Biomechanics of Facet Loading in the Lumbar Spine

King, Albert I.

doi:10.1007/978-3-319-49792-1_10

Albert I. King²

1759 Accesses

Abstract

Although the biomechanics community has now accepted the concept of facet loading, the idea took a long time to take hold. Even in the 1980s, it was necessary to continue to prove conclusively that facet loads are real. To that end, El-Bohy et al. (1989) obtained contact pressure data from the tip of an inferior lumbar facet to show that it did indeed bottom out on the lamina below in order to transmit spinal load. Other topics covered in this chapter are spinal models simulating seat ejection, a model simulating the ditching of an aircraft at sea, and a brief overview of finite element models of the spine simulating impact.

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Department of Biomedical Engineering, Wayne State University, Detroit, MI, USA
Albert I. King

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Appendices

Questions for Chapter 10

10.1.
In the study by El-Bohy et al. (1989), he simulated loading on the spine due to body weight and a load held in his hands in front of him
1. [ ] (i)
  There was no facet load when the man was just standing erect and not carrying a load and
2. [ ] (ii)
  The experiment demonstrated that the simulated muscle load increased disc pressure but not facet contact pressure
3. [ ] (iii)
  The load on the spine was magnified when the man carried a weight in front of him
4. [ ] (iv)
  The experiment demonstrated that when facet contract pressure there was no change in disc pressure
5. [ ] (v)
  None of the above
10.2.
The objective of the experiment performed by El-Bohy et al. (1989) was to show that
1. [ ] (i)
  spinal muscles exerted a lot of load on the spine
2. [ ] (ii)
  the inferior facets bottomed out on the laminar to transmit facet load
3. [ ] (iii)
  disc pressure increased with load borne by the spine
4. [ ] (iv)
  the extensor muscles of the spine were activated when a man is carrying a weight in front of him
5. [ ] (v)
  an increase in extensor muscle force resulted in a corresponding increase in disc pressure
10.3.
The measurement of lumbar facet load was accomplished by:
1. [ ] (i)
  Indirect means in which the facet load was deduced from measuring the total spine load and the disc load
2. [ ] (ii)
  Indirect means in which the contact pressure between the facet tip and the lamina was measured during quasi-static loading
3. [ ] (iii)
  Direct means, using a miniature load cell under the facet
4. [ ] (iv)
  Direct means, using a pressure sensitive mat under the facet
5. [ ] (v)
  (i) and (ii)
10.4.
Based on data from quasi-static testing of lumbar motion segments, it was found that:
1. [ ] (i)
  There is no facet loading during normal erect standing
2. [ ] (ii)
  There is facet load during normal erect standing
3. [ ] (iii)
  There is facet load when the person is carrying a 10 lb weight some 4 in. in front of his chest
4. [ ] (iv)
  (i) and (iii)
5. [ ] (v)
  (ii) and (iii)
10.5.
When carrying or lifting a heavy object, the extensor muscles of the back are activated. Assuming that the average eccentricity of these muscles relative to the center of a lumbar disc is 20 mm, the estimated force on the spine due solely to muscle action, to lift a 100 N weight, held 400 mm in front of the disc center, is:
1. [ ] (i)
  2 kN
2. [ ] (ii)
  4 kN
3. [ ] (iii)
  5 N
4. [ ] (iv)
  10 N
5. [ ] (v)
  None of the above
10.6.
When the extensor muscles are activated, the pressure in the intervertebral discs
1. [ ] (i)
  Is decreased
2. [ ] (ii)
  Is not affected by the muscle action because there is an equal increase in the flexor muscle force
3. [ ] (iii)
  Is increased
4. [ ] (iv)
  Is not affected by the muscle action because the facets take all the load
5. [ ] (v)
  Goes up momentarily and returns to its original state
10.7.
During pilot ejection, the intervertebral load in the lumbar spine can exceed the total inertial load sustained by the spine because:
1. [ ] (i)
  Of the high stiffness of the facets in comparison with that of the disc
