Development and feasibility study of pedicle screw implantation guided by ultrasonic pedicle pathfinder

English Keywords:Pedicle pathfinder  Ultrasonic osteotome system  Pedicle screw  Assisted placement of pedicle screw

English Abstract:

  【Abstract】 Objectives: To explore the accuracy and safety of using ultrasonic pedicle pathfinder to assist pedicle screw placement. Methods: 2 adult spine specimens (T1-L5) were selected as experimental subjects, including 1 male of 62 years old, and 1 female of 57 years old, excluding deformity, trauma and osteoporosis. The left pedicle of the specimen was setas the experimental group, inwhich the pedicle screw implantation was guided by ultrasonic pedicle pathfinder; and the right pedicle was set as the control group, in which the screw was implanted by freehand. CT scans were performed during and right to measure the distance between the long axis of the positioning pin and the cortex of the pedicle. After the operation, the distance between the pedicle screw and the pedicle cortex was measured and the placement levels of screws were graded by Neo′s method, and the quantitative and qualitative analysis of the results were performed. Then, the differences between accuracy placement rate(Neo′s level 0), acceptable placement rate(Neo′s level 0 or 1) and failure placement rate(Neo′s level 2 or 3) were compared between the two groups. Besides, the differences of both groups in the cortex penetration screws in the upper, middle, lower thoracic spine, and lumbar spine were analyzed to evaluate the differences in the accuracy and safety of screw placement between the two groups. Results: 34 positioning pins were placed in each group during the operation. The minimum distances of experimental group and control group between the positioning pins and the cortical bone of the pedicle were respectively: 2.77mm±1.05mm and 0.59±2.31mm in the upper thoracic spine, 1.97±1.01mm and 0.98±1.70mm in the middle thoracic spine, 3.02±0.93mm and 2.53±0.83mm in the lower thoracic spine, and 4.14±1.04mm and 3.80±0.59mm in the lumbar spine. 6 pins in the experimental group had risks to penetrate, while the number in the control group was 14. In the experimental group and control group,the accurate placement rates were 82.36% and 58.82% respectively, the acceptable placement rates were 97.06% and 82.36%, and the failure placement rates were 2.94% and 17.64%. Among all the screws penetrated cortex(namely screws of level 1, 2 or 3), the experimental group had 1 in the upper thoracic spine(level 1), 2 in the middle thoracic spine(1 of level 1 and 1 of level 2), 2 in the lower thoracic spine(level 2), and 1 in the lumbar spine(level 1); while the control group had 6 in the upper thoracic spine(2 of each level) and 5 in the middle thoracic spine(3 of level 1, 1 of level 2 and 1 of level 3), 3 in the lower thoracic spine(level 1), and 0 in the lumbar spine. In addition, the ratios of penetrated screws in the upper thoracic spine(T1-T4) between the experimental group and the control group was statistically different(P<0.05). But there was no significant difference in the middle and lower thoracic spine and lumbar spine(P>0.05). Conclusions: Compared with freehand, pedicle screw insertion guided by ultrasonic pedicle pathfinder can achieve higher accuracy and safety in the thoracolumbar level.