Biomechanics of the Lumbar Spine

Structure of the Lumbar Region

• The lumbar spine consists of 5 vertebrae (L1-L5) and 23 intervertebral disks.
• The first four lumbar vertebrae (L1-L4) have a similar structure.
• The fifth lumbar vertebra (L5) has a unique structure adapted for articulation with the sacrum.

Characteristics of the L5 Vertebra

• L5 has the largest body and transverse processes of all vertebrae.
• The anterior aspect of the L5 body is taller than its posterior aspect, creating the lumbosacral angle.

Forces Acting on the Spine

• Forces acting on the spine include body weight, tension in the spinal ligaments, tension in the surrounding muscles, and intra-abdominal pressure.
• The primary form of loading on the spine is axial.

Upright Position and Spinal Compression

• In an upright position, the spine is subjected to constant forward bending moment and torque.
• Spinal compression results from body weight and weight held by arms and hands.
• The total body center of gravity is anterior to the spinal column.

Torque and Counteraction

• Torque is defined as the rotary effect of a force about an axis of rotation, measured as the product of the force and the perpendicular distance between the force's line of action and the axis.
• To maintain an upright position, torque is counteracted by tension in the back extensor muscles.

Low Back Pain

• 75%-80% of Americans experