Analysis of screw placement accuracy and learning curve of robot-assisted cortical bone trajectory internal fixation in the treatment of lumbar degenerative diseases

English Keywords:Lumbar degenerative disease  Orthopedic robot  Cortical bone trajectory screw  Accuracy  Learning curve

English Abstract:

  【Abstract】 Objectives: To evaluate the accuracy of screw placement, the contact of cortex, and the learning curve of cortical bone trajectory(CBT) screw fixation technique assisted by orthopedic robot in lumbar degenerative diseases. Methods: The data of 45 patients with L4-5 degenerative disease treated with orthopedic surgical robot-"TiRobot" assisted CBT screw implantation from October 2019 to April 2021 were analyzed retrospectively. There were 27 males and 18 females, aged 64.3±6.9 years old, which included 8 cases of lumbar disc herniation, 28 cases of lumbar spinal stenosis and 9 cases of degenerative spondylolisthesis. The patients were divided into three chronological groups of A, B and C according to the date of operation with 15 cases in each group. The operative time, the amount of bleeding, the scores of VAS and JOA before and at six months after surgery were collected, and the ln curve regression analysis was used to reflect the changing trend of operative time with the number of operation cases. The accuracy of screw placement and the number of contacted cortical bone layers were evaluated by CT after operation, and screw loosening, interbody fusion, and cage subsidence and migration were evaluated by X-ray and CT during follow-up. Results: All the patients completed the operation successfully. The operative time was 140-195min(163.5±11.3min) and the blood loss was 140-265ml(210.0±28.9ml). A total of 166 screws were implanted with an acceptance rate of 97%(161/166). The average total cortical contact layers and pedicle cortical contact layers were 4.9±0.6 and 3.3±0.6 respectively. The operative time and blood loss in groups B and C decreased compared with group A, and the differences were significant(P<0.05), while there was no statistical difference between groups B and C(P>0.05). The operative time(y) decreased with the increase of the number of cases(x) [y=-10.243ln(x)+192.89, R2=0.637, P<0.001], which reached a relatively stable level in groups B and C. There was no statistical difference in the screw placement accuracy and cortical contact layers among the three groups(P>0.05). At six months after surgery, the VAS score of low back pain decreased from 4.8±0.7 to 1.9±0.6(P<0.001), the VAS score of leg pain decreased from 7.5±0.7 to 1.8±0.6(P<0.001), and the JOA score increased from 11.3±1.8 to 23.3±1.6(P<0.001). During the follow-up period, interbody fusion occurred in 41 cases, while cage migration occurred in 1 case, and no screw loosening or cage subsidence were observed. Conclusions: Robot-assisted CBT screw fixation has a high screw placement accuracy in the treatment of lumbar degenerative diseases, which enjoys a high security through ensuring a full contact between screw and cortex. With the increase of the number of surgical cases, the operative time and the blood loss gradually decreases and tends to be stable after 15 cases.