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The Spine

Understanding the Mid & Lower Spine

THORACIC SPINE

The thoracic spine is middle portion of your spine, it consists of 12 vertebrae. The vertebrae of your spine are numbered, they start with the letter ‘T’ (short for thoracic). The first two vertebrae, T1 and T2, this pattern continues until T12. All the vertebrae in your thoracic spine are classic vertebrae, having a body, pedicles, laminae, spinous processes, and facet joints. These vertebrae move the spine and protect the spinal cord which is the bundle of nerves connected to the brain.

LUMBAR SPINE

The lumbar spine is most commonly referred to as the lower back. This is the point where the spine curves inward toward the abdomen. Lumbar spine connects the thoracic spine to the next section known as the sacral spine. The lumbar spine consists of 5 Vertebrae labelled with L1 through to L5. All the vertebrae in your lumbar spine are classic vertebrae.

SACRAL SPINE

The sacral spine, also known as the sacrum is a series of triangular-shaped bones, they consist of five segments the labelling follows exact same pattern as previously discussed, S1 to S5. These bones are fused together. The sacrum connects to the coccyx which is the very bottom of your spine, it looks almost like a tail.

 

 

Discs

Discs are located in between the vertebrae of your spine. These discs are jelly like materials that cushion and stop the bones from rubbing on each other. If the discs move out of place, bulge, or leak they can cause a lot of pain. If they press on a nerve when they move out of place, the pain can be very severe.

Muscles

Many muscles support the vertebrae of the thoracic and lumbar spine. These muscles move the spine and helps maintain correct posture. These muscles are striated (striped) in appearance. It is innervated (full of nerves), they are under voluntary control. These types of muscles have the fastest contraction rate of all muscles in the body. Prior to a muscle contracting, a nerve impulse originates in the brain and travels through the spinal cord to the muscle.

The muscle groups are listed in the below table.

 

THORACIC MUSCLES FUNCTION NERVE
Longissimus Thoracis Extension, lateral flexion of vertebral column, rib rotation Dorsal primary divisions of spinal nerves
Iliocostalis Thoracis Extension, lateral flexion of vertebral column, rib rotation Dorsal primary divisions of spinal nerves
Spinalis Thoracis Extends vertebral column Dorsal primary divisions of spinal nerves
Semispinalis Thoracis Extends & rotates vertebral column Dorsal primary divisions of spinal nerves
Rotatores Thoracis Extends & rotates vertebral column Dorsal primary divisions of spinal nerves

LUMBAR MUSCLES FUNCTION NERVE
Psoas Major Flexes thigh at hip joint & vertebral column L2, L3, sometimes L1 or L4
Intertransversarii Lateralis Lateral flexion of vertebral column Ventral primary division of spinal nerves
Quadratus Lumborum Lateral flexion of vertebral column T12, L1
Interspinales Extends vertebral column Dorsal primary divisions of spinal nerves
Intertransversarii Mediales Lateral flexion of vertebral column Dorsal primary divisions of spinal nerves
Multifidus Extends & rotates vertebral column Dorsal primary divisions of spinal nerves
Longissimus Lumborum Extends & rotates vertebral column Dorsal primary divisions of spinal nerves
Iliocostalis Lumborum Extension, lateral flexion of vertebral column, rib rotation Dorsal primary divisions of spinal nerves

 

Tendons

Tendons are elastic tissues that connect muscles to bones. The tendons main role is to stabilize the vertebrae across your back. The main tendons in your back can be seen on the left, they attach to the muscles mentioned above to the vertebral discs.
Notice the colour of the tendons, they are white. Whereas muscles are red. The reason is due to blood flow, muscles have good blood flow, whereas tendons do not. The rotator cuff tendons require careful observation, since many of the tendons attach in a similar location it may sustain damage easily.

 

Ligaments

Many ligaments, or bands of connective tissue, wrap around the spinal column and connect its vertebrae (like “sticky” rubber-bands). These ligaments also prevent excessive movement that could damage the spinal column.

There are several major ligaments in the spine, two of which connect the entire spine together and many others that function for specific parts, these are listed below.

