Introduction

Minimally invasive spinal surgical techniques have revolutionised the field of spinal surgery in the last three decades. This is based on the fact that “Less is More and More is Less”. Minimal post operative pain, less injury to tissues, reduced hospitalisation, and early recovery are some of the advantages to the patient. Brilliant visualisation of the pathology is the most important advantage to the surgeon. But the drawback is the high cost of the surgical instruments and the prolonged learning curve.

Beginning

In the past, the standard technique for lumbar disc removal was laminectomy and later hemilaminotomy. In his quest to find an alternative to this technique Hijikata et al. (1) in 1975 pioneered the advent of minimally invasive lumbar disc surgery by manually removing nucleus pulposus percutaneously through a postero-lateral approach. Kambin (2) used an arthroscope to this approach to aid in illumination and visualization in 1983. Smith originally introduced the concept of chemical nucleolysis in 1962 by injecting chymopapain in the disc space by passing a needle through a postero-lateral approach.

Classification

Based on the work of Hijikata and Kambin, various techniques have been introduced in the realm of minimally invasive techniques to remove the lumbar disc. These techniques can be broadly classified into two headings.

1. Minimally invasive techniques without using endoscope (Fig 1)
2. Minimally invasive techniques using endoscope

The techniques that do not use endoscope are also called as percutaneous approaches and use the trans foraminal route to enter the disc. This is assisted by X -ray imaging.

The techniques which use the endoscope can be further sub divided by their approach.

i.  Trans-Foraminal Endoscopic techniques using the postero-lateral approach

ii. Inter-Laminar Endoscopic techniques using the midline approach

De Antoni and Abdul Gaffar (author of this article) pioneered the double portal midline endoscopic technique which does not use any specialist instruments. The advantage of the technique is its versatility and maneuverability since the working instruments are not constrained by a funnel or tube. The other advantages are detailed below.

i. There are no dedicated or specialist instruments. A 30-degree arthroscope is used as the endoscope. Routine spinal instruments are employed to make the fenestration and to remove the prolapsed disc. (Fig 1). Hence the investment cost is low. 

Figure 1

Instrumentation

ii. All types of disc herniations – prolapsed, extruded, sequestrated, and migrating can be tackled. (Fig 2)

Figure 2

Types of herniation

iii. It is a minimally invasive procedure, reducing hospitalisation, with minimal post operative pain, and earlier recovery.
iv. Visualisation of structures is excellent due to brilliant illumination and magnification. (Fig 3)

Figure 3

Endoscopic view

The Technique

The indication for surgery is unrelenting sciatic pain due to (MRI confirmed) unilateral lumbar disc herniation with or without root canal stenosis. Surgery is done under general anaesthesia with hypotensive technique to reduce bleeding which can obscure visibility.

The patient is placed in the lateral position with the affected side uppermost. The affected disc space is ascertained with an image intensifier and marked on the skin. A 4 to 5 mm portal is made beside the spinous process at the marked level which serves as the working portal for the introduction of operating instruments. A second portal (as the optical viewing portal) is made about 2.5 cm away from the first portal through which a 5 mm arthroscope is introduced (Fig 4). The scope and the working instruments triangulate over the ligamentum flavum at the inter laminar space. Normal saline is used as irrigation fluid. A fenestration is created in the ligamentum flavum and part of the inferior lamina and part of the medial facet is burred away. Thus, one enters the epidural space and then the traversing nerve root is identified. The prolapsed disc is visible when the nerve root is retracted and the disc is removed. The nerve root is probed to make sure that no sequestrated fragments are left behind. The portals are then closed.

Figure 4

Intraoperative procedure

The skills that are to be developed are good grasp of endoscopic spinal anatomy, hand to eye coordination, precise hand control, and triangulation techniques.

Results

From February 1998 to August 2015, 850 patients underwent this type of surgery. The average age was 36.2 years. There were 428 herniated, 146 extruded and 226 sequestrated discs. The most common level of herniation was L4-L5. The average duration of surgery was 65 minutes. All patients were generally discharged the next day. Modified McNab criteria were employed to measure the outcome. 92% had good-excellent results. 6.2% had a fair outcome and 1.8% had a poor outcome. It should be mentioned that all patients from the early days of this technique have been included which includes the patients in the learning curve.

The complications which were encountered, all in the first twenty patients, were the following:

1. Transient cerebral hypoxia – 1
2. Extra Pyramidal Symptoms – 1
3. Post op Head Ache – 4
4. Nerve injury – 3

The first three complications were related to excessive hypotensive anaesthesia, which caused cerebral hypoxia and raised intra cranial tension. All patients recovered completely. This is further discussed later.

The causes for fair to poor results were identified. Obese individuals, non-compliant patients, elderly patients, multi-level disc lesions, centro-lateral disc problems, and patients with chronic symptoms had poor results. Best outcome was seen in young individuals, compliant patients, sequestrated disc prolapses and in cases of lateral root canal stenosis causing neurogenic claudication pain. Hence case selection is important to achieve good results.

With careful selection of patients and mastery of the technique with experience, the results can be vastly improved. Patients generally can be discharged the same day or the next day. No post-operative physiotherapy is required. Only two or three post-operative outpatient visits are required.

