Simulation-based anatomical feasibility of full-endoscopic transforaminal approach at the L5/S1 level using 3D-MRI/CT fusion imaging: influence of age, sex, and anatomical obstacles.

purposeFull-endoscopic lumbar discectomy with the transforaminal approach (FED-TF) is a minimally invasive spinal surgery for lumbar disc herniation. However, anatomical constraints at the lumbosacral levels (L5/S1), such as the iliac crest, present anatomical challenges. This study aimed to evaluate the simulation-based anatomical feasibility of the FED-TF approach at L5/S1 using three-dimensional (3D) fusion imaging of lumbosacral nerve roots from magnetic resonance imaging (MRI) and of the lumbosacral spine and iliac from computed tomography (CT) images. Moreover, the study assessed simulation-based anatomical feasibility trends based on age, sex, and anatomical obstacles.

methodsA total of 208 cases (416 simulations) were randomly selected from patients who underwent 3D MRI/CT fusion imaging. Using these images, we assessed the simulation-based anatomical feasibility of reaching the medial edge of the L5 pedicle at the L5/S1 intervertebral disc level without resection of the superior articular process (SAP). In cases judged anatomically infeasible on simulation, anatomical obstacles were analysed by age group and sex.

resultsThe FED-TF approach at L5/S1 was judged anatomically feasible without SAP resection in 62.5% of simulations, with significantly higher simulation-based anatomical feasibility in females than in males (72.6% vs. 52.4%, p < 0.01). The FED-TF approach tended to be infeasible in older patients, particularly those in their 70s and 80s. The sagittal insertion angle was significantly greater in males than in females (14.0° [9.0-18.5] vs. 6.0° [3.0-11.0], FDR-adjusted p < 0.001). The SAP was the most common anatomical obstacle to the FED-TF approach (65 simulations), of which 64.6% were judged anatomically feasible on simulation with partial SAP resection (outside-in technique).

conclusionsFED-TF simulation using 3D MRI/CT fusion images demonstrated that the simulation-based anatomical feasibility of FED-TF at L5/S1 was 72.6% with the outside-in technique. These findings indicate that FED-TF approaches tended to be difficult due to pelvic morphology and degenerative changes in older and male patients. 3D MRI/CT fusion imaging may be useful for preoperative anatomical assessment and trajectory planning at L5/S1.