Technique ELDF

 

Endoscopic Lumbar Decompression & Foraminoplasty

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Endoscopic Approach

Once the index level has been targeted by segmental probing and radiopaque discography, indigo carmine marker dye is inserted in to the disc to distinguish annulus from scar and disc pad.
Once the discography needle has been replaced with the solid guide wire, the standard cannula and dilator are railroaded to the foramen using an oscillating rotating action. Additional local anaesthetic may be needed to secure comfort at the rib margin or iliac crest margin. When two-dimensional X-rays confirm that the dilator has been placed in the foramen, the standard cannula is replaced with the “Cut Away” slotted cannula, which can more easily be introduced without the curved edges snagging tissues during insertion. The cannula is attached to the suction Friction Lock Water Seal, the 00 or 200 endoscope is inserted over the guide wire and the position of the guide wire in relation to the exiting nerve root and the facet joint ascertained. With experience, the guide wire is removed once the cannula is in situ.

Camera & Drape setup

The 00 endoscope is selected early in the learning curve. The camera is attached via a sterile tubular drape (Mildrape® camera drape, Surgical Innovations Ltd, Leeds, England) that is secured with an additional a supplied adhesive thong. The camera is locked on the objective eyepiece of the endoscope and the objective is rotated to orientate the picture.

Endoscope choice & setup

The endoscopes are shaped elliptically to match the configuration of the foramen. The system consists of a small-bore 00 and 200 elliptical endoscope and a large bore 200 elliptical endoscope. In the initial learning stages, the small-bore 00 endoscope is to be recommended. The 200 endoscope improves visualisation across the midline of the epidural space, improves epidural visualisation medial to the proximal and distal pedicles and visualisation of the posterior annulus during intradiscal surgery. With experience and orientation established, the use of the 200 endoscope becomes the more versatile instrument and can be used throughout the procedure.
Positive suction drainage is linked to the drain tap on the cannula. The endoscope is designed to be attached to two 3-litre bags of saline on the side taps. These are elevated to between approximately 1 - 2 metres above the height of the endoscope.
Bleeding in the operative working zone is controlled by the balance of gravity fed inflow and the rate of suction and irrigation dictated by the drainage tap. The use of the laser to seal bleeding points should be carried out meticulously throughout the procedure. Cooling the inflow fluid and the use of adrenaline in the irrigant are not usually necessary. Excessive inflow pressure should be avoided as it increases tissue fluid extravasation and may cause pressure effects upon the dura with consequent effects on cerebral and neural blood flow.
Oblique endoscope taps are provided for back flushing of the working channels if they become blocked or for use of additional straight firing laser probes, ultrasonic or radio-frequency probes.
The large bore Elliptical endoscope is utilised after adequate clearance of the foramen and definition and mobilisation of the nerves has been achieved. The function of this endoscope is to transmit larger instrumentation such as reamers or punches. To ensure the safe use of such equipment, vital structures such as the nerve must be sufficiently mobilised to ensure their safeguard.
As the large bore endoscope has only one irrigation channel, suction should be applied to the cannula with irrigation applied to the irrigation channel of the endoscope and the laser probe. When using the reamer reversal of connections with fluid applied to the cannula and suction applied to the reamer may be the optimal configuration especially when working in tight corners. The powered reamer may be exchanged for large bore punches or osteotomes.

ELF Lasing Technique

The side-firing laser probe has individual irrigation led from a 1-litre bag of saline attached by a giving set with a Luer lock and 3-way tap. This allows continuous flow during use and irrigation over the mirror and side fire window with preservation thereof. The focus of the beam is tested prior to insertion against a white swab using the guide or pilot beam.

 

Setting and Double pulse (DP)
Power (Watts)
Pulses per Second
Maximum Duration (Seconds)
Energy    (Joules per pulse)
DP1
12
12
6
0.500
DP 2
20
18
20
0.556
DP 3
30
18
20
0.833
DP 4
40
18
20
1.111
DP 5
50
18
20
1.389

Table 1 Laser settings used in endoscopic laser foraminoplasty

The Omnipulse Max® (Trimedyne Inc., Irvine, California) laser generator is set at DP1 for the initial clearance stage (see Table 1 above). The single pulse mode is less effective for bone ablation and in this mode; higher wattages need to be used to achieve the same effect and the patient feels greater thermoacoustic discomfort from each impact.
The position of cannula, endoscope and probe is checked in the AP and lateral planes radiographically before commencing. Clearance of the soft tissues commences seeking to define the bone margin of the facet joint.
Once the soft tissues have been defined, facet joint undercutting may be started. Bone ablation is best effected at a setting of DP3 to DP5. The total energy used ranges from 40 – 150,000 Joules.
Care should be maintained to avoid energy flashback from reflective structures such as bone as the rebounding energy will damage the side-firing window. Maintaining an appropriate distance from the target and approaching while observing the ablation effect avoids flashback.
Haemostasis is achieved by either reducing the energy levels or increasing the distance between the probe and the target.

