Cortical bone trajectory for lumbosacral fixation: penetrating S-1 endplate screw technique: technical note.
OBJECTIVE
A cortical bone trajectory (CBT) is a new pedicle screw trajectory that maximizes the thread contact with cortical bone surface, providing enhanced screw purchase. Despite the increased use of the CBT in the lumbar spine, little is known about the insertion technique for the sacral CBT. The aim of this study was to introduce a novel sacral pedicle screw trajectory. This trajectory engages with denser bone maximally by the screw penetrating the S-1 superior endplate through a more medial entry point than the traditional technique, and also has safety advantages, with the protrusion of the screw tip into the intervertebral disc space carrying no risk of neurovascular injury.


METHODS
In this study, the CT scans of 50 adults were studied for morphometric measurement of the new trajectory. The entry point was supposed to be the junction of the center of the superior articular process of S-1 and approximately 3 mm inferior to the most inferior border of the inferior articular process of L-5. The direction was straight forward in the axial plane without convergence, angulated cranially in the sagittal plane penetrating the middle of the sacral endplate. The cephalad angle to the sacral endplate, length of trajectory, and safety of the trajectory were investigated. Next, the insertional torque of pedicle screws using this technique was measured intraoperatively in 19 patients and compared with the traditional technique.


RESULTS
The mean cephalad angle in these 50 patients was 30.7° ± 5.1°, and the mean length of trajectory was 31.5 ± 3.5 mm. The CT analysis revealed that the penetrating S-1 endplate technique did not cause any neurovascular injury anteriorly in any case. The new technique demonstrated an average of 141% higher insertional torque than the traditional monocortical technique.


CONCLUSIONS
The penetrating S-1 endplate technique through the medial entry point is suitable for the connection of lumbar CBT, has revealed favorable stability for lumbosacral fixation, and has reduced the potential risk of neurovascular injuries.
Department of Orthopaedic Surgery, National Defense Medical College, Tokorozawa, Saitama; and.
Keitaro
K
Matsukawa
Yoshiyuki
Y
Yato
Takashi
T
Kato
Hideaki
H
Imabayashi
Takashi
T
Asazuma
Koichi
K
Nemoto
D000328:Adult; D000368:Aged; D001863:Bone Screws; D005260:Female; D006801:Humans; D008159:Lumbar Vertebrae / Q000000981:diagnostic imaging / Q000473:pathology / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D011857:Radiographic Image Interpretation, Computer-Assisted; D012447:Sacrum / Q000000981:diagnostic imaging / Q000473:pathology / Q000601:surgery*; D013122:Spinal Diseases / Q000000981:diagnostic imaging / Q000473:pathology / Q000601:surgery*; D013123:Spinal Fusion / Q000295:instrumentation* / Q000379:methods; D014057:Tomography, X-Ray Computed; D019415:Torque; D016896:Treatment Outcome
BMD = bone mineral density; CBT = cortical bone trajectory; PES = penetrating S-1 endplate screw; cortical bone trajectory; insertional torque; lumbarbicortical sacral screw; lumbosacral fixation; sacral endplate; sacrum; technique