Ligament Spinal Region Limits…
Anterior Longitudinal Axis – Sacrum Extension & reinforces front of annulus fibrosis
Posterior Longitudinal Axis – Sacrum Flexion & reinforces back of annulus fibrosis
Ligamentum Flavum Axis – Sacrum Flexion
Supraspinous Thoracic & Lumbar Flexion
Interspinous Lumbar Flexion
Intertransverse Lumbar Lateral flexion
Iliolumbar Sacroiliac joints Stability & some motion
Sacroiliac Sacroiliac joints Stability & some motion
Sacrospinous Sacroiliac joints Stability & some motion
Sacrotuberous Sacroiliac joints Stability & some motion

Cartilage

In the spine facet joints are a key part of the spine’s flexibility. A facet joint is comprised of hard yet smooth cartilage on the upper and lower surfaces to protect the back part of vertebral bones. Cartilage is only located in the facet joints, not the discs. Cartilage also acts a shock absorber however, cartilage wears out and cannot repair itself.

Joint Capsule (lubrication membrane)

The capsule is a thick, fibrous structure that wraps around the facet joint. Inside the capsule is the synovial membrane which is lined by the synovium, a soft tissue that secretes synovial fluid and provides lubrication for the facet joints. The synovial fluid is both viscous and sticky lubricant. Synovial fluid is what allows us to flex our joints under great pressure without wear.

 

Nerves & Dermatomes

A dermatome is the area of the skin where we feel sensation that is based on a spinal sensory nerve root. These nerves start at a particular point and branch out the peripheral systems throughout our body. As we already know, nerves allow us to feel sensations such as burning, tingling, numbness, pressure, and more.

It is important to understand the anatomy of the spine, so we can become familiar with dermatomes. When we look in to the nerve roots from the spine, there are nerves at the front (anterior) as well as the back (posterior). The anterior nerve roots are responsible for motor signals to the body, and posterior nerve roots receive sensory signals like pain or other sensory symptoms.

There are specific dermatomes for each of these spinal nerves, dermatomes are used to represent the patterns of sensory nerves that cover various parts of the body. For example, if an issue occurs in the L4 vertebrae and this creates pressure or inflammation on the posterior nerves, you may feel shooting pains or numbness around the surface above your knee down to the inner part of your calves.

Pathological Conditions of the Spine

Facet joint osteoarthritis:

Osteoarthritis is the most common form of arthritis, and often affects the facet joints. Caused by aging and wear and tear of cartilage, osteoarthritis symptoms may include pain, stiffness, and swelling. Osteoarthritis is not simple to understand, there are many links with the wear and tear of cartilage that also affects every other part of your joint. We discuss this in our treatment information pack.

Degenerative disc disease:

Degeneration that occurs as a part of the aging process not only affects cartilage in the facet joints, it also affects the discs that are in between the vertebrae. The jelly-like disc materials begin to fray, it can lead to compression of the disc as fluid leaks out. This creates pressure and inflammation around the nerves of the spine.

Issues that often occur with Osteoarthritis or Disc Degeneration

Disc bulge:

Degenerative and weakened discs can lead to jelly like fluid trying to escape the disc, this causes a ‘bulge’. It is similar to a car tyre that has developed an egg on the side wall.

Disc herniation:

Herniation is the process by which the jelly like material actually leaks out of the disc.

Nerve impingement:

Nerves of the spine can become compressed or impinged if discs are bulging/herniated. This can also occur due to spine canal stenosis which is narrowing of the spine canal where spinal fluid is maintained.

Tendonitis:

Inflammation of the tendons that are connecting muscle to bone. Tendonitis is very common. It can occur due to simple overuse, overstrain or even underuse. Tendons can become weak very quickly and they take a very long time to repair due to lack of blood flow.

ligament strain or tear: The ligaments of your spine can strain when one of the muscles supporting the shoulder, head or upper back joint is stretched beyond its limit. In severe cases this can lead to a tear, not just a strain.  If the ligaments are degenerate due to low activity, this will be more likely to tear.

 

 

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