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What is DISH?

  • Diffuse idopathic skeletal hyperostosis


  • A very common disorder
  • Unknown aetiology
  • characterised by presence of non marginal syndesmophytes at 3 successive levels involving 4 contiguous vertebrae

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What is DISH aka ?



What is DISH define by?

  • ( different from Ankylosing spondylitis = MARGINAL SYNDESMOPHYTES)


What are syndesmophytes?

  • Vertical outgrowths that extend across the disc space


Where do syndesmophytes  occur?

  • Anywhere in the spine
  • usually THORACIC T7-11 region, > on RIGHT side thought to be due to the protective effect of the pulsatile aorta on the left thoracic spine!!!
  • Symmetrical ( R+L) in CERVICAL and LUMBAR SPINE

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What is the epidemiology of difuse idiopathic skeletal hyperostosis?

  • Overall incidence 6-12%
  • uncommon before 50 years
  • less common in africans, asians


  • anywhere in spine
  • most common Thoracic spine - Right side >cervical >lumbar
    • thought due to protective nature of pulsatile aorta on left thoracic spine
    • symmetrical sides in cervical/lumbar


What are the risk factors for developing diffuse idiopathic skeletal hyperostosis?

  • Gout
  • Hyperlipidaemia
  • diabetes


What is DISH associated with?

  • Lumbar spine stenosis
  • Cervical spine
    • hoarness
    • sleep apnoea
    • cervical myelopathy
    • dysphagia and stridor
  • Spine fx and instablity
    • Ankylosis creates long lever arm-> displacement with minimal force
    • hyperextension injuries are common


What are the symptoms and signs of diffuse idopathix skeletal hyperextosis?


  • Often asymptomatic & discovered incidentally
  • thoracic/lumbar spine
    • mild chronic pain
    • stiffness esp in mane
      • aggrevated cold weather
  • cervical
    • pain & stiffness
    • dysphagia
    • stridor
    • hoarness
    • sleep apnoea

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What investigaitons are useful in dx of DISH?

  • xrays
    • ap and latera spine
    • non marginal syndesmphytes at 3 successive levels ( 4 continous vertebrae)
    • thoracic syndesmophytes on right side
    • c spine ant bone formation with preservation of disc space ( unlike ank spon)
    • lumbar spine- symmetrical syndesmophytes
    • other joint involvement -elbow
  • Technetium bone scan
    • increased uptake in areas of involvement

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Is Diffuse idiopathic skeletal hyperextosis related to HLA-B27?

  • NO associated with HLA-B28 -pt with DISH and DM


what are the radiographic findings of DISH

  • NON MARGINAL SYNDESMOPHYTES at 3 successive levels ( 4 contiguous vertebra)
  • Flowing candlewax
  • preservation of disc space
  • no ostepenia
  • no assoc with HLA- B27
  • age - older middle age
  • No involvement in SI JOINT

cf ankl spon

marginal syndesmophytes, bamboo spine, ossificiation of disc space, osteopenia, strong assoc wiht HLA b27, younger pts, bilateral sacroilitis

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What is the tx of someone with Diffuse Idopathic Skeletal Hyperextosis?

non op

  • activity modification. physical therapy, brace wear, NSAIDS, BISPHOSPHONATES
    • most cases


    • for lumbar stenosis, cervical myelopathy, adult spinal deformity


What are the complications of DISH?

  • Mortality
    • C spine trauma in DISH
      • 15% tx operatively
      • 67% tx non operatively
  • Heterotrophic ossification
    • increased risk of HO after THR
    • 30-50% for THR with DISH cf <20% wout


Define ankylosing spondylitis?

A chronic systemic autoimmune spondyloarthropathy characterised by

  • HLA- B27 histocompatablity complex positive
  • RH negative- seronegative
  • primarily affecting spine

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What is the pathoanatomy of ankylosing spondylitis?

  • exact mechanism unknown
  • likely autoimmune reaction to an envirnomental pathogen to gentically susceptible individual
  • theories in relation to HLA- B27
    • HLA- B27 aggregates with peptides in joint -> degenerative cascade
  • Enthesitis
    • entheses inflammation -> bony erosions, surrounding soft tissue ossification and joint ankylosis (diff from RA- synovial)
  • Disc space involvement
    • Inflammation of the annulus -> bridging of osteophyte formation- syndemosphyte

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What is the epidemiology of ankylosing spondylitis?

  • 4:1 Male : female
  • affects 0.2% caucasians population
  • usually presents at 30 years
    • juvenile form <16 yrs inc enthesitis
    • fewer than 10% HLA-B27 positive pt have symptoms
  • Genetics
    • HLA- B27 on 6th chromosome, B locus
    • genetic predisposition but mode of inheritance is unknown


What are the dx criteria?

  • Bilateral sacroilitis
  • +/- uveitis
  • HLA- B27


What are the systemic manifestations?

