Lx Biomechanics

Question 1

Which movements are available at the lumbar spine, and what is the typical range of motion for each?

Answer 1

Flexion: 50
Extension: 15
Lateral flexion: 40 (20 each side)
Rotation: 5 (in total)

Question 2

Describe the biomechanics of flexion and extension at the lumbar spine

Answer 2

In flexion, the inferior facets of upper vertebrae slide superiorly and anteriorly on superior facets of lower vertebrae

In extension, the inferior facets of upper vertebrae slide inferiorly and posteriorly on superior facets of lower vertebrae

Question 3

Which structures resist excessive flexion and extension at the lumbar spine?

Answer 3

Excessive flexion resisted by:
facet joint capsule
IVD
supra & infraspinous ligaments
ligamentum flavum

Excessive extension limited by:
bony contact of SPs
anterior longitudinal ligament

Question 4

What is the impact of flexion and extension on the vertebral column and IVDs?

Answer 4

Flexion:

• increases anterior compressive force on IVDs (pressing the IVDs posteriorly)
• transmits force from the facet joints to the IVDs
• increases the volume and size of the vertebral canal and intervertebral foramina

Extension:

• decreases anterior compressive force on IVDs
• transmits force from the IVDs to the facet joints
• decreases the volume and size of the vertebral canal and intervertebral foramina

Question 5

What is lumbopelvic rhythm and how does it impact on flexion and extension in the lumbar spine?

Answer 5

Lumbopelvic rhythm is the co-ordination of the hips and the lumbar spine in the movements of flexion and extension.

In flexion:

• 40 degrees Lx
• 70 degrees hips

In extension (from forward flexed standing):

• extension should initiate from the hips first using hip extensor muscles, followed by engagement of the lumbar spine extensor uscles
• if the hip extensors do not contribute to lumbopelvic rhythm, extensors of the lumbar spine will overwork

Question 6

describe the movement of axial rotation at the lumbar spine

Answer 6

Axial rotation is extremely limited at the lumbar spine given the almost sagittal plane orientation of the facet joints of the vertebrae, which creates a bony block to rotational movements

This limitation on axial rotation enhances the stability of the lumbar spine

There is a total of 5 degrees of rotation available at the lumbar spine (1 degree approx each vertebrae)

Question 7

Describe the biomechanics of lateral flexion at the lumbar spine

Answer 7

Lateral flexion is coupled with ipsilateral rotation in the lumbar spine

Question 8

Describe the biomechanics and implications of anterior and posterior pelvic tilt

Answer 8

In anterior pelvic tilt:

• pelvis is tilted anteriorly
• lordosis in lumbar spine is exacerbated
• excessive lordosis in lumbar spine places excessive anterior compressive forces on IVDs and exacerbates lumbo-sacral angle
• mm shortened: the mm of the lumbar spine, the hip flexors
• mm lengthened: the hamstrings, the anterior trunk

In posterior pelvic tilt:

• pelvis is tilted posteirorly
• reduces lordosis in the lumbar spine
• reduces anterior compressive shear on IVDs of lumbar spine and reduces lumbo-sacral angle and associated anterior compressive shear forces at the LSA
• lengthens lumbar extensor muscles and hip flexor muscles
• stronger engagement of the anterior trunk and hip extensor muscles

Question 9

Describe the impact of chronic ‘slumped’ posture on the lumbar spine

Answer 9

In this posture there is excessive posterior pelvic tilt and the lumbar spine is placed into unnatural kyphosis

This weakens the passive posterior structures of the lumbar spine, including the facet joint capsules and the posterior ligaments, rendering them less able to resist extreme flexion and to resist posterior herniation of the IVDs

This position is also associated with dysfunctional biomechanics higher up the vertebral column:

• tips Tx and Cx into excessive flexion / kyphosis
• associated with forward head posture

Question 10

Describe the lumbosacral angle

Answer 10

(LSA) formed by the junction of the L5 and the S1

• base of sacrum is tilted anteriorly and inferiorly 40 degrees
• base of L5 tilted posteriorly to meet the base of the sacrum
• interaction of body weight to LSA creates strong anterior shear forces at the LSA
• anterior shear force exacerbated by anterior pelvic tilt and increased lumbar lordosis
• anterior shear force offset by posterior shear force of erector spinae muscles