Lumbar Disc Injuries
In our last blog, we learnt about the anatomy of the lower back (lumbar spine) and what structures can contribute to low back pain. We learnt that the spine is a complex structure made up of bony vertebrae stacked one on top of another, separated by spongy cushions known as intervertebral discs, and that the discs have several important functions including shock absorption, keeping the vertebral column stable, and allowing movement of the spine by giving the vertebrae pivot points.
You may remember that the disc is made of 2 parts – the elastic outer shell made of cartilage rings (annulus fibrosis) and the jelly-like centre (nucleus pulposus). Intervertebral discs can handle quite a lot of pressure without damage, with movement happening within the annulus as it adjusts to the pressures placed on your spine. However, certain types of pressure can damage the outer shell and push the contents of the jelly-like centre out.
The degree of injury to an intervertebral disc can vary considerably from mild disc strains or damage contained within the disc, to mild, moderate or severe disc bulges, through to complete rupture of the disc resulting in herniation of the nucleus through the wall of the annulus. Age can also affect discs, leading to them drying out or thinning, also resulting in pain.
The following picture illustrates the different types of disc injuries that can occur:
Degenerative Disc Disease
Degenerative disc disease generally occurs as part of the aging process. The discs of a young child are plump and moist, but as we age, the water content in the discs reduces until the discs become comparatively thin and hard.
As a result of these changes to the discs, it is thought that friction between the bones of the spine increases, resulting in bone spurs or osteophytes forming around the discs.
Often these age-related changes do not cause any problems, however in some people it can result in pain, most commonly after holding the same position (usually sitting or standing) for too long. Degenerative disc disease is one of the most common causes of chronic back pain in older people.
Bulging or Protruding Discs
Most people will have heard the term “slipped disc”, however this term is not entirely accurate. “Slipped disc” paints the picture that the disc has moved out of position, however they are in fact held firmly in place by surrounding ligaments, muscles and vertebrae. Instead, “bulging”, “herniated”, “ruptured” or “prolapsed” are more accurate terms for disc injuries, and describe a continuum of differing severity.
When a bulging disc, disc herniation or disc rupture occurs, it is usually due to either:
- a pre-existing weakness in the annulus (accumulated microtrauma), or
- a sudden increase in pressure through the disc causing fibres of the annulus to tear (sudden unexpected load)
Accumulated microtrauma over an extended period of time can lead to disc injury. Repeated microtrauma can cause a disc to lose its ability to absorb shock and its outer wall can become weak. Poor posture is the best example of accumulated microtrauma. Extended periods in a slouched position can lead to overstretching and weakness of the annulus fibrosis. Over time, the fluid contained in the nucleus of the disc is displaced and can bulge outwards into the annulus.
A sudden unexpected load can occur in traumatic situations, such as a motor vehicle accident, or through an incident such as lifting an excessive load. In these cases, unexpected load or torsion on a disc can result in tearing of the fibres of the annulus fibrosis. As with accumulated microtrauma, this allows the fluid in the nucleus to be displaced in to the annulus.
In extreme cases of both types of injuries, the fluid in the nucleus can burst through the outer cartilage, causing severe pain.
Disc injuries follow a continuum of increasing severity. These are:
- degeneration – the outer wall becomes weak and the disc bulges
- prolapse – the nucleus of the disc pushes out into the annulus
- extrusion – a tear in the outer annulus allows the nucleus to completely protrude through
- sequestration – the nucleus protrudes completely through the annulus, with fragments of disc material free-floating
The following pictures illustrate this continuum of disc injuries:
Image credit: https://perfectformphysio.com.au/portfolio/disc-injury/
How do disc injuries cause pain?
Disc injuries can cause pain in a few different ways.
Although intervertebral discs are generally thought to have a poor nerve supply, recent studies have shown that the outer layers of the annulus do have some nerve supply which mainly consists of sensory nociceptive fibres, which are the nerve fibre types that detect pain.
Studies of degenerative intervertebral discs show an increase in these nerve fibre types, resulting in the pain associated with degenerative disc disease, although the exact reasons for the increase in the growth of nerve fibres are not known.
In a more acute injury, an inflammatory response is triggered by the body which causes stimulation of the pain fibres mentioned above, resulting in a pain sensation.
When an intervertebral disc bulges far enough, it may come in contact with nerve roots, causing irritation of the nerve and resulting in pain or other symptoms such as numbness, pins and needles or weakness. Depending on which nerve is affected, these symptoms may be felt in other areas away from the back, such as the leg or foot. This is commonly known as sciatica…the topic of our next blog!
Symptoms of Disc Injuries
The symptoms of a lumbar disc injury can vary according to its location and severity. Some common signs can include:
- low back pain
- pain radiating down one or both legs
- increased pain associated with bending or sitting down for a prolonged period of time
- increased pain with activities such as coughing or sneezing
- pins and needles, tingling or numbness in one or both legs
Causes and Risk Factors
Common causes of disc injuries include:
- poor sitting and standing postures, especially when maintained for long periods
- poor lifting techniques, especially when twisting and bending
- prolonged periods in slouched or forward bending postures
Some people are more susceptible to disc injuries than others. Risk factors that may increase your risk include:
- advancing age
- obesity – carrying extra weight increases the stress on the lumbar spine
- poor muscle tone
- gender – men have approximately twice the risk of disc injury compared with women (although this is most likely because men generally tend to have more physical jobs than women)
- lack of regular exercise
- physically demanding work – pulling, pushing and twisting actions can add to risk if done repeatedly
- smoking – nicotine reduces blood flow to spinal discs which speeds up the degeneration process and affects healing
- poor posture
- incorrect lifting techniques
- family history
How is a disc injury diagnosed?
Your doctor or physiotherapist will usually suspect a disc injury based on the history of your injury and the behaviour of your symptoms. They will then perform a thorough assessment to confirm a disc injury and to determine whether there are any signs of nerve compression. The most accurate diagnostic tests to confirm the presence and severity of a disc injury are MRI or CT scan.
However, it is important to note that many people who show evidence on imaging of damaged discs often have no symptoms. Whilst imaging can provide valuable information in some instances, findings do not always correlate with a patient’s symptoms, and therefore should be used in conjunction with the full clinical picture to guide management.
Most minor and moderate disc injuries can be managed conservatively without the need for surgery. Treatment for a disc injury is usually centred around encouraging the fluid in the nucleus to remain in the centre of the disc to allow all the damaged outer layers of the annulus to heal.
Treatment can include:
- exercises or advice on the best positions to stay in to reduce pressure on the disc
- taping or bracing
- manual therapy
- heat or ice treatment
- an exercise program to improve strength and flexibility
- anti-inflammatory and pain-relieving medications
with the aim of first reducing pain and inflammation, then restoring normal joint alignment and range of motion to gradually restore full function. The final stage is to prevent a recurrence by improving strength, flexibility, and muscle control.
Back pain is a major concern in Australia, with 70-90% of us suffering from some form of low back pain in our lives. If you experience even back discomfort – either during activity or rest – it’s likely you fall into this group. Remember, accumulated microtrauma over an extended period can lead to disc injury, so take heed the warning signs and book yourself in for a once over.
If you do present with symptoms of probable injury, your physiotherapist will guide you on the most appropriate treatments and develop an individualised program based on your functional requirements. For more information, speak to us at Revive, or your local healthcare practitioner!