Prolapsed Intervertebral Disc

Anatomy of Intervertebral Discs

Function

• allows spinal motion and provides stability

• links adjacent vertebral bodies together

• responsible for 25% of spinal column height

Composition

• Annulus Fibrosus

• Nucleus Pulposus

• End plates

Annulus Fibrosus• outer structure that encases

the nucleus pulposus

• strong radial tire–like structure made up of lamellae; concentric sheets of collagen fibers connected to the vertebral end plates. (sheets are orientated at various angles)

• fibres of annulus run obliquely between vertebrae and are arranged primarily in concentric layers

• at periphery some annular fibers extend past cartilage edge plate to enter the bone of body as Sharpey's fibers

• deep fibers either insert into the cartilage at each end of disc or bend with nucleus pulposus

Nucleus Propulsus

• central portion of the intervertebral disc that is surrounded by the annulus fibrosus

• network of delicate collagenous fibers in a mucoprotein gel rich in polysaccharide

• composed of type II collagen, water, and proteoglycans

• approximately 88% water

• hydrophilic matrix is responsible for height of the intervertebral disc

End Plate and Fixation

• attached to vertebral bodies by hyaline cartilage

• cartilage end plate (cranial and caudal interfaces of vertebrae) contains no fibrillar connection with collagen of subchondral bone of the vertebrae;

• this lack of interconnection between end plate and the vertebrae may render disc biomechanically weak against horizontal shear forces

• outer 2/3 of annulus fibrosus are firmly anchored into vertebral bodies

As with taxes and death…

• With age, water content declines and is reduced by pressure borne by the disc, accounting for loss in the height of a person

• HOW?• gradual loss of proteoglycan content explains the loss of

water with aging; also loss of noncollagenous protein whereas collagen increases- especially in nucleus and posterior quadrants of disc

• after the third decade, there is gradual loss of fluid and

concomitant fibrosus replacement of the nucleus by sixth or seventh decade the nucleus has become fibrocartilage. Distinction between the nucleus propulsus and annulus blurs.

• Biochemically, ageing increases the ratio of keratin sulfate to chondroitin sulfate (glycoaminoglycans)

• proportion of chondroitin-4-sulfate to chondroitin-6-sulfate changes, with a parallel decrease in water content

• Proteoglycan synthesis decreases, which decreases the osmotic swelling and the traffic of oxygen and nutrients to the disc.

Blood Supply

• the disc is avascular with capillaries terminating at the end plates

• nutrition reaches nucleus pulposus through diffusion through pores in the endplates

Innervation• the dorsal root ganglion gives rise to the sinuvertebral nerve which

innervates the superficial fibers of annulus

• no nerve fibers extend beyond the superficial fibers

• neuropeptides thought to participate in sensory transmission include:• substance P• calcitonin• VIP• CPON

Disc Biomechanics• Disc• viscoelastic characteristics

– demonstrates creep which allows for deformity over time: the tendency of a solid material to slowly move or deform permanently under the influence of stresses.

– demonstrates hysteresis which allows for energy absorption with repetitive axial compression• this property decreases with time

• Stresses• annulus fibrosus

– highest tensile stresses• nucleus pulposus

– highest compressive stress

• intradiscal pressure is position dependent– pressure is lowest when lying supine– pressure is intermediate when standing– pressure is highest when sitting and flexed forward

with weights in the hands– when carrying weight, the closer the object is to the

body the lower the pressure

Pathophysiology

• Trauma is the single most common cause of rupture of the nucleus pulposus through the annulus fibrosus.

• Loss of intrinsic ability of disc to withstand extrinsic forces

• Annulus and end plate degenerate -> tear secondary to trauma -> disc bulges/ herniates

Pathoanatomy

• Disc Herniation- associated with a spontaneous increase in the production of:Subs p• osteoprotegrin (OPG)• interleukin-1 beta• receptor activator of

nuclear factor-kB ligand (RANKL)

• parathyroid hormone (PTH)

Anatomic Classification• Herniation • Definition:• A localized displacement of disc material beyond the limits

of the intervertebral disc space.