  • Acute anterior uveitis/ iritis
  • Heart disease
  • pulmonary fibrosis
  • renal amyloidosis
  • ascending aortic conditions- regurge, stenosis
  • Klebsilella peumoniae synovitis
    • HLA-B27 more susceptible to these


What are the orthopaedic manifestations of ank spon?

  • Bilateral sacroilitis
  • progressive spinal kyphotic deformity
  • cervical spine fractures
  • large joint arthritis


What is enthesis?

  • Insertion of tendon, ligaments or muscle to bone


What are the symptoms of ank spon?

  • Lumbosacral pain and stiffness
    • most pts
    • worse in mane
    • insidious onset 3rd decade
  • Neck and upper thoracic pain
    • late in life
    • acute neck pain- raise suspicion of fracture
  • Sciatic
  • loss of horizontal gaze
  • shortness of breath
    • costovertebral joint involvement-> reduced chest expansion

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what are the signs of ank spon?

  • Limited chest wall expansion
    • <2cm more specific dx HLA- B27 
  • Decreased spine motion
    • Schober test- used to elevate stiffness
  • Kyphotic spine deformity
    • chin on chest flexion- see pic
    • caused by multiple microfx over time
    • Chin brow to vertical angle
      • measured on lateral 
      • correction of this angle- improved surgical outcome
  • Hip flexion contraction
    • exam in supine and sitting position helps differentiate sagittal plane imbalance due to hip flexion contractures or kyphotic spinal deformity
  • Sacroiliac provocation test
    • faber test
    • flexion/abduction/ ext rotatation of ipislateral hip causes pain

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What imaging is useful in dx ank spon?

  • Xrays spine
    • full length AP, lateral axial spine
    • negative in 50% with spinal Fx
    • Squaring of vertebra with vertical Marginal syndemosphytes- see pic
    • Late vertebral scalloping - bamboo spine
    • measure chin to brow vertical angle
    • xray of pelvis
      • ​ferguson pelvic tilt view
      • xray beam 10-15 degree cephalad-see SI
      • Bilateral symmetrical sacroiliac erosions


  • Will show bony changes but no active inflammation
  • best for dx of Cervical Fx


  • Will detect Inflammation - detect early AS

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What is the tx of ank Spon?

Non operative

  • NSAIDS, COX-2 inhibitors and PT
    • first line of tx for pain and stiffness
    • oral steriods not recommended
  • TNF alpha blocking agents
    • 2nd line
    • infliximab, etancerpt, adalimumab
    • improvement in symptoms


  • depends on cervicothoracic fx
  • spinal deformity
  • large joint arthritis


What is the epidemiology of cervicothoracic fractures in AS?

  • Most occur midcervical and cervicothoracic junction
  • Often extension type- involve all 3 columns
  • maybe occult- consider CT scan
  • High mortality rate 2ary to epidural haemorrhage
    • 75% neurologic involvement
    • neurologic symtpoms often present late


What is the tx of cervicothoracic Fx?

Non operative

  • Traction, orthotic, halo immobilisation
    • stable spine fractures with no neurological deficits
    • low weight traction may faciliate reduction


  • Spinal decompression with instrumented fusion
    • Progressive neurological deficit
    • epidural haematoma with neurologic compromise
    • unstable fx pattern
    • decision to go ant vs post depends on Fx level, presence & location of haematoma & osteoporosis
    • Outcomes
      • high rate of complications
      • progressive deformity
      • nonunion
      • hardware failure
      • infection


What are the tx for spinal deformity with AS?

  • Kyphotic deformity
  • elliminate hip conttractures as reason for deformity


  • Lumbar osteotomy
    • thoracolumbar kyphotic deformity
    • goal to restore sagittal balance & horizontal gaze
    • closing wedge (pedicle subtracting) osteotomy
    • hinge located on ant spine
    • greater deformity correction 30-40o per level
    • better fusion & stability due to direct bony apposition
    • Vertebral body resection
      • entire vertebral body resected and replaced by cage
    • Single-level opening wedge osteotomy
      • ​hinge on post edde vertebral body
      • requires rupture of ALL
  • C7-T1 cervicothoracic osteotomy
    • for chin to chest deformity
    • slight under correction with final chin to brow angle 10o
    • adv vertebral art ext to transv foramen, larger canal diameter
    • post op halo immobilisation used as pt poor bone quality

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What is the tx for large joint arthritis in AS?

  • Asymmetric involvement of large joints
  • shoulder and hip commonly involved


  • Total hip replacement
    • pt with severe arthritis hip 2ary to AS
    • pts have more VERTICAL/ ANTEVERTED Acetabulum
    • may lead to ANTERIOR DISLOCATIONS after THR
  • Bilateral total hip arthroplasty
    • kyphotic deformity due to hip flexion contracture deformity
    • at risk of dislocation


What is the epidemiology of cervical spondylitis?

