Historical background
Ottolenghi and Argentina in 1955 performed the first posterolateral biopsy of the spine. In 1983, Kambin and Gellman performed modified arthroscopic lumbar discectomy using a working sheath of 6.5 mm outer diameter.

In 1993, Mayer and Brock discussed the use of endoscope for percutaneous discectomy and in the same year, Dr. Jean Destandau performed endoscopic discectomy by the posterior approach. Subsequently Smith et al designed instruments and dedicated endoscopy equipment for a microendoscopic approach to the lumbar spine.

Mack et al in 1993 published the results from the first thoracoscopic spine series, which led to development of equipment capable of performing biopsies and drainage of paravertebral abscesses. Around the same time use of laparoscopic techniques to approach the lumbar spine also gained popularity. Thoracoscopic and laparoscopic intervertebral fusion and instrumentation are now, routinely performed at specialized centres worldwide.

The difference between Microdiscectomy and Endoscopic discectomy
Microdiscectomy is the procedure of disc excision with the aid of loupe magnification or a surgical microscope through an open yet limited “smaller” incision.

Endoscopic discectomy is performed with the aid of the endoscope and only uses “stab” incisions, enough to allow insertion of narrow instruments. The operation is monitored on video-TV unit. More importantly the endoscopic techniques approach the anatomical structures from without the spinal canal.

Indications for Endoscopic Spine Surgery

Disc prolapse and spinal stenosis
Presently these are the main indications for posterior endoscopic lumbar surgery. Lumbar canal stenosis can be decompressed by either the uniportal or biportal technique.

With conventional surgery, the surgical management of the lateral disk is technically difficult. Open procedures require extensive muscle dissection and may have a destabilizing effect on the spinal architecture. Excessive facet resection can complicate about 2% of decompressions for spinal stenosis and cause recurrent leg and back symptoms. With endoscopic discectomy, stripping of the paraspinal musculature and soft tissue trauma are minimized thus causing minimal morbidity and complications. The risks of causing post-operative iatrogenic instability is also low.

Contraindications
There are no absolute contraindications for these techniques as a trained endoscopic spine surgeon can tackle most if not all disc problems endoscopically.

Relative contraindications are extreme instability and epidural scaring at the operative site. Instability warrants instrumentation and fusion, while in epidural scaring the risk of dural tear and neural injury is high in endoscopic techniques.

Another relative contraindication is inexperience of the operative surgeon.

Techniques
Three major techniques are in vogue to tackle spinal symptoms:

A Posterior endoscopic approaches
B Thoracoscopic surgery
C Laproscopic surgery

(A)Posterior Endoscopic Lumbar Surgery
1) Triangular Working Zone: This procedure involves placing a needle in the “triangular working zone”. This triangular working zone, defined by Kamin and Gellman, is bordered superiorly by the exiting nerve root, medially by the proximal articular process and dural sac and inferiorly by the endplate of the inferior vertebra. The sinu-vertebral nerve and the vertebro-medullary branch of the segmental artery lie superior to the triangular working zone and are not usually at risk. Several venous structures often cross the working zone and need to be carefully retracted or coagulated.

2) Portals
2a) Postero-lateral portal is the classic endoscopic approach, which allows easy access to the annulus, disk, lateral recess, foramen and the far lateral spine.

2b) Posterior Paramedian Portal
This portal is a supplement to the postero-lateral portal. The skin stab incision is made on the contralateral side to the postero-lateral portal, approximately one centimeter from the midline. The needle is inserted through the interspinous ligament and ligamentum flava, just medial to the inferior articular facet.

2c) Posterior Midline Portal
This portal establishes entry into the posterior or lateral epidural space and provides access to the central and paracentral portions of the intervertebral disk. It is possible to advance the endoscope into the lateral recess from this portal for addressing pathology directly under the pars.

2d) Transforaminal Portal
In this technique, an endoscope can be passed into or through the neuroforamen and provides access not only to the epidural and intra-discac lesions but can also access pathology from the axilla of the nerve root to the lateral pedicle.

3) Technique of Posterior endoscopic discectomy:
With the patient prone the disc level is localized on image intensifier and the incision taken slightly paramedian. Following this the outer tube with obturator is introduced so that the outer tube rests on the lower half of the lamina & the upper half on the ligamentum flavum. Now the ligamentum flavum is cut & excised cranio-caudally.

The medial facet is undercut. The nerve root is identified & retracted with a special nerve root retractor incorporated in the system.

This presents the disc to vision which is now excised with disc forceps.

If lumbar canal stenosis is evident on the MRI the undersurface of the spinous process and contralateral lamina can be nibbled at.

4) Technique of Posterolateral endoscopic discectomy
With the patient positioned prone the level is localized with image intensifier. The skin incision for the portal is located approximately 8-12 centimetres from the midline and the path for instruments is established with a needle introduced under fluoroscopy into the triangular working area (Fig. 1). Now dilators are introduced over the guide wire and finally introduce a cannula over the dilator and is docked with the disc. Through the cannula the scope and instruments are introduced and discectomy is executed (Fig.2)

5) Advantages of Posterior systems over the Postero-lateral systems
Posterolateral systems approach the disc posterolaterally and involve very little bone excision. This cannot tackle concomitant canal stenosis and also cannot excise discs which have migrated caudally or excessively.

Posterior systems approach the disc through the interlaminar window. This involves slight excision of the lower edge of the lamina. The ligamentum flavum is also excised and the medial facet is undercut.

