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< The Study | The Outcome Questionnaire | Results | Failure Rates | Discussion | My Concern >

Yeung AT, Tsou PM. “Posterolateral Endoscopic Excision for Lumbar Disc Herniation.” Spine 2002; 27(7):722-731

Imagine having a symptomatic disc herniation removed without having to endure the traumatic surgical slicing of the skin, muscle, fascia, ligamentum flavum, bone, and a nest of epidural vessels. By using an endoscope, a spinal surgeon can ‘by-pass’ all of the latter anatomy and do the job through a relatively tiny 7mm hole that passes from the skin of the back obliquely into the disc [posterolateral percutaneous methodology]. It sure sounds exciting; however, I’m still not so sure it’s time to jump on the endoscopic band-wagon just yet.

Let’s take a look at one version of the “minimally invasive” endoscopic discectomy procedure that seems to be gaining popularity in the spinal surgical community, i.e., Dr. Anthony Yeung’s posterolateral endoscopic discectomy. (This, by the way, is NOT the same procedure as the SED (selective endoscopic discectomy) procedure, which is used for the treatment of chronic lumbar discogenic pain secondary to symptomatic annular tears and not herniation. (click here for the SED paper)

First off, let’s clear one thing up right now:   The term “minimally invasive” is a misnomer, for the only thing minimally invasive about this procedure is the fact that there is no long incision through skin, muscle, fascia and bone of the lower back.   Unfortunately, this surgical technique is extremely invasive to the intervertebral disc and calls for some serious tunneling, digging and hollowing within the already damaged disc; the ramification of the latter certainly can’t be a good thing for the long term health of the disc [2012--> this was proven by Carragee to be true: creating new holes in the disc dooms it to degeneration and a higher frequency of re-herniation].

All in all, however, this investigation yielded some very impressive subjective and objective results, although the investigators completely 'dropped the ball' by failing to used any of the standardized outcome tools (Oswestry, Roland-Morris, VAS) for measuring the degree of success or failure of the endoscopic surgical procedure. The latter choice made it impossible to compare the results of this investigation with the results of the many classic investigations into the efficacy of traditional open discectomy. That said, the objective and subjective methods for measuring the patients outcome in this study were adequate and fair, just not standard.

The results of endoscopic discectomy, as concluded in this investigation, were certainly comparable with the time-tested traditional open discectomy (note the above paragraph) in that 80% of disc herniation-suffering patients obtained a good and excellent outcome, and amazingly, 90% of the cohort (study group) would have chosen to have the procedure again if they were in the same predicament. 

As a bonus, this study even dared to include forms of disc syndromes (such as foraminal herniations, extra-foraminal herniations, and post-surgical recurrent herniations) that are almost always left out of outcome investigations because of their known surgical complication rate.   Very impressive indeed!

The biggest pitfalls of this investigation were as follows: the follow-up period was rather short – 12 to 18 months; the outcome assessment tools were non-traditional – no Oswestry, Roland-Morris, or VAS – and vague; the entry criteria were quite narrow – only straight forward disc herniation-associated radiculopathy cases, which muscle damage in the lower limbs were included; the study methodology was not conducted prospectively or blinded; and there was no control group or randomization of the patients into both a traditional open discectomy group and a endoscopic discectomy group.

For me, the bottom-line of this investigation was this: Dr. Yeung’s posterolateral endoscopic discectomy technique seems to be just as effective as the traditional open discectomy and may be even preferred for the treatment of foraminal and/or extraforaminal type herniations; however, it certainly inflicts major internal damage within a disc that is already internally disrupted, which can’t be good for the long term health of that disc.   I would prefer to wait until the longer term effects (5 years) of the procedure are known before I endorse the procedure for run-of-the-mill paracentral type disc herniations (which are the most common).   However, the good doctors SED procedure, which I plan on reviewing next, may be another matter.

