ANNULUS – Ring shaped structure, such as the outer edge of an intervertebral disc.
The external portion of the disc and consists of fibrous material in which the fibres are arranged at 40 – 60 degrees to the vertical and arranged in concentric circles such that each layer of fibres is set at 60 degrees offset to the adjacent layer. The well-organised collagen fibres of the outer disc resist torsion and flexion stresses as well as radial tension induced by axial loading. The annulus is comprised of inner type II fibro-cartilagenous fibres attached to the vertebral end plates and outer type I collagenous fibres that anchor directly into the vertebral body as Sharpey’s fibres and to the longitudinal ligaments.
ARACHNOIDITIS – Inflammation of the arachnoid membrane.
The condition in which nerve roots within the theca (water jacket) are noted to be clumped together and bound together by vascular fibrous bands. Whilst this state is often blamed as an irremediable cause of symptoms, it may be unjustly attributed. Arachnoiditis may be asymptomatic and the cause of symptoms may be the cause of concurrent inflammation arising from an annular tear, annular leak or other discogenic or foraminal sources external to the Theca.
ASCENDING FACET JOINT – The ascending facet joint is the term coined by spinal endoscopists for the superior articular facet, which arises from the inferior vertebra. The term superior for a structure bounding the inferior zone of the foramen is confusing during demonstration of the foramen and the contained structures, so the more readily perceived term for this facet is the “ascending facet”.
AXILLA – This typically refers to the pyramid shaped space forming the underside of the shoulder between the upper arm and the side of the chest.
In the lumbar spine, the spinal cord usually ends at the lower border of the first lumbar vertebra. The nerve roots form the appearance of a horse’s tail (Cauda Equina) below this point with the nerves leaving the dura at intervals in their course. The point where the nerves leave the dura is termed the “Anatomical Axilla” of the lumbar nerve. However, the nerve lies adjacent to the dura until it exits at the appropriate foramen. The endoscopist perceives this point as the “Functional Axilla” of the nerve. The “Functional Axilla” lies within the epidural space, visualised superiorly within the foramen. It is a triangular space bounded by the transiting (descending) nerve and theca medially and the exiting nerve root superiorly and laterally.
AXIAL – Pertaining to or situated on the axis of a body structure or part.
CARTILAGE – A non-vascular supporting connective tissue composed of chondrocytes and various fibres. It is found chiefly in the joints, the thorax and various rigid tubes, such as the larynx, trachea, nose and ear. Temporary cartilage, such as sesamoid bones (knee) and those that compose most of the foetal skeleton at an early stage are replaced later by bone. Permanent cartilage remains unossified, except in certain diseases and sometimes in advanced age.
CAUDA EQUINA – The lower end of the spinal cord at the first lumbar vertebrae and the bundle of lumbar, sacral and coccygeal nerve roots that emerge from the spinal cord and descend through the spinal canal of the lumbar spine, sacrum and coccyx before reaching the intervertebral foramina of their particular vertebrae. The Cauda Equina resembles a horse’s tail.
COLLAGENOUS FIBRE – Any one of the tough white protein fibres that constitute much of the intercellular substance and connective tissue of the body. Collagenous fibres contain collagen and are often arranged in bundles that strengthen the tissues in which they are imbedded.
DEGENERATIVE DISC DISEASE – Degenerative disc disease is not defined by any one set of generally accepted criteria. Confusion arises with the difficulty in distinguishing between age-related changes and those arising from a disease process. Degeneration is a progressive irreversible process that occurs in all connective tissue structures including the intervertebral disc. Distinguishing benign degenerative changes from disease seems to hinge on the relationship between specific structural or biochemical changes and the presence of symptoms or impaired function. Some investigators may interpret impaired functioning in performance terms, such as a restriction of normal activities, or by other researchers in structural terms, such as a loss in mechanical properties of the disc. The age related changes may be present for years and may remain asymptomatic. Other factors including the release of irritative breakdown products, extradiscal micro-trauma, abnormal micro-movements, neural tethering and displacement may provide the trigger by which the degenerate age related changes cause the onset of symptoms.
