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Transcript
The Fifth Lumbar Vertebra
Brief Overview
The flexible spinal column is comprised of 26 bones – 7 cervical, 12 thoracic, 5 lumbar (which make up the 24
articulating vertebrae), 1 sacral (which is usually made up of 5 fused vertebrae) and 1 coccygeal (which is
also comprises 3 to 5 fused vertebrae). The spinal column’s primary roles and function are integral to the way
we live our lives today. These functions include everything from providing protection for the spinal cord,
vertebral artery and nerves; to allowing the body to move in the fashion that it does, with stability, flexibility
and mobility; and even acting as the anchor point for countless ligaments, tendons and muscles that help the
body move and stabilise; not to mention supporting the weight of the head and body.
Evolution
Fossil records show us that this defining anatomical feature first appeared 500 million years ago and, pardon
the pun, it has been the backbone of the anatomy of fish, reptiles, birds and mammals ever since. It is evident
in early quadrupeds where the spine functioned as a suspension bridge for organs, and in modern bipeds the
vertebral bodies have evolved to deal with the load bearing forces of gravity.
The Fifth Lumbar Vertebra
The fifth lumbar vertebra, also known as the L5 vertebra, is the last of the five lumbar vertebrae and also the
last of the articulating vertebrae in the spinal column. It is positioned above the sacrum. Due to this
positioning in the spinal column, and to the evolution of mankind and the laws of gravity, the fifth lumbar
vertebra is a lot more robust than the rest of the articulating spinal vertebrae.
A larger kidney-shaped articulating body allows it to withstand the forces of gravity and provides substantial
support for the weight of the spinal column and connecting weight of the body above. Also L5’s body differs
from the rest of the lumbar vertebrae in that the anterior face of this vertebral body is distinctly larger than the
posterior side. So, when teamed up with the fourth lumbar vertebra, it accounts for approximately 50 % of
lumbar lordosis. It has strong pedicles, and a broad lamina, resulting in a smaller vertebral foramen in
comparison to the cervical vertebrae, as well as quite thick transverse processes. On the other scale L5’s
spinous process is smaller than its other lumbar counterparts and features a wide tick notch-like characteristic.
The superior articulating processes are wider than they are tall, with a wide medial and posterior facing
diagonal space and concave faces, whereas the inferior articulating processes face forwards and laterally in
a wide spacing and are slightly longer than wider with a convex face.
Structurally, you could say the L5 vertebra has the role of a strong man in a circus.
Function of the Fifth Vertebra
We have already touched on some of the function of L5 in the above paragraph, and on the way its features
have developed to withstand the forces of weight and gravity as humans have evolved from quadrupeds to
the bipeds we are today. Obviously the tight, large, stocky nature of L5 will impair some ranges of movement
in order to give way to structural soundness.
Due to the characteristics of the body of the fifth lumbar vertebra (including the smaller size of its spinous
process and the shape of the superior and inferior articular processes), L5 mainly aids in flexion and extension
of the spine, with 16 degrees on average in the L4- L5 articulation and 17 degrees in the L5- S1 articulation. This
obviously varies from person to person depending on age, gender, underlying conditions and structural
characteristics. Flexion and extension in the lumbar spine is also a result of a combination of rotation and
translation in the sagittal plane between vertebrae.
Also, because of the nature and shape of the superior and inferior articulating processes, lateral flexion in L4-L5
is only, on average, 6 degrees and in L5-S1 is only, on average, 3 degrees; while rotation on the transverse
plane is about 2 degrees for L4- L5 and 1 degree for L5- S1.
Attachments
The fifth lumbar vertebra has a few attachments, such as the Iliolumbar ligament that connects from the
transverse processes of L5 to the posterior iliac crest right in front of the sacroiliac joint. This assists in stability in
the sacroiliac and lumbo-sacral joints.
Psoas also has an origin on the transverse processes of L5 and inserts into the lesser trochanter of the femur,
which then plays a part in anchorage for hip flexion. However, if the thigh itself is anchored it then plays a part
in lumbar flexion instead.
Also originating from L5’s transverse processes and inserting to the base of spinous processes of the superior
vertebra are rotatores, which aid in extension and contra-lateral rotation of the vertebrae.
The intertransversarii also insert and originate between the transverse processes of the vertebrae that cause
lateral flexion of the vertebral column.
Then there are the interspinales, which attach to the spinous process and aid in extension of the vertebral
column.
And of course multifidus, which originates from the intermediate tubercles of sacrum and posterior superior
iliac spine and the mamilary processes of the lumbar vertebrae. Multifidus inserts into the spinous processes
and posterior surfaces of the lamina from L5 up to T10 in a diagonal intervertabral fashion, making it an allrounder (so to speak) helping with extension, contra-lateral rotation, and proprioception as well as
stabilisation.
Not to mention all the intervertebral ligaments for stabilisation that attach to L5 as well.
L5 also is the exit point for a lot of nerves connecting to our legs, feet and toes, the biggest of which being the
sciatic nerve. When impinged at L5 level you can experience localised pain, as well as a referral down the
front of the of the lower leg all the way to the feet and toes, which might manifest as tingling, numbness or
even weakness.
Conditions Due to Function
Due to L5’s positioning and load-bearing nature, when combined with rotation and flexion L5’s intervertebral
disc is extremely prone to pathologies such as bulges, prolapses, herniations and, over time, degeneration.
Because of this susceptibility it is quite important that we protect our back when moving in extreme ranges of
motion as well as when under extreme load. We can do this by training the body to use correct muscle
recruitment patterns and building proprioceptive awareness.
Summary
As humans have evolved our structure has, by necessity, evolved too. L5 has done exactly that, becoming a
thick, load-bearing bone for the whole upper quadrant of the body, as well as the anchor point for countless
muscles and ligaments that stabilise the body and keep us upright. As for movement, L5 is key in flexion and
extension of the spine, and aids with rotation and lateral flexion, and with supplying the nervous system to our
body’s lower quadrant. Even though in Pilates terminology L5 is not our “centre”, it does come pretty close.
Without this important little bone we would all be in a lot of difficulty with our posture, not to mention the pain
we would also incur via force loading and sacroiliac joint instability. There are plenty of bones through
evolution that mankind have discarded but this robust little bone is here to stay!
Author: Benjamin Rashleigh
Diploma of Professional Pilates Instruction
Level 1 Instructor, Aligned for Life Pilates