The Study:

During the 1990s, 307 consecutive disc herniation patients, whose average age was 42, were operated by Dr. A. Yeung using his posterolateral endoscopic discectomy technique.   All patients had failed at least 2 months of conservative care, and had suffered and average of 10 months with back and leg pain (sciatica).  The other entry criteria were as follows: 1) a confirmed 5mm or greater disc herniation; 2) “major motor weakness” – which was not further defined; 3) intractable leg pain; and 4) functional impairments – which was not further defined.   All non-radiculopathic disc protrusions were excluded, along with chronic discogenic pain patients, stenotic patients, and pyogenic discitis patients.

Although I was disappointed by the vagueness of the aforementioned descriptions of the entry criteria, I was quite impressed with the fact that these investigators allowed the following more complicated types of conditions into the study: 1) foraminal disc herniations, 2) extraforaminal disc herniations, and 3) post-surgical recurrent disc herniations.   This was very brave indeed, for these types of herniation are much tougher to operate upon, traditionally speaking.

All patients were followed, retrospectively, for a minimum of one year, although the average follow-up period was 19 months.   An excellent 91% of these patients responded to the non-standardized outcome questionnaires that were mailed to them.   All 307 (100%) patients were post-operatively examined at the 12 month mark by a physician; this examination was, again, retrospectively reviewed.

One of my favorite inclusions in the study was a separate category for the patients who were engaged in litigation via Workers’ Compensation or Personal Injury. This is really quite necessary in all investigational outcome studies, for it is well known that the latter groups do not often tell the whole truth about their recovery from a procedure for fear of damaging their cases and lessening their pending monetary award (12,29).   Luckily, the litigation group made up only a minority of the investigation; there were 83 (27%) workers’ compensation patients, and 22 (7%) personal injury patients in this study.

The Outcome Questionnaire:

Although I was quite disappointed by the authors decision not to use any of the standard outcome assessment tools, such as the Oswestry Disability Index, Roland-Morris Disability Questionnaire, or Visual Analog Scale (here for more info), I was pleasantly surprised by the amount of 'tough questions' that this investigations outcome assessment questionnaire had, which included questions like "are you satisfied with the outcome of your endoscopic operation?", and "would you select the same endoscopic spine surgery again in the future, given the same disc herniation and your personal familiarity with the operative experience?" If the patients answered NO to either of the latter question, they were automatically put into the Poor category, which indicated failure. Now that sure seemed fair to me.

Here’s how it worked:   The patients were mailed a questionnaire containing 8 straight forward questions concerning the success or failure of their endoscopic surgical procedure.   Based upon the answers, they were placed into one of the following groups:  excellent, good, fair, and poor.

Here are the exact questions:  

1)   Since your endoscopic spine surgery, have you had subsequent lumbar spine surgery at the same level? (yes / no)

2)   Are you satisfied with the outcome of your endoscopic operation? (yes / no)

3)   Would you select the same endoscopic spine surgery again in the future, given the same disc herniation and your personal familiarity with the operative experience? (yes / no)

4)   Are your current back or leg symptoms, if any, worse than before your endoscopic back surgery? (yes / no)

Note: A negative response to any one of the first four questions (above) resulted in the automatic placement of the patient into the ‘Poor’ category.   If the patient responded ‘Yes’ to all of the above questions, then the patient was required to answer the final four questions.

5)  What is your current level of ‘Recovery’ from the endoscopic discectomy: Complete (3 pts), Almost Complete (2 pts), Partial (1 pt), No Improvement (0 pts).

6)   How long did it take to resume your customary occupation? [2 months (3 pts); 3 to 6 months (2 pts); 7 to 12 months (1 pt); 13 month or longer (0 pts)]

7)  How long did it take to resume the normal activities of daily living including all recreational sports? [2 months (3 pts); 3 to 6 months (2 pts); 7 to 12 months (1 pt); 13 month or longer (0 pts)]

8)   How long did it take you to stop taking prescription analgesics and anti-inflammatory medication? [2 months (3 pts); 3 to 6 months (2 pts); 7 to 12 months (1 pt); 13 month or longer (0 pts)]


9-12: Excellent Surgical Outcome

5-8:    Good Surgical Outcome

3-4:    Fair Surgical Outcome

0-2:    Poor Surgical Outcome

Patient were also rate by a retrospective assessment (looking back at) of their objective examination findings: Results were determined to be “Excellent, Good, Fair, or Poor” by the Mac Nab Classification (23):   I won’t get into all the details but in order to be classified as Fair, Good, or Excellent, the patients subjectively must have stated that they would do the endoscopic surgery again in the future given the same circumstances of their pain.   These more objective results matched the subjective outcomes given by the patients.