  • Present in 90% of pts with Rheumatoid Arthritis
  • Diagnosis often missed
  • included 3 main types
    • Atlantoaxial Subluxation
    • Basiliar Invagination
    • Subaxial Subluxation


What is the classification of Rheumatoid cervical spondylitis?

  • Ranawat

  • Class 1- Pain , no neurologic deficit
  • Class 2- Subjective weakness, hyperreflexia, dyssthesias
  • Class 3A- Objective weakness, long tract signs, ambulatory
  • Class 3B- Objective weakness, long tract signs , non ambulatory


What are the signs and symptoms of rhematoid cervical spondylitis?


  • Similar to cervical myelopathy
  • neck pain
  • neck stiffness
  • occipital headaches
  • gradual onset of weakness and loss of sensation


  • Hyperreflexia
  • upper & lower extremity weakness
  • Ataxia- gait instability/loss of hand dexterity


What imaging is useful in dx of cevical spondylitis?

  • Xrays
    • Flexion-extension
      • obtain before elective surgery
  • CT 
    • better for bone anatomy & surgical planning
  • MRI
    • identify degree of spinal cord compression


What is the general tx of cervical spondylitis?

Non op

  • Pharmacology


  • Spinal decompression and stabilisation
    • goal is to prevent further neuroloigcal progression and surgery may no reverse existing deficit


What is atlantoaxial subluxation?

  • Presents in 50-80% pts with RA
  • most common to have
  • Anterior Subluxation of C1 on C2 ( can have lat/post)

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what is the mechanism for atlanoaxial subluxation?

  • A pannus forms between the dens and C1
  • Leads to destruction of Transverse Ligament & Dens

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What measurements are used to define stability on lateral extension-flexion views?

  • Atlanto-Dens Interval = ADI
    • instability = >3.5mm of motion between flexion and extension views
    • instability alone is not an indication for surgery
    • > 7mm = alar ligament disruption
    • >10mm associated with increased risk of neurological injury= surgery
  • ​Space available for cord (SAC) & Posterior atanto-dens interval =PADI same thing
    • <14 mm assoc with increaed risk of neurological injury = surgery
    • >13 mm-most important radiological finding that may predict complete neural recovery after decompression surgery

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What is the tx of atantoaxial subluxations?

Non operative

  • IN stable atlantoaxial subluxations


  • Posterior C1-2 Fusion
    • if ADI >10mm (even if no neuro)
    • SAC/PADI <14mm (even if no neuro)
    • Progressive myelopathy
    • indication- must be able to reduce C1 onto C2 - no need to remove C2 post arch
    • add transarticular screws avoid use of halo
    • Post op ct to identify location of vertebral arteries
  • Occiput -C2 fusion
    • if atlantoaxial subluxation is combined with basilar invagination
    • resection of C1 post arch required for complete decompression
  • Odontoidectomy
    • rarely indicated
    • used as a secondary proceedure when there is redisual anterior cord compression due to pannus formation that fails to resolve with time following a posterior spinal fusion

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What is Basilar invagination?

  • Superior migration of Odontoid
  • Tip of dens migrates above foramen magnum
  • present in 40% RA pts
  • often seen in combination with fixed atlantoaxial subluxation

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Describe the mechanism of basilar invagination?

  • Cranial migration of dens from EROSION and BONE loss between occiput and C1/C2


What lines are useful on lateral xray to dx basilar invagination?

  • Ranawat C1-C2 index
  • Most reproducible measurement
  • centre of C2 pedicle to line conecting the anterior & posterior C1 arches
  • normal  men 17mm, women 15mm
  • distance of <13 mm consistent with impaction

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What is the tx of basilar invagination?

  • Operative
    • C2 to Occiput fusion
      • for progressive canal migration >5mm
      • neurological compromise
      • cervicomedullary angle <135o on MRI
    • Transoral/ anterior retropharyngeal odontoid resection
      • ​for brainstem compromise


What is the epidemioogy of subaxial subluxation?

  • Present in 20% pt wth RA
  • Often occurs mutiple levels
  • combined upper c spine instability
  • lower spine involvment more common with 
    • steriod use
    • males
    • seropositive RA
    • nodules present

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What is the pathophysiology of subaxial subluxation?

  • Pannus formation and soft tissue instability of facet joints and Luschka joints


What is seen of subaxial subluxation on radiographs?

  • Subaxial subluxation of vertebral body of >4mm or 20% = cord compression
  • Cervical height index ( body height/width) <2.0 almost 100% sensitive and specific for predicting neurologic compromise

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What are the tx of subaxial subluxation?

  • Operative
    • Posterior fusion & wiring
      • for >4mm subaxial subluxation in intractable pain and neurological symptoms


What are the operative complications are tx a pt with rheuamatoid cervical spondylitis?

  • Failure to improve symptoms
    • outcomes less reliable with Ranawat Grade 3B
  • Pseudoarthrosis
    • 10-20% pseudoarthrosis rate
    • decreased by extension to occiput
  • Adjacent Level degeneration