Power osteotome utilisation

A power driven oscillating osteotome (MDS, Zurich, Switzerland) can be inserted down the 00 & 200 endoscopes for the removal of facet joint overhang and osteophytes under direct vision the osteotome consists of a longitudinal hand piece in to which can be inserted straight and curved osteotomes with straight working edges. The tips have marks at 1 mm intervals to guide the surgeon as to the depth of entry of the osteotome blade in to the bone.
The power generator should be set at 0.1 Bar and single shots initially. As the surgeon becomes familiar with the technique then the setting can be upgraded to repetitive shots and the power increased to 2 - 4 Bar.
The osteotome can be used to clear the deepest reaches of the foraminal isthmus where laser clearance may be impeded by the presence of the transiting nerve passing across the deep/epidural face of the foramen and often lying obscured by the lower border of the medial facet. The laser can be used to trim and seal the bone surface subsequently.
The osteotome can be used to remove larger segments of bone from the foraminal entrance by joining up the indentations made by the osteotome until the section of bone becomes loose. The segment can be mobilised by gentle twisting of the osteotome in the cleavage created. The fragment is then removed by punches either through the small or large bore endoscope or through the cannula with the endoscope removed.

Manual Instruments

Instruments are available for use through the large and small-bore endoscopes described on page 196
Powered reamer utilisation
The powered reamer consisted of an electric hand piece in to which slotted the reamers. The speed, direction of rotation or oscillation was controlled by a foot piece. The standard reamers consisted of burrs with a distal guard to allow bone resection and undercutting of the foramen. Powered eccentric reamers were available for specific applications such as endplate reaming in preparation for endoscopic fusion.

Flexible Endoscopes

Flexible fibreoptic endoscopes were available with a working channel for a forward firing laser fibre for inspection and clearance in the epidural and intradiscal space.

Extraforaminal Zone

The initial view in the extraforaminal region is dictated by the underlying pathology. In a case of prior surgery with advanced settlement, short pedicles and perineural scarring the first view is likely to be a wall of scar with evidently tender structures trapped within.

Figure 1 Extraforaminal initial endoscopic clearance

This contrasts with an unadulterated surgical field in a patient with a large protrusion and reasonable disc height and normal pedicle lengths. In this situation, the exiting nerve will be readily visible together with readily definable foraminal margins containing a disc protrusion occluding the foramen.
The surgeon aims for the bone margin of the foramen and clears the anterior margin and lateral surfaces of the facet joint. The borders from the superior pedicle, the facet joint margin and the external surface of the inferior pedicle are cleared. In the area of the inferior pedicle, the exiting nerve root can be found and identified more easily as it may be less incarcerated at this point.
The side-firing laser is suited to the clearance of scar because of the discrete depth of laser ablation and the concurrent self-sealing effect. Irrigated lasing maintains a clear field of view and appears to deter subsequent scarring.
The scar and infolded ligamentum flavum found anterior to the facet joint capsule and in the superior and inferior notches are gradually removed until the exiting nerve root is freed from the bone of the ascending facet joint, the superior notch, the disc and the inferior notch boundaries.
The Intertransversus muscle may be seen passing from the superior transverse process and overlaps the lateral border of the exiting nerve root especially where there is scoliosis. The nerve root may be adherent to this muscle. The view of the lateral border and the limits of the nerve may be obscured by this structure. The medial muscle fibres may need to be divided and the adherent border dissected from the nerve to mobilise the nerve and gain line of sight.
Lateral osteophytes may form an overhanging claw incarcerating the exiting nerve or more commonly may displace the nerve dorsally and medially in to the extraforaminal zone and foramen. The soft tissues need to be removed from the bone. Subsequently the overhanging or underlying osteophytes need to be resected from the posterior and anterior aspects of the nerve. These frequently occur at the lateral margin of the vertebral body and the nerve may be inflamed and narrowed along this discrete section.