An autopsy study of 86 subjects showed close to a 100% probability of at least one ruptured disc at 64 years of age and a similar occurrence of other findings such as osteophytes, facet joint osteoarthritis and end-plate irregularities (Videman et al 1990). However, at 65 years of age 100% of the population does not exhibit back pain and or sciatica. This confirms that additional factors are required to provoke symptomatology other than gross pathologic changes alone. This study showed that occupations that involved mixed activities of sitting, standing, and walking without heavy physical loading were associated with the least degeneration. Workers with heavy physical loading had the highest frequency of annular ruptures. This suggests that the mode of loading may one of the multi-factorial precursors for symptomatic degenerative disc disease.
DELAMINATION – The vertical curtains of fibrous tissue that make up the annulus are cross-linked by protein ties. As degeneration progresses within the annulus, these ties may fragment allowing the annulus to bulge outwards. The loss of water content and bulk within the nucleus pulposus reduces the physical support on the inner aspect of the wall, allowing the inner layers to bulge inwards. This process is termed delamination and results in abnormal stresses being applied to the lamina and contained cells with propagation of the degenerative process.
DERMATOME – An area on the surface of a body innervated by afferent fibres from one spinal root. Dermatomal describes the sensory and motor territories deemed to be supplied by individual nerve roots.
DESCENDING FACET JOINT – The descending facet joint is the term coined by spinal endoscopists for the inferior articular facet arising from the superior vertebra. The term inferior for a structure bounding the superior zone of the foramen is confusing during the demonstration of the foramen and contents, so the term for this facet is more clearly described as the “descending facet”.
DISC – The intervertebral disc consists of an outer wall (Annulus) and a more gelatinous centre (Nucleus Pulposus). The body of the disc consists of curtains of fibrous material arranged in onion ring circles attached to the vertebral body endplates above and below. These curtains are reinforced by long chain proteins combined with sugars called “Glycosaminoglycans”. Through the middle of the disc horizontal fibres are arranged. In the middle of the disc, the contents are more gelatinous in an area termed the nucleus pulposus.
DISTAL – Away from or farthest from a point of attachment.
DORSUM – The back of the body, the posterior or upper surface of a body part.
DURA – Outermost and most fibrous of the three membranes surrounding the brain and spinal cord.
ENDPLATE – Neural or Vertebral
The motor endplate in the nervous system, located at the terminal membrane of an axon and the post-junctional membrane of the adjoining muscle tissue.
The vertebral body endplate is either the upper or the lower surface of the vertebral body. It blends with the vertical walls of the boxlike vertebra. The edges of the endplates are strongly supported but at the centre, it is weak. It is covered with Hyaline cartilage. It provides attachment for the vertically arranged laminae in the disc wall and some of these fibres pass through the endplate to gain attachment to the vertebral bone. The watertight integrity of the disc is related to the thickness of the endplate. Thin endplates allow water to escape and the disc contents to dry out abnormally. Such desiccation or dehydration may impair cell nutrition and metabolism with promotion of degeneration.
ENDOSCOPY – The visualisation of the interior organs and cavities of the body with an endoscope.
ENZYME – Enzymes are any class of chemical complex substances that can cause chemical transformations. Complexes may be produced by living cells and catalyse chemical reactions in organic matter. Most enzymes are produced in tiny quantities and catalyse reactions within the cells. Enzymes such as metalloproteases are involved in the degeneration process and others such as leucotrienes may be liberated causing pain and tissue irritation (Freemont et al 1997)
EPIDURAL SPACE – The space immediately above and surrounding the dura mater of the brain or spinal cord, beneath the endosteum of the cranium and the spinal column.
EXTENSION – Backward bending
EXTRUSION – To push out
As the disc degenerates, areas of breakdown coalesce and form shear planes. These cleavages amalgamate causing the disc material to assume the consistency of crabmeat. The wall of the disc thins asymmetrically (irregularly). Commonly, the shear planes pass to the posterior lower endplate. Delamination occurs in the posterior wall and often at the posterolateral corners. Pressure from the unfettered nucleus pulposus then distorts the wall of the disc at these points of weakness forming a disc protrusion or bulge. The process of pressure, inflammation and failure may eventually cause the wall to fail and the contents to burst forth as a disc extrusion. In this situation the disc wall is disrupted and the contents are uncontained. The highly irritant contents are then exposed in the anterior epidural space causing intense pain and irritation.
