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Tuesday, November 5, 2013

Medical Media Images Patient Information Article: What is a Lumbar (low back) Disc Herniation?

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What is a Lumbar (low back) Disc Herniation?

Disc herniations are also called “slipped discs” or “ruptured discs”. When a patient has a disc herniation, the outer ring of the disc (annulus fibrosus) ruptures and allows some of the softer inner core material (nucleus pulposus) to escape. An analogy would be a tube of toothpaste which was stepped on where the cap comes off and some of the toothpaste leaks out.

                                                                 
This image is an MRI scan of the low-back (lumbar spine). The front of the spine is to the right, the back to the left. The vertebrae are shown in orange, separated by the discs in green. A large disc herniation is shown in red where the disc material has leaked out of the center of the disc and has been pushed into the spinal canal next to the spinal nerves.
What should I know about the Anatomy of the Lumbar Spine (low back) to better understand a Disc Herniation?


 
 
Figure 1: This illustration shows the spine from the side. The front of the spine is to the right, the back to the left. The discs between the vertebrae are shown in blue. A disc herniation (red) can be seen pushing backwards towards the spinal nerves (yellow).


Figure 2: This illustration is a cross-section (slice cut across the spine) of a vertebra. The front of the vertebra is at the bottom, the back at the top. The discs outer ring (annulus) in green is seen separated, allowing a disc herniation (red) to push out through it. The material of the disc herniation originally belonged to the nucleus (green)
 
What is the Difference between a Lumbar (low back) Disc Bulge, Disc Protrusion, Disc Herniation, and a Disc Fragment?
It is often thought that any change in the disc beyond a normal and health appearance is a disc herniation. This is not the case. There are several different changes in the shape of the disc which can occur:

1. Normal Disc

                                                              
Figure 1: This image is an illustration of a cross-section (cut across the spine) of the spine. The front of the spine is at the bottom and the back at the top. The disc’s core (nucleus) is shown in green and the outer ring (annulus) in blue. The canal in the center of the vertebra is also shown, as is the lamina bone on the back of the spine.

2. Disc Bulge


                                                          
Figure 2: This image is an illustration of a cross section (cut across the spine) of the spine. The core of the disc is seen bulging outward against the outer ring.
 
A “disc bulge” is a change in the shape of the disc where the outer layer (annulus fibrosus) is weakened and allows a change in the shape to happen. The outer layer is only weakened to the point where it allows the pressure from the inner core to change its shape, but will not allow material to actually push all the way through and herniate. To qualify as a “bulged disc”, the change in the disc or bulging has to consist of more than 50% of the circumference of the disc when looking at it from the top down (cross-section). An analogy would be a hamburger which is too big for its bun and bulges out. Disc bulges are often part of the normal aging process of the spine and may not be part of a spine disease.


3. Disc Protrusion 

                                                                                                         

Figure 3: This image is an illustration of a cross section (cut across the spine) of the spine. A portion of the core of the disc is seen protruding outward against the outer ring, pushing it towards the spinal canal.
 
A “disc protrusion” is a change in the shape of the disc where the outer layer is weak in a smaller area. This weakness is more profound than in a “disc bulge” and allows that part of the disc to push out significantly more but in a smaller area. In a “disc protrusion”, some of the core material (nucleus) will push very hard against the weakened area and its material will be part of the protrusion, but not leak out through the outer ring (annulus) of the disc.
 
 
4. Disc Herniation
 
                                                               
Figure 4: This image is an illustration of a cross section (cut across the spine) of the spine. A portion of the core of the disc is seen braking through the outer ring, herniating into the spinal canal.

 
 
 
A “disc herniation” goes beyond what happens in a disc bulge or a disc protrusion. To qualify as a true herniation, core material (nucleus pulposus) of the disc must have escaped from the main part of the core. Sometimes, a small amount of annulus still remains, coating this material, while at other times the core material is completely outside the outer ring (annulus fibrosus) and becomes a disc fragment.
 
5. Disc Fragment
 
                                                      
Figure 5: This image is an illustration of a cross section (cut across the spine) of the spine showing a piece braking loose from a disc herniation and pushing out into the spinal canal. This is called a “Disc Fragment”.

 
Who is most likely to get a Lumbar (low back) Disc Herniation?
A true disc herniation is most common in younger adults aged 35-45, but can occur at any age. The rarest cases occur in children.
Studies have found that disc herniations are present in 5% of the population under the age of 40 who have no symptoms. Over the age of 40 this number doubles to 10%. Very few of these people actually have symptoms.
The most common spinal levels for discs to herniate are at the two lowest Lumbar (low back), L4/5, and L5/S1 disc segments.
 
Which part of the Lumbar (low back) Disc is most likely to herniate?
 

This illustration is a cross-section of a vertebra (slice cut across the spine). The front of the spine is at the top, the back at the bottom. A piece of the core of the disc (nucleus) shown in blue can be seen pushing through the outer ring (annulus) shown in blue. This disc herniation (red) can be seen pushing on a spinal nerve which is getting inflamed (red).
The most common area for a herniation is on the sides of the back of the disc (posterior-lateral), where the outer ring (annulus fibrosus) is thinnest. Next to this part of the disc we have a spinal nerve on each side. When a disc herniates in this location, a spinal nerve can be affected. Depending on how much disc material herniates, a spinal nerve can either be irritated and inflamed or actually compressed.
 
How common are Lumbar (low back) Disc Herniations?
 
Lumbar disc herniations account for only 5% of all low back problems, however they are the most common reason for Sciatica (Nerve Root Pain). They are also the most common reason for surgery of the spine.
 
Why do Lumbar (low back) Disc Herniations happen?
 
Disc herniations happen for a variety of reasons. In some patients it is the final result of many small injuries. For instance, patients who work in manual labor and are exposed to frequent heavy lifting may have lifting injuries from time to time. In this case, the outer ring of the disc (annulus fibrosus) may become inflamed and eventually gets weaker. When it reaches the limits of its ability to keep the inner core (nucleus) in its place, it may take only a small event such as coughing or sneezing to completely rupture the outer ring (annulus fibrosus). These patients are often surprised that they could have herniated a disc from a cough or sneeze. The reality is that the disc herniation was the result of many different events which happened over time and not just the cough or sneeze.
Other patients have a relatively normal disc, but suddenly overload it through a significant unusual weight loading which suddenly increases the pressure inside the core of the disc. The outer ring (annulus fibrosus) which normally could resist the force of incremental changes cannot compensate for the sudden, dramatic pressure against it and ruptures. This can happen in patients who lift a weight which is much heavier than what they are used to, or lift it with poor posture (legs straight, rather than bent). An example would be someone who is normally relatively sedentary and then has to move a refrigerator.
Disc herniations can also have a genetic component, i.e. can run in families. Sometimes one of the genes in charge of making a certain disc protein can be defective, leaving the disc weakened from birth.
Stay tuned for our next Blog, where we will discuss the Symptoms and Treatments for Lumbar (low back) Disc Herniations.
 
 

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