Background: Traditional lumbar interbody fusion has many limitations, such as large trauma, severe damage to the normal posterior structure, and long postoperative recovery period. With the advance of minimally invasive surgery and spinal endoscopy, new fusion technologies such as percutaneous endoscopic transforaminal lumbar interbody fusion (PE-TLIF) and endoscopic transforaminal lumbar interbody fusion (Endo-LIF) through Kambin’s triangle with less trauma, less bleeding and faster recovery have been developed. However, nerve root injury and dural tears are important complications, and Kambin’s triangle is not "safe". Moreover, fusion after decompression often requires placement of a 14-mm channel, removal of more articular processes, fixation with posterior percutaneous pedicle screw, and changes of intraoperative position or anesthesia, which are inconvenient. One-stop percutaneous endoscopic transforaminal oblique fixation from posterior corner in lumbar spine overcomes the above limitations, and realizes one-stop decompression, fusion and fixation in a single regular minimally invasive channel. The purpose of this study is to measure the neuroimaging anatomic parameters of the nerves related to oblique fixation from posterior corner in lumbar spine through Kambin’s triangle, to define and evaluate the safe working area in Kambin’s triangle, and to identify the optimal target area for endoscopic fusion and fixation.
Methods: Sixty volunteers (27 males and 33 females) underwent lumbar MR examination (VISTA,3D-STIR-TSE Sequence) and the data were uploaded to Philips (Achieva 1.5T MR) workstation. Three working targets (P1, P2, P3) were preset for oblique fixation from posterior corner in lumbar spine. The distances from the working targets to exiting nerve roots and dural sac/traversing nerve roots in the coronal and sagittal planes, and the distances from the exiting roots to the dural sac/traversing nerve roots in the upper and lower endplate planes were measured and statistically analyzed.
Results: In L1/2–L5/S1, the P values of paired t-test for the distances (c1, c2, c3, c4, c5 and c6) from each target (P1, P2 and P3) to the ipsilateral exiting nerve roots and dural sac/traversing nerve roots were all greater than 0.05. There were no statistically significant differences between the targets at both sides of the same segment, and the mean values of both sides were calculated. The c1, c2, c3, c4, c5 and c6 all increased and then decreased, gradually increased from L1/2, maximized in L4/5, and decreased slightly in L5/S1. As the targets (P1, P2, P3) moved laterally along the horizontal midline of the posterior margin of intervertebral disc, the distance to the dural sac/traversing nerve roots gradually increased, while the distance to the exiting roots gradually decreased. The distance from P1 to exiting nerve roots was significantly greater (1–3 mm) than that to dural sac/traversing nerve roots. The distance from P3 to exiting nerve roots was significantly smaller (1–3 mm) than that to dural sac/traversing nerve roots. The distances from P2 to exiting nerve roots and to dural sac/traversing nerve roots did not different significantly in each segment, and the differences in means were within 1 mm.
The distances from exiting nerve roots to dural sac/traversing nerve roots in the upper and lower endplate planes (d1, d2) gradually increased in L1/2–L5/S1 (P<0.0001) and the means of d2 were greater than d1 (P<0.05). There was no statistically significant difference between the left and right sides in the upper and lower endplates in each segment (P=0.26).
In L1/2–L5/S1, the P values of paired t-test for the distances (s1, s2, s3, s4, s5, s6) from the projection points of posterior-inferior (posterior-superior) corner of upper (lower) vertebral body to exiting nerve roots in the sagittal planes passing the targets were all greater than 0.05. There was no statistically significant difference between both sides of the same segment, and thus the mean value was calculated. With the outward shift of the targets in the sagittal planes, s1, s3 and s5 gradually decreased (s1>s3>s5), and the same trend was found for s2, s4 and s6 (s2>s4>s6). The distances gradually increased in each segment from the smallest value in L1/2 to the largest value in L5/S1.
Conclusion: Kambin’s triangle can be used as a working area for oblique fixation from posterior corner in lumbar spine, but the actual safe area is smaller than theoretical prediction. The intersection point between the vertical line from the medial 1/3 of pedicle and the horizontal midline of the posterior margin of intervertebral disc (P2) is an ideal "target" for oblique fixation from posterior corner in lumbar spine. It is neuroanatomically feasible to achieve one-stop complete decompression, fusion, and fixation in a single channel under spinal endoscopy. Further biomechanical studies and clinical trials are needed to determine whether it can be a new option for posterior spinal fusion.