the intervertebral disc / disk comprises the annulus fibrosus and the nucleus pulposus.
degenerative disc disease (DDD) results from proteoglycans within the nucleus pulposus breaking down and losing their ability to retain water, thereby reducing the volume of intervertebral discs and decreasing their weight-bearing capacity, subsequent mechanical loading then shifts to the annulus fibrosus, creating fissures and tears that leak crucial factors in the pain to cascade into the intradiscal space and trigger inflammation
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 and often has an abrupt sudden pain event often following seemingly innocuous triggers but can follow a significant event such as lifting heavy weights, over-reaching or twisting, or perhaps due to coughing or sneezing with the spine in a vulnerable position
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 however, genetic factors may account for 8.1% of the common variation in LDH risk
1)
at least 64 gene regions are associated with risk
2)
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
3):
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
they develop in some 14% of people