Foraminoplasty is a term originally coined by the Martin Knight to describe the procedure where a transforaminally approach was optimised to define the incubus of pain sources and specifically and discretely treat or remove the causal pain sources under endoscopic view with the patient in the aware state. Once the foramen has undergone total “nettoyage” then the simpler problem of disc herniectomy or removal of extrusion or sequestration can be treated by Endoscopic Intradiscal Discectomy or direct epidural exploration.
Regrettably there are web sites built upon the prosecution of Endoscopic Intradiscal Discectomy who have yet to learn the benefits and technique of Endoscopic Lumbar Decompression and Foraminoplasty which make adverse comments regarding Foraminoplasty. This web site presentss the results of research examining this technique, much of which is independently reviewed and over extended periods.
Please examine the specific sections on Endoscopic Lumbar Decompression and Foraminoplasty and Endoscopic Lumbar Decompression.
Many convnetional observers hold concerns at the use of modern surgical modalities such as laser or radiofrequency systems of ablation. Laser cuts to a depth of 0.2mm in bone and 0.4mm in soft tissues when applied in a sustained fashion and through a side firing laser probe. The accuracy is much refined upon that achievable with a knife. Laser ablation conducted in the Aware State has the added advantage that a patient will advise the surgeon if the nerve is becoming warm a protection not available to the patient being cut with a knife under general anaesthesia.
Below is laid out a summary of the surgical technique of Endoscopic Lumbar Decompression and Foraminoplasty which may demonstrate to you the comprehensive nature of the technique.
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.
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.
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 2 The Quadrangular 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.
Figure 3 Right hand side approach to L4/5 Foramen with inset lateral X-ray
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
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.
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;
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
Figure 7 Intradiscal Clearance
The powered reamers can be inserted in the disc space for additional clearance. The endoscope is replaced with the 20 degree 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).
The 20 degree 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 20 degree 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.
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.