FACET JOINT – The synovial joint between the articular processes of the vertebrae.
At every segmental level in the spine with the exception of the first and second cervical and the sacral and fused coccygeal levels, the skeletal construct is grossly the same. The mobile elements of each segment consist of a disc in front (anteriorly) and facet joints behind (posteriorly). The facet joints consist of working surfaces covered in low friction hyaline cartilage. These are lubricated by synovial fluid produced by the synovial membrane. This membrane encloses the joint margins and is supported by a joint capsule. This capsule is strong and consists of fibres aligned to resist maximal loading. The facet joints are aligned in the cervical spine to allow rotation and flexion (forward bending) and extension (backward bending). In the thoracic spine movements are confined to minor flexion (forward bending) and minor extension (backward bending) for at these levels movements are splinted by the ribs. In the lumbar spine the joints are set up to allow flexion (forward bending) and extension (backward bending) under load with much reduced ability to rotate.
FIXATION – The spinal nerves exit the canal at foraminae. In the lumbar spine the segmental nerve leaves the epidural space below the ipsinumeric (same numbered) pedicle. For example the 5th lumbar nerve leaves below the 5th lumbar pedicle at the L5/S1 foramen. The nerves of the lumbar spine amalgamate in to a plexus and are redistributed to form peripheral nerves supplying viscera (organs) and the limbs. The distribution follows a pathway deemed to be dermatomal and related to the segmental formation of the body and limbs. The 5th lumbar nerve is typically deemed to supply the skin of the anterolateral shin, dorsum (top) of the foot and the 1st web space between the 1st and 2nd toes. Equally, it is expected to supply the extensor muscles of the great toe amongst others. It is accepted that communication within the plexus may be displaced upwards or downwards on occasions. This is deemed “pre-fixation” or “post-fixation” of the plexus commensurately. Such alteration in fixation may profoundly impair the diagnosis of the symptomatic intervertebral level involved in the causation of symptoms.
FLEXION – Forward bending
FORAMEN – An opening or aperture in a membranous structure or bone, such as the apical dental foramen and the carotid foramen. In the spinal column, the intervertebral foramen is the portal or hole through which nerves enter or exit from the spinal canal
The intervertebral foramen is bounded posteriorly by the ascending and descending facet joints, facet joint capsule and foraminal ligament. The SFL, superior and inferior pedicles bound the vertical limits whilst the vertebral bodies and disc bound the anterior margin.
GANGLION – A knot or knot-like mass.
The dorsal root ganglion is the point of (synaptic) junction of the upwardly (proximally) transmitting sensory nerves and those linking to the nerves of the (synaptic) junctions in the dorsal horns of the spinal cord. From the dorsal horns communicating fibres will link sensory impulses to the thalamus and brain. The junctions are effected at a synapse where the electrical impulse causes the release of a transmitter substance that activates the next nerve nucleus to fire an onward impulse.
HEMIVERTEBRA – An abnormal condition characterised by the congenital failure of a vertebra to develop completely.
INFLAMMATION – Inflammation is the process by which the body addresses insults. The insult may be an infection or a reaction to abnormal or degenerate tissue materials lying “in situ” (normal site) or in an abnormal site in the body spaces. Degenerate disc material may excite a reaction within the disc causing pain to arise from irritant breakdown products emanating from this site. The breakdown products are usually short chain protein such as leucotrienes or prostaglandins or more potent stimulants including acids and alkalis. The reaction produced may serve to aggravate the degenerative process, dissolving more of the degenerate material in an effort to remove the irritant focus but inadvertently increasing the accumulation of breakdown products and local pain.
