Did you know that lower back pain can be caused by injury to muscles attached to the vertebral column? This lesson identifies and describes the major erector spinae muscles responsible for erect posture and movement.
Did you know that Americans spend at least $50 billion a year on lower back pain? Lower back pain can be caused by a variety of problems, including injury to muscles attached to the vertebral column. Let's take a look at these muscles. If we peel away the trapezius and the latissimus dorsi muscle that are on the superficial part of the back, we can see the muscles responsible for our posture.
The erector spinae is a group of muscles that work together to extend the vertebral column and thus maintain good posture. The muscles are innervated by the spinal nerves. Many of these muscles are small and therefore susceptible to injury. In this lesson, we will identify the specific erector spinae muscles in two layers: the superficial layer and the deep layer. It's important to note that all the muscles discussed in this lesson are paired - located on each side. While we will look at each muscle on one side, it is paired on the other side.
Superficial layer muscles of the erector spinae help maintain posture.
Let's look at the superficial erector spinae muscles first. These are located deep to the latissimus dorsi and the trapezius and divided into three groups. If you look at the lumbar and sacral regions down low, you can see these three muscle groups are pretty much non-distinct; they look as if they're one muscle. The groups separate at their superior attachments.
The spinalis group is most medial of the three, and it includes muscles that originate on vertebrae and insert on more superior vertebrae. The thoracis spinalis belongs to this group of muscles. With contraction, the spinalis muscles extend the neck and the vertebral column - once again, good posture.
The longissimus group of muscles helps to extend the neck and vertebral column, as these muscles originate on vertebrae and insert on more superior vertebrae and even some ribs. These are long muscles and thus named accordingly - for example, the longissimus thoracis.
The iliocostalis group is easy to remember due to its attachment. Many of these iliocostalis muscles - for example, the iliocostalis thoracis - originate on the ilium of the pelvic girdle and insert on the ribs, or the costal bones (thus, iliocostalis).
As with the spinalis and longissimus muscles, the iliocostalis muscles help to extend the neck and the vertebral column. Additionally, these muscles can move the ribs, as they're attached to the ribs.
Now that we've identified the superficial erector spinae muscles, we can look at what lies beneath. These muscles are many in number and small in size, and the small size makes them susceptible to injury. Let's take a look at two of the more prominent deep muscles.
The quadratus lumborum aids in lateral flexion of the vertebral column.
The quadratus lumborum originates on the ilium and inserts on the last rib as well as lumbar vertebrae. When these muscles contract, they depress (or pull down) the ribs, and they also aid in lateral flexion of the vertebral column. Let me go back to a previous note: all of these muscles are paired. So, when they contract together as a pair, they will extend the vertebral column. Now, if one side contracts while the other side relaxes, that's where we'll get bending - or as in this case, lateral flexion of the vertebral column.
The multifidus muscles extend and rotate the vertebral column.
Moving medially, we can see the multifidus muscles that originate on the sacrum and vertebrae and insert on more superior vertebrae. Due to these attachments, they extend and rotate the vertebral column. Again, extension occurs when they contract as a pair. Rotation would occur when they contract individually. They serve to stabilize movements and thus take weight off the vertebral discs - that's a very important function! As they are very thin muscles, they are subject to injury. In fact, persons with lower back pain commonly have weak multifidus muscles. Furthermore, these are among the most commonly injured lower back muscles. Let me make a very important point. With the multifidus, it's a very small muscle, yet a very powerful and important muscle. Such is the case with many of these erector spinae muscles.
In summary, the erector spinae muscles are innervated by spinal nerves, and they cause extension of the vertebral column, resulting in erect posture. The superficial erector spinae include the spinalis, longissimus and iliocostalis groups of muscles. These muscles extend the neck and the vertebral column, while some will even move the ribs.
The deep erector spinae muscles include the quadratus lumborum and multifidus muscles. These muscles are located under the superficial muscles and are responsible for similar action: extension and rotation of the vertebral column. As these muscles are paired, contraction of both sides results in erect posture, while contraction of one side causes movement, such as lateral flexion. As many of these muscles are small, they are susceptible to injury. Weakness and/or injury of these muscles can cause lower back pain.
Following this video, you will have the ability to:
- Describe the structure of the three superficial erector spinae muscle groups
- Identify two of the deep erector spinae muscles
- Explain the function and movements created by the superficial and deep erector spinae muscles
- Summarize what causes lower back pain