Thoraco-lumbar Disc Disease

Disc Herniation

Epidemiology

• Thoracic:
  • Rare <1%
  • Usually caudal levels (T11-12 most common)
  • Scheuermann’s kyphosis is a risk factor
  • More likely to cause myelopathy
  • Men = Women
• Lumbar:
  • Common
  • 90% >60 years have MRI disc changes
  • 40% <40 years have MRI changes
  • 5% actually become symptomatic
  • Men 3:1 Women
  • L4/5 most common, then L5/S1
  • Risk factors: Smoking; manual work; genetic

Aetiology

• With ageing, disc changes are:
  • Increased Keratin Sulphate: Chondroitin Sulphate ratio
  • Decreased water content
  • Decreased proteoglycan concentration
• MRI features:
  • Hypointense on T1 & T2 – dehydrated
  • Loss of disc height
• Types of herniation:
  • Protrusion: Disc still contained within annulus
  • Extrusion: Disc outside annulus but not free
  • Sequestration: Free disc fragments in canal

Anatomy of Herniation

• Thoracic:
  • Tend to be paracentral – rarely far lateral
• Lumbar:
  • 95% paracentral/posterolateral
    • Through weakest part of PLL
    • Affect traversing root
  • 5% far lateral/foraminal
    • Affect exiting root
  • Axillary herniation:
    • May affect both traversing & exiting root

Diagnosis

• Sciatica is hallmark – usually to below knee
• Differentiate from referred pain to thigh/buttock (same mesodermal lineage)
• May be preceded by low back pain (annular tear)
• History of bending/lifting but not always
• Pain worse on flexion

Imaging

• XR:
  • May show degenerative disease, spondylolisthesis etc.
• MRI:
  • Gold standard for assessing disc herniation – high false positive rate
  • Findings must correlate to clinical features
  • Contrast (gadolinium MRI):
    • Useful for recurrent disc herniation or post-surgery herniation
    • Scar tissue is vascular – high signal
    • Disc is dehydrated & avascular - hypointense on all sequences

Examination

• Nerve root irritation tests:
  • SLR, Bowstring, Lhermitte’s
  • Lesague sign: Contralateral SLR is most specific test
• Rule out cauda equina
• Screen for red flags to rule out tumour/infection

Management

• Non-operative:
  • Natural history is good
  • 90% resolve within 3/12 – disc is resorbed
• Physio:
  • Stay mobile; extension exercises; aerobic exercise; reassurance & support
• Epidural Steroid Injection:
  • Foraminal root injection
  • Caudal
  • Good sustained relief when they work
  • Enables earlier return to function
  • Only effective in 60% though

Surgery

• Best results before 6/12 – do not leave indefinitely
• Indicated for:
  • Failure of non-operative Rx
  • Intractable pain
  • Progressive motor weakness – urgent
  • Cauda Equina – emergency

Technique

• Thoracic Disc:
  • Posterior surgery relatively contraindicated – high rate neurologic injury
  • Options:
    • Anterior transthoracic approach
    • Anterior via costotransversectomy - easier
• Lumbar Disc:
  • Open partial laminectomy & discectomy is gold standard
  • Foraminal discs may be easier via an intertransverse approach (Wiltse)
  • Microdiscectomy & endoscopic no proven long-term benefit

Complications – rare but potentially devastating

• Recurrent or continued symptoms:
  • Most commonly because foraminal root impingement underappreciated
• Nerve Root injury (<1% in lumbar spine)
• Epidural Haematoma
• Epidural abscess
• Dural Tear
• CSF leak/fistula
• Haemorrhage:
  • Anterior perforation through disc into great vessels
  • Pack, close, turn over & stop bleeding via transabdominal approach
  • 50% mortality

Degenerative Disc Disease & Discogenic Back Pain

Epidemiology

• 80% will have back pain during their lives
• 30-50 year olds most common for acute back pain

Pain Generators

1. Disc
2. Facet joints
3. Muscular pain
4. Instability
5. Spondylolysis & Spondylolisthesis
6. Nerve root impingement
7. Stenosis

Disc Generated Pain

• Normal Ageing Degeneration:
  • Proteoglycan content decreases
  • Water content decreases
  • Keratin Sulphate increases compared to chondroitin sulphate
  • Disc height reduction
• End plate microfractures
• Disc Herniation
• Altered mechanics & spinal loading:
  • Osteophyte formation
  • Facet joint arthrosis
  • Segmental Instability

Modic Changes

• Represent MRI features seen in the vertebral body & endplates with DDD

Lumbar Segmental Instability

• Caused by degenerative disc disease, facet arthrosis & subluxation
• Classic symptom: Catch & pain going into extension from a flexed posture
• Imaging shows >4mm translation on flexion, extension views
• Can be difficult to correlate with symptoms
• Treatment: Surgical fusion if thought to be cause of pain

Diagnosis of DDD

• Rule out red flag lesions
• Rule out treatable radiculopathy & stenosis
• XR only if pain persists >6 weeks with no red flags

Waddell’s Non-organic Signs

1. No pain on distraction
2. Vague symptoms & history
3. Simulation pain – e.g., Axial pressure causes low back pain
4. Pain on light touch
5. Non-dermatomal pain
6. Numbness & pain simultaneously
7. Hysteria

MRI

• Disc height deterioration
• Loss of signal in disc
• Facet hypertrophy
• Subluxation
• Modic changes

Management

• Non-operative is mainstay:
  • Physiotherapy:
    • Aerobic exercise program
    • Core stability training
    • Support & education
    • Multimodal analgesia
  • Chiropractic treatment:
    • Some evidence this works
• Surgery:
  • Results are unpredictable
  • Rule out other diagnoses first
  • Diagnostic injections pre-surgery are useful
  • Best results are in:
    • None of Waddell’s signs
    • Modic type 1 changes
    • Single level disc disease
    • Other treatments failed

Technique

• Arthrodesis – gold standard:
  • PLIF, TLIF, Posterior fusion, Anterior fusion
  • Instrumentation improves fusion rate which improves outcome
  • No technique shown to be superior
• Non-Fusion options:
  • Interspinous distraction devices – more for stenosis
  • Dynamic Stabilisation systems:
    • Not validated in literature for chronic low back pain
  • Total Disk Arthroplasty:
    • Good results for single level disease
    • Not for multilevel disease or instability
    • Long-term results and revision issues not known