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Transcript of Back Pain
: at least 4 in 5 people will suffer from back pain some time in their lives
Occurs in many workplaces, especially in
with bending and/or lifting tasks
crucial in the
of back pain
Types of Back Pain
abrupt pain short in duration
within the plastic region of the stress-strain curve; result of load on the spine that one is not able to handle
pain long in duration (usually >3months)
within the elastic region of the stress-strain curve; results from repetitive loading of the spine
- taller = larger moment arm = higher risk
- certain diseases (obesity; those affecting the neuromuscular system, etc. ) may increase back injuries
- fetus in womb changes mother's center of gravity, especially during the later stages of pregnancy
- overstressing the spine may cause damage
- strength decreases with age
with frequent sitting or bending/lifting tasks
The spine includes:
- the vertebrae
are made up of
and thus weaker and less stiff than cortical bones
- the porous property allows it to
, giving it its ability to
loaded on it
- has a high
, meaning it remodels itself more often than cortical bones
between each vertebra
that allow for some motion and act as
which receive and send signals to and from the brain
no blood vessels
, which delays healing
with increased surface area
during movement while providing
- abundant in
, which helps to distribute the force loads
- hence we are taller in the morning and shorter at night as the compressive forces we withstand all day causes the water to be pushed out. When we sleep, the nucleus pulposus retains water and restores height
in fibrocartilage are strong due to its
small deformation range
Split into 5 regions:
, in which
24 are movable
and contribute to movement of the spine.
As you move towards the lumbar segment on the vertebae, you will notice an
increase in vertebral area
which is evident to deal with the
increase in compressive forces
it experiences - the stress level is equal despite that (since force is divided by area).
low back pain
is usually associated with the
Vertebral Column Anatomy cont'd
Cervical Spine (7 vertebrae)
wide range of motion
supports the head
curvature depends on the position of head
Thoracic Spine (12 vertebrae)
Lumbar Spine (5 vertebrae)
larger and broader due to weight it carries
little bit of range of motion
5 fused sacral vertebrae
4-5 fused vetebrae of the coccyx
connects spine to pelvis
strong and solid for transferring weight of upper body to lower body via the
(at base of spine)
What is Back Pain?
5 Regions of the Vertebral Column
Spine Curvature Irregularities
However, abnormal curvatures may occur:
of the lumbar and cervical vertebral column
anterior pelvic tilt
of the spine, usually in a S or C-shape
Pain felt in the posterior part of the human torso, especially in the
Pain: "an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage."
Can be either
Exact mechanism/cause of low
back pain is not well understood
we position ourselves in our daily lives is important because it affects the
type of forces
placed on our spine. As most of us are seated for many daily activities including eating, working and studying, we shall look at some advice to reduce the likelihood of creating forces that are prone to causing spinal injuries.
Types of Forces
Before we look into the types of forces that are created, let's look at
why we should even bother considering the types of forces involved.
First off, we have to understand that there are
three primary types of forces:
is a type of force that acts to squeeze an object at opposite ends
is a type of force that acts to pull an object at opposite ends
is a type of force that acts perpendicular to both ends of an object
Now that we understand that it is best to minimize shear forces by having a
on our back as opposed to having a rounded back, we shall look at how to achieve that in a common activity we participate in daily:
Postural Modifications to Minimize Shear Forces
To minimize shear stresses, keep in mind:
Position of the hip and knee joint
Keep your knee and hip joints ~90 degrees apart and make sure both feet are flat on the floor.
* It is best not to cross your legs over the other knee as this increases stress on the lower back.
Arch in lower back
Sit with a neutral position of the spine. This should engage your core muscles.
* A good way to check for this is to place your palm on your lower back to ensure that there is an gap.
Lower your shoulder blades and allow them to relax. Do not allow the shoulders to protract forward as this does not support a neutral arch; instead, this does the opposite and creates shear forces. This may further cause shoulder pain.
* This further affects the moment arm of the torso weight. By following the steps given, you minimize the force placed on your spine.
