The Clinical Outcomes of Transforaminal Percutaneous Endoscopic Discectomy in Treating Lumbar Disc Herniation : A Review

Percutaneous endoscopic lumbar discectomy (PELD) is a minimally invasive technique started during the late 20 century. This process is done through microscopic view under local anesthesia. There is a growing but still insufficient evidence that lumbar EDS shows slightly better results in terms of minor tissue damage, shorter hospital stay, faster return to ordinary daily activities, and patient satisfaction. Recurrence rate still remains a matter of debate, and is related with the surgical skills of the surgeon. The complication rate seems to be similar in both of the techniques i.e., open and endoscopic. More randomized controlled trials, systematic reviews and meta-analysis are needed to clarify whether lumbar EDS can be considered comparable if not superior to standard open discectomy. In spite of lacking defined clinical evidence, lumbar EDS is without doubt a rapidly expanding PELD and its future developments are incredibly promising. Due to less complication rate this technique can be considered as a gold standard compared to the open discectomy. The surgeons still require more cadaveric practices for learning the curve and to approach the herniated disc area. The main objective of this review article is to show the clinical outcomes of the Transforaminal Percutaneous Endoscopic Discectomy in treating the lumbar disc herniation.

root pain which severely affects the quality of life of the adults.LDH is the herniation of the soft central portion (nucleus pulposus) which is located in the middle of the outer fibrous ring (annulus fibrosus) of the intervertebral disc which leads to severe lower back pain, numbness or weakness, sciatica and sometimes leads to paralysis or bladder incontinence.The Figure 1 shows the clear anatomical view of the normal lumbar disc and the herniated lumbar disc.
Earliest successions of Endoscopic discectomy are reported after the late '80s.
Kambin and Schaer reported their successive treatment in 88% of patients who underwent percutaneous discectomy [1] and the related outcomes after the introduction of the minimally invasive technique so called arthroscopic discectomy [2].In the late '80s and the beginning of the '90s other authors stated analogous outcomes [3] [4] [5] [6] [7].It is reported as a technique with a far lateral or posterolateral approach to disc through the lateral foramen.This surgery is performed under radiological guidance, endoscopically introduced cannulated system for the herniated nucleus pulposus fragment removal.
Consequential combination of the procedures headed to the extension of reports in the mid '90s.With the developing surgical proficiency, the far lateral approach was criticized by many professionals.In 7% to 11% of the cases, patients underwent re-exploration surgery because of the lack of radicular pain relief [8] [9] [10] [11].In a relative review Kim and Park mentioned that the percutaneous discectomy is limited to anatomical factors, such as iliac crest, large facet joint, or L5 transverse process [12].To get rid of these problems, endoscopic interlaminar approach was consequently developed and popularized by many professionals [13]

Surgical Technique
As stated above, Endoscopic discectomy has been widely practiced, and many changes in the procedures were reported.However, to summarize we can say that endoscopic discectomy has two different approaches: the first one being the transforaminal approach; possible variations of this name include far lateral endoscopic approach, posterior-lateral endoscopic approach, and arthroscopic far lateral/posterior-lateral approach.The second one is the interlaminar approach as described by Ruetten et al. [14].Indications and procedures for these approaches are different, and both need thorough postop assessments.The Figure 3 explains the transforaminal approach to the herniated disc and removal of the herniated nucleus pulposus.Transforaminal Approach: Indications: Patients complained with severe lower back pain which is non-responsive to epidural steroidal injection, to remove the inflammatory section that causes discogenic pain and to decompress the compressed nerve components.
Advantages: It's a minimally invasive approach, there is lower degree of muscle manipulation/damage, reduced low back pain after surgery, reduced postop fibrosis (both muscle and periradicular), and limited bone decompression prevent risk of postop instability due to excessive removal of facet joint, direct visualization of decompressed root from its extracanalar route.
Disadvantages: Lack of experience and learning curve for surgeons who are used to standard micro-discectomy, gradu0ally more limited movements as the foramen is entered, and no possible treatment for L5-S1 level and median disc herniation.

