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52 Cards in this Set

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How are the trabeculae aligned within the cortical bone of the vertebral bodies?
Along the most common stress lines
Can the trabeculae within the vertebral bodies be damaged without damaging the surrounding cortical bone?
Yes - if a large compressive load causes a stellate fracture in the end plate resulting in a Schmorl's node.
Are stellate fractures and Schmorl's nodes more common in the elder or in younger adults? Why?
Younger. The nucleus pulposa of the disk is still hydrated so there is fluid material present to be forced into the vertebral body.
What event can lead to the binding up of a Z joint?
A fold of the capsular ligament can get caught within the Z joint, which can result in the development of adhesions if the joint stays closed very long.
What type of load commonly causes failure of the posterior bony elements and avulsion of an end plate?
A-P shear loading
Do the posterior elements usually fail due to fatigue failure or from a single, large load?
Usually from a single, large load
In regards to fatigue failure, what is meant by the term endurance limit?
The largest amount of stress a specimen that be repeatedly exposed to for unlimited number of times without failing (causes no microdamage at all - the edge of the elastic region)
What is an asymptote?
A straight line that is approached, but never reached, by a curved line.
Does fatigue failure of bone come with fewer repititions of compressive loading or of tensile loading?
tensile loading
What is the difference between elastic and plastic deformation?
Elastic deformation does not involve damage (the specimen will return to its original shape)._
Plastic deformation implies that some damage has been done to the specimen.
What is a brittle material?
One that will not deform very much before it breaks, like glass._
(says nothing about how strong it is)
What term is used to describe a material that will deform a lot without breaking?
ductile - like gold for example_
(has nothing to do with how strong it is)
How is a creep and recovery test performed?
A constant load is applied to a viscoelastic material for a time and then removed._
The amount of stretch is observed throughout the time of the test.
How does an elastic material respond in a creep and recovery test?
Goes to maximum stretch right away and stays there until the load is removed.
How does a viscoelastic solid that is not damaged respond to a creep and recovery test?
Stretches out fairly quickly when the load is first applied and then less and less as time goes on._
When the load is removed, it starts to contract quickly but slows down as time goes on. It will eventually return to the original shape.
How does a viscoelastic solid that is damaged by the test, or a viscoelastic liquid respond to a creep and recovery test?
Stretches out fairly quickly when the load is first apllied and then less and less as time goes on._
When the load is removed, it starts to contract quickly but slows down as time goes on. It never does return to the original shape.
How is a stretch and relaxation test performed?
A viscoelastic material is stretched a certain amount and then held in that position._
The amount of force required to hold it in that position is measured over time until the end of the test.
How does an elastic material respond in a stretch and relaxation test?
Takes the same amount of force to hold the position throughout the entire test.
How does a viscoelastic solid respond to a stretch and relaxation test?
Takes less force to hold the position as time goes on, but will never drop below some particular amount of force.
How does a viscoelastic liquid respond to a stretch and relaxation test?
The amount of force required to hold the position reduces over time until it takes no force at all.
What are the characteristics of a viscoelastic material?
1. Although it is either a liquid or a solid, it has properties of both._
2. It takes time to reach maximum deformity when exposed to a load._
3. The stretching causes internal components to rub against each other, resulting in a loss of energy as heat due to friction.
What are the basic components of the intervertebral disc (IVD)?
annulus fibrosus and nucleus pulposus_
Some consider the end plate as a part of the IVD although some think of it as part of the vertebral body.
What is the biomechanical significance of the alternating direction of the slant of the collagen fibers in the alternating layers of the annulus fibrosus of the IVD?
Enables the IVD to resist rotation in either direction
What harmful effect can result from excessive compression of a dehydrated IVD (typically in an older person)?
The layers of the annulus can separate (delamination).
In what age group do herniated discs usually occur? Why?
Younger people, because the disc is still well hydrated._
(there is no fluid to be pushed out if the disc is old and dehydrated)
What conditions are usually associated with the herniation of an IVD?
1. The disc is usually in a younger person and at the edge of the range of motion._
2. There has usually been a lot of repetitive loading (like 25,000 cycles)._
3. It usually happens to people who sit a lot
According to our author, McGill, what is the primary function of the short muscles of the cervical spine?
Stabilizers (not prime movers)
How does the biomechanical function of a back extensor muscle tend to vary depending on whether the tendon for that muscle runs superficially or deep?
The ones with tendons that run superficially tend to be extensors (longer moment arm)._
The ones with tendons that run deep tend to be stabilizers.
What is the biomechanical significance of oblique muscle fibers in deep lumbar muscles?
They apparently are designed to protect against shear forces._
(they surely aren't intended to cause sliding of one vetebra relative to its neighbor)
What is the apparent role of the abdominal oblique muscles?
Trunk rotation and stabilization but not flexion.