Position of your head/neck
Make sure you have the tension out of your shoulders as mentioned in step 3). A good way to check for this is to make sure that your ears are aligned with your shoulders. Do not flex or extend your neck as this may cause the shoulder out of its relaxed position and may cause your position to deviate, causing your shoulders to protract and consequently placing your lower back to deviate from its neutral position. This may further cause neck and shoulder pain.
Prevention, Rehabilitation and Treatment
Consult your doctor or a medical professional, but in general:
exercises to keep back muscles strong, e.g.
for healthy bones
lifting objects with
(via chiropractor, physiotherapist)
(pain relievers; analgesics; anesthetics)
(removal or repair of damaged bones, tissue, discs; spinal fusion)
Any structure associated with the spine can, hypothetically, contribute to back pain (acute, chronic, or both): ligaments, muscles, nerves, vertebral discs, etc.
Shortening of Muscles During Prolonged Sitting
Kumar theorized that our muscle tissues can suffer injuries due to
. He states that overexertion of forces, over exposure time and limited range of motion with tissue strength may lead to injuries.
It is vital to realize that
further leads to
Relating this to the position most of us sit, we come to realize that as our legs bend, we have our hips contracted - our
hip flexors shorten
. This shortening of the hip flexors and psoas is not the primary problem. The primary problem instead lies on the
individuals remain seated for. While our fascia are flexible, it has the tendency to prefer staying in the position our muscles are regularly positioned - this means that individuals who remain seated for prolonged durations, at a set point (no range of motion involved) and force have the tendency of having their
hip flexors fascia adapt to being flexed
. Consequently, these individuals have
tight hip flexors and psoas muscles
Viewing the anatomical structure, it is important to note that our
hamstrings cross the knee and hip joints
. As a result of the positioning of the hamstring, it compensates the shortened hip flexors by being
When we are sitting, our
gluteus maximus relaxes
and adapts to being relaxed. Individuals who are required to remain seated for long durations throughout the day may subsequently have
weak gluteus maximus
These three changes (shortening of the hip flexors and psoas; weak gluteus maximus; lengthened hamstrings and erector spinae)
changes our normal standing positioning
as we have the tendency to
, placing stress on our lumbar spine. This forward tilt lifts our hips up in the back which
tightens our lower back
. This common dysfunction is known as the
Anterior Pelvic Tilt
Examining other postural positions, we can see that this reasoning applies to common pain in areas including the
. Another contributing factor is the adapting of our
as we remain seated for a long duration.
Another point to note is that out
are activated when more compressive forces on the joint is increased (such as when you are seated with a neutral curve), whereas it is less active when there is decreased muscle activity (such as when seated)!
In summary, it is best to
avoid long durations of static activities!
Adams, M. (n.d.). Biomechanics of back pain. Retrieved from http://aim.bmj.com/content/22/4/178.long
Anterior pelvis tilt. (2013). Retrieved from http://fixflatfeet.com/anterior-pelvic-tilt/
Asher, A. (2010, June 05). How to sit with good posture. Retrieved from http://backandneck.about.com/od/ergonomics/ht/goodsittingposture.htm
Brook, S., Daniel, C., & Lee, J. (2009). The facts: Back pain. Oxford: Oxford University Press.
Calin, A. & Swezey, R. L. (2012). Fast facts: Low back pain (2nd ed.). Oxford: Health Press.
Chai, H. M. (2003, June 09). Seated Work. Retrieved from http://www.pt.ntu.edu.tw/hmchai/bm03/BMoccupation/SeatedWork.htm
Hamil, J. & Knutzen, K. (2003). Trunk. In Biomechanical basis of human movement. 3rd ed. (pp. 259-292). Philadelphia: Lippincott Williams & Wilkins.
