A modified four-zone classification of the posterior lumbar spinal canal: An anatomical study and clinical application in microchannel surgery

Abstract

This study introduces and evaluates a modified four-zone classification of the posterior lumbar spinal canal, assessing its anatomical basis and clinical utility in guiding microchannel surgery. Current minimally invasive lumbar procedures rely predominantly on fluoroscopic imaging of bony landmarks for localization, often neglecting the consistent anatomical boundaries provided by the ligamentum flavum for surgical orientation and trajectory planning. Anatomical measurements were performed on six fresh-frozen human cadaveric spines to define key parameters of the ligamentum flavum and their spatial relationships with adjacent structures. A retrospective clinical analysis compared 223 patients undergoing microchannel surgery: 103 patients in the conventional localization group (Group A) and 120 patients in the modified four-zone classification group (Group B). Outcomes assessed included fluoroscopy time, microchannel tilt angle, estimated blood loss, operative duration, length of hospital stay, VAS scores, ODI, and Modified MacNab criteria. Anatomically, the interligamentum flavum space measured 12.3 ± 1.8 mm on the left and 11.9 ± 1.9 mm on the right, with the S-point located approximately midway between the ligamentum flavum boundaries. Clinically, Group B demonstrated significant reductions in fluoroscopy time (4.4 ± 1.4 vs. 5.7 ± 1.7 min, p < 0.01), microchannel tilt angle (7.8 ± 2.7° vs. 10.1 ± 3.6°, p < 0.01), blood loss (44.7 ± 12.7 vs. 58.5 ± 13.5 ml, p < 0.01), operative time (69.4 ± 22.5 vs. 81.4 ± 27.1 min, p < 0.01), along with less early postoperative incision pain and length of hospital stay (p < 0.01). While long-term improvements in back pain VAS and ODI scores were similar between groups, Group B demonstrated superior outcomes in both leg pain VAS scores (final score: 0.5 ± 0.6 vs. 1.8 ± 0.8, p < 0.01) and patient satisfaction (Modified MacNab Excellent/Good rate: 85.8% vs. 75.7%, p = 0.03).The modified four-zone classification offers an anatomically reliable framework for posterior lumbar microchannel surgery, enabling precise anatomical targeting, reducing radiation exposure, and improving both perioperative and long-term functional outcomes, This approach may facilitate the standardization and enhancement of procedural precision.