We have 23 vertebrae in our spines and 23 intervertebral discs (though some people can have 24) The intervertebral discs are spacers between each vertebra which not only act as a fulcrum for movement between the vertebrae above and below but they also absorb compression through our spine.
The discs are made up of the Annulus Fibrosus and the Nucleus Pulposus.
The Annulus is the outer casing of the disc. It is made of interwoven collagen fibres which give structure and support to the disc. It also gives attachment of the disc to the vertebrae above and below.
The Nucleus Pulposus has a jelly like centre to the disc acting as a soft pivot point of movement between the vertebrae. Also made from collagen it is also has a water content of 90 percent in childhood, sadly decreasing as we get older to under 60 percent and less if the spine has sustained any previous trauma.
A simple X ray (Radiograph) can show diminished space between the vertebrae due to this loss of liquid content within the disc.
This image shows the 5 intervertabral disc spaces of the lumbar spine. The top 3 vertebrae have good intervertebral disc spacing however the lower show signs of discal narrowing.
Intervertebral disc narrowing can arise from many reasons though the most common are overloading due to heavy physical repetition from sport or occupation, being overweight, repetitive compression through the spine such as horse riding or long distance running and direct trauma such as a fall or road traffic accident.
Disc problems in the cervical spine frequently occur following a whip lash injury to the neck as in a car crash or a direct blow to the head ..for example .. a dive into the shallow end of a swimming pool!
The term “slipped disc” is somewhat misleading, implying that the disc has altered its position when what is actually happening is that the Nucleus has sustained enough force to cause it to bulge and even herniate through the Annulus which then puts pressure on the nerve root where it is exiting the spine.
Signs of a slipped disc in the neck will include pain, loss of range of movement in the neck and if the nerve root has been compromised, then there will be some neurological symptoms which may manefest as referred pain or numbness in the upper arm or tingling and/or numbness in the fingers.
The most common episode from a slipped disc in the lower back is the notorious Sciatica which can cause a pain in the buttocks, particularly when siting or driving and is generally eased when walking. These symtoms derive from Lumbar and Sacral nerve origins L4/5 and L5/S1. Pain can travel down the back of the thigh, lower leg and into the foot causing weakness in the hip extensor muscles, such as climbing stairs.
It is important to note that sciatic nerve disc impimgement can occur showing only leg symptoms not necessarily with any associated back pain.
When we are upright the weight of our body under gravity is absorbed not only from our spine but also through our hips knees and ankles. When in sitting the weight is absorbed only in our lower spine through the pelvis which is why sitting and driving cause the greatest pressure through the lower discs.
A little higher up the lumbar spine is where the Femoral nerve exits to supply the legs with muscle and sensory innervation. The same rules apply as with the Sciatic nerve disc herniations although the pain distribution is different. Nerve roots for the Femoral nerve exit from L2/3 and L 3/4 and supply the front of the hip and upper thigh muscles and so there would be sensory issues down the front of the thigh and in a more extreme discal herniation there may be a reduced reflex and muscle strength in the quadraceps muscles.
It is not possible to palpate the discs as they are surrounded by bone protecting the spinal cord and X Ray only shows the disc spacing so accurate diagnosis as to severity and direction of the disc bulge or herniation is done with Magnetic Resonance Imaging which is non invasive imaging technology that can provide 3 dimensional pictures of the discs, providing your Orthopaedist and Physiotherapist a much clearer view of how to treat your symptoms.
Photo credits: @ Mayo Foundation for Medical Education & Research
Tracey Evans MCSP SRP COFIB col 220
Tel : +34 609 35 38 05