Post-Surgical Schedule
It being a minimally invasive procedure the patient can walk after 1 -2 hr of the surgery.However, during local anesthesia, the patient sometimes experiences numbness because of lidocaine infiltrating the exiting nerve.Bed rest is advised in this case.Patients can be discharged in 1 to 3 days prior to the surgery.He/she is allowed to do office work after 4 -5 days, and they are not allowed to lift heavy weights for 6 -8 weeks to avoid recurrence of the herniation.The patient can take up sports 5 -6 weeks after the surgery in most of the cases but contact sports should carefully be determined.

Surgical Indication
Far-lateral HNP: Direct insertion of the cannula can be done into the HNP for those located outside the canal.This makes it relatively easy to remove the mass avoiding the need of insertion of the cannula through the intervertebral foramen.Under local anesthesia, a far lateral HNP can be removed at every lumbar levels by the posterolateral approach [17] [18].
Recurrent HNP: There are scar tissues and adhesions around the nerve root.Because of this reason, it is technically demanding to safely remove a recurring HNP at the same level by Love's or micro Love's technique or MED.For PED, the transforaminal approach can be used as the initial operation.Based on their experience of 463 cases [19], Ruetten et al. commented on the usefulness of PED for recurrent HNP and consequently reported its utility [20].For classifying the clinical outcomes between the two micro and endoscopic discectomy so many studies were analyzed by smith and his teammates and among them only 4 RCT's matched with the criteria which is eligible to compare the two techniques and the results were not up to the expectations [22]- [27] Teli et al., published on of the largest randomized study and reported so many clinical outcomes with many complications regarding the ED (endoscopic discectomy).

Clinical Outcome
Precisely Rasouli et al. [28], did a detailed RCT comparing all minimally invasive surgical techniques in which he elaborated all the clinical outcomes of the endoscopic discectomy includes the pain index, recurrence rate, complications and the postoperative hospital stay and the major risk factors.Overall one meta-analysis was reported with 9 RCT's comparing all the above mentioned outcomes by using the VAS, ODI and the MacNab which showed a good significant statistical analysis in regarding the risk factors like neural weakness, blood loss [29].Although the results of this meta-analysis is very satisfying still many authors needs more clinically done randomized controlled trials for future improvements and to make the endoscopic discectomy as the standard procedure for the lumbar disc herniation.
The re-herniation rate of 20% in patients underwent transforaminal approach endoscopic discectomy in treating LDH was reported [30], and similar results was stated by Wang et al. in a study relating two different surgeons in learning the curve [31].Complications including the dysesthesia, CSF leak, nerve root damage, etc. are quite identical in all series.
The first clinically evaluated outcomes of the endoscopic discectomy were done by Yeung and Tsou [32].

Complications
Complications should be primarily informed by the surgeon to the patient as a consent which are as follows 1) Unable to access to the area involved with a high iliac crest.2) Lumbar plexopathy 3) Hematoma can occur in the subcutaneous tissue or between the psoas major and minor muscles superficially or deep layered [33].
The complications which were observed during and after PELD with the transforaminal approach includes: 1) Exiting nerve root injury 2) Dural tear 3) Infection near the surgical site 3) Cauda equina injury 4) Hematoma 5) Vessel injury.
Surgeons should be very much attentive regarding the intracranial hypertension while performing surgery because it might result in headaches, seizures and even death.Choi et al. reported 4 seizure cases [4].The patients who are observed with seizures complained of neck pain, so the neck pain was considered as the most possible sign of the subsequent seizure.

Future Perspectives
PELD technique can be done by laminectomy with a high-speed drill for lumbar spinal canal stenosis [34] and by radiofrequency thermal annuloplasty for low back pain [35].These techniques are not widely in use so more clinical trials and more technical seminars and laboratory experiments should be done on fresh cadavers for future benefits and clear details of these advanced techniques.