The release of disc material in to the spinal canal and thus an abnormal tissue site produces an even more intense reaction within the spinal canal not only producing pain but also on occasions producing unwanted scarring around the theca and or nerves. The release of inflammatory products has been shown to produce arachnoiditis (Olmarker et al 1995) (Haughton et al 1993)
INSTABILITY – Instability is the termed loosely applied to denote loss of normal movement patterns between vertebral bodies. The clinical relevance and misconceptions surrounding this term are explored in Lumbar Instability on page 52 and Clinical Relevance of Foraminal Pain Sources on page 149.
LAMINA – Any thin, flat layer of membrane or other bulkier tissue. It may be structure less or part of a larger structure, such as the lamina of the vertebral arch or the laminae of the annulus. In addition it refers to the transverse bar of bone linking the pedicles posteriorly and enclosing the posterior aspect of the spinal canal on a segmental basis. These are angled inferiorly and bear the spinous processes posteriorly.
LIGAMENTUM FLAVUM – The bands of yellow elastic tissue connecting the laminae of adjacent vertebrae from the axis to the first segment of the sacrum. They are thin, broad, and long in the cervical region, thicker in the thoracic region, and thickest in the lumbar region. They help to hold the body erect.
This Ligament is attached to the lamina of the vertebra above and below the disc level. It forms a mobile soft tissue curtain completing the posterior wall of the spinal canal It allows movement to occur between the posterior bony laminae but as the disc mass is reduced so the ligamentum flavum tension is lost and it buckles in to the spinal canal, compromising the available canal space, compressing the theca and nerves.
LEUCOTRIENES – A class of biologically active compounds that occur naturally in leucocytes and produce allergic and inflammatory reactions similar to those of histamine. They are thought to play a role in the development of allergic and auto-allergic disease such as asthma and rheumatoid arthritis.
NERVE ROOTS – The exiting nerve root is the nerve leaving the intervertebral foramen at a given level. The traversing nerve root is the accompanying nerve that passes distally to the next foramen. It passes beside the descending medial facet of the joint and may be visible in the posterior zone of the foramen.
NUCLEUS PULPOSUS – The central part of each intervertebral disc consisting of a pulpy elastic substance that loses some of its resiliency with age. The nucleus pulposus represents the remnant of the embryonic notochord and is normally composed of a well-hydrated gelatinous matrix consisting of proteoglycans containing randomly distributed collagenous fibres situated in the centre of the disc The nucleus pulposus may be suddenly compressed and squeeze out through the annulus causing a herniated disc and pain.
OLISTHESIS – Bone slippage
Disc degeneration results in loss of disc bulk, disc turgor and thus allows displacement of the adjacent vertebral bodies. The consequent displacement results from the direction of forces arising from the inherent posture of the local section of the spine relative to the overall loading of the entire spine and the integrity of the bony structures and the alignment of the facet joints and the integrity of the facet joint capsule.
Anterior displacement is termed anterior olisthesis and when found in association with fracture of the pars interarticularis it is termed spondylolytic spondylolisthesis.
Posterior displacement is termed retrolisthesis. Anterior olisthesis or retrolisthesis may occur in association with degenerative disc disease and at various intervertebral levels within the same spine.
OSTEOARTHRITIS – A tissue response to joint surface degeneration and mechanical wear in which one or many joints undergo degenerative changes, including subchondral bony sclerosis, loss of articular cartilage and proliferation of bone spurs and cartilage in the joint. Inflammation of the synovial membrane or joint is common late in the disease. The most common form of arthritis, its cause is unknown but may included chemical, mechanical, genetic, metabolic and endocrine factors. The presence of the condition usually presents with pain after exercise or use of the joint.
The process leads to widening of the working joint surfaces, thinning of the working surfaces and the build up of bone spurs (osteophytes) at the joint margins. This is referred to as Osteoarthropathy in its early stages and osteoarthritis in its more advanced stages.
OSTEOARTHROPATHY – A disorder affecting bones and joints.
OSTEOPHYTES – A bony outgrowth usually found around the joint area.