• The disc material may be nucleus, cartilage, fragmented apophyseal bone, annular tissue, or any combination thereof.

• The endplates of the vertebral body define the disc space cranially and caudally; the outer edges of the vertebral ring apophyses, exclusive of osteophytic formations, define it peripherally.

• Disc bulge • is not a true herniation, per se.• Generalized symmetrical or asymmetrical

circumferential extension of the disc margin beyond the margins of the adjacent vertebral endplates.

• Protrusion• Eccentric bulging with an intact annulus• Disc protrusion describes herniation of nuclear

material through a defect in the annulus, producing a focal extension of the disc margin; it can further be defined if the greatest distance, in any plane, between the edges of the disc material beyond the disc space is less than the distance between the edges of the base, in the same plane.

Symmetrical presence (or apparent presence) of disc tissue "circumferentially" (50-100%) beyond the edges of the ring apophyses may be described as a "bulging disc" or "bulging appearance", and is not considered a form of herniation. Furthermore, “bulging” is a descriptive term for the shape of the disc contour and not a diagnostic category.

Asymmetrical bulging of the disc margin (50%-100%), such as is found in severe scoliosis, is also not considered a form of herniation.

• Extrusion• Disc material herniates through annulus

but remains continuous with disc space• A disc is classified as an extrusion if (1) any

distance between the edges of the disc material beyond the disc space is greater than the distance between the edges of the base measured in the same plane, or (2) there is a lack of continuity between the disc material beyond the disc space and the material in the disc space.

• Sequestered fragment (free)• Disc material herniates through annulus

and is no longer continuous with disc space

• The term migration may be used to signify displacement of disc material away from the site of extrusion, regardless of whether sequestrated or not.

Disc herniation classification. A: Normal disc anatomy demonstrating nucleus pulposus (NP) and annular margin (AM). B: Disc protrusion, with NP penetrating asymmetrically through annular fibers but confined within the AM. C: Disc extrusion with NP extending beyond the AM. D: Disc sequestration, with nuclear fragment separated from extruded disc.

• When a relatively large amount of disc material is displaced, distinction between protrusion (A) and extrusion (B or C) will generally only be possible on sagittal MR sections or sagittal CT reconstructions. In Figure C, although the shape of the displaced material is similar to that of a protrusion, the greatest cranio-caudal diameter of the fragment is greater than the cranio-caudal diameter of its base at the level of the parent disc, and the lesion therefore qualifies as an extrusion. In any situation, the distance between the edges of the base, which serves as reference for the definition of protrusion and extrusion, may differ from the distance between the edges of the aperture in the anulus, which cannot be assessed on CT images and is seldom appreciated on MR images. In the cranio-caudal direction, the length of the base cannot exceed, by definition, the height of the intervertebral space

Key Differences Lumbar and Cervical Spine

• 1) Pedicle Nerve Root Mismatch• 2) Anatomy of Nerve Root – exiting and

descending nerve root

Nerve root anatomy

• Key differences between cervical and lumbar spine:

• Pedicle/nerve root mismatch– cervical spine C6 nerve root travels under C5 pedicle (mismatch)– lumbar spine L5 nerve root travels under L5 pedicle (match)– extra C8 nerve root (no C8 pedicle) allows transition

• Horizontal (cervical) vs. vertical (lumbar) anatomy of nerve root– because of vertical anatomy of lumbar nerve root a paracentral

and foraminal disc will affect different nerve roots• because of horizontal anatomy of cervical nerve root a

central and foraminal disc will affect the same nerve root

Lumbar Disc Herniation• Epidemiology• 95% involve L4/5 or L5/S1 levels

– L5/S1 most common level• peak incidence is 4th and 5th decades• only ~5% become symptomatic• 3:1 male:female ratio