2. [ ] (ii)
  Of a drop in the load borne by the disc
3. [ ] (iii)
  Of an increase in forward flexion moment acting on the spine
4. [ ] (iv)
  Of the loosening of the ligaments during spinal compression
5. [ ] (v)
  None of the above
10.8.
Towards the end of the ejection sequence, during pilot ejection, the facets go into tension. The majority of the tensile load can be taken by:
1. [ ] (i)
  The facet capsule
2. [ ] (ii)
  The ligamentum flavum and the posterior longitudinal ligament
3. [ ] (iii)
  The interspinous and supraspinous ligament
4. [ ] (iv)
  (i) and (iii)
5. [ ] (v)
  (ii) and (iii)
10.9.
A computer model of the spine simulating pilot ejection was developed by Prasad and eventually improved upon by Tennyson. It has several characteristics. Select the incorrect answer:
1. [ ] (i)
  The model has been validated against cadaveric experiments in terms of spinal load and facet load
2. [ ] (ii)
  The model was modified to simulate living muscular response
3. [ ] (iii)
  The model is based on a finite element mesh developed by Prasad
4. [ ] (iv)
  The model is a discrete parameter model made up of masses, springs, and dampers
5. [ ] (v)
  The model can be used for both vertical and horizontal input accelerations
10.10.
Spinal compression due to shoulder restraint systems occurs in automotive crashes. This was discovered by the Prasad model and subsequently measured experimentally in cadavers. The biomechanical basis for the existence of this spine load is:
1. [ ] (i)
  Due to fact that the seat back is inclined rearward
2. [ ] (ii)
  Due to the lordosis of the lumbar spine
3. [ ] (iii)
  Due to the kyphosis of the thoracic spine
4. [ ] (iv)
  Due to the lordosis of the cervical spine
5. [ ] (v)
  Due to the elasticity in the belt material
10.11.
The articular facets of the lumbar spine transmit vertical compressive load down the spine by:
1. [ ] (i)
  Compression between the cartilaginous surfaces of the facets
2. [ ] (ii)
  Pulling on the ligamentum flavum
3. [ ] (iii)
  Contact of the tips of the inferior facet with the lamina of the vertebra below
4. [ ] (iv)
  Transmitting the load through the spinous process
5. [ ] (v)
  Using the flexor muscles of the back
10.12.
When a jet aircraft attempts to land on an aircraft carrier and misses the deck, it ditches (crashes into the ocean) alongside the carrier. In most cases, the pilot fails to eject before the aircraft sinks. The Tennyson spine model predicted that there were several possible causes of injury. Select the incorrect answer:
1. [ ] (i)
  There is contact of the odontoid process with the spinal cord, causing cord concussion
2. [ ] (ii)
  There is stretch of the cervical cord, causing cord concussion
3. [ ] (iii)
  There is chin-chest contact, causing cerebral concussion
4. [ ] (iv)
  There is a neck shear at C1-C2 with head rotation (flexion), causing injury to the cord
5. [ ] (v)
  There is very high linear acceleration of the head, causing cerebral concussion
10.13.
When a jet aircraft attempts to land on an aircraft carrier and misses the deck, it ditches (crashes into the ocean) alongside the carrier. The Tennyson spine model studied the influence of the helmet worn by the pilots during ditching. Assuming that the peak +G_z and the peak –G_x accelerations occur simultaneous, the model predicted that
1. [ ] (i)
  The helmet had no effect on odontoid displacement
2. [ ] (ii)
  The helmet caused a significant increase in head angular acceleration
3. [ ] (iii)
  The helmet caused the cord stretch to almost double
4. [ ] (iv)
  The helmet caused the chin-chest contact force to increase by 50%
5. [ ] (v)
  None of the above
10.14.
When a jet aircraft attempts to land on an aircraft carrier and misses the deck, it ditches (crashes into the ocean) alongside the carrier. The Tennyson spine model studied the influence of the helmet worn by the pilots during ditching. General conclusions that can be reached are:
1. [ ] (i)
  Head and neck responses are not sensitive to changes in the location of the c.g.
