Transforaminal Endoscopy - 20 Years Experience

 

Transforaminal Endoscopic treatment of the Degenerating Lumbar Spine - 20 Years Experience.

Martin Knight MD, FRCS, MBBS.

Introduction

The plethora of concepts purporting to explain the source and therefore the treatment of back pain confirms the poverty of understanding which has arisen from deductions from the inert sources of anaesthetised surgery, changes on adynamic non-weight bearing X-rays and pathology on MRI or CT scans. Transforaminal Endoscopic Lumbar Decompression and Foraminoplasty (ELDF) uses Aware State Surgery and the pain-centric concept of “let the patient lead the surgeon to the pain source, liberate the nerve and accommodate residual pathology with physiotherapy”. This algorithm allows a wide range of “conditions” to be treated by this “Keyhole” technique with encouraging long-term outcomes, because it resolves the problems of 'the wrong diagnosis, the wrong level, the wrong target – and we hope the wrong solution'.

Endoscopically determined mechanisms and sources of symptoms

ELDF is Pain centric and with the patient conscious, the surgeon can in reality see the interplay of factors as they produce the patient’s pain. These effectors include:

  • Nerve Mobility: The foramen is shaped to allow the nerve superiorly in extension & ipsilateral axial rotation and move inferiorly in flexion and contralateral rotation. Tethering the nerve can causes a vicious circle of repetitive micro-trauma and further tethering.
  • Overriding facet joints: Overriding facet joints due to loss of turgor/disc height causing the apex of the facet joint to press into the nerve, in turn causing reactionary tethering and superior and often medial displacement of the nerve.
  • Facet joint hypertrophy: Facet joint hypertrophy crowding the nerve and associated with bulging of the capsule, and integrated Ligamentum Flavum. This results in repetitive irritation or bruising of the nerve and in turn inflammatory reaction and engorgement of the tissues in the foramen and tethering.
  • Ligament thickening: Thickening and shortening of the many ligaments in the foramen, whether by age or the response to repeated abnormal distortion and strain, increases tethering of the nerve.
  • Short Pedicles: Short pedicles diminish the volume of the foramen rendering the exiting nerve vulnerable to ageing pathologies and abnormal micro-movements.
  • Osteophytes: Lateral osteophytes displace the nerve dorsally and tether the nerve laterally in its pathway, whilst facet joint osteophytes impinge on the nerve dorsally. “Shoulder” osteophytes’ arising at the dorsolateral margin of the vertebral body, impinge directly into the front of the nerve and are difficult to detect on the CT scan or MRI scan.
  • Superior Foraminal Ligament: The Superior Foraminal Ligament passes from the apex of the ascending facet joint to the base of the transverse process. It occupies a sickle-like configuration over the superior portion of the foramen and coexists with the lower extremity of the dorsal root ganglion. This ligament may fulfil some kind of suspensory function but in the presence of irritation it becomes tethered directly to the nerve and, with loss of disc height, impinges on the nerve like a guillotine blade. Removal of this structure represents an important stage in foraminoplasty by providing increased space in the upper reaches of the foramen. By removing such impingement on the nerve and ganglion, the nerve is liberated and freed to avoid the effects of impingement aggravated by malposture.
  • Olisthesis: Olisthesis (anterior olisthesis or retrolisthesis) is often associated with the term “Instability” when in fact the spine is not unstable, but merely moving through an increased range of micro-movement sufficient to impinge or distort the nerve. This may be present for a considerable period of time asymptomatically, only producing symptoms when the nerve becomes embarrassed by the presence of tethering and internal swelling. Prior to this, the mobile nerve can avoid painful impingement by normal displacement within the distorted foramen. Degenerate olisthesis can only progress to Grade II displacement, but this provides for substantial distortion of the structures within the foramen.
  • Spondylolytic Spondylolisthesis: Endoscopy reveals that in Spondylolytic Spondylolisthesis, the exiting nerve is attached to the “osteophytic” excrescences of the Pars fracture site. The functional foraminal volume is not only distorted in the anterior posterior dimension but is “waisted” and compromised by scarring. The nerve is particularly tethered to the pars and evidently irritated. Palpation at this point reproduces the presenting buttock symptoms. The descending nerve may be tethered to the hard distorted disc wall and causal of additional referred pain.
  • Scoliosis: Scoliosis may derive from ageing within an adolescent scoliosis or occur as a consequence of degeneration within the local segments of the spine. There is a combination of compensatory or degenerative facet joint overgrowth, osteophytosis (facet joint, shoulder or lateral varieties) and intradiscal tilting with narrowing of the foramen on the closing side, or bulging of the disc wall on the convex aspect. In most cases, the body compensates and arrests the progress of the scoliosis by these means. Accepting this adjusted state, the symptoms can then be locally relieved by addressing the pain source directly and leaving the pathological balance undisturbed. There is a small group of patients in whom the degree of curve has reached a point of self-perpetuation and where the compensatory mechanisms are insufficient. This point may lie with a Cobb angle of between 300 and 400 and these patients require close monitoring and may need fusion and scoliosis correction.
