Study Design. Applied anatomical study and clinical application.
Objective. To design and optimize the method of cervical pedicle screw placement for cervical vertebrae C3–C5, and to test it in clinical applications.
Summary of Background Data. Most of the anatomical studies on cervical pedicle screw placement previously published focused on the lower cervical vertebrae. Clinically, it is much more difficult to place C3, C4, and C5 screws than C6 and C7 screws; therefore, anatomical measurements of C3–C5 pedicles and design of an appropriate screw placement method are required.
Methods. A total of 20 cervical vertebrae specimens were prepared, and bilateral pedicle screws were manually inserted for C3–C5. The intersection of the horizontal line through the midpoint of the transverse process root and the vertical line through the mediolateral third of the superior articular process was used as the entry point. The screws were inserted along the axis of the pedicle, with the axis of the screw coinciding with that of the pedicle. The specimens were truncated along the horizontal or sagittal plane of the pedicle, and a variety of measurements were made to determine appropriate screw type and placement. Finally, this screw fixation technique was applied in clinical situations with the placement of 26 C3 screws, 26 C4 screws, and 38 C5 screws.
Results. Pedicular height was larger than pedicular width for the same segment of C3–C5, and pedicular width of the different segments did not significantly vary. The lengths of the screw channels for C3–C5 screw placement were similar. The transverse angles of C3–C5 segments displayed a decreasing trend, whereas the vertical angles did not. In all clinical cases, all screws were properly within the pedicles examined using postoperative computed tomography scan. Only 1 C3 screw penetrated the medial cortex and slightly entered the spinal canal, but no clinical symptoms occurred.
Conclusion. The intersection of the horizontal line through the midpoint of the transverse process root and the vertical line through the mediolateral third of the superior articular process represents a superior frame of reference for the entry point for C3–C5 pedicle screw fixation. Clinically, we recommend the transverse angles to be 90° for C3 and 80° for C4 and C5, and the vertical angles to be 70° for C3–C5. We found that screws with a diameter of 3.5 mm and length of 20 mm or 22 mm to be safe, objective, and reliable.