Pearls & Pitfalls

Careful selection of patients helps in improving the outcome. One has to develop proficiency in interpreting the MRI, rather than depending on the radiologist’s report. The clinician has the advantage of assessing the patient. He must co relate patient’s pain distribution pattern, neurological symptoms, and signs with the MRI findings. He must also differentiate pain arising from root canal stenosis due to neurogenic claudication and acute discogenic pain. The prolapsed/ sequestrated discs must be studied as to their location and migration.

Plain X rays must be evaluated carefully for transitional vertebrae, and to study the medial facet anatomy, disc angle and disc height. (Fig 5)

Figure 5

Intraoperative procedure

Pre-operative education of the patient about post-operative care of the back is important. Often patients drop their caution as post-operative pain is minimal and there is rapid and vast improvement from their pre-operative pain. We advise them to wear a lumbar support for three weeks to train the patients on their posture and back care.

An empty bladder helps to reduce bleeding.

A bolster under the iliac crest helps to keep the spine straight, particularly in individuals with a wide pelvis, which may cause the lumbar spine to sag while in lateral position.

It is preferable to have the blood pressure measuring cuff wrapped around the upper arm (as the patient is in the lateral position) to get a true reading instead of the lower arm where there is a possibility of vessel occlusion in lateral position. The diathermy pad is also applied to the upper thigh.

Pre-operative X ray localization of the level to be operated is a very important step. A simple skin mark is made at the level of the disc space and this should be frequently referenced during surgery (Fig 6). The mark should not be hidden under the drapes.

Figure 6

Marking

The temptation to use shavers/resectors to remove any soft tissue over the ligamentum flavum must be resisted as this may cause bleeding which may obscure vision. Unipolar diathermy can be used to achieve hemostasis before the epidural space is exposed.

It is very important to define the lateral edge of the nerve root before opening the annulus of the disc or removing any disc material. Exception can be made at L5-S1 level to remove disc fragments through the axilla of (medial to) the nerve root, but only in exceptional situations.

The nerve root must be probed posteriorly to check for any loose fragments, before opening the annulus and also before the end of the operation.

“Red-Out” Phenomenon

Just like a ‘black-out’, even minimal bleeding can obscure vision. This is termed as “red-out”. This is more common in obese patients, alcoholics, hypertensives and patients on aspirin. Bleeding is also caused by Bernoulli effect, where the aggressive use of saline can draw blood from the vessels, just as a shower curtain is drawn inside due to flow of water from the shower nozzle.           

The following methods can be adapted to reduce bleeding.

1. Controlled hypotensive anaesthesia. The mean arterial pressure (M.A.P) must be maintained between 50 and 55 to render adequate cerebral perfusion.
2. By raising the height of the normal saline bags used for irrigation.
3. Using RF ablation to coagulate bleeding vessels.
4. By temporarily occluding the working portal to stop outflow of fluid (“Dutch boy technique”)

Advantages of this technique

1. Shortens the hospital stay – Patients are admitted on the day of surgery and discharged the next day. The need for one night’s stay is mainly for post general anaesthetic care.  Some patients leave the same day.
2. Improves cost effectiveness – Instruments used in the technique are found routinely in the armamentarium of any orthopaedic surgical theatre. There are no expensive specialist instruments meant for spinal endoscopy. Since hospitalisation is only for one day it is cost effective for the patient. Patients are given instructions for home based exercises. Hence there is no need for any post-operative physiotherapy which further reduces the cost and saves time for the patient. Post-operative follow up visits are usually restricted to two or three visits only; one for suture removal and another for instructions on exercises and back discipline. Recovery is rapid and return to work is earlier thus reducing loss of working hours.
3. Improves safety – Unlike in other spinal endoscopic procedures there is no continuous exposure to X rays during the procedure. Only one X ray shot is taken at the beginning of the procedure. Thus irradiation to the patient and theater staff is negligible. Since the surgery is done with the patient on his side, unlike the other spinal procedures which are commonly done in the ‘praying’ knee-chest position, anaesthetic safety is reasonably high with less pressure on ventilation and more ease in anaesthetic monitoring. Positioning of the patient is simple with reduced physical labour to the theatre staff compared to the routine positioning. This position is also good and safe for a patient who has knee and cervical disease. The surgeon does not have to stoop down since he operates looking straight at the TV monitor with relative ease for his neck and back. Visualisation of structures is brilliant because of good illumination and magnification – an advantage offered by endoscopy. The endoscope can be maneuvered inside, thus improving visualisation further – the concept of “an eye inside rather than outside” as compared to a microscope. Brilliant visualisation of nerve roots eliminates the risk of injury thus greatly enhancing safety margin. Video recording of the entire procedure is possible which helps in intra operative documentation. This helps to educate the patient later and also the surgeon who can gain experience by going through the video at a leisurely pace.
4. Less traumatic – Only two 5mm skin portals are employed. There is no retraction of the vital para vertebral muscles thus preserving their nerve and blood supply.  Formation of post-operative scarring is minimal thus reducing post surgery morbidity. This technique is minimally invasive and thus less traumatic.

Conclusion

Minimally invasive spinal surgical techniques will soon become the gold standard in lumbar disc interventional management with distinctive advantages to the patient as well as the surgeon. The technique of Inter Laminar Endoscopic Lumbar Discectomy we described here will be an effective tool in the armamentarium of a spinal surgeon.