Masters, M. (2010, October 26). Why your desk job is slowly killing you. Retrieved from http://www.nbcnews.com/id/39523298/ns/health-mens_health/t/why-your-desk-job-slowly-killing-you/
May, S. (2008, May 06). Sitting 101: Desk Ergonomics. Retrieved from http://www.fitsugar.com/Sitting-101-Desk-Ergonomics-1669975
More, H. (2014). Mechanical Properties of Tissues 1 [PowerPoint slides]. Retrieved from Lecture Notes Online Web site: http://www.canvas.sfu.ca
More, H. (2014). Mechanical Properties of Tissues 2 [PowerPoint slides]. Retrieved from Lecture Notes Online Web site: http://www.canvas.sfu.ca
More, H. (2014). Spinal Mechanics [PowerPoint slides]. Retrieved from Lecture Notes Online Web site: http://www.canvas.sfu.ca
More, H. (2014). Stress and Strain [PowerPoint slides]. Retrieved from Lecture Notes Online Web site: http://www.canvas.sfu.ca
Robinovitch, S.N. Biomechanics of lifting and lower back pain. [PDF document]. Retrieved from Lecture Slides Online Web site: http://www.sfu.ca/~stever/kin380/lecture_outlines/Biomechanics_lifting_p1_1pp.pdf
The anterior portion has:
2 separate vertebral bodies
an intervetebral disc
The vertebral bodies are shaped thicker on the front side to handle compressive forces.
The intervetebral disc withstands
Vertebral Column Anatomy Continued Further
The posterior portion has:
(labeled as intervertebral joints) connect the vertebrae
causes shear and tensile forces
causes tensile & compressive forces
It is important to mention here that sitting without a back rest increases the amount of force placed on the lumbar spine due to the
backward tilt of the back
, which tends to flatten the lower back. This shifts the center of gravity forward.
Therefore, it is important to
sit on a chair with a back rest
, which will help reduce the disk pressure and shear forces created by having the shift of gravity reduce the moment arm of the upper body weight done onto the lumbar disks.
Musculature of the Back
Muscles help to reduce shear forces placed on the joints.
help to reduce shear forces on joints; instead, it may increase these forces.
Proper Lifting Technique
(active when seated upright)
(active for extension activities)
It is important to
strengthen our trunk
within it due to the demand placed on it in many activities.
Key points to take note of when performing trunk exercises:
in the spine
the erector spinae with the
increases stiffness and stability
and increases the amount of compressive force present (recall that our bones are strongest under compressive forces, so this reduces the likelihood of injuring yourself)
- higher level of activity from the abdominals helps to stabilize the pelvis
- i.e. sit ups
- higher level of activity from erector spinae
- i.e. deadlifts
Trunk Rotators and Lateral Flexors
- i.e. bicycle and oblique ball twist
- using an exercise ball activates stabilizer muscles
Next off, we have to understand that our bones are
. This means our bones have
different mechanical properties
in reference to the
that it is loaded. Our bones are stronger when under compressive stress, weaker under tensile stress and weakest under shear stresses.
In fact, when our lower back is rounded, there is more shear stress;
when we keep our back in a neutral position, there is less shear stress.
Mechanical Causes of Back Injury
on the spinal cord or nerve roots
in the annulus fibrosus of the vertebral disc
(often from rotational movements)
(places pressure on the spinal nerves)
As we age, there is narrowing within the joint space which
placed on the disc.
The discs may lose height while losing its fluid region, displacing the stress onto the annulus fibrosus.
The spine has 4 natural curvatures:
cervical, thoracic, lumbar, sacral
Lack of activity
- bone resorption and muscle inactivity makes the spine weak and susceptible to injury
- men engage in riskier activities than women
- previous trauma, injury, surgery on spine
- family history
Improper lifting technique
- compressive and shear forces on spine (as discussed later)
- overtime may lead to chronic back pain
Endplate fractures, intervertebral disc degeneration
nerve root irritation
That may contribute to back pain (not discussed)
*Bed rest is not recommended
further emphasizes through the
that unless there is a load stressing on the bone that causes the body to build stronger bones, the immobilized bones will be more prone to deformation and injuries.
