Cortical Bone Trajectory for Thoracic Pedicle Screws: A Technical Note

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Study Design:A morphometric measurement of new thoracic pedicle screw trajectory using computed tomography and a biomechanical study on cadaveric thoracic vertebrae using insertional torque.Objective:To introduce a new thoracic pedicle screw trajectory which maximizes engagement with denser bone.Summary of Background Data:Cortical bone trajectory (CBT) which maximizes the thread contact with cortical bone provides enhanced screw purchase. Despite the increased use of CBT screws in the lumbar spine, no study has yet reported the insertional technique for thoracic CBT.Methods:First, the computed tomography scans of 50 adults were studied for morphometric measurement of lower thoracic CBT. The starting point was determined to be the intersection of the lateral two thirds of the superior articular process and the inferior border of the transverse process. The trajectory was straight forward in the axial plane angulated cranially targeting the posterior third of the superior endplate. The maximum diameter, length, and the cephalad angle were investigated. Next, the insertional torque of pedicle screws using this new technique was measured and compared with that of the traditional technique on 24 cadaveric thoracic vertebrae.Results:All morphometric parameters of thoracic CBT increased from T9 to T12 (the mean diameter: from 5.8 mm at T9 to 8.5 mm at T12; the length: from 29.7 mm at T9 to 32.0 mm at T12; and the cephalad angle: from 21.4 degrees at T9 to 27.6 degrees at T12). The mean maximum insertional torque of CBT screws and traditional screws were 1.02±0.25 and 0.66±0.15 Nm, respectively. The new technique demonstrated average 53.8% higher torque than the traditional technique (P<0.01).Conclusions:The detailed morphometric measurement and favorable screw fixation stability of thoracic CBT are reported. The insertional torque using thoracic CBT technique was 53.8% higher than that of the traditional technique.

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