Acute Disc Injuries Flashcards
Who is at highest risk of an acute disc injury?
Aged 30-50
Males more likely than females
Sustained periods of submaximal loading
What kind of lifting increases risk of acute disc injuries?
Heavy lifting of combined Lx Flexion and Rotation - sustained over time
What are the types of acute disc injury?
Torsional Injury
Internal disc degredation
What is a torsional disc injury?
“Twisting” injury in flexion
Combination of rotation and lateral shearing resulting in circumferential tears of the AF
Why does lifting in flexion increase the risk of torsional injury?
Posterior AF is stretched - usually have already some disc degeneration
What is a internal disc disruption injury?
More common than torsion injury
Degredation of the nucleus and development of fissures inside the disc
How are internal disc disruption injuries graded?
Based on how progressed the internal tear is:
- Grade I = radial fissure within the inner annulus
- Grade II = radial fissure in to the middle annulus
- Grade III = radial fissure in to the outer annulus
- Grade IV = circumferential tear throughout the whole annulus
What causes an internal disc disruption injury?
Sudden compression of a degenerate disc causing the end plate to fail
E.g. due to heavy unaccustomed movement or a fall
How does an end plate ‘fracture’ occur?
When there is internal disc disruption resulting in a tear which penetrates the cartilage end plate
How does an end plate fracture result in disc degeneration?
Buckling of the disc into the end plate increases the volume of the NP = drop in hydrostatic pressure of NP = Inflammatory process occurs disrupting homeostasis = decreased proteoglycans and release of destructive enzymes
What is the overall effect of end plate fractures?
Degeneration of the disc from the NP outwards - loss of water binding capacity and deterioration for nuclear fracture (less able to withstand compressive forces)
What occurs when the degenerate NP extends into the annulus?
Forms fissures and the degraded NP follows the path of least resistance through the AF via fissures - NP ‘herniates’ through the AF
When does internal disc disruption become painful?
When the NP has become degeraded and herniates through the outer 1/3rd of the annulus which is innervated
What type of pain does a contained herniation cause and why?
Diffuse, non-deramatomal somatic and somatic referred pain
Because there is stretching of the outer 1/3rd of AF
Also stretching the PLL and surrounding soft tissues
What type of pain does an uncontained herniation cause and why?
Somatic pain & Radicular pain with potential Radiculopathy
NP penetrates outer AF and PLL (causing somatic pain) and is in contact with spinal nerve root (causes inflammation of the nerve root)
What happens when the NP completely herniates?
Inflammatory cytokines within the degenerate NP cause irritation and compression of the exiting nerve root - causing radicular pain in a dermatomal pattern
What directions can herniation occur and what is the significance?
- Posterolateral - more common due to incomplete lamellae of the AF here
- Central - more serious as can cause cauda equina syndrome in Lx spine
What is the healing potential for AF fissures?
Able to heal by granulation tissue - llamelae are lost so mechanically weaker than normal
What is the healing potential for a herniated NP?
Able to resorb extruded disc material by inflammatory process
Why are Cx spine discs less likely to herniate?
Because NP in cervical disc is fibrosed in mid-teens and so less fluid
What is the effect of disc herniation on the nerve roots?
Compression and stretching of the nerve roots causing increased nerve root tension
Nerve become sensitised by inflammatory chemicals within the degenerate NP
What is the effect of sustained compression of nerve roots on the blood vessels?
Compression of blood vessel surrounding a nerve = increased permeability of vessel = oedema = pain
Interneural oedema = decreased BF = ischemia
What is the effect of sustained compression of nerve roots on their function?
Compression of BVs = oedema = fibroblast invasion = decreased fibre glide = tissue irritation = decreased conductivity and decreased axonal transport
Eventually leads to nerve degeneration and demyelination
What causes radicular pain?
Interneural inflammation and ischemia of nerve roots due to prologued compression
What is the likely cause of radicular pain in patients under 50?
IV disc herniation
What is the likely cause of radicular pain in patients over 50?
Degenerate changes causing lateral spinal stenosis (impinging nerve root in the IV foramen)
