The methods for inserting lumbar bicortical pedicle screws from the anatomical perspective of the prevertebral great vessels

Background At present, bicortical pedicle screws (BPSs) are not used clinically because they carry the potential risk of damaging the prevertebral great vessels (PGVs). The authors observed the anatomical relationship between the PGVs and simulated BPSs at different transverse screw angles (TSAs), exploring the insertion method of the BPS. Methods Computed tomography angiography (CTA) images from 65 adults were collected. A total of 4–5 TSAs of the BPSs were simulated on the left and right sides of L1-L5 (L1-L3: 0°, 5°, 10°, 15°; L4-L5: 0°, 5°, 10°, 15°, 20°). There were three types of distances from the anterior vertebral cortex (AVC) to the PGVs (D AVC-PGV ); D AVC-PGV < 0.50 cm , D AVC-PGV ≥ 0.50 cm , and D AVC-PGV↑ ; these distances represented close, distant, and noncontact PGV, respectively. Results The ratio of every type of PGV was calculated, and the appropriate TSA of the BPS was recommended. In L1, the recommended left TSA of the BPS was 0°, and the ratio of the close PGV was 7.69%, while the recommended right TSA was 0°-10°, and the ratio of the close PGV was 1.54–4.62%. In L2, the recommended left TSA of the BPS was 0° and the ratio of the close PGV was 1.54%, while the recommended right TSA was 0°-15° and the ratio of the close PGV was 3.08–9.23%. In L3, the recommended left TSA was 0°-5°, and the ratio of the close PGV was 1.54–4.62%. In L4, the recommended left TSA was 0°, and the ratio of the close PGV was 4.62%. BPS use was not recommended on the right side of either L3 or L4 or on the either side of L5. Conclusions From the anatomical perspective of the PGVs, BPSs were not suitable for insertion into every lumbar vertebra. Furthermore, the recommended methods for inserting BPSs were different in L1-L4.