Of the 307 patients who were consecutively entered into this investigation, 280 (91%) of them completed the subjective outcome questionnaire and 307 of them (100%) were re-examined at the one year mark. Here are the results:    

Outcome Results:

Physician Performed Assessment:

Patient-Based Assessment by Questionnaire

Worker and Personal Injury-Related Cases

No. of patients in Category:




Excellent or Good  

250 (81%)

234 (84%)

65 (62%)


24 (8%)

20 (7%)

25 (24%)


33 (11%)

26 (9%)

15 (14%)

Unfortunately, the authors failed to divide the ‘Excellent Outcome’ results from the 'Good' results; I would have liked to have seen just how many completely recovered from their pain. The investigators really should have asked more questions and had the patient complete a simple VAS, and take the Oswestry.

Predictably, the litigation group (Workers' Comp & Personal Injury-Related Cases), subjectively, did not do nearly as well as the others, although this is certainly not surprising and anticipated (12,29). Also, it was certainly reassuring to see that the Physician Performed Assessment group numbers (one year exam results) were virtually identical to that of the Patient-Based Assessment by Questionnaire (the patients’ words of how they recovered).

Failure Rates:

Roughly, 11% of the patients suffered a failed endoscopic discectomy.   This number is certainly comparable with the reported failure rates for traditional open discectomy.   The exact results are as follows: 10.7% suffered a poor result as determined by the one-year doctor exam, 9.3% suffered a poor result as determined from the returned patient outcome questionnaires, and 14.3% suffered a poor result within the litigated group of patients.

Second Surgery Rates (Surgical Revisions):

Quite impressive was the fact that only 4% of cohort needed a revision surgery.   This number is almost 50% lower than most outcome studies report for traditional discectomy and microdiscectomy; however, I believe this result is probably due to the fact that no small disc protrusions (<5mm), non-radiculopathic cases, and no stenosis complications were allowed into the study.   Small disc protrusions, which are notorious for re-herniating (6) (, would have probably raised the number up to a level more compatible with traditional open discectomy, although the fact that the researchers allowed foraminal and extra-foraminal herniations into the study may have counters the exclusion of small contained herniations. The bottom line is that endoscopic surgery certainly in comparable with traditional open discectomy and not any riskier... initially.

Surgical complication rates:

Again, the surgical complication rate was also compatible with traditional discectomy, in that 3.6% of the patient developed surgical complications.   There was no mention of the occurrence of epidural fibrosis, a rare but dreaded complication that is seen with traditional open microdiscectomy.   I’ve attempted to e-mail the author for clarification.  


This was a very well done investigation that certainly demonstrated the efficacy of posterolateral endoscopic surgery for the treatment of disc herniation-induced radiculopathy.   The overwhelming majority (80%) of these patients, via non-standardized outcome reporting, obtained either an excellent or good subjective result by one year status-post endoscopic surgery, and over 90% of the cohort (study group) would have chosen to have the endoscopic procedure again given the same circumstances.   VERY IMPRESSIVE!   These numbers are should be comparable with the outcome studies that have investigated the efficacy of traditional open discectomy procedures for the treatment of disc herniation (11-16), although because of the use of a non-standardized outcome assessment tool, the date from this study must stand alone and can NOT be directly compared with the other studies.   Even more impressive was the fact that this study ‘dared’ to include the more complicated types of disc herniations (foraminal, extra-foraminal, and post-surgical recurrent disc herniation) and still produced an excellent result. Why in the world the authors chose not to have the patients fill out a pre-surgery and post-surgery Oswestry and VAS is beyond me and could have made this good study GREAT.  

The Concern: Why I chose not to have my discectomy performed endoscopically.