Foraminal Zone

Figure 2 The Quadrangular Space

The foraminal zone consists of a quadrangular space as shown in Figure 75. The superior and inferior notches function as sumps to accommodate the exiting nerve in extension and flexion respectively and ipsilateral and contralateral rotation respectively.
These notches become obscured by hypervascular soft tissues and the superior foraminal ligament in the superior notch or by the disc inferiorly. The middle notch becomes narrowed by facet joint hypertrophy, ligamentum flavum infolding and shoulder osteophytes with further compromise due to the tethering of the nerve to the ascending facet or disc.

Figure 3 Right hand side approach to L4/5 Foramen with inset lateral X-ray

This figure shows the laser probe tip with the window pointing towards the facet joint margin. The nerve has been partially cleared but further tethering scar needs to be removed. The cannula and endoscope position in the foramen is demonstrated in the lateral X-ray insert. The nerve is freed of incarcerating scar or tethering bands. The laser probe is then directed at the facet joint margin to undercut the facet to allow access to the epidural space.
The right angle probe or dissector may be insinuated anterior to the facet and swept along the medial surface of the facet joint in order to mobilise the traversing nerve root that is often tethered to the medial aspect of the facet joint. In cases of settlement or facet joint hypertrophy or extensive scarring, the power reamer or osteotome may be used once the nerves have been displaced to a point of safety.
The external surface of the facet joint may be addressed with the power osteotome once it has been cleared by lasing. A curved line is marked out on the bone. The cut of the osteotome is directed as horizontally as needed and deepened at each point along this line to form a continuous fissure. The action of the osteotome is observed directly and the depth of cut monitored from the millimetre gauge marks on the osteotome blade and on the AP X-ray view. Penetration is ceased when the epidural space is entered or at the first evidence of neural discomfort from the patient. Until experience is gained, it is safer to angle the osteotome towards the annulus at the midpedicular line. With experience a more horizontal direction may be used but penetration beyond the medial pedicular line should be avoided. The osteotome cuts are amalgamated until the fissure is widened and the bone fragment becomes loose. The fragment is mobilised by gently rotating the osteotome blade in the bone fissure.

Figure 4 Powered Osteotome mobilising a fragment of facet joint rim

The fragment may be removed through the large bore endoscope or the endoscope may be removed and the fragments grasped by forward bone graspers and withdrawn through the approach cannula. The raw bone surface is then sealed with the laser to control oozing. This process will provide more space in which to manoeuvre the endoscope. If the cavity of the foramen remains too small, the process can be repeated or additional power reamers and punches may be used. This clearance allows the medial border of the oft flattened and medially displaced nerve root to be clearly visualised and the foramen to be effectively undercut and decompressed.
Further exploration of the superior notch and clearance of the impinging Superior Foraminal Ligament is then undertaken using the laser probe to ablate scar, tethering, the SFL and local facet margin osteophytes until the “functional” axilla is exposed and cleared. Clearance may be supplemented by use of the powered guarded burr and bone punches.

Figure 5 TheL4/5 Superior Foraminal Ligament

This video shows the exiting nerve after clearance of scar and ligaments with the SFL still needing to be fully resected.  probing the medial border of the nerve produces back pain whilst the core produces more dermatomal responses.  The weak posterolateral corner of the disc is evident during this palpation.