Discussion
For highly migrated disc herniation, PELD in transforaminal approach is still challenging due to the limited view and ease of access to the target fragment.
Therefore, for highly migrated herniations open surgery was recommended.
This review has some major limitations and, as stated earlier, our goal was to provide an update about this topic, focusing on the current issues (recurrence/complications rate) and on possible future advances.At present the number of centers and surgeons practicing EDS is exponentially increasing [36].
Considering from the early '90s, in the last decade there is a rapid increase in the application of EDS.51 surgical series were reported in the English literature, and far more were found in other languages.Moreover, our focus was only on transforaminal endoscopic discectomy, excluding recurrence series and series focused on a specific aspect.
In 2015 one of the largest series of EDS reported was published which included 10228 patients treated through a transforaminal approach [37].In 2.8% of the cases, the authors reported an incomplete removal and recurrence rate of 0.8%; both of these two types of data are comparable to those reported on standard microdiscectomy series.Amazingly, the authors determined their focus on the rate of incomplete removal and recurrences related to the learning curve of the surgeons and the inappropriate positioning of the surgical equipments, which were found to be the main causes of negative outcome in this particular study [38].The vital importance for the outcome is appropriate indications.According to the authors' experience and basis of the literature data, these procedures are applicable in patients observed fresh or relatively fresh fragments, even migrated, with minor or no signs of diffuse spinal degenerative disease, such as broad disc bulging, spinal stenosis secondary to hypertrophic ligament/osteophytes, and spinal instability [39].Additionally, for surgeons not used to the techniques and endoscopic kit, use of the endoscope in spinal procedures may be very challenging and it requires training and learning curve.Two series which were recently reported highlighted the results obtained from surgeons with varying level of experience in EDS.In particular, both of these articles reported higher rate of recurrence/residual in patients who were operated by surgeons at the earlier stage of their learning curve [40].
Lack of RCT's keeps us wary about the clarification of these outcomes.Preferably, a multi-centered RCT's enrolling huge number of patients and surgeons with similar degree of experience should elucidate whether results of EDS are similar or better than the ones with standard micro-discectomy.

Conclusions
In spite of lacking defined clinical evidence, lumbar EDS is without doubt a rapidly expanding PELD and its future developments are incredibly promising.
Based on the available data about lumbar EDS, following points are highlighted.
1) There is a growing but still insufficient evidence that lumbar EDS shows slightly better results in terms of minor tissue damage, shorter hospital stay, faster return to ordinary daily activities, and patient satisfaction.
2) Rate of recurrence/residual still remains a matter of debate, and it seems to be strictly related to appropriate surgical indications and level of training of the surgeon.
3) In both open and endoscopic techniques, rate of complications seems similar; however the reported results are enormously nonhomogeneous in different series.
4) More randomized controlled trials, systematic reviews and meta-analysis are needed to clarify whether lumbar EDS can be considered comparable if not superior to standard open discectomy.
Figure 2 we can see the herniated lumbar disc at l4 -l5 level and the spinal nerve compressed by the herniated nucleus pulposus.

Figure 1 .
Figure 1.Anatomical view of the lumbar disc (a) normal disc showing the annulus fibrosus (AF), nucleus pulpous (NP), spinal nerve and (b) herniated disc showing the herniation of the nucleus pulposus leading to the compression of the nerve root.
Numerous studies have been published regarding the endoscopic discectomy compared with the microscopically open surgeries and open lumbar discectomy.Among all the reviews published recently Dorham and Mansour showed an outstanding report of the outcomes between the microdiscectomy and the endoscopic discectomy which are surprisingly so similar [21].The main drawback of B. Rakesh, Y. T. Wang DOI: 10.4236/ojo.2018.8200861 Open Journal of Orthopedics their review was they don't explain about the recurrence rate and complications.The main drawback behind the clarification of the endoscopic discectomy as a standard technique to lack of proper RCT'S and proper comparisons between the two micro and the endoscopic techniques.
It showed a highest satisfactory result among all the patients and it is almost equaled the outcome rate compared to the open surgeries.Many comparisons were made by many authors and among them Ruetten et al. reported the same results compared with the micro and endoscopic discectomy and thee study shows 82% of the patients did not resulted in the postoperative leg pain and 12% resulted in intermittent pain.Birkenmaier et al. made five comparative studies of the present technique and conventional open surgery and came to the conclusion that PED had similar clinical outcomes.They also highlighted the advantages of PED which are as follows: shorter operating time, lower estimated blood loss during surgery, fewer surgery-related complications, less surgical site pain immediately after surgery, less need for postoperative pain medication, shorter hospital stay, and a faster return to work.