Percutaneous Endoscopic Transforaminal Discectomy (PETD) was developed after Yeung et al11 and Hoogland et al3 introduced the Yeung endoscopic spine system (YESS) and the transforaminal endoscopic spine system (TESSYS), respectively. Foraminoplasty techniques are effective surgical approaches for improving indications of PETD5. Knight, Martin T. N. et al12 report that PETD without foraminoplasty aggravates incipient lateral recess or foraminal stenosis. PETDF is associated with good clinical outcomes12,13. However, Li J et al4 report that all biomechanical indexes are deteriorated in the three-dimensional lumbosacral model with one-half excision of the superior articular process. These findings indicate that foraminoplasty may increase risk of biomechanical deterioration. Qiao P et al5 report that PETDF in L4-L5 increases lumbar instability and postoperative recurrence rates. Currently, at least 95% of LDH cases occur at the L4-L5 or L5-S1 segment. Therefore, the differences in clinical outcomes and radiographic measurements due to different levels of disc herniation in patients after undergoing PETDF should be explored.
The clinical outcomes of PETDF recorded in this study were similar to findings reported in previous studies12–14. Analysis showed significant improvements in pain score and functional status of all patients during the final follow-up. These findings imply that PETDF is effective in relieving both low back and leg pain in patients with LDH.
Interestingly, contralateral foraminal area (CFA) significantly decreased in all patients at the final follow-up. A few studies have explored degeneration of contralateral intervertebral foramen and lateral recess after PELDF. Lumbar facet joints are the conventional methods for guiding and stabilizing the spinal motion segment, especially in maintaining lumbar stability in forward flexion15–17. A previous study using nucleotomy model18 reports that facet joints supported significantly greater load after nucleotomy. Supported load (15.8%) was almost doble the applied external force (8.6% of). Notably, low quantity of nucleus removal (range: 0.7-1.7g) increased the forces transmitted over the facet joints. Previous studies report that destruction of lumbar facet joints results in increase in rotation, loss of strength, and decrease in stiffness of spinal motion segment16,19,20. Moreover, facetectomy results in facet joint diseases and lower back pain, especially on the contralateral side4. Therefore, discectomy and foraminoplasty performed during PETDF may result in increased contralateral facet joint loading in order to maintain spinal mechanical stability in a variety of directions and loading scenarios. This increase in contralateral facet joint loading ultimately results in decreased CFA.
Maintenance of Intervertebral space height (ISH) is a good prognostic index after PETD21,22. However, several studies on PETD report reduction of ISH post-operation5,23. Reduction of ISH is attributed to loss of the nucleus-pulposus volume; loss of nucleus-pulposus constituent due to use of bipolar radiofrequency, including loss of mucopolysaccharide protein complex, chondroitin sulfate and high amounts of water; defects in annulus fibrosus during surgical discectomy; and intervertebral disc degeneration5. In our study, ISH decreased in the two groups. Eun, Sang Soo et al23 report that the average postoperative disc-height ratio in patients (73.7% patients were at L4-L5 spinal level, 10.5% patients were at L5-S1 spinal level) who underwent PELD was 81.54% of the original disc height at 10 years prospective follow-up. These findings were consistent to findings of our study. In addition, Qiao P5 reports reduction of ISH post-operation in 64 patients with L4/5 spinal level who underwent PETDF. These findings show that higher reductions of ISH are correlated with higher increase in intervertebral space angle (ISA). Furthermore, pain is correlated with decrease in lumbar ISA24, whereas ISA increases with decrease in pain after operation.5 Although, ISA increased in the two groups, ISA was not correlated with decrease in ISH. This finding can be attributed to the small sample size.
This study has several limitations. First, there may be errors associated with measuring the FA on MRI. We measured the FA in the sagittal T2 images at the most stenotic sagittal plane. However, these sagittal images may be heterogeneous due to differences in the cutting angle of the MRI resulting from individual anatomic variations and technical problems. A 3.0 mm slice of sagittal T2-weighted MR image is also thicker than an ideal slice. Second, this study only used FA measurement. Therefore, our results may be limited regarding measurement of the nerve root pressure or morphologic changes. Finally, another limitation of this study is its retrospective nature.