Learning Curve of Percutaneous Endoscopic Lumbar Discectomy Based on the Period (Early vs. Late) and Technique (in-and-out vs. in-and-out-and-in): A Retrospective Comparative Study

Abstract

Objective: To report the learning curve of percutaneous endoscopic lumbar discectomy (PELD) for a surgeon who had not been previously exposed to this procedure based on the period and detailed technique with a retrospective matched comparative design.

Methods: Of 213 patients with lumbar disc herniation encountered during the reference period, 35 patients who were followed up for 1 year after PELD were enrolled in this study. The patients were categorized by the period and technique of operation : group A, the first 15 cases, who underwent by the 'in-and-out' technique; group B, the next 20 cases, who underwent by the 'in-and-out-and-in' technique. The operation time, failure rate, blood loss, complication rate, re-herniation rate, the Visual Analogue Scale (VAS) for back and leg were checked. The alteration of dural sac cross-sectional area (DSCSA) between the preoperative and the postoperative MRI was checked.

Results: Operative time was rapidly reduced in the early phase, and then tapered to a steady state for the 35 cases receiving the PELD. After surgery, VAS scores for the back and leg were decreased significantly in both groups. Complications occurred in 2 patients in group A and 2 patients in group B. Between the two groups, there were significant differences in operative time, improvement of leg VAS, and expansion of DSCSA.

Conclusion: PELD learning curve seems to be acceptable with sufficient preparation. However, because of their high tendency to delayed operation time, operation failure, and re-herniation, caution should be exercised at the early phase of the procedure.

Keywords: Intervertebral disc herniation; Learning curve; Percutaneous endoscopic lumbar discectomy.

Fig. 1. Preoperative and postoperative dural sac cross-sectional area (DSCSA) (mm²) at the index level. The space was drawn by an imaginary area at the narrowest lesion on the T2-weighted axial MRI.

Fig. 2. The entry point is indicated between the tip of the spinous process and the spino-laminar junction. Once the facet contact was established (1), the needle was withdrawn and redirected (dotted arrows) towards the posterolateral annulus by hooking the ventral border of the facet (2). F : Facet joint.

Fig. 3. The obturator should be directed towards posterolateral annulus by pushing the other end of the obturator down.

Fig. 4. After removal of central disc fragment, the working sheath was moved back to the epidural space (A), and the posterior longitudinal ligament (PLL) was removed in half-and-half view (B). D : herniated disc stained by indigocarmine, F : epidural fat, P : posterior longitudinal ligament.

Fig. 5. After removal of PLL, the posterolateral target fragment (gray area) was removed by introducing the working sheath from lateral to medial area.

Fig. 6. Flowchart depicting patient selection.

Fig. 7. Clinical outcomes using VAS scores. There were significant differences between the groups for the leg VAS at 3, 6, 12 months after surgery (p=^*0.019, ^†0.001, ^‡0.033, respectively). VAS : visual analogue scale.

Fig. 8. Expansion of DSCSA. There was significant difference between the groups (^*p=0.002). DSCSA : dural sac cross-sectional area.

Fig. 9. Operation time was rapidly reduced in the early phase, and then tapered to a steady state for the 35 cases receiving the PELD. PELD : percutaneous endoscopic lumbar discetomy.