The discs involved in cervical spondylosis are between the bones of the spine, made of tough gristle. They hold the spinal bones together and share weight bearing, while allowing shock absorption and a limited amount of movement.
Discs are living material which needs to obtain nutrition and dispose of waste.
There are no blood vessels in the disc, so this exchange of nutrition and waste is by seepage from the bones above and below.
This seepage is helped by our body weight compressing the disc while we are upright, followed by the disc expanding when we sleep.
Nutrients and wastes follow the fluid entering and leaving the discs.
Normal movement of the spine also helps this exchange.
The causes of cervical spondylosis are uncertain, but one cause is probably stiffness of posterior spinal joints, with restriction of this movement and so of fluid exchange.
These paired posterior (back) joints very frequently get stiff or completely stuck. This is definitely a cause of neck pain, but a joint may remain stiff and the pain can settle.
The living cells which maintain the disc (“chondrocytes”) may then be deprived nutrition and die. The gristle loses fluid and shrinks, so an X-ray will show the bones closer together.
The weakened disc bulges, stretching the outer fibers. Bone grows out as knobs (osteophytes) where these fibers are attached around the edge of the discs.
This process of dessication of discs and development of osteophytes does not cause neck pain. Cervical spondylosis diagnosis clinically depends on demonstrating a stiff neck on sidebending.
Stiffness is the only cervical spondylosis symptom unless there are complications.
In cervical spondylosis with myelopathy the bulging disc has squeezed the spinal cord too much. This can produce weakness in limbs and means surgery.
A diseased disc can even rupture. It can then leak irritant material which inflames the nerves leaving the spine between the disc and the posterior joint. Extruded material from the ruptured disc can damage nerves by compressing them.
This can cause very severe arm pain called brachial neuralgia.
A very sensitive way to detect this type of disc disease, is “magnetic resonance imaging”(MRI) which picks up the loss of fluid from the disc.
When a ruptured disc is suspected after your doctor has assessed you, this is very helpful in working out where a pain is coming from as it also shows disc fragments and the nerves.
Sometimes as the disc becomes weaker, it permits abnormal movement between the bones of the spine. This can lead to instability.
X-rays of your neck taken from the side, with your head fully bent down and up, are used to demonstrate instability. An unstable joint will have more movement than the other joints.
Vertebrobasilar artery syndrome ("insufficiency") in cervical spondylosis can be caused by bony knobs pressing on the vertebral artery in the neck.
This may be a cause of drop attacks in elderly people, when there is a sudden, brief loss of muscle strength and the person falls to the floor wide awake.
The little holes in the bone beside the disc, pictured above, are for the vertebral artery to pass through on it's way up the cervical spine.
It is quite close to the action, and has little room to move.
These posterior joints are also called facet joints.
In advanced disease, these posterior joints (labeled P) become arthritic also.
Being a synovial joint, like our knee, this involves loss of gristle and bony knobs at the edges of the joint.
These knobs can narrow down the holes through which our nerves
leave the spine, compressing and irritating them. This can cause arm
pain like sciatica - sharp shooting or burning type.