Osteophytes are bone spurs that may arise from bone margins either in response to repetitive traction or osteoarthrosis affecting a joint margin. They may secondarily cause pain by impingement upon or distortion of adjacent structures, innervated tissues or nerves.
PARS DEFECT – The pars defect arises at the junction of the descending facet joint and the pedicle of origin. Causation in early childhood may arise as a fracture occasioned by excessive stress due to abnormal alignment of the load transmitting facets (alignment stress). In later life it may arise by trauma, tumour, pathology or surgery. It may be associated with anterior displacement and is then termed spondylolytic spondylolisthesis.
POSTERIOR LONGITUDINAL LIGAMENT (P.L.L.) – This is a fibrous structure, intimately blended with the posterior disc wall and stretching across the backs of the vertebral bodies like a bowstring. Vertebral arteries and veins pass under the bowstring and across the back of the vertebral body. The P.L.L. contains numerous nerve fibres many of which contain sympathetic nerves, rapidly transmitting pain and influencing the vascular and venous status of the subjacent (associated) limb.
This figure represents a diagrammatic axial view of the spinal cord and descending nerve roots. It is equivalent to a horizontal slice through the body. The disc wall and nucleus pulposus overlay the vertebral body.
PEDICLE – A narrow stalk, stem or tube of tissue attached to a tumour, skin flap, bone or organ. In the spine, it represents the paired tubes of bone originating from the back of the vertebral bodies supporting the facet joints and laminae.
PLEXUS – A network of intersecting nerves and blood vessels or of lymphatic vessels. The body contains many plexuses, such as the brachial plexus, the cardiac plexus, the cervical plexus, and the lumbar plexus.
PSEUDO – Prefix meaning false
PSEUDARTHROSIS – The term describes a false joint and in the lumbar spine may arise between an enlarged transverse process on the 5th Lumbar vertebra and the sacrum or iliac bone. These are termed lumbosacral pseudarthroses or ilio-lumbar pseudarthroses respectively. They can produce pain in their own right due to abnormal movements occurring within the pseudarthrosis or enforced upon adjacent working facet joints or discs. These pseudarthroses by their abnormal construct may impede movements at their own segmental level. This results in overload at the level above and may cause accelerated degeneration in the disc or facet joint at these adjacent levels.
RADICULOPATHY – A disease involving a spinal nerve root
The word is derived from the Latin for root and disease. The disease process may be of systemic origin affecting nerves in a widespread form and would more properly be termed neuropathy. When multiple nerve roots are affected then the presentation may be termed polyradiculopathy. Where a more discrete affliction arises then this may be termed radiculopathy or a radicular syndrome. The presence of objective neural functional deficit distinguishes compressive radiculopathy from non-compressive radiculopathy. The latter describes pain in the limb either of a dermatomal pattern or of a pattern encompassing overlapping dermatomes but without neurological functional deficit. This pattern arises from irritation of either the exiting or traversing nerves or those in the posterior longitudinal ligament.
SACRUM – The large triangular bone at the posterior aspect of the pelvis, inserted like a wedge between the two iliac (hip) bones. The base of the sacrum articulates with the last or 5th lumbar vertebra and its apex articulates with the coccyx and various muscles attach to its spinal crest controlling the lower limb. The sacrum is shorter and wider in women than in men.
SAFE WORKING ZONE – This is a triangle bounded by the functional axilla superiorly. This comprises the transiting nerve and theca medially and the exiting nerve root laterally and the dorsum of the inferior vertebra and pedicle inferiorly.
SCIATICA – An irritation of the sciatic nerve usually marked by pain and tenderness along the course of the nerve through the thigh and leg. It may result in a wasting of the muscles of the lower leg when associated impaired transmission due to compression. The term sciatica is derived from the neolatin word ischialgia. Ischialgia is composed from the Attic Greek words for pain and buttock or hip. Sciatica literally means pain in the lower buttock and the upper part of the thigh. It is often misapplied to denote pain radiating down to the extremity of the leg.
SEQUESTRUM – A fragment of dead bone that is partially or entirely detached from the surrounding or adjacent healthy bone.