• Pathoanatomy• recurrent torsional strain leads to tears of outer annulus which leads to herniation of

nucleus pulposis• Prognosis• 90% of patients will have improvement of symptoms within 3 months with

nonoperative care.• size of herniation decreases over time (reabsorbed)

– sequestered disc herniations show the greatest degree of spontaneous reabsorption• macrophage phagocytosis is mechanism of reabsorption

Classification - Location

• Central Prolapse• often associated with back pain only• less frequently, a protruded disc

above second lumbar vertebra may compress spinal cord itself or or may result in cauda equina syndrome

• Posterolateral (paracentral) • most common (90-95%)• PLL is weakest here• affects the

traversing/descending/lower nerve root – at L4/5 affects L5 nerve root

• protrusion is usually posterolateral into vertebral canal, where it may compress the roots of a spinal nerve;

- with posterolateral herniation, disc will not affect nerve corresponding in number to that intervertebral discs (that nerve emerges above disc); - note that each nerve emerges through upper part of foramen and lies against body of vertebra above; - protruded disc usually compresses next lower nerve as that nerve crosses level of disc in its path to its foramen; - hence, protrusion of fifth lumbar disc usually affects S1 instead of L5; - in this case, an L4-L5 disc herniation will protrude on the L5 nerve root

• Foraminal (far lateral, extraforaminal) • less common (5-10%)• affects exiting/upper nerve root – at L4/5 affects L4 nerve root

– may compress the nerve root above the level of the herniation (hence a L4-L5 far lateral herniation may result in a L4 radiculopathy); - occurs in 6-10% of all lumbar disc herniations; - L4 nerve root is most often involved; - patient typically have intense radicular pain (sciatic 25% and femoral 75% of the time); - when pain is femoral, sleep in the prone position is especially painful; - localized steroid injection: - in the study by Weiner and Fraser (JBJS 1997), sustained relief of symptoms occured in 27 out of 30 patients; - surgical approach may consist of a muscle splitting intertransverse approach, which gives exposure of to spinal nerve and dorsal

• Axillary• can affect both exiting and descending nerve roots

• Symptomscan present with symptoms of• axial back pain (low back pain)– this may be discogenic or mechanical in nature

• radicular pain (buttock and leg pain)– often worse with sitting, improves with standing– symptoms worsened by coughing, valsalva, sneezing

• Cauda equina syndrome (present in 1-10%)– bilateral leg pain– LE weakness– saddle anesthesia

• bowel/bladder symptoms

Physical exam • motor exam• ankle dorsiflexion (L4 or L5)

– test by having patient walk on heels• EHL weakness (L5)

– manual testing• hip abduction weakness (L5)

– have patient lie on side on exam table and abduct leg against resistance• ankle plantar flexion (S1)

– have patient do 10 single leg toes stands• provocative tests• straight leg raise

– a tension sign for L5 and S1 nerve root– technique

• can be done sitting or supine• reproduces pain and paresthesia in leg at 30-70 degrees hip flexion

– sensitivity/specificity• most important and predictive physical finding for identifying who is a good

candidate for surgery

• contralateral SLR– crossed straight leg raise is less sensitive but more specific

• Lesegue sign– SLR aggravated by forced ankle dorsiflexion

• Bowstring sign– SLR aggravated by compression on popliteal fossa

• Kernig test– pain reproduced with neck flexion, hip flexion, and leg extension

• Naffziger test– pain reproduced by coughing, which is instigated by lying patient

supine and applying pressure on the neck veins• Milgram test

– pain reproduced with straight leg elevation for 30 seconds in the supine position

• gait analysis• Trendelenburg gait• due to gluteus medius weakness which is innervated by L5

Investigations• Radiographs• may show

– loss of lordosis (spasm)– loss of disc height– lumbar spondylosis (degenerative changes)

