CT-based Morphometric Analysis of Approach of Percutaneous Transforaminal Endoscopic Lumbar Interbody Fusion

A radiographic study was designed to measure the relationship of the exiting nerve root and its surroundings to the corresponding intervertebral disc for percutaneous transforaminal endoscopic lumbar interbody fusion to better understand the regional anatomy and to improve clinical applications.

A retrospective study from January 2017 to October 2017 was conducted at Tianjin Hospital. CT images were obtained from patients presenting low back pain (110 patients), and analysis was performed bilaterally from L_2-3 to L₅ S₁ . In the rotating coronal plane we analyzed: the nerve root-dural sac distance at the superior and inferior margins of the disc (Js, Ji); the nerve root-pedicle distance at the medial, middle, and lateral borders of the pedicle (Pa, Pb, Pc); the pedicle width (W); and the safe working zone, defined as a trapezoid bounded by the inferior pedicle and the exiting nerve root (S). In the transverse plane, the nerve root-articular process and the shortest distance for the nerve root-articular process joint surface were analyzed at the superior and inferior margins of the disc (Gs, Gi), respectively. The groups were analyzed using ANOVA, and paired t-tests were used to compare the left and right sides.

From L_2-3 to L₅ S₁ , the distance of the nerve root to the dural sac was larger at the inferior margin of the disc. From L_2-3 to L₅ S₁ , each segment of the vertebral nerve root-pedicle distance gradually decreased from medial to lateral. From L_2-3 to L₅ S₁ , the distance from the exiting nerve root to the middle and lateral margins of the pedicle gradually decreased, with L₅ S₁ being the minimum. Some significant differences were observed between the left and right sides for L_4-5 and L₅ S₁ . The pedicle width of the vertebral body and the mean area for the safe working zone gradually increased from L_2-3 to L₅ S₁ . In the axial plane, the shortest distance between the nerve root and articular process joint surface at the inferior margin of the disc was greater than the distance for the nerve root to the articular process at the superior margin of the disc from L_2-3 to L₅ S₁ . There were no significant differences between the two sides.

It is more difficult to implant a cage with a width of 10 mm above the L_3-4 level. By removing part of the superior articular process, the safe working area can be expanded, and damage to the nerve or other structures can be avoided when implanting a cage.