Disc sequestration represents the end stage of the process of disc extrusion where the degenerate contents of the disc have parted company with the remainder of the disc and may have slipped up or down within the spinal canal
STENOSIS – An abnormal condition characterised by the constriction or narrowing of an opening or passageway in a body structure. The word is derived from the Attic and Ionic Greek and may be translated as “being narrow”. Spinal presentation is subdivided into axial stenosis and Lateral Recess Stenosis.
Lateral Recess Stenosis denotes narrowing of the foraminal pathway. Enlargement of the descending facet joint crowds the lateral angle of the epidural space at and above the foramen. Overgrowth and displacement of the ascending facet joint crowds and narrows the foramen. These effects may be aggravated by osteophytic outgrowths from the joint and by disc protrusion in to the lateral recess and foramen.
Central or more appropriately termed, axial stenosis denotes the presence of factors causing central constriction of the epidural space. This can arise from a combination of ligamentum flavum infolding, central disc bulging, facet joint overgrowth and forward or backward displacement of one vertebra upon another with gross reduction of the volume available to the dura and contents.
The typical clinical presentation of axial stenosis involves bilateral weakness of the limbs aggravated by exercise and a desire to lean forwards to open the dimensions of the epidural space or symptom aggravation with lumbar extension. The symptoms ease with cessation of activity. Lateral Recess Stenosis because it predominantly afflicts the foramen, presents as painful back pain and compressive or non-compressive radiculopathy aggravated by exercise and eased by lying down. Both may present as non-compressive radiculopathy.
SUPERIOR FORAMINAL LIGAMENT – The superior foraminal ligament passes from the apex of the ascending facet joint to the base of the transverse process and borders the superior limit of the foramen. It is visualised particularly by the posterolateral approach and may be found bound to the exiting nerve.
SUBLUXATION – A partial abnormal separation of the articular surfaces of a joint.
The working surfaces of joints are fashioned to glide smoothly over each other whilst preserving perfect apposition of the surfaces. Thus, the transmitted load passes at right angles across the working surfaces in an evenly distributed fashion. If the joint is stretched and the capsule of the joint damaged or elongated then the working surfaces do not pass smoothly and congruently over each other. They pass in to positions of partial displacement termed subluxation where the surfaces have passed beyond their congruent working limits. This results in the margins or working surfaces bearing on one another with increase in local load. This process of “High spotting” damages the surfaces and results in a reaction that leads to bone overgrowth as the bone tries to compensate by increasing surface area to reduce the overload.
SYSTEMIC – Pertaining to the whole body rather than to a localised area or regional part of the body.
THECA – a sheath or capsule, such as the theca cordis or pericardium
The water jacket of the spinal cord is termed the theca. It consists of several layers, the outer of which is called the Dura Mater. The water jacket envelops the brain and extends around the spinal cord and the roots as they extend in to the foraminae and down in to the sacrum. It contains cerebro-spinal fluid responsible for supporting, cushioning and nutrifying the neural tissues.
TORSION – The process of twisting in a positive (clockwise) or negative (counter-clockwise direction).
TRANSVERSE PROCESS – The transverse process originates from the side of the pedicle and provides attachment for stabilising muscles.
VERTEBRA – The vertebra or vertebral body is a box bone. It is built like a cardboard box with firm walls containing soft cancellous bone. Under vertical load it is strong but under asymmetrical (unbalanced) or torsional load it is vulnerable to collapse. This construction allows energy absorption during fracture whilst protecting the vital neural structures in the spinal canal. It is constructed thus to afford sufficient working strength at the optimal structural weight.
There are usually 7 cervical vertebrae, 12 Thoracic vertebrae and 5 Lumbar vertebrae. However just to confuse the spinal surgeon, anatomist and patient, certain vertebrae may develop abnormally by incorporating features of the vertebra above or below. Such vertebrae are termed transitional vertebrae. In addition, due to vascular, muscular or genetic abnormalities one side of a vertebra may fail to grow to full size resulting in an asymmetrical Hemivertebra.
VISCERA – Internal organs enclosed within a body cavity.
