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Is a right pedicle screw always away from the aorta in scoliosis?
Katsushi Takeshita1, Toru Maruyama, Shurei Sugita
1Department of Orthopaedic Surgery, the University of Tokyo, Tokyo, Japan. Takeshita-ort@h.u-tokyo.ac.jp
Study Design:
Retrospective analysis.
Objective:
We evaluated the aorta safety in placement of a right pedicle screw in scoliotic patients.
Summary Of Background Data:
Past reports emphasized the aorta risk in placing pedicle screws on the concave left side in right thoracic scoliosis. However, risk on the right side has drawn limited interest.
Methods:
Thirty-four scoliotic patients with an average age of 18.0 years were evaluated. The Cobb angle averaged 59.0° ± 14.0°. From computed tomographic data, we evaluated the aorta location relative to the spine at each level from T4 to L4 and simulated placement of a right pedicle screw with a direction different from the ideal trajectory. Sensitivity analysis was performed independently by variable direction errors and screw length: the maximum error of trajectory was set to 5° in the medial direction and to 5°, 10°, or 20° in the lateral direction, and a screw length was set at 40, 45 or 50 mm. We defined "aorta-at-risk" when a patient has some level where a simulated pedicle screw involves the aorta, and compared the curve characteristics (the apical vertebral translation, the Cobb angle and the Nash-Moe grade) between the aorta-at-risk cases and the aorta-no-risk cases.
Results:
In left thoracic or lumbar curves, the aorta often resided in front of right pedicles at the periapical level. In a scenario of a simulated pedicle screw with a maximum error of 20° in the lateral direction and a screw length of 50 mm, the aorta was at risk in 7 (33%) of 21 left lumbar curves. Curve characteristics of the aorta-at-risk cases at L1 were a larger apical vertebral translation (P = 0.003), a larger Cobb angle (P = 0.006), and a larger Nash-Moe grade (P = 0.017) compared with those of the aorta-no-risk cases.
Conclusion:
Surgeons need to pay attention to the position of the aorta in placing a pedicle screw on the right at the periapical level of a left curve either in thoracic or lumbar spine.
