Degenerative Disc Disease
physiotherapist in markham showing his patient a spine model.
In order to understand degenerative discs, it’ll first be important to understand what a normal and health disc is, and how it normally ages.
Normal disc aging
The most common feature of an aging disc is the loss of proteoglycan molecules from the nucleus of the disc. Proteoglycans are proteins that are found in abundance in the disc. It is responsible for keeping the disc hydrated so that it can create hydrostatic pressure to resist forces. This hydrostatic pressure also prevents unnecessary innervation of pain sensitive nerve endings into the disc.
When proteoglycan volume is decreased, so does the hydrostatic pressure. This leads to growth of pain sensitive nerve endings into the disc, ultimately leading to low back pain.
Currently it is proposed that the initial cause of proteoglycan loss is a decrease in nutrition. This happens secondary to a loss of discal blood supply above the vertebral end-plates.
What affects disc aging?
Disc aging can be affected by lifestyle factors. Lifestyle factors that decrease nutritional delivery to the disc can lead to disc aging or degeneration. Some factors include:
Smoking
Diabetes
Exposure to vibration frequencies (truck drivers)
End-plate calcification
The loss of proteoglycan content is progressive and can create a ‘snowball effect’. This is due to the combined effect of losing nutritional supply and the decrease in hydrostatic pressure. A decrease in hydrostatic pressure can slow the production of proteoglycans by disc cells, causing a further decrease of disc hydration.
Negative effects of losing hydrostatic pressure
The loss of hydrostatic pressure has two main negative effects on the disc.
As previously mentioned, the loss of pressure will lead to a decrease in circulating proteoglycan aggrecan molecules. This is because the disc cells require a hydrostatic pressure of 3 atm to function normally.
It will change the compression load distribution. Axial loads will be distributed to the outer rim of the disc instead of being evenly distributed through the disc. This leads to suboptimal loading of the disc, and increased stress on the periphery of the disc. The areas that will experience increased loads include the outer anulus, zygapophyseal joints, and the ring apophysis.
How do discs distribute stress?
A healthy disc’s stress profile will reveal even distribution of stresses throughout the disc. Even distribution of forces is observed between the anterior and posterior disc, with both vertical and horizontal forces.
As the disc starts to age, the stress profile reveals increased concentrations of stress in the posterior annulus. The rest of the disc experiences a relatively even distribution of forces throughout the rest of the disc. This type of stress profile is that of a middle aged disc.
In old age the stress profile of the disc reveal multiple stress concentrations along the annulus. Multiple peaks and valleys are observed in the stress distribution along the disc.
Figure 1. Stress profiles of a healthy, middle aged, and old age disc.
Degenerative disc disease
A degenerative disc is an aging disc that starts to cause pain. Unlike an aging disc, degenerative disc disease (or DDD for short) is thought to be caused by trauma to some extent. About 10% of the population will develop life long back pain as the result of accelerated disc aging.
It is important to note that some health care practitioners may incorrectly use DDD and natural disc aging interchangeably.
Two types of disc degeneration
There have been two main types of DDD observed based on the type of structural damage occurring in the disc:
Endplate-drive disc degeneration and endplate defects
Annulus-drive disc degeneration and radial fissure and/or disc prolapse
Endplate-driven DDD
This type of degeneration is due to the inwards collapse of the annulus. It has high genetic relevance, and mostly affects discs in the upper lumbar spine and the thoracic spine. This type of back pain usually starts to develop before the age of 30, and is usually of moderate intensity. This type of DDD is associated with compressive injuries such as a fall on the buttock.
Endplate-driven DDD occurs when the vertebral endplate becomes damaged through a high compressive load (such as falling on the bum from an elevated surface). This can subsequently cause a Schmorl’s node to form. A Schmorl’s node is when nuclear material from the disc has driven through the end plate and into the vertebral body. This relocation of nuclear material then causes a decrease in hydrostatic pressure. As previously mentioned, once this occurs, increased stress will then be experienced at the periphery of the disc, with emphasis on the posterior aspect of the disc.
Annulus-driven DDD
This type of DDD has low genetic relevance and often affects the low lumbar spine. This type typically progresses after the age of 30 years, and can lead to high intensity back pain and sciatica. This type of DDD has been associated with repetitive stress injuries involving bending and lifting.
Why do some aging discs cause pain and others do not?
The reason why some aging discs become painful is still controversial. There are a two known risk factors that can contribute to the development of DDD:
Traumatically induced damaged to the annulus or the endplates
Genetics
It is thought that there may be a genetic link relating to the collagen found in discs, blood supply, or disc metabolism. It is also believed that inherited small discs, heavy torsos, or small internal levers are linked to DDD.
Additionally, gene mutations relating to the production of discal collagen, discal proteoglycan aggrecan molecule, and a Vitamin D receptor gene has been associated with DDD.
How does DDD cause pain?
As it turns out, the actual process of developing DDD is not thought to be painful. Rather, it is the end phase of disc degeneration and associated conditions that can cause pain. This occurs as the degeneration causes other issues to occur, namely internal disc disruption, disc herniations, and nerve in growth.
Internal disc disruption occurs when the loss of hydrostatic pressure causes the annular fibers to separate and tear. These weakened areas can cause the disc to bisect allowing the nuclear material to travel to the outer pain sensitive regions of the disc.
Disc herniations can cause pain as nuclear material exits the disc and compresses your nerve roots. To learn more about disc herniations, read about it here.
As previously mentioned, the loss of hydrostatic pressure can allow nerve in growth into the disc. The nerves that can be affected include the recurrent meningeal nerve (or sinuvertebral nerve) and the grey rami communicante nerve. Normally these nerves only innervate the outer 1/3 of the annulus (and are therefore not exposed to the inner nuclear material). However, when hydrostatic pressure is lost, these nerves can begin to grow into the inner aspects of the annulus. These nerves can then be exposed to degenerated nuclear material, and pain can occur as these pain sensitive nerves become chemically irritated.
What are my treatment options for DDD?
Pain associated with a degenerative disc can be managed by a qualified physiotherapist, chiropractor or acupuncturist. Using a mixture of techniques such as myofascial release, electroacupuncture, cupping therapy, and exercise rehabilitation you can recover from DDD pain. To book in a visit at a Rehab Hero clinic click the button below.
chiropractor in markham Dr. David Song