Morphometric measurement of the lumbosacral spine for minimally invasive cortical bone trajectory implant using computed tomography.

PURPOSE: The cortical bone trajectory (CBT) is a novel lumbar pedicle screw trajectory. The aim of this study was to conduct a detailed morphometric measurement of the lumbosacral spine for CBT pedicle screw, using the inferior facet of the cephalad level as a bony landmark. METHODS: The three-dimensional computed tomography (3D-CT) scans of 86 adults who underwent examination of the lumbosacral spine were studied. The distances from the starting point to the inferior, lateral and medial border of the inferior facet of the cephalad level were measured. The angles formed between the screw trajectory and the sagittal plane, the superior endplate of the vertebral body and the posterior margin of the pars interarticularis were defined as the transverse angle (TA), cephalad angle 1 (CA1) and cephalad angle 2 (CA2), respectively. RESULTS: The distances from the inferior border of inferior facet to the starting point from L1 to S1 were 8.9, 6.3, 4.1, 2.9, 1.4 and 0 mm, respectively. The distances from the medial border of the inferior facet to the starting point from L1 to S1 were between 3 and 4 mm. TA from L1 to S1 was 9.0°, 9.6°, 11.3°, 13.5°, 15.5°, and 8.2°, respectively. CA1/CA2 from L1 to S1 was 26.7°/38.7°, 26.0°/38.7°, 26.9°/38.0°, 24.4°/37.2°, 22.9°/35.1° and 18.4°/47.8°, respectively. The maximum screw diameters from L1 to S1 were 4.8, 5.1, 6.1, 6.8, 7.8, and 6.1 mm, respectively. Twenty-five millimeter can serve as a safe maximum length of CBT pedicle screws. CONCLUSIONS: The inferior facet of the cephalad level is an attractive bony landmark for establishing a starting point of CBT for minimally invasive spine surgery.