see also:

• back pain in the ED
• sciatica
• cauda equina syndrome (CES)
• high lumbar disc prolapse
• cervical disc prolapse

• the intervertebral disc / disk comprises the annulus fibrosus and the nucleus pulposus.
• lumbar disc herniation occurs when the nucleus pulposus protrudes from the defective annulus fibrosus because of its degeneration and it's a common and important cause of low back pain.
• 1st described as being due to vertebral disc prolapse in 1939, it has traditionally been ascribed to aging, degeneration, extended sitting (eg office workers, taxi drivers), or poor heavy lifting techniques.
• recent evidence suggests at least 60% of the aetiologic factors are genetic
• a normal 20 yr old can sustain a force load on the annulus of up to 800kg without trauma to the annulus fibrosus whereas, an average 50 yr old is likely to sustain damage with loads over 450kg
• the load on the lumbar disk in an average adult:
  • whilst standing is ~50kg
  • whilst bending forward to lift something on the ground is ~350kg (7 fold increase due to mechanics of leverage), and worse, instead of the forces being distributed equally around the disc, they are now directly mainly backwards and this is where disc prolapses occur
  • whilst bending forward to lift a 10kg object off the ground held at arms length is ~800kg!
  • keeping your back straight and a 10kg load close to the body can reduce the load on the disc from 700kg to only 100kg as well as keeping an even spread of forces on the disc fibres!
• localised degeneration of the annulus fibrosus fibres results in disc bulge and later potentially prolapse - this is largely a sign of ageing and most cases are asymptomatic, screening of asymptomatic individuals revealed ¹⁾:
  • of 40 yr olds, 68% had evidence of disc degeneration, 50% a disc bulge and 33% disc prolapse
  • of 50 yr olds, 80% had evidence of disc degeneration, 60% a disc bulge and 36% disc prolapse
  • of 60 yr olds, 88% had evidence of disc degeneration, 69% a disc bulge and 38% disc prolapse
  • of 70 yr olds, 93% had evidence of disc degeneration, 77% a disc bulge and 40% disc prolapse
• 75% of flexion and extension occurs at the lumbosacral joint (although little torsion occurs here) and 20% at L4/5 while only 5% at L1-3
• although it can occur at any spinal level, it is most common at the L4-5 and L5-S1 levels with only 1-2% occurring at upper levels (L1-2 or L2-3).
• it most commonly affects men aged 30-50yrs but also occurs in women and those outside this age range
• an acute symptomatic prolapse causing sudden severe pain may be precipitated by sneezing, coughing, lifting, twisting or even just pulling weeds out of the garden

• disc prolapse at L1-2 is rare and thus L1 radiculopathy is uncommon
• causes pain, paresthesia, and sensory loss in the inguinal region.

• there is marked overlap of L2,L3, and L4 myotomes and thus these are often grouped together
• pain radiating to the anterior aspect of the thigh down into the knee and occasionally down the medial aspect of the lower leg as far as the arch of the foot.
• weakness of hip flexion, knee extension, and hip adduction
• reduced knee reflex

• most common lumbar radiculopathy
• pain radiating lateral aspect of the leg into the foot
• weakness of foot dorsiflexion, toe extension, foot inversion, and foot eversion
• sensory loss is confined to the lateral aspect of the lower leg and dorsum of the foot, but may be obvious only when testing sharp sensation in the web space between the first and second digits
• reflexes generally normal
• the L5 root can be compressed by:
  • a central disc protrusion at the L2-3 or L3-4 level
  • a lateral disc protrusion at the L4-5 level
  • a disc protrusion into the foramen at the L5-S1 level

• pain radiates down the posterior aspect of the leg into the foot from the back
• weakness of plantar flexion (gastrocnemius muscle)
• sensation reduced on the posterior aspect of the leg and the lateral edge of the foot.
• loss of ankle jerk

• may be caused by a large central disc compressing the nerve roots intrathecally at a higher level such as L5
• sacral or buttock pain that radiates down the posterior aspect of the leg or into the perineum
• weakness may be minimal
• urinary and fecal incontinence
• sexual dysfunction
• see also cauda equina syndrome (CES)

• it is likely that genetics plays a large role (perhaps > 60%) in the degenerative and herniation processes²⁾
• lumbar disc degeneration is determined by:
  • multiple genes
  • some environmental factors
  • gene-gene interactions
  • gene-environment interactions
• Collagen I is an important ingredient of bone and anulus fibrosus of disc.
• Collagen IX, a structural component of nucleus pulposus and annulus fibrosus of intervertebral disc, is considered to serve as a bridge between collagens and non-collagenous proteins in tissues.
  • tt is a heterotrimer of three Alpha chains, 1(IX), 2(IX), and 3(IX), encoded by the genes COL9A1, COL9A2, and COL9A3, respectively.
  • it consists of three collagenous (COL1 to COL3) and four non-collagenous (NC1 to NC4) domains
  • risk of disc prolapse for a given genetic mutation appears to be population specific
    • some populations with COL9A2 with the Trp2 allele seem pre-disposed while the risk is 3x for those with Trp3 allele in some populations
• the vitamin D receptor gene may also be responsible for increased risk
  • it appears that the t allele of vitamin D receptor Taq I is associated with a high risk of degenerative disc disease and disc bulge developing, especially in individuals younger than 40 years.
  • however, as this gene is on 12q12 chromosome and close to the genes for type-2 collagen (COL2A1) gene and insulin-like growth factor (IGF) type-1 gene, the polymorphism may only be a marker for mutations in those genes
• matrix metalloprotease-3
  • the 5A allele of the human MMP-3 promoter may be a crucial risk factor for the acceleration of intervertebral disc degeneration, especially in the older population.
• interleukin-1
  • contributes to disc degeneration by inducing enzymes that destroy proteoglycan and it is involved in the mediation of pain.
  • The TT genotype of the IL-1 gene was associated with more than a 3-fold increase in the risk of disc bulges among middle-aged occupationally active men.
  • -511T>C SNP in IL-1β gene appears to associate with lumbar disc disease in Chinese
• CILP-TGF-beta system
  • a single nucleotide polymorphism in the CILP (cartilage intermediate layer protein) causes inhibition of transforming growth factor beta (TGF-beta) and is associated with increased prevalence of prolapse.³⁾
• PARK2 gene
  • it appears this gene may be switched off in people with LDD