%), and critical (65.6%) perforations. The rate of successful screw screw placement compared with the rate of perforation by level for group 1 is shown in Figure 9.
Figure 6. Graphic representation showing angular morphometric measurements of the subaxial cervical pedicles.
Figure 6. Graphic representation showing angular morphometric measurements of the subaxial cervical pedicles.
Table 4. Topographic Guidelines: Pedicle Screw Placement
Table 4. Topographic Guidelines: Pedicle Screw Placement
Figure 7. Graphic representation showing offset morphometric measurements of the subaxial cervical pedicles.
Figure 7. Graphic representation showing offset morphometric measurements of the subaxial cervical pedicles.
Table 3. Entry Point Offset
Table 3. Entry Point Offset
Figure 8. Overall comparative accuracy of cervical pedicle screw insertion by technique. Cass = computer-assisted surgical system.
Figure 8. Overall comparative accuracy of cervical pedicle screw insertion by technique. Cass = computer-assisted surgical system.
lengths remained fairly consistent at each level, chord length was greatest at C5 and C6. This likely reflects the higher incidence of degeneration with associated ante- rior osteophytes at these levels.
lengths remained fairly consistent at each level, chord length was greatest at C5 and C6. This likely reflects the higher incidence of degeneration with associated ante- rior osteophytes at these levels.
expectation of precise adherence to specific topographic guidelines even if they could be provided. Correlation between surgeons’ recording of linear measurements was “sood” at best (0.50 < r* < 0.75), and in only one instance (C7 transverse angulation) was correlation “ex- cellent” (r? > 0.75) with regard to angular measure- ments. Ironically, the highest correlation between sur- geons’ measurements occurred with those of transverse and sagittal offset, the same parameters that had exces- sively high ranges and standard deviations.
expectation of precise adherence to specific topographic guidelines even if they could be provided. Correlation between surgeons’ recording of linear measurements was “sood” at best (0.50 < r* < 0.75), and in only one instance (C7 transverse angulation) was correlation “ex- cellent” (r? > 0.75) with regard to angular measure- ments. Ironically, the highest correlation between sur- geons’ measurements occurred with those of transverse and sagittal offset, the same parameters that had exces- sively high ranges and standard deviations.
contained in their respective pedicles. When this technique was used, 65% of the screws encroached on critical ana- tomic structures (Figure 12). Although the C7 pedicle had the highest rate of successful screw placement (25%) and the lowest rate of critical breaches (12.5%), this still represents an unacceptable risk to the patient. Clearly, more information on pedicle position and orientation are required for the surgeon to apply transpedicular instrumen- tation safely in the cervical spine. et al.'* The incidence of pedicle wall violation by the three described techniques is much higher than those re- ported clinically by Abumi et al.? There may be several reasons for this. Fluoroscopic guidance was not used to aid screw placement in either groups 1 or group 2. The addition of fluoroscopic guidance may have allowed the trajectory of the drill bit to be amended to allow for coaxial placement of a pedicle screw. Moreover, once the starting point was established, a pedicle probe was not used before screw insertion to direct the trajectory of the screw. The method in this study used a power drilling technique, which may not provide the surgeon with the tactile feedback cue received when a manually inserted 2-mm pedicle probe is used.
contained in their respective pedicles. When this technique was used, 65% of the screws encroached on critical ana- tomic structures (Figure 12). Although the C7 pedicle had the highest rate of successful screw placement (25%) and the lowest rate of critical breaches (12.5%), this still represents an unacceptable risk to the patient. Clearly, more information on pedicle position and orientation are required for the surgeon to apply transpedicular instrumen- tation safely in the cervical spine. et al.'* The incidence of pedicle wall violation by the three described techniques is much higher than those re- ported clinically by Abumi et al.? There may be several reasons for this. Fluoroscopic guidance was not used to aid screw placement in either groups 1 or group 2. The addition of fluoroscopic guidance may have allowed the trajectory of the drill bit to be amended to allow for coaxial placement of a pedicle screw. Moreover, once the starting point was established, a pedicle probe was not used before screw insertion to direct the trajectory of the screw. The method in this study used a power drilling technique, which may not provide the surgeon with the tactile feedback cue received when a manually inserted 2-mm pedicle probe is used.
roup III: Computer-Assisted Surgical System Group Ill: Computer-Assisted Surgical System % Non-Critical Breach
roup III: Computer-Assisted Surgical System Group Ill: Computer-Assisted Surgical System % Non-Critical Breach
Figure 12. Computed tomography (CT) scan: bilateral critical breaches from group 1. Right pedicle screw violates the vertebral artery, and left pedicle screw violates the foramen transversarium.
Figure 12. Computed tomography (CT) scan: bilateral critical breaches from group 1. Right pedicle screw violates the vertebral artery, and left pedicle screw violates the foramen transversarium.
Figure 13. CT scan (group 3: bilateral coaxially placed pedicle screws).
Figure 13. CT scan (group 3: bilateral coaxially placed pedicle screws).
Related topics:
Biomedical EngineeringCervical VertebraeReproducibility of ResultsX ray Computed TomographySpinal Fusion
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