Advantage with posterior systems is that any concomitant lateral canal stenosis can be tackled at the same time. Migrated discs do not pose a problem in this system.

6) Tubular Lumbar Microdiscectomy
The technique used is similar to traditional open surgery except that a tubular retractor is used , placed through a small incision centered over the lumbar pathology. By using a muscle-splitting approach and sequential dilator, a working channel is established which allows passage of instruments and use of microscope or endoscope for visualization and intervention.

(B)Thoracoscopic techniques [VATS]
Thoracoscopic techniques, initially introduced in 1910 have gradually developed attempting to overcome the morbidity associated with open thoracotomy procedures.

These newer techniques avoid the risk of shoulder girdle dysfunction and intercostal neuralgia is low. Video Assisted Thoracoscopic Surgery (VATS) has replaced most open thoracotomy procedures.

Thoracoscopic techniques are useful in midline thoracic disc herniation, for biopsy and debridement of infections and tumours and as adjuvant in managing spinal deformities. Thoracoscopic bone grafting and spinal fusion and instrumentation are now being increasingly performed at specialized centres.

Technique
Thoracoscopy is performed with the patient under general anaesthesia with a double lumen endotracheal tube. With this the contralateral lung is inflated and the ipsilateral lung is actively deflated. 4 portals are required . The viewing portal is made on the anterior axillary line followed by the rest of the portals for introducing the instruments.

Advantages
In properly selected patients, thoracoscopic procedures reduce incisional pains, reduce chest tube drainage, minimize respiratory difficulties and improve shoulder girdle function.

(C)Laparoscopic spine surgery
Laparoscopic spine procedures are generally indicated to manage anterior lumbar

spine pathology (the vertebral body and the intervertebral disc). Specific applications include biopsy and debridement of tumours and infection, fusion for pseudoarthrosis, deformity or instability and discectomy for herniated or degenerative disks.

Technique
Three laparoscopic techniques have been described:

1) Transperitoneal approach
Carbon dioxide gas is used to insufflate the intraperitoneal space. Instruments are then introduced through special portals for diagnosis and intervention. This is an excellent technique for approaching L5-S1 pathology.

2) Retroperitoneal approach
The laparoscopic retroperitoneal approach provides the same approach as the standard retroperitoneal approach. Therefore unlike the transperitoneal approach this can be applied to the entire lumbar spine.

The viewing portal is established through a small incision in the left flank just superior to iliac crest. After bluntly dissecting the retroperitoneal space with a digit the dissecting balloon is introduced and inflated under laparoscopic visualization to create a working space and allows access to the lumbar spine.

A second portal is made on the anterior abdominal wall lateral to the peritoneal reflection to introduce instruments into the abdomen.

3) Endoscopically assisted mini-laparotomy
This technique combines the benefit of laparoscopy and that of open surgery. The primary goal of the endoscopic portion of the procedure is to develop the retroperitoneal

Pitfalls and Complications Of Endoscopic Spinal Surger
y Endoscopic discectomy has a steep learning curve and poses several challenges for the aspiring surgeon; the most essential of which is mastering hand-eye co-ordination. Also working with long instruments without tactile feedback can lead to iatrogenic injury to important anatomic structures. There is lack of depth perception as 3-dimensional structures are viewed in 2-dimension. A thorough knowledge of surgical and endoscopic anatomy is essential for achieving success in endoscopic surgery.

The complications encountered are dural tears with CSF leak, neural injury, recurrent disc herniation due to inadequate disc removal and wrong level surgery.

Incidence of discitis is less than that of open procedures as the incision site is smaller & the instruments for discectomy go through the outer tube and do not touch the skin prior to entry.

The complications of thoracoscopy are much lesser as compared to open thoracotomy. Pulmonary complications, most commonly atelectasis occur in 10-15% of the patients is easily managed with chest physiotherapy. Injury to dura can occur if the pathology is adjacent or adherent to the dura. In case of such an eventuality primary repair should be done. If required open thoracotomy should be considered.

In Laparoscopic spine surgery, visceral injury can occur (1% of all the procedures) including intestinal, urinary tract & vascular injury with overall mortality rate of 4-8 deaths per 100,000 procedures. A constant pneumoperitoneum can result due to gas insufflation. The newer system using gasless retroperitoneum & laproscopic assisted mini open processes eliminate the risks from a constant pneumoperitoneum.

Summary
In properly selected patients endoscopic spine surgery gives excellent results with minimal complications. Apart from an aesthetic scar there is minimal postoperative pain with early return to activity. With good technique the anatomical structures are better visualized with reduced risk of dural leak or nerve root injury.

Bibliography

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4. Ruetten S, Komp M, Gondolias G. A new full endoscopic technique for the interlaminar operation of lumbar disc herniation using 6 mm endoscopes: prospective 2 year results of 331 patients. Minim Invasive Neurosurg.2006 Apr ; 49(2) :80-7
5. Jang JS, An SH, Lee SH. Transforaminal percutaneous endoscopic discectomy in the treatment of foraminal and extraforaminal lumbar disc herniations, J. Spinal Discord Tech 2006 July;19(5) :338-43.
6. Das K, Rothberg M. Thoracoscopic surgery : Historical perspectives. Neurosurg Focus 2000 Oct:15;9(4):e10
7. Mick J, Richard Fessler, Noel Perin. Review: Complications of Minimally Invasive Spine Surgery. Neurosurgery 51(supplement 2) 26-36, 2002 .
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9. Francis H. Shen, D. Greg Anderson: Arthroscopy of the Spine, Textbook of Orthopaedics, 2004 Elsevier.

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