  • Modic changes: During endoscopy within the disc space it is evident that when Modic changes are present, the end plates of the vertebral body manifest cracks to the point where the surface can look like crazy paving. Modic changes are therefore not due to “instability” but are due to degradation and leakage through the end plates themselves. The pattern of these changes correlates more often with angular dysfunction seen on weight bearing X-rays rather than the translational dysfunction associated with “instability”.
  • Disc protrusion / extrusion / sequestration: Whilst disc protrusions, extrusions and sequestra can produce symptoms from their space-occupying and compression effects, it behoves us to be sure that:
      • The bulging of the disc wall is actually causing symptoms from the effect of the bulge
      • Should that bulge be removed (for in so doing further disc material will have been removed with aggravation of the disc height loss) then the potential for abnormal micro-movements and Lateral Recess Stenosis may be increased.
      • Very often, the nerve appears to be markedly tethered. Therefore, liberation of the nerve may be more important than removing the modest disc bulge. So, the concept of disc “herniectomy” rather than “discectomy” must be borne uppermost in pursuing the treatment of both compressive as well as irritative/non-compressive radicular symptoms.
  • High Intensity Zones and leaking discs: High Intensity Zones (HIZs) can be an important cause of pain but may be present and unprovocative of pain. Their effect would appear to arise from the idiosyncratic production of breakdown products. Where noxious breakdown products are produced, their effect depends upon the structures upon which they alight.
      • In the midline, irritation may aggravate the posterior longitudinal ligament and descending nerves producing widespread back pain extending as dysaesthesia globally into one or both limbs. This may be attended by vascular changes (mottling/blanching), sensory misperception (causalgia/formication /icy or boiling water pouring down the leg) or sensory signs (hyperaesthesia/hypoaesthesia) Irritation of the descending nerves may cause dermatomal pain but also sphincteric disturbance, Tenesmus or bladder dysaesthesia (absence of fullness, frequency etc)
      • They commonly extend or open into the foramen. In this position, at the weakest area of the disc wall, they cause irritation and tethering of the exiting nerve root but on occasions, the leakage may track down to the foramen below, thus irritating the descending and exiting nerve root. This provides for a concept of “double level irritation” similar to the “double crush” scenario.
      • The relevance of the dehydrated or black leaking disc or HIZ is best determined by the combination of Spinal Probing and Discography because discography alone is an imperfect means of determining whether the leak is causal.
  • Axial Stenosis: is usually a slow process of accretion of the facet joints, loss of disc height and infolding of the Ligamentum Flavum. During this process, the descending nerves adapt to the compressing forces until ischaemic or compressive symptoms finally manifest. Where this is associated with a disc protrusion, the removal of such a protrusion in the adapted scenario can do much to reverse the patient's symptoms. However, Axial Stenosis is commonly confounded by the presence of Lateral Recess Stenosis at the same or adjacent levels, with the latter being the more pertinent pathology.
  • Lateral Recess Stenosis: results from a combination of the effects of the pathologies above and their enhancement by abnormal micro-movements. It may result in irritation and oedema of the nerve aggravated by posture or activity, producing pains and neural dysfunction at rest or upon loading. Concurrent hypervascular scarring surrounding the nerve and the nerve itself become engorged resulting in classical claudication exercise weakness or aggravated pain. Therefore, “Keyhole” liberation of the nerve from tethering in the foramen, removal of the hypervascular scar, osteophytes and ligaments, removes the adverse effects of the micro-movements and reverses the presenting symptoms with limited tissue disturbance and undercutting.
  • Discogenic Pain: meaning that most back pain arises from within the disc - may be over diagnosed. Aware state Spinal Probing and Discography reproduced pain directly from palpating the disc wall or manipulation within the disc in only 11% of patients referred to the Spinal Foundation. Back pain was however produced during palpation of the medial border of the nerve.
  • “Instability”: The term conjures up the concept that significant abnormal movement is involved in the generation of the symptoms of back pain. The required treatment therefore, must be to restore disc height and restore “normal” movement or immobilise the segment.
      • However, endoscopy reveals that all that is required to produce the symptoms of “instability” are micro-movements that bring these provocative factors to bear upon the irritated (sensitised) nerve.
      • ELDF tackles the actual causal factors (foraminal tethering, facet, apical and shoulder osteophytes and the disc protrusion) directly. This removes their irritative effects, leaving the patient with asymptomatic abnormal micro-movements which can themselves be constrained by rehabilitation of the core muscles using programmes such as Muscle Balance Physiotherapy.
  • Pain Distribution: Referred pain is considered to follow dermatomal patterns. Aware state endoscopy demonstrates multiple overlap in the distribution pattern of referred pain. The exiting nerve at L5/S1often produces pain in the shin, heel and outer border of the foot, the traditional S1 distribution.
      • These patterns have been attributed to facet joint pain but endoscopy indicates that the source is more probably the nerve in the foramen, which accounts for the temporary nature of facet joint interventions.

