What trajectory is safe for double penetrating endplate screw posterior spinal fusion surgery in the thoraco-lumbar region?

Abstract Background The penetrating Endplate Screw (PES) technique improved the fixation strength of the pedicle screw by penetrating the endplate in posterior fusion. The "Double" PES, of which trajectory penetrates both the upper endplate of the corresponding vertebra and the lower endplate of the upper adjacent vertebral body, provides a stronger tricortical fixation but requires more strict trajectory. The purpose of this study was to measure the cephalad angles from T7-L5 that would allow a safe trajectory for “Double” PES. Methods We analyzed 1078 pedicles of 539 vertebral bodies of 50 consecutive cases (27 males and 23 females, mean age, 63.3 years) who underwent computed tomography (CT) myelography for evaluation of spinal disorders. The mean cephalad angle to obtain double PES trajectory of each vertebra was examined, except for cases in which the appropriate trajectory would perforate the pedicles. Results The cephalad angle for the appropriate trajectory of “Double” PES ranged from 23.4 to 37.6° in the thoracic spine and 34.8 to 40.8° in the lumbar spine. The ratio of pedicle perforation was significantly higher at T7 (16%), L4 (26%) and L5:(52%). Conclusions It is important to measure the optimal cephalad angle by preoperative CT imaging according to the vertebral level. In L4 and L5, “Double” PES should be avoided because it is often unsafe.