I see a lot of people coming through my clinics in the city at Sydney Osteopathic Medicine and at Harley Place Health in Bondi Junction with back pain problems arising from their discs, so I have decided to write a little about discs to help inform you about these irascible parts of our back and the nature of damage to them. I will also talk about how an integrative osteopathic approach can help you manage these conditions or where other approaches may be advised.
Today I am going to talk a little about the basic anatomy of the intevertebral discs.
The intervertebral discs are soft but tough cushions lying between the spinal vertebrae, with the exception of between the first and second cervical (or neck) vertebrae.
They have a threefold function:
1) They form a cartilaginous joint between each vertebra and act as the spine’s shock absorbing system.
2) They are anchored to the bony vertebra via the cartilaginous end plates of the bones. In this way the discs act as ligaments holding the vertebra of the spine together.
3) They also help promote some vertebral movement acting as a pivot point. While movement between individual vertebra is limited, the motion of a region is increased when the action of several discs combine together.
The vertebral body is composed of hard cortical bone on the outside and less dense cancellous bone on the inside. The top and bottom of the vertebral body are called the end plates. The intervertebral disc, sandwiched between two vertebral bodies, is attached to these end plates. Changes in the disc may be accompanied by changes in the end plates.
The disc contains a tough outer layer known as the annulus fibrosis and the soft jelly-like inner nucleus pulposus.
The annulus fibrosis consists of 15-25 concentric collagen, or fibrous, sheets wrapping round the outside of the disc a bit like the layers of an onion. The fibres of one layer are at 90 degrees to the adjoining layer. This configuration makes them very tough and able to contain the pressurized inner nucleus and helps distribute pressure evenly across the disc.
The nucleus is the softer water-rich central portion which has a gel like consistency and is roughly spherical in shape. It is placed under very high pressure when we are upright, especially in the sitting position. It acts to support the downward weight of the body and to allow the bones to pivot around its shape. It acts as a shock absorber, taking on the impact of the body’s activities.
The pressure in the nucleus is 5 – 15 times higher than blood pressure. As a result, blood cannot reach the nucleus; Also, there are no nerves in this central nucleus or even in the inner two thirds of the annulus. The nerves are only found in the outer one third of this fibrous ring. This explains why the disc can degenerate without pain until it affects this outer layer. While the disc may wear out, there are no nerves to receive and transmit pain.
There are a number of conditions that are affected by the wearing down and damage to the discs including degenerative disc disease, disc bulge, disc herniation and internal disc disruption leading to a variety of presenting symptoms. I will go on to talk about some of these and how an osteopathic approach may help you in further blogs.