• MRI without gadolinium• modality of choice for diagnosis of lumbar and cervical disc herniations

– highly sensitive and specific– helpful for preoperative planning– useful to differentiate from synovial facet cysts

• however high rate of abnormal findings on MRI in normal people• indications for obtaining an MRI

– pain lasting > one month and not responding to nonoperative management or– red flags are present

• infection (IV drug user, h/o of fever and chills)• tumor (h/o or cancer)• trauma (h/o car accident or fall)• cauda equina syndrome (bowel/bladder changes)

• MRI with gadolinium• useful for revision surgery• allows to distinguish between post-surgical fibrosus (enhances with gadolinium) vs. recurrent herniated disc

(does not enhance with gadolinium)

Treatment• Nonoperative• rest and physical therapy, and antiinflammatory medications

– indications• first line of treatment for most patients with disc herniation

– 90% improve without surgery

– technique• bedrest followed by progressive activity as tolerated• medications

– NSAIDS– muscle relaxants (more effective than placebo but have side effects)– oral steroid taper

• physical therapy– extension exercises extremely beneficial– traction– chiropractic manipulation

• Selective Nerve Root Corticosteroid Injections– indications• second line of treatment if therapy and

medications fail– technique• epidural• selective nerve block

– outcomes• leads to long lasting improvement in ~ 50%

(compared to ~90% with surgery)• results best in patients with extruded discs as

opposed to contained discs• utilizes a paraspinal approach of Wiltse

• Operative

• laminotomy and discectomy (microdiscectomy) – indications

• persistent disabling pain lasting more than 6 weeks that have failed nonoperative options (and epidural injections)

• progressive and significant weakness• cauda equina syndrome

– technique• can be done with small incision or through "tube" access

– outcomes• positive predictors for good outcome with surgery

– leg pain is chief complaint (as opposed to back pain)– positive straight leg raise– weakness that correlates with nerve root impingement seen on MRI

• outcomes of surgery– improvement of pain and function – 70% improvement of back pain– neurologic recovery less predictable

» 50% motor or sensory recovery» 25% reflex recovery

– patients with worker's compensation claims have less relief from symptoms and less improvement in quality of life with surgical treatment

• far lateral microdiscectomy – indications

• for far-lateral disc herniations – technique

Complications of Surgery

• Dural tear (1%)• if have tear at time of surgery then perform water-

tight repair• Recurrent HNP• can treat nonoperatively initially• Discitis (1%)• Vascular catastrophe• caused by breaking through anterior annulus and

injuring vena cava/aorta

Throacic HD• Relatively uncommon and makes up only 1% of all H

NP.

• Epidemiology• demographics

– most commonly seen between 4th and 6th decades of life• as the disc desiccates it is less likely to actually herniate

• location– usually involves middle to lower levels– T11-T12 most common level– 75% of all thoracic disc herniations occur between T8

and T12• risk factors• underlying Scheuermann's disease may predispose

to thoracic HNP

Symptoms• pain– axial back or chest pain is most common symptom– thoracic radicular pain

• band-like chest or abdominal pain along course of intercostal nerve

– arm pain (see with HNP at T2 to T5)• neurologic– numbness, paresthesias, sensory changes– myelopathy– paraparesis– bowel or bladder changes (15% - 20% of patients)– sexual dysfunction

Physical exam• localized tenderness• root symptoms

– dermatomal sensory changes (paresthesias and dysesthesia)• cord compression and findings of myelopathy

– weakness• weakness or mild paraparesis• abnormal rectal tone

– upper motor neuron findings• hyperreflexia• sustained clonus• positive Babinski sign

– gait changes• wide based spastic gait

• Horner's syndrome• seen with HNP at T2 to T5

Investigations• Radiographs• lateral radiographs

– may show disc narrowing– may show calcification (osteophytes)

• MRI• most useful and important imaging method to demonstrate thoracic disc

herniation– allows for identification of neoplastic pathology– can see intradural pathology– will show myelomalacia– may not fully demonstrate calcified component of herniated disc

• disadvantage is high false positive rate– in a study looking at asymptomatic individuals

• 73% had thoracic disk abnormalities • 37% hand frank herniations

• 29% of these had cord compression.

