Biomechanics of the Lumbar Spine Flashcards
What is the most important characteristic of the lumbar spine?
it must bear tremendous loads created by body weight that interact with forces generated by lifting and other activities involving powerful muscle actions
The lumbar spine is largely responsible for what?
trunk mobility
Describe the anatomy of the facets of the lumbar spine
large
thick
strong
L/S inferior articular processes are CONVEX and face what direction?
anterolaterally
L/S superior articular processes are CONCAVE and face what direction?
posteromedially
In what plane are the L/S facets?
sagittal
What occurs to the facets at the lumbosacral junction?
they become more coronal
What do the facet configuration of the L/S limit? and allow?
limits: rotational flexibility
allows: for greater mobility in flexion and extension
What is the facet configuration of L1-4?
sagittal orientation
limits axial rotation (øy)
What is the facet configuration of L5-S1?
coronal orientation
limit posterior/anterior shear (z translation)
The lumbar facets normally carry ____% of axial load and up to ____% in extension.
18%
33%
What is the primary movement in the Lumbar spine?
Flexion/extension (øx)
What % of trunk flex/ext occurs in the L/S?
75%
TWICE as much FLEXION as extension
What rotation is limited in the L/S overall due to sagittal facet orientation?
øy Axial rotation
Lateral bending in the L/S is coupled with axial rotation; what side does the spinous go to?
ipsilateral (may switch at L4 and L5)
Where is the nucleus located in the L/S?
somewhat posteriorly in the disc
What is the disc height-to-body height ratio in the L/S?
1:3
(this relationship allows for more movement than T/S, but less movement than C/S and gives the disc greater resistance to axial compressive forces
What does the L/S canal contain and protect proximally?
conus medularis
What does the L/S cancel contain and protect distally?
cauda equina & spinal nerves distally
Where does the spinal cord end?
L2; nerve roots continue down the spinal canal as the cauda equina
CNS is tethered to the coccyx by what?
filum terminale
NRs exit the dura slightly above the foraminal opening, causing their course to be more ___________ and their length to increase.
oblique
When does the secondary lordotic curve of the L/S occur?
starts to develop ~ 9-12 months of age/beginning to sit up. Becomes established as they learn to stand (~18m)
Where is the apex of the L/S lordotic curve?
L3-4 disc
What should the normal lumbar lordosis angle be?
20-60 degrees
Changes in the sacral angle can influence the depth of the ______ curves in the spine.
A-P
What happens to the sacral base angle with an anterior pelvic tilt?
increases; resulting in an increase in the lumbar lordosis, which places more weight-bearing responsibility on the facets
What happens to the sacral use angle with a posterior pelvic tilt?
decreases; resulting in a decreased lumbar lordosis, placing more weight-bearing responsibly on the disc and a decrease in spines ability to absorb axial compression forces
What is the major stabilizer of the L/S?
(QL) Quadratus Lumborum
How much is the QL lumborum active?
Heavy lifts?
isometrical lateral bending holds?
standing isometric twists?
74%
54%
42%
What are the characteristics of the ALL & PLL of the L/S?
Restricts excessive flex/ext
Well developed (ALL>PLL)
Attached to the vertebral body and the annulus
What are the characteristics of the Ligamentum Flavum in the L/S?
Highly elastic
Acts as a barrier to material that would otherwise encroach on cord during ROM
What are the characteristics of the Lumbodorsal Fasica in the L/S?
Attachment for: Transverse Abdominis, internal oblique, lattissimus dorsi
Acts like a large extensor retinaculum to constrain long tendons of thoracic and lumbar extensors
What are the characteristics of the Interspinous lig in the L/S?
Acts like a collateral lig, controls vertebral rotation to follow an arc through flexion range
What are the characteristics of the supraspinous leg in the L/S?
provides resistance against excessive forward flexion
What are the characteristics of the facets in the L/S?
Well developed
Restricts joint flex
Restrics distraction of facet surfaces during axial rotation
What is lig damage in the L/S caused by?
joint laxity; joint degeneration follows
ligament damage mark the beginning of the end