The Endoscopic Solution

“Instability”, Discogenic pain and Axial Stenosis are often over-diagnosed whilst High Intensity Zones and Lateral Recess Stenosis underestimated. In Degenerative Disc Disease or discectomy where disc material is removed:

  • The foramen becomes smaller and the lateral recess compromise aggravated.
  • Loss of Turgor results in increased micromovements.
  • Posterior triangular disc collapse increases with dysfunctional load transmission.
  • Facet overriding increases and subluxation exposes the apex of the superior facet which then impinges upon the nerve.
  • Facet joint hypertrophy & osteophytosis (facet margin/apical, vertebral/shoulder/lateral) occur.
  • Repetitive nerve trauma occurs causes perineural scarring, tethering & irritation.
  • Redundant disc wall distorts the trapped nerve.
  • Noxious intradiscal contents permeate on to the nerve to irritate it further.

Resolution logically lies in liberating the nerve in its course, predominantly in the foramen, by Endoscopic Lumbar Decompression and Foraminoplasty followed by postural rehabilitation. This technique allows discectomy to be limited to herniectomy and so limits the undesirable side-effects listed above. In addition, it allows the specific treatment of the causal factors laid out above without the need for widespread open decompression, Fusion or Total Disc Replacement.

Endoscopic Lumbar Decompression and Foraminoplasty by treating impingement, degenerate disc contents and liberating the nerve has a wide range of applications if examined from the viewpoint of conventional taxonomy. It can be used to treat pain, whether arising in the back or as part of compressive or non-compressive radicular pain, in age ranges from the young and fit to the elderly or infirm.

Clinical Outcomes

The pain-centric ELDF has been used to treat a wide variety of taxonomies and pathologies ranging from protrusions, extrusions, sequestra to Spondylolytic Spondylolisthesis, Perineural scarring, long term foot drop, Lateral Recess Stenosis, Axial Stenosis, High Intensity Zones and leaking discs, Failed Total Disc Replacement, Failed Fusion Surgery and Failed Back Surgery. 80% of our work is Failed Back Surgery or Failed Chronic Pain Management and Cognitive Behavioural Therapy.

To achieve a meaningful clinical impact according to our patient survey all sectors of the patients pain (Back, Buttock /groin & leg) must be reduced by more than 50% and sustained beyond 2 years following surgery.

Our ongoing clinical audit and publications indicates that ELDF achieves these desired outcomes in 80% of our patients. The rate of minor complications in the first 1,000 was 2.4%. Our ongoing audit shows an infection incidence of 9 in 4,300 cases treated by transforaminal endoscopic surgery.

Where suitable training and safeguards are employed it would appear that rolling out this technique to other centres would result in cost savings.  For fuller details of our research please click here.

Conclusions

Endoscopic Lumbar Decompression and Foraminoplasty is a versatile means of addressing symptoms arising from degenerative spinal disease. It offers encouraging clinical outcomes with low complication rates; both in the elderly and infirm as well as in the young and fit. It provides a means of treating Failed Spine Surgery and should be considered as an alternative to conventional surgery as the primary intervention. It holds promise as a vehicle for future advances such as keyhole nucleus replacement and robotic assisted surgery.

References

1.THE EVOLUTION OF ENDOSCOPIC LASER FORAMINOPLASTY – MD Thesis M.T.N. Knight Manchester University 2002

2. ENDOSCOPIC FORAMINOPLASTY: A PROSPECTIVE STUDY ON 250 CONSECUTIVE PATIENTS WITH INDEPENDENT EVALUATION MTN Knight AKD GOSWAMI; JT PATKO, N BUXTON Journal of Clinical Laser Medicine & Surgery Vol 19, Number 2, 2001

3. REVIEW OF SAFETY IN ENDOSCOPIC LASER FORAMINOPLASTY FOR THE MANAGEMENT OF BACK PAIN MTN Knight, DR Ellison, A K D GOSWAMI, V F Hillier J Journal of Clinical Laser Medicine & Surgery, Vol 19, Number 3, 2001.

4. MANAGEMENT OF ISTHMIC SPONDYLOLISTHESIS WITH POSTERLOLATERAL ENDOSCOPIC FORAMINAL DECOMPRESION MTN Knight, AKD Goswami – SPINE, Volume 28 Number 6, March 2003.