In fact, we know that if we either do too much or too little, we are more prone to sustaining injuries. Therefore we should
minimize the duration of being seated
for too long, as this causes our muscles to fatigue, compromising their functions and thus increasing the risk of injuries.
Minimizing Shear Forces Continued
When we sustain a
during prolonged sitting, there is
placed throughout our spine. With the additional stress placed on the spine along with our own body weight,
is evident - this results in
Changes to Vertebrae During Prolonged Sitting
Flexion of the lumbar spine:
, displacing the nucleus pulposus posteriorly
increases pressure and stress
inside the disc.
Extension of lumbar spine:
, displacing the nucleus pulposus anteriorly, which also increases pressure and stress inside the disc.
in either direction (flexion or extension) of the spine leads to a
rearranges the collagen fibers
squeezes fluid out
Upon removal of the load, there is a
in elasticity that was initially increased when the load was applied (
). It slowly recovers back to its original deformation length as
back into the articular cartilage.
However, if the load is sustained long enough, tissues become more prone to
and there will be an increase in potential for
to occur there, known as
(more common in the
). This is more commonly due to injury to the
of the vertebrae and the
motor end plates
than of the entire disc itself.
Disc prolapse forces the nucleus pulposus into the annulus fibrosus. In prolonged sitting, a posterior prolapse is evident.
In addition to this, repetitive occurrence of this squeeze more fluid out and over time, causes surrounding ligaments to become less stiff.
Keep entire back engaged (maintain a neutral spine)
Keep knees bent
Have the weight close to pelvis (reduces strength output required due to reduced moment arm)
Minimize movement to be within one plane only (vertically up/down or horizontally left/right)
Avoid flexion and extension of the trunk
Contract abdominal muscles for support
Lift at a comfortable pace (not too high or low velocities)
Take breaks if needed!
Muscle and tendon strain
may occur with poor
lifting technique which may lead to
Calculating Compression and Shear Forces
Force of Muscle: 3020 N
Force of Weight: 450 N
Force of Pull (external weight): 200 N
Recall that compressive forces act along the spinal column while shear forces act perpendicular to the spinal column
According to the National Institution for Occupational Safety and Health (
), there should be a maximum disk compression force of
on the lumbosacral area. The compressive force in this situation is
. Therefore, damage will be done to the back through this movement.
Biomechanics of Back Pain and Sitting
of the fluid within the fibrocartilage to resist shear stress has been shown to lead to
under a lower amount of load and deformation when under
- important to work through functional range of motion
- important to work at one plane at a time to reduce excessive loading on the vertebrae
- important factor as inflexibility of the hamstring may contribute to increased strain placed on the lumbar-spine
- area between the sternum and the knee that provides stability of the spine
- more emphasis on the abdominals, low back and hips
Edwin Leung, Marcus Too, Carmen Ho
Background image source: www.paradoja7.com
T = F x d
(moment) is the force that causes rotation about an axis. In the human body, this is caused by
moving body segments, which leads to
about a joint
(the axis of rotation).
However, most of us tend to slouch when we sit, and this creates larger moment arms and resulting torques. This causes biomechanical changes in the spinal column as larger shear forces are created, and this will result in back pain and injury.
The mass of our upper body (plus any external forces/loads) creates a negative (forward) torque about the hip joint. To counter this and maintain our upright positions, our
back extensor muscles
have to constantly be activated to generate equal and opposite forces.
Finding the Right Chair and Table
Find a chair that has:
1) an appropriate seat height and slope that allows you to place your feet flat on the ground and your knees bent at an angle of 90 degrees
2) an appropriate arm rest that allows comfortable placement of your forearm on it without the need to lean forward or shrugging of shoulders
3) a soft and adjustable backrest
- backrest height should be fitted for individual
- backrest should allow neutral spine
4) soft seat to reduce pressure placed on the posterior thigh
Find a table that has:
1) an appropriate height to allow neutral positioning of the shoulders with no excessive protraction/retraction/shrugging
2) ample leg room to sit comfortably