My biggest concern regarding endoscopic discectomy - that was also alluded to by the authors in the last pages of the paper - is the amount of damage that is undoubtedly inflicted upon innocent discal tissue.   It is certainly a misnomer to call endoscopic discectomy a “minimally invasive procedure”, for the endoscopic procedure described in this investigation significantly damages the posterolateral (back-side) portion of the already damaged intervertebral disc; certainly much more so than traditional microdiscectomy would.   More explicitly, not only does this endoscopic technique call for the excavation (digging) of a 7mm wide, 20mm deep hole (tunnel) in the posterolateral portion of virgin anular disc tissue, but the technique also calls for the excavating of a “working cavity” within the disc itself – at the end of the 20mm deep hole.  The authors noted that this cavity (cavern, working space), which is absolutely needed in order to give the surgeon the necessary 'space' to operate his endoscopic equipment, severed the following purposes: 1) it “decompress the disc, reducing the risk for further acute herniation.”; and 2) it “removes unstable nucleus material to prevent future reherniation.”

The aforementioned ‘digging’, undoubtedly destroys a lot of innocent disc tissue and was one of the reasons I opted for a traditional microdiscectomy.   I just don’t know what the long-term effects of this degree of intra-discal destruction may be, and eagerly await a longer follow-up with this group of patients.

If one were to believe all the sheep and pig experiments of the 1990s (1-5), (which demonstrated that even a thin 5 mm deep surgically created scalpel-slit in the outer portion of the disc always lead to total inward progression of the wound into the nucleus (full thickness anular tear) (1) and the dooming of that disc to rapid degenerative changes (1), endplate degeneration (5), and even facet joint degeneration (3)), then one would certainly think the digging of a 20mm deep 7mm wide hole into the anulus would have at least some future ill effects as well.


1) Osti OL, et al. Volvo Award - "Anulus Tears & Intervertebral Disc Degeneration: an Animal Model" - Spine 1990; 15(8):762-766

2) Moore RJ, et al. “Remodeling of Vertebral Bone after Outer Anular Injury in Sheep.” – Spine 1996; 21(8):936-940

3) Moore RJ, Osti OL, Vernon -Roberts B, “Osteoarthrosis of the Facet Joints Resulting From Anular Rim Lesions” – Spine 1999; 24(6):519-524

4) Key  JA, Ford LT “Experimental intervertebral disc lesions” – J Bone Joint Surg 30A:621, 1948

5) Moore RJ et al “Changes in Endplate Vascularity After an Outer Anulus Tear in the Sheep” – Spine 1992; 17(8):874-877

6) Morgan-Hough CVJ, et al. (2003) "Primary and revision lumbar discectomy: A 16-Year review from one center" J Bone Surg [Br] 2003;85-B:871-4

11) Abernathey CD, Yasargil MG. “Results in microsurgery. In: Watkins RG, ed. Microsurgery of the lumbar spine. Rockville, MD: Aspen Publishers, 1990:223-6

12) Abramovitz JN, Neff SR. Lumbar disc surgery: Results of the Prospective Lumbar Discectomy Study of the Joint Section of Disorders of the Spine and Peripheral Nerves of the American Association of Neurological Surgeons and the Congress of Neurological Surgeons.” Neurosurgery 1991; 29:301-8

13) Kambin P, Brager MD. “Percutaneous posterolateral discectomy: Anatomy and mechanism.” Clin Orthop 1987;223:145-54

14) Nykvist F, et al. "A prospective 5-year follow-up study of 276 patients hospitalized because of suspected lumbar disc herniation" Int. Disabil. Studies - 1989; 11(2):61-67

15) Padua R, et al. "Ten- to 15-year outcome of surgery for lumbar disc herniation:" Eur Spine J - 1999; 8:70-74.

16) Carragee EJ, et al "Clinical outcomes after lumbar discectomy for sciatica:   The effects of fragment types and anular competence" J Bone Joint Surg Am - 2003; 85(1):102-108

23) MacNab I. “Negative disc exploration: An analysis of the causes of nerve root involvement in sixty-eight patients.” J Bone Joint Surg [AM] 1971; 53:891-903

29) Taylor V, Deyo R, et al. “Patient-oriented outcome from low back surgery.” Spine 2000; 25:2445-52

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