Spinal Biomechanics Flashcards

1
Q

What is the role of the spine?

A
  1. Tolerates & transfers weight to pelvis
  2. Protects spinal cord
  3. Allows flexibility in all directions
  4. Key role in posture
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2
Q

What is the smallest functional unit of the spine?

A

FSU: 2 vertebrae + IVD

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3
Q

What components contribute to the spinal axial load?

A
  1. Gravitational forces due to mass of body segments
  2. External forces & moments
  3. Muscle tension (provides equilibrium)
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4
Q

List the factors that affect axial loading of spine:

A
  1. Type, rate & duration of loading
  2. Age
  3. Posture
  4. Condition of anatomical structures
  5. Integrity of nervous system
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5
Q

What posture has least amount of pressure on spine?

A

Supine (25lbs)

Almost any motion increases loads on spine.

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6
Q

What posture causes the greatest pressure on spine?

A

Flexion while lifting (>600lbs)

Almost any motion increases loads on spine. Nachemson studied pressure in L2-L3 (150lb man).

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7
Q

Ideal lifting posture is:

A

Lifting w/knees bent & back straight, with object close to body.

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8
Q

What is intracavitary pressure?

As it relates to spinal axial load.

A

The pressure within the abdomenal cavity, created by muscles.
The rigid-walled cylinder supports a portion of spine loading.

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9
Q

What is the implication of weakened abdominal muscles on the spine?

A

Weakening of the abdominal muscles causes increased spine loading & the risk of lower back pain.

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10
Q

What is a major anterior compressive load bearing element?

A

Intervertebral Disc (IVD)

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11
Q

What is the load carrying capacity of the spine?

A

Maximum load the axial spine can tolerate w/o collapse.

Influenced by: muscle & bone health

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12
Q

What model demonstrates the contribution of orthotic devices to the load carrying capacity?

A

Euler Model

1 end fixed: 8x; 2 ends fixed: 16x; Milwaukee Brace is an orthotic illustration.

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13
Q

What load increases LCC?

LCC = load carrying capacity

A

Transverse Load

All orthoses provide some form of transverse laod; braces increase LCC.

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14
Q

True or False: Most spinal orthoses provide some sort of intracavitary pressure.

A

True

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15
Q

What is the consequence of lifting weights?

A

Lifting imposes significant load on spine; contraction of back extensors produces large compressive forces, which may cause failure/fracture.

Especially true in pts w/Osteoporosis

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16
Q

How are shearing forces generated?

A

Flexion, extension and lateral bending

17
Q

How are shearing forces resisted?

A

They are passively resisted by bonds btwn annulus fibrosus & vertebral endplates.

18
Q

How are shearing forces minimized?

A

Active stabilization by axial musculature.

19
Q

What are the zones of the Stress-to-Strain Curve?

A
  1. Neutral zone
  2. Elastic zone
  3. Plastic zone
  4. Failure zone
20
Q

What injuries occur in the Failure Zone?

A

Subluxation, fracture or other traumatic injuries

21
Q

Which zone has damaging deformation?

A

Plastic Zone

22
Q

What zones are within the Physiological range?

A

Neutral & Elastic zones

Physiologic range: safe; neutral zone has the load or stress.

23
Q

What zones are within the Traumatic range?

A

Plastic & Failure zones

Plastic: change; failure: rupture

24
Q

Compression & tension are caused by:

A

Bending

Prime mover muscles initiate bending, esp. weight of upper body.

25
Q

Widening of the intervertebral foramen occurs during:

A

Flexion

IVD widens and narrows anteriorly and/or posteriorly when there is flexion and/or extension.

26
Q

How do antagonistic muscles control motion?

A

By resisting gravitational pull (eccentric contraction*)

*When a muscle lengthens while under tension.

27
Q

What spinal structures influence ROM?

A
  1. Facet joints
  2. IVDs - annulus fibrosus
  3. Ligaments
  4. Thoracolumbar fascia
  5. Abdominal fascia

Tension in both 4 & 5

28
Q

What is the ROM in various spinal levels?

A

Cervical: +++ in 3 planes
Thoracic: limited
Lumbar: resists rotation

29
Q

Sagittal plane motion occurs:

50% of cervical motion

A

Occiput & Atlas

30
Q

Transverse plane motion occurs:

50% of cervical motion

A

Atlas & Axis

Articulating facets in cervical vertebrae face 45 degrees to transverse plane, and lie parallel to frontol plane.

31
Q

Facet joint orientation in Thoracic spine is:

A
  • 60 degrees to transverse plane
  • 20 degrees to frontal plane

Least mobile portion of spine due to restriction of rib cage & spinous processes.

32
Q

Facet orientation of Lumbar spine is:

A
  • Right angle (90 degrees) to transverse plane
  • 45 degrees to frontal plane
  • Favors: flexion, extension, lateral bending

Additional ROM from pelvic tilt.

33
Q

How is spinal instability measured?

A

Stiffness - the spine’s ability to resist loads

Loss of stiffness = increased mobility

34
Q

Instability

Fractures & Dislocation cause:

A

Macroinstability

35
Q

Instability

Disc degeneration, facet joint degeneration & subluxation cause:

A

Microinstability

36
Q

What is decompression?

A

Surgical decompression is the opening or removal of bone to relieve pressure and pinching of spinal nerves.

Lateral stenosis (root); central stenosis (top of cord); foraminal (nerve)

37
Q

What are the types of decompression?

A
  1. Discectomy
  2. Facetectomy
  3. Foraminotomy
  4. Laminectomy

Laminectomy: more common, w/possible spinal fusion (which is surgical stabilization).