LECTURE 1 QUIZ

Lumbar Spine Biomechanics

Vertebral Body

• Designed to support mainly compressive loads
• Composed of a thin shell of cortical bone surrounding a core of porous cancellous bone
• Cancellous bone is formed from vertical and horizontal trabeculae
• Not solidly filled with bone, allowing for 'springy' and 'cushion' effects when loaded suddenly

Neural Arch

• Paired pedicles formed from cortical bone to resist tension and compression during spinal movements
• Paired laminae that enclose the posterior portion of the vertebral foramen
• Give rise to the spinous process
• Superior and inferior articular processes resist lumbar rotation and protect the intervertebral disc from excessive torsional stress

Facet Joint

• Guides motion between adjacent vertebrae
• Orientation changes between spinal segments
• Shares load transmitted between vertebrae with the intervertebral disc, carrying 18-20% of compressive load

Vertebral Foramina

• Typically triangular, bordered by vertebral body, intervertebral disc, pedicle, and lamina
• Functions as a passageway for spinal nerves

Functional Unit or Spinal Motion Segment

• Components:
  • Two adjacent vertebrae
  • Intervertebral disc
  • Associated ligaments

Intervertebral Disc (IVD)

• A viscoelastic material composed of:
  • Annulus fibrosis (10-20 layers of collagen fibers)
  • Nucleus pulposus (mucopolysaccharide gel with 70-90% water content)
• Vertebral end plate connects the disc to adjacent vertebrae

Mechanical Properties

• During compression: Hoop phenomena with radial expansion
• During bending: Nucleus pulposus deforms in the opposite direction of motion
• During rotation: Disc is less able to tolerate torsional forces, designed to resist compressive loads

Clinical Relevance

• Smoking, exposure to vibration, and prolonged immobilization can impair proteoglycan synthesis
• Most lifting injuries to the low back occur in the morning
• Flexion avoidance in the morning may help reduce pain
• Elevated disc fluid volume early in the morning predisposes the disc to injury during lumbar flexion