Treatment• Nonoperative• activity modification, physical therapy, and symptomatic treatment

– indications• the majority of cases

– modalities include• immobilization and short term rest• analgesic• progressive activity restoration• injections may be useful for symptoms of radiculopathy

– outcomes• majority improve with nonperative treatment

• Operative• discectomy with possible hemicorpectomy or fusion

– indications• surgery indicated in minority of patients• acute disc herniation with myelopathic findings attributable to the lesion, especially if there is progressive

neurologic deterioration• persistent and intolerable pain

– technique• debate between discectomy with or without fusion is controversial.

– most studies do indicate that anterior or lateral (via costotransversectomy) is the best approach

• Transthoracic discectomy• indications

– best approach from central disc herniations• complications

– intercostal neuralgia

• techniques– can be done with video assisted thoracic surgery (VATS)

• Costotransversectomy• indications

– lateral disc herniation• extruded or sequestered disc

Cervical Disc Herniation• are most frequent at C 6-7 level but also

occur at C 5-6 & to a lesser extent at C4-5 & other levels; - in relatively younger persons soft disk protrussion is more common than hard disk protrussion; - differential diagnosis: - types of herniation: - intraforaminal herniation: - most common type: - cause predominately sensory changes; - posterolateral type: - occurs near near entrance zone of foramen; - causes predominately motor changes; - central type: - if disc herniation occurs more to the midline (ie posterior herniation), then it compresses spinal cord in addition to, or instead of the nerve root; - results in cervical myelopathy:\

• Symptoms: - neck pain from nerve root compression; - pain radiating into ipsilateral upper extremity w/ paresthesias, numbness, or weakness; - pain & paresthesias may be intensified by neck movement, especially by extension or by lateral flexion to side of herniation, & by coughing or straining;

Cervical radiculopathy and Myelopathy

- limitation of neck extension - downward head compression increases pt's radicular pain & paresthesias, especially if neck is flexed to side of involvment; - shoulder abduction relief test: - significant relief of arm pain with shoulder abduction; - this sign is more likely to be present w/ soft disc herniation, whereas, the test is likely to be negative with radiculopathy caused by spondylosis (osteophyte compression)

• - Spurling's Sign: - mechanical stress, such as excessive vertebral motion, may exacerbate symptoms; - the provocation of the patient's arm pain with induced narrowing of the neuroforamen - gentle neck hyperextension with the head tilted toward the affected side will narrow the size of the neuroforamin and may exacerbate the symptoms or produce radiculopathy; - ipsilateral rotation of the neck will also increase radiculopathy; - downward head compression increases the patient's radicular pain and paresthesias, especially if the neck is flexed to the side of involvment; - provocation of pt's arm pain w/ induced narrowing of neuroforamen - oblique cervical extension augments root compression & increases symptoms; - lower motor neuron dysf(x) (muscle weakness & hypotonia, reduction of deep tendon reflexes) at level of cord compression; - upper motor neuron dysfunction (spasticity, clonus, increased deep tendon reflexes, Babinski's sign, reduction of sensation) below level; - loss of erection, bladder, & bowel f(x) may occur;

• Treatment: - surgery is usually performed by a posterior approach through a hemi-laminectomy or by an anterior approach to approach the intervebral disc; - anterior approach: - anterior approach tends to be more popular with orthopaedic surgeons and is especially indicated for central or peri-central disc herniation; - decompression is usually followed by arthrodesis; - posterior approach: - posterior decompression is a smaller operation that takes less time and does not require a bone graft; - posterior decompression is most indicated for far-lateral disc herniation

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