Modeling optimal trajectory for tricortical pedicle screw fixation in adult thoracic spine: an imaging study using the three-dimensional reconstruction technique.

Background: Tricortical pedicle screw (TCPS) is a novel method for thoracic fixation to prevent proximal junctional kyphosis in scoliosis correction surgery. However, there is limited reports on the radiographic parameters of TCPS trajectories. Through computational simulation of TCPS placement in thoracic vertebrae utilizing three-dimensional digital modeling, this study sought to elucidate the ideal radiographic trajectory parameters and compare them with the real data from clinical practice, evaluating the technique's feasibility and safety, thereby providing essential radiological reference data for surgical strategy optimization.

Methods: A total of 207 ASD patients were retrospectively reviewed (Group C), including 74 patients who underwent TCPS fixation (Group T). Additionally, 74 age-matched individuals without anatomical abnormalities of the thoracic vertebrae were included as the control group (Group C). In Group C and Group C, 3D thoracic vertebra models were constructed with Mimics software to simulate ideal TCPS trajectories. Imaging parameters, including length, sagittal angle (SA), and transverse angle (TA), were compared between male and female patients. In Group T, the actual TCPS trajectories were assessed using the picture archiving and communication system and compared with the ideal trajectory parameters.

Results: For the ideal trajectory parameters simulated in Group C1 and Group C2 patients, the parameters were comparable between the two groups. When stratified by sex, males exhibited significantly longer trajectory lengths at each vertebral level compared to females (p < 0.05). For both males and females, the greatest SA was observed at T, while the smallest SA was at T. The greatest TA was at T for both genders, whereas the smallest TA occurred at T in males and at T in females. In Group T, the TCPS entry points were primarily located at T, T, and T. The actual screw length gradually increased from T to T, with all actual trajectory parameters aligning with the ideal trajectory parameters (p > 0.05).

Conclusions: Our comprehensive radiological assessment of ideal and actual TCPS screw trajectories elucidated gender-specific variations and demonstrated the clinical feasibility of achieving ideal trajectory in female patients. These findings provide valuable information on TCPS insertion protocols in clinical practice.