Lumbar Biomechanics

Question 1

Lumbar Flexion

Answer 1

• „Straightening of the lumbar curve
• Flexion of the trunk is controlled by eccentric contraction of the multifidus and erector spinae
• Lying supine, the psoas muscle is needed for a full sit-up
• Psoas produces anterior shear as well as compression
• cont..
• „At the end of full flexion, the lumbar spine assumes a straight alignment or is curved slightly anterior
• „Reversal of the lordosis occurs primarily at the upper levels and in some individuals at L4-5. L5-S1 does not normally reverse in the lordosis.
• Flexion relieves posterior compression of the inter-body joints, and the lumbar facets
• Anterior interbody joint compresses and intra-discal pressure increases
• At end range, after a brief period, the extensor muscles stop firing (“flexion relaxation”)

Question 2

Limiting Flexion

Answer 2

„Limiting flexion:

• „Facet joint capsules
• Joint capsules = 39%
• Facet joints limit anterior translation
• Ligaments posterior to the axis of motion
• Supraspinous and interspinous ligaments = 19%
• Ligamentum flavum = 13%
• Intervertebral disc = 29% resistance

Question 3

Lumbar FLX/EXT Sagittal Plane Motion

Answer 3

Flexion:

• Upward slide of bilateral facet joints,
  
  • “opening movements.”
  • Anterior translation

Extension:

• Downward slide of bilateral facet joints,
  
  • “closing movements.”
  • Posterior Translation.

Question 4

Extension

Answer 4

• „Posterior sagittal plane rotation
• „Small amount of posterior translation
• „Downward movement of the inferior articular process and the spinous process, limited by bony impaction (between the spinous processes)
• „Impaction also occurs between the inferior articular process and the subjacent lamina
• „When back muscles are active, substantial compression occurs, increasing the loading on the facet joints and the interbody joints.

„The zygapophyseal joints become weight- bearing.

„Initiated by the long back extensors, multifidus, and controlled by the abdominal muscles.

Question 5

Axial Rotation

Answer 5

• „Described as the direction the body moves (rotates)

„Described as the superior vertebra moving on the inferior vertebra

• Primarily produced by abdominal muscles (obliques).
• „Internal oblique - ipsilateral rotation
• External oblique - contralateral rotation
• Multifidus is active bilaterally to control movement, prevent flexion.
• „Involves twisting or torsion of the intervertebral discs and impaction of the zygapophyseal joints.
• „Supraspinous and interspinous ligaments are taut.
• „At the zygapophyseal joint, water is squeezed out of the articular cartilage with compression - reabsorbed when compression is released.
• Ipsilateral joint does not gap, but decompresses.
• „Primarily the load is born by the impacted facet joint and the intervertebral disc (35% due to disc).
• „The ipsilateral facet joint capsule is taut.
• „A minor amount of translation occurs with rotation.

Question 6

Lateral bending

Answer 6

• „Coronal or frontal plane rotation
• „May be accompanied by flexion or extension - inconsistent, but extension occurs more frequently
• „Translation most common to the contralateral side.
• Frontal plave motion:
  
  • Downward slide on the concave side (lateral bend towards).
  • Upward slide on the convex side (lateral bend away).
  • Translation to the convex side.
  • Coupled with rotation

Question 7

Coupled movements

Answer 7

• „Axial rotation and lateral flexion are coupled with one another.
• Axial rotation is variably coupled with flexion or extension, either may occur.
• Lateral flexion is more frequently coupled with extension, but small amounts of flexion may occur.
• Example:
  
  • „Flexion of a lumbar segment involves 8 to 13 degrees sagittal plane rotation and 1 to 3 mm anterior translation.
  • Some small amplitude and inconsistent in direction vertical and lateral translations occur.

Question 8

Coupling with lateral flexion and axial rotation

Answer 8

• „Axial rotation of the upper three segments typically coupled with contralateral lateral flexion.
• Lateral flexion is coupled with contralateral rotation

Question 9

Coupled motion: Fryette’s Law

Answer 9

„Fryette’s Law:

• In neutral, rotation and lateral bending are coupled to opposite sides.
• In flexed or extended positions, lateral bending and rotation are coupled to the same side.
• *(some references report same side coupling only with extension)

Question 10

Coupled motion: L5-S1

Answer 10

• „Axial rotation of L5-S1 is accompanied by ipsilateral lateral flexion, and lateral flexion is accompanied by ipsilateral axial rotation.
• Not all individuals demonstrate the same degree of coupling, or the same direction of coupling.