Applied anatomical study on pedicle screw placement in C6 and C7

English Keywords:Cervical vertebra  C6  C7  Pedicle  Screw  Anatomic

English Abstract:

  【Abstract】 Objectives: To investigate pedicle screw placement in C6 and C7, and to design C6 and C7 pedicle placement based on the isthmus as anatomic mark. Methods: 15 adult cervical specimens were used regardless of gender or age. No deformity or damage to the specimen was noted. Only the C6 and C7 specimens were used. Pedicle width(PW) and pedicle height(PH) were measured. The area below the lower edge of the superior articular process, above the upper edge of the inferior articular process, and between the medial and lateral edges of the superior articular process of the same cervical segment was defined as the isthmus respectively. The isthmus was divided into three equal parts, and two vertical lines were drawn, with the medial third as the posterior plane of the isthmus and lateral third as the posterolateral plane of the isthmus. The entry point was chosen as the intersection of the horizontal line through the midpoint of the transverse process root and the vertical line through the posterolateral plane and the posterior plane of the isthmus. The screw with a diameter of 3.5mm and suitable length was inserted to ensure the end of screw to reach the cortical bone. The axis of screws was consistent with the axis of pedicle. The angle formed by the axis of cervical pedicle screw on the horizontal plane to the posterolateral plane of isthmus was defined as the transverse angle of the inserted screw(E). The angle formed by the axis of cervical pedicle screw on the sagittal plane to the posterior plane of isthmus was defined as the vertical angle of the inserted screw(F). The two angles and the full length of pedicle screw channel(FSC) were measured. Results: There was no statistical significance as for the measurement between left side and right side at the same segment(P>0.05), therefore the bilateral data were combined. PW and PH of C6 was 6.12±0.78mm and 7.48±0.81mm respectively. PW and PH of C7 was 6.85±0.73mm and 8.03±0.38mm respectively. C6′s PW and PH were less than C7′s(P＜0.05), while at the same segment PW was less than PH(P＜0.05). Using Hierarchical cluster analysis, the results showed that E angle tended to be two kinds as E1 and E2. The E1, E2, F angle, and FSC between C6 and C7 were not significantly different(P>0.05), the data of the same index in C6 and C7 were combined, and FSC was 30.83±0.91mm, E1 angle was 89.61°±1.24°, E2 was 59.71°±1.10°, F angle was 75.86°±1.12°. Conclusions: The intersection of the horizontal line through the midpoint of the transverse process root and the vertical line through the mediolateral third of the isthmus can be used as the entry point for pedicle screw placement, and the screw channel should be along the pedicle axis and referenced to the E and F angle. This method is practical and reliable.