The SFL takes origin from the ascending facet joint and attaches to the base of the transverse process. This often binds on to the exiting nerve root, a feature often declared by the presence of marked local injection and hyperaemia of the nerve at this point. Under these circumstances, the SFL needs to be resected and the nerve mobilised. Attention is then directed to clearance of the nerve root axilla and thereafter the inferior notch to expose the disc.
At this stage, the nerve root may be mobilised along the medial and lateral border of the nerve. The laser probe or the angled dissector may be used to free gradually the anterior surface of the nerve from the bone and disc. The nerve may evidence discrete areas of redness and inflammation. Examination of these areas may reveal a shoulder osteophyte lying anterior to the nerve if the redness is coincident with the vertebral body margin or a leaking annular tear if coincident with the annulus. Under these circumstances, the shoulder osteophyte should be ablated by lasing, powered reaming or forward cutting punches. Mobilising the nerve until it is clear of the tear and entering the disc at the point of the tear and removing degenerate disc material from the margins of the tear and clearing degenerate intradiscal tissues and nucleus pulposus should effectively address the radial tear.
A thick sheet of sensitive hypervascular tissue often masks the annulus, termed the “Disc Pad“. This needs to be cleared to define the margins of the disc wall. The disc pad may be adherent to Dura or to the local nerves
In the superior notch, hypervascular sensitive tissues may bind the posterior aspect of the vertebra to the adjacent nerve and occasionally to the facet joint capsule and forming a firm tender mass in the superior part of the SWZ (see Figure 54 on page 199). This should be mobilised and ablated until the functional axilla is mobilised. Removal of this tissue, swollen veins and the fibrous impediment may play a significant part in relieving neural claudicant symptoms. Clearance still leaves a venous complex around the nerve and balances concern regarding excessive venous ablation jeopardising the vascular supply locally or within the dura (Crock 1981).
The dorsal ganglion may be bound to the superior pedicle and the superior notch and may require mobilisation.
In cases of LRS, the exposed superior notch is commonly the site of facet joint osteophytes attached to the exiting nerve. These need to be mobilised from the nerve and resected especially when the nerve is reddened at this point. This is effected by laser ablation and power burrs.
The nerve, once mobilised should be displaced and restored to the correct pathway. Inspection of the nerve may reveal particular adherence at the level of the vertebral margin. The nerve needs to be rolled laterally to expose a shoulder osteophyte. This is often covered by a fibrous cap. This offers a plane for dissection and neural mobilisation. With the nerve displaced and protected by the “Cut Away” cannula, the shoulder osteophyte may be removed by side fire laser ablation and forward bone cutting punches with laser haemostasis.

Intradiscal Zone 

After the disc surface has been cleared of the attendant disc pad by laser ablation and manual punches, the annular knife is passed through the endoscope and placed upon the disc wall. The position is checked by bi-dimensional radiography to ensure an ideal placement of the annular entry point, equidistant between the endplates at the mid-pedicular line.
Figure 6 Endoscopic views of a large disc protrusion (Above left) and an intradiscal view (Above right)
In cases of advanced disc degeneration, the knife may be replaced by the laser probe or alternative ablative or thermoplastic instruments in the entry point and rotated until the entry portal is enlarged to allow easy egress of gases generated during lasing or intradiscal clearance.
In cases of larger disc protrusion or degeneration, the endoscope may be removed and trephines used to open the disc wall. The discal contents may be removed by manual punches passed through the cannula under x-ray control. Removal should be confined to disc material staining darkly with indigo carmine. The paler the staining, the healthier the disc wall and the more likely that it should be retained. When degeneration is widespread, the endoscope is removed and forward cutting, back cutting and dynamically angled punches are inserted to remove freely degenerate disc material
The powered reamers can be inserted in the disc space for additional clearance. The endoscope is replaced with the 200 endoscope to facilitate visualisation of the posterior annulus, the recesses of the disc and the endplates. The side-firing laser probe is used to complete removal of residual degenerate intradiscal tissue and to allow thermoplastic shrinkage of the posterior wall from within the annulus (Thermoplastic Annealing).

Transforaminal Zone 

The 200 endoscope is withdrawn from the intradiscal space and passed through the isthmus of the foramen. Sufficient foraminal enlargement and resection of the ascending facet joint should have been completed prior to discectomy. The laser can be used to enlarge the foramen where it binds on the endoscope and limits exploration. The 200 angle allows the dura to be visualised, together with improved inspection of the medial aspect of the facet joint. Medial overhanging bone can be freed from the transiting nerve by the use of the angled probe, the spatula or the distal end of the side-firing irrigated laser probe itself. Once the transiting nerve is mobilised and displaced then the curtain of remaining bone can be removed by lasing or by upcutting punches.
Rotation of the endoscope allows examination of the inner aspects of respective pedicles and the dorsum of the disc. In this way, the dorsal protrusion of the disc can be visualised and shrunk by additional external thermoplastic annealing of the collagen in the disc wall. In the case of an extrusion or sequestra, lasing and flexible grasping forceps may be used to remove the disrupted disc material; Haemostasis is achieved by lasing the bleeding vessels.
Dorsal osteophytes can be cleared and freed from the dura by direct visualised lasing.
In patients without prior surgery, the dura pulsates once suction is open. After prior surgery the dura may be adherent to the PLL and the disc and may have to be dissected free by a combination of spatula dissection and lasing. This is achieved by using side fire lasing parallel to the dural margin or angled anteriorly, thus avoiding perforation.

