[Imaging study on the safety of freehand lumbar pedicle screw placement based on the cat's eye segmentation of X-ray films].

OBJECTIVE: To investigate the safety of manual lumbar pedicle screw placement based on the position of the cat's eye (pedicle projection) on X-ray films.

METHODS: A total of 150 patients with lumbar spine disorders from December 2022 to June 2024 were enrolled and classified into three types according to the cat's eye position on AP X-rays:type A (the lateral edge of the cat's eye extends beyond the lateral edge of the vertebral body); type B (the lateral edge of the cat's eye largely coincides with the lateral edge of the vertebral body);and type C (the lateral shadow of the pedicle is located at the medial edge of the pedicle). Patients were divided into two groups:the imaging-guided simulation group (90 patients, 30 each in types A, B, and C) and the imaging review group (60 patients, 20 each in types A, B, and C). All patients underwent screw insertion at the intersection of the inferior third of the transverse process and the lateral edge of the articular process. In the imaging-guided simulation group, the lumbar spine was divided into three regions from medial to lateral on AP X-rays;the screw direction was adjusted so that the tip of the screw tract corresponded to these three regions on the virtual projection, and CT analysis was performed to evaluate accuracy and determine whether the medial wall of the pedicle or the lateral edge of the vertebral body was penetrated. The imaging review group included 60 patients with lumbar pedicle screw placements;their AP and lateral X-ray images as well as postoperative CT data were analyzed to quantify the number of screws at corresponding positions and assess effectiveness via postoperative CT evaluation.

RESULTS: In the imaging-guided simulation study, the rate of successful screw placement in zone 3 for type A patients was 96.67% (29/30), significantly higher than that in zone 1 50%(15/30) and zone 2 86.67%(26/30), with a statistically significant difference(P<0.05);In type B cat's eyes, the placement rates of screws in zone 1 and zone 2 were 90.00% (27/30) and 93.33% (28/30), respectively, significantly higher than those in zone 3 70% (21/30), with a statistically significant difference (P<0.05);In type C cat's eyes, the placement rate in zone 1 was 90.00% (27/30), superior to that in zone 2 63.33%(19/30) and zone 3 40%(12/30), also showing a statistically significant difference(P<0.05). Imaging analysis revealed that among patients with type A cats eyes, screw placements were in zone 1(3 cases), zone 2 (10 cases), and zone 3 (7 cases);the placement rates in zones 2 and 3 were 90% (9/10) and 100% (7/7), respectively, significantly higher than that in zone 1 33.3%(1/3), with a statistically significant difference (P<0.05). For patients with type B cat's eyes, the placement rates in zones 1 and 2 were both 100% (5/5) and 100% (12/12), significantly higher than that in zone 3 33.3%(1/3), with a statistically significant difference (P<0.05). In patients with type C cat's eyes, the placement rate in zone 1 was 100%(10/10), significantly higher than that in zones 2 and 3 87.5%(7/8) and 0%(0/2), respectively, with a statistically significant difference (P<0.05).

CONCLUSION: By analyzing the relative positions of the cat's eye and vertebral body on anteroposterior X-rays, this study establishes a quantitative correlation between cat's eye zones and screw placement areas for the first time, effectively preventing spinal cord injury and reducing surgical risks.