ObjectiveTo analyze the pressure change and distribution of the intervertebral disc of upper thoracic spine in vertical pressure and 5° flexion, extension, or lateral bending. MethodsTwelve thoracolumbar spinal specimens were harvested from mini pigs and were divided into 2 groups (n=6). T1, 2, T3, 4, T5, 6, and T7, 8 segments were included in one group, and T2, 3, T4, 5, T6, 7, and T8, 9 segments were included in the other group. The data from both groups represented the complete upper thoracic vertebra data. Biomechanical machine and pressure sensitive film were used to measure the pressure on the vertebral columns under loadings of 100, 150, and 200 N in vertical pressures and 5° flexion, extension, or lateral bending. The pressure change of each intervertebral disc under different loads and in different movement conditions was analyzed. ResultsIn flexion, the anterior annulus pressure of the upper thoracic vertebra increased (P < 0.05), whereas the posterior annulus pressure showed no significant change (P > 0.05) or an increasing trend (P < 0.05). In extension, the anterior annulus pressure of the upper thoracic vertebra decreased (P < 0.05), whereas the posterior annulus pressure decreased (P < 0.05) or had no obvious change (P > 0.05). In lateral bending, the pressure on the concave side of the annulus increased significantly (P < 0.05). ConclusionThe upper thoracic vertebra has unique biomechanical characteristics under different loadings; moreover, the posterior vertebral structure plays an important role in the movement of the upper thoracic vertebral segment and pressure distribution. In lateral bending of the upper thoracic vertebra, the concave side pressure will increase significantly, which suggests that asymmetrical force is an important cause of scoliosis progression. Gravity plays an important role in the progression of scoliosis.
ObjectiveTo investigate the clinical application of three-dimensional (3D) printing technique combined with a new type of thoracic pedicle screw track detector in thoracic pedicle screw placement.MethodsAccording to the characteristics of thoracic pedicle and common clinical screw placement methods, a new type of thoracic pedicle screw track detector was independently developed and designed. The clinical data of 30 patients with thoracic vertebrae related diseases who underwent posterior thoracic pedicle screw fixation between March 2017 and January 2020 were retrospectively analysed. Among them, there were 18 males and 12 females with an average age of 56.3 years (range, 32-76 years). There was 1 case of thoracic disc herniation, 4 cases of thoracic canal stenosis, 2 cases of ossification of posterior longitudinal ligament of thoracic vertebra, 16 cases of thoracic trauma, 2 cases of thoracic infection, and 5 cases of thoracic canal occupation. Three-dimensional CT of the thoracic vertebra was routinely performed preoperatively, and the model of the patient’s thoracic vertebra was reconstructed and printed out. With the assistance of the model, preoperative simulation was performed with the combination of the new type thoracic pedicle screw track detector, and detected no nails after critical cortical damage. During operation, one side was randomly selected to use traditional hand screws placement (control group), and the other side was selected to use 3D printing technique combined with new type thoracic pedicle screw track detector to assist thoracic pedicle screws placement (observation group). The single screw placement time, adjustment times of single screw, and blood loss during screw placement were compared between the two groups. The accuracy of screw placement in the two groups was evaluated according to postoperative CT imaging data.ResultsThe single screw placement time, adjustment times of single screw, and blood loss during screw placement in the observation group were significantly less than those in the control group (P<0.05). Postoperative CT examination showed that the observation group had 87 screws of grade 1, 3 screws of grade 2, and the acceptable screw placement rate was 100% (90/90); the control group had 76 screws of grade 1, 2 screws of grade 2, 11 screws of grade 3, and 1 screw of grade 4, and the acceptable screw placement rate was 86.7% (78/90); showing significant difference in screw placement between the two groups (χ2=12.875, P=0.001). All patients were followed up 6-18 months, with an average of 11.3 months. There was no complication of vascular, nerve, spinal cord, or visceral injury, and screws or rods broken, and no patient was revised.ConclusionThe 3D printing technique combined with the new type of thoracic pedicle screw track detector assisted thoracic pedicle screw placement is convenient, and significantly improves the accuracy and safety of intraoperative screw placement, and overall success rate of the surgery.