Far-Lateral Zone 

For far lateral disc protrusions and lateral osteophytes. The medial and lateral borders of the nerve are identified and mobilised by neurolysis from the disc protrusion and or lateral osteophytes. The protrusion may be anterior to the nerve or protruding both from the medial or lateral aspect of the nerve. The nerve is often adherent to the disc wall and must be mobilised before the protrusion can be defined and removed. The protrusion is then entered by incision with the endoscopy knife. The laser probe widens the entry portal. Clearance is effected by laser ablation and manual clearance as outlined above. The osteophytes are resected by gradual endoscopic laser ablation, side-arm manual punches and powered tools.
The osteophyte is usually covered with a fibrotic layer and the nerve can be mobilised using this plane. Once the nerve is fully mobilised then the laser probe can be used to retract the nerve and by aiming at 90 degrees away from the nerve, the osteophyte can be ablated progressively and safely.

Procedure Endpoint Tests

The endpoint of the procedure is dependant on the pathology. The surgeon should seek to limit surgery to the minimal effective necessity. The following useful endpoint guides should be considered as means of determining the adequacy of the intervention:

 Push-up test  Leg flexion test  Leg extension test
 Isthmic passage  Epidural clearance  Intradiscal clearance
 Axillary clearance  Inferior notch clearance  Nerve root mobility

Push-up test

The push-up test attempts to reproduce the patient’s predominant symptoms by extending their arms, pushing the shoulders fully whilst leaving the hips on the operating table, hyperextending the spine and encouraging the abdomen to sag.
This test must be carried out prior to surgery as some patients may find that this manoeuvre may provoke their symptoms on the flattened surface of a clinical examination couch but not on the hump backed posture of the operating table.

 

Figure 7 The push-up test with the patient flexed and prone (Above left) and extended prone (Above right)
If the test reproduced leg pain prior to the procedure but does not do so at the end, then sufficient clearance has usually been effected. This test is valuable in evaluating efficacy of clearance of leg pain but less so for buttock and back pain

Leg Extension Test

 

 

 

Figure 8 The leg extension test
If at the beginning of the operation leg extension as shown in Figure 81 above, aggravates the back or leg pain, then this may be repeated at the end of the procedure. Clearance of symptoms is a reassuring sign of sufficient neural mobilisation and treatment of the painful pathology.

Leg Flexion Test

This test reproduces symptoms when the hip is abducted and flexed with the knee extended over the side of the hump-backed table. The test must be carried out prior to surgery because symptoms may not be reproduced on the hump backed operating table. This test is valuable in evaluating efficacy of clearance of leg pain but less so for buttock and back pain

Isthmic Passage

Passage through the isthmus demonstrates that sufficient facet/disc/posterior vertebral body clearance has been achieved. Passage through the mid isthmus and inferior notch will be appropriate in the treatment of disco-neural compression and passage through the superior notch or mid isthmus will be appropriate in the treatment of FBS.

Epidural Clearance

If free areolar tissue exists between dura, disc, posterior vertebra surface vessels and the PLL, then sufficient dural mobility is present. The endpoint is achieved when accessible sequestrum or disc protrusion has been visually removed and the protrusion has been thermoplastically reduced and scarring between dura and traversing nerve or PLL has been dissected and mobilised.

Intradiscal Clearance

After manual discectomy, adequate clearance still needs to be confirmed endoscopically and remaining loose tissue removed by laser ablation and washout. In the case of large protrusions, the removal needs to be confirmed from the epidural approach.

Axillary Clearance

Passage of the endoscope through the isthmus or superior notch indicates that adequate clearance of the superior working zone was achieved. This is confirmed by the presence of free ebb and flow of epidural fat through the foramen in response to altered water pressure in the operative zone.

Inferior Notch Clearance

Clearance of the inferior notch, inferior pedicle and mobilisation of the nerve from the disc and removal of any discrete “knuckle” of disc bulge indicates that the endpoint has been achieved.

Nerve Root Mobility

The adequacy of nerve root mobility should be checked from functional axilla to inferior pedicle ensuring mobility from the disc surface, intertransverse muscle, ligamentum flavum, facet joint, superior foraminal ligament, superior notch osteophytes, shoulder osteophytes and removal from the portal of any radial tear.

 

Synoptic overview of ELDF performed on an 80 year old lady with large lateral osteophytes and settled disc with co-morbidities.  Operation performed in 1998 and has moved on since then.