2. [ ] (ii)
  Injury parameters are generally more severe when the peak vertical and horizontal accelerations occur simultaneously
3. [ ] (iii)
  Helmets tend to decrease odontoid displacement
4. [ ] (iv)
  Chin-chest contact force is the highest when the peak vertical and horizontal accelerations occur simultaneously
5. [ ] (v)
  Cord stretch is high when the peak G_z acceleration precedes the peak G_x acceleration
10.15.
A computer model of the spine simulating pilot ejection was developed by Prasad and eventually improved upon by Tennyson. It has several characteristics. Select the correct answer:
1. [ ] (i)
  The model has not been validated against cadaveric experiments in terms of spinal load and facet load
2. [ ] (ii)
  The model was not modified to simulate living muscular response
3. [ ] (iii)
  The model is based on a finite element mesh developed by Prasad
4. [ ] (iv)
  The model is a discrete parameter model made up of masses, springs, and dampers
5. [ ] (v)
  The model cannot be used for horizontal input accelerations
10.16.
In a frontal crash, an occupant restrained by a three-point belt
1. [ ] (i)
  can sustain a thoracolumbar vertebral fracture
2. [ ] (ii)
  cannot sustain a thoracolumbar vertebral fracture
3. [ ] (iii)
  cannot exert additional load on the seat pan
4. [ ] (iv)
  can frequently rupture his/her lumbar intervertebral disc
5. [ ] (v)
  can sustain a Chance fracture
10.17.
In the quasi-static facet load confirmation experiment by El Bohy et al. (1989),
1. [ ] (i)
  Body weight was not simulated
2. [ ] (ii)
  Facet tip pressure and disc pressure were measured using identical pressure transducers
3. [ ] (iii)
  Rubber bands were used to simulate muscle
4. [ ] (iv)
  Facet load was deduced to be present when a person is standing and carrying no load in the hands
5. [ ] (v)
  Facet load would be generated only when the person is carrying a load in the hands
10.18.
The articular facets of the lumbar spine:
1. [ ] (i)
  Cannot transmit vertical compressive load down the lumbar spine
2. [ ] (ii)
  Are unable to provide shear resistance to the lumbar spine
3. [ ] (iii)
  Do not make contact with the lamina of the vertebra below
4. [ ] (iv)
  Transmit vertical load through the spinous process
5. [ ] (v)
  None of the above
10.19.
To escape from a disabled jet aircraft, the pilot needs to
1. [ ] (i)
  open up the canopy and quickly bale out off the side of the aircraft
2. [ ] (ii)
  activate the seat ejection system with an acceleration of about 30 g for 300 ms
3. [ ] (iii)
  activate the seat ejection system with an acceleration of about 10 g for 100 ms
4. [ ] (iv)
  turn the plane upside down and disconnect all belt systems so he/she can fall out of the aircraft
5. [ ] (v)
  None of the above
10.20.
After the pilot of a disabled jet has ejected and cleared the tail of the aircraft, the following events occur
1. [ ] (i)
  A seat parachute deploys and he lands while still in his seat
2. [ ] (ii)
  He separates from the seat and his personal parachute opens immediately even if he is several thousand meters above ground level
3. [ ] (iii)
  He separates from the seat and his personal parachute opens when he free falls to an appropriate altitude
4. [ ] (iv)
  He separates from the seat and needs to manually open his personal parachute whenever he feels it is safe to do so
5. [ ] (v)
  None of the above

Answers to Problems by Chapter

Prob	Ans
1	(iii)
2	(ii)
3	(v)
4	(v)
5	(i)
6	(iii)
7	(iii)
8	(v)
9	(iii)
10	(iii)
11	(iii)
12	(v)
13	(v)
14	(ii)
15	(iv)
16	(i)
17	(iv)
18	(v)
19	(v)
20	(iii)

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King, A.I. (2018). Biomechanics of Facet Loading in the Lumbar Spine. In: The Biomechanics of Impact Injury. Springer, Cham. https://doi.org/10.1007/978-3-319-49792-1_10

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DOI: https://doi.org/10.1007/978-3-319-49792-1_10
Published: 22 July 2017
Publisher Name: Springer, Cham
Print ISBN: 978-3-319-49790-7
Online ISBN: 978-3-319-49792-1
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