What are 3 possible benefits of the rectus abdominus muscle having multiple bellies?
1. Reduce amount of bulking when contracting to reduce pressure on underlying viscera_
2. Allow the abdomen to bend while the rectus abdominus is contracted (and therefore rigid)_
3. Prevent hoop stresses from intra-abdominal pressure from splitting the muscle fibers apart
In general, how do muscles that are prime movers tend to differ from stabilizers?
Prime movers tend to attach in few places and be active in only certain movements._
Stabilizers tend to attach to many places and are active in a wide variety of movements.
The ligamentum flavum is the most elastic ligament in the body. Why is it stretched even in the neutral position?
To prevent anything from getting into the spinal canal during movements of the spine.
What is the biomechanical significance of the oblique fibers in the interspinous ligament?
Helps to resist shear forces.
What is the name of the structure that surrounds tendons to isolate them from surrounding structures and guide them around corners?
paratenon
In regards to the attachment of tendons to bone, what is meant by the term strain relief?
A progressive increase in stiffness as the flexible tendon approaches the rigid bone._
(reduces the risk of the tendon snapping off at the attachment site)
What mechanism might explain the sensation of pain in a particular structure when there is nothing wrong at the structure?
Spurious input to the nerve supplying that structure could be induced by a subluxation at the IVF. The brain would interpret activity in that nerve as pain in the structure with its sensors.
Which area of the spine, below the cervicals, has the most rotation?_
Has the most flexion/extension?
The upper thoracics have the most rotation._
The lumbars and lower thoracics have the most flexion/extension.
What characteristics of the range of motion of an individual provide an indication of pathelogical abnormalities?
Excessive or reduced range of motion as compared to normal, or especially assymetrical range of motion._
However, unusual ranges of motion could merely be reflective of normal variation.
What are the 4 steps for determinining the center of rotation of a vertebra which has moved from one position in an x-ray to another as shown in another x-ray when one of the x-rays has been laid over the top of the other?
1. Determine and mark the same two points on the vertebra on each of the two images of that vertebra._
(the two points should be as far apart from each other as possible)_
2. Draw a line connecting the point on one image to the same point on the other image._
(do that for each of the two points selected on the vertebra)_
3. Draw a perpendicular bisector through each of the two lines._
4. The intersections of the two perpendicular bisectors is the center of rotation for that movement.
Describe the location of the instantaneous centers of rotation of the movement of one lumbar relative to its lower neighbor in a healthy spine during flexion and extension:
The various centers will tend to be localized in the disc between the two vertebra
Describe the location of the instantaneous centers of rotation of the movement of one lumbar relative to its lower neighbor in a biomechanically unstable spine during flexion and extension:
The various centers will tend to be relatively spread out below the disc between the two vertebra
Spinal stiffness is evaluated subjectively by motion palpation. What are two objective methods of quantifying spinal stiffness that we discussed in class?
1. Calculating Young's modulus from stress/strain data taken by pressing on the spine_
2. Measuring the response to a ping on the spine (PulStar system)
When the trunk is fully flexed, why do paraspinal muscles relax?
Because the ligaments carry the load of supporting the weight - only when fully flexed_
(known as the flexion/relaxation phenomenon)
How can the flexion/relaxation phenomenon be used to distinguish between normals and those with low back pain?
Normals usually show a distinct relaxation of paraspinal muscles at full flexion - low back pain sufferers usually do not.
How and why does the length of the spine typically vary during the course of a 24 hour period?
The spine is longer after sleeping because water is imbibed into the IVDs making them thicker (There is reduced load from your body weight on IVDs while you are horizontal)._
The spine is shortest just before going to bed because water is pushed out during the day when your are upright, putting more load (body weight) on the IVDs, making them thinner.
Why shouldn't a truck driver hop out of his truck and begin manual unloading immediately after making a long run?
His muscles have been conditioned to sitting and it takes a few minutes for them to adjust to effectively handle heavy loading.
What does McGill think is the role of interabdominal pressure during heavy lifting?
To prevent buckling of the spine (not to reduce pressure within the IVDs)
What are the four possible roles of the lumbodorsal fascia as proposed by McGill?
1. spine extension via muscle attachments_
2. retinaculum_
3. "strapping"_
4. provide support during lateral bending
In regards to a proposed role of the lumbodorsal fascia, what is meant by "strapping"?
Providing pressure on the extensor muscles of the spine to reduce bulging which increases the amount of force they can develop.
How is tensegrity defined?
The use of tensile forces to maintain the integrity of a structure._
(it is a contraction of the words tensile and integrity)
What explanation does McGill propose for why a seemingly trivial load within normal motions can sometimes lead to a back injury?
It could be that the brain sends an inappropriate message to one or more muscles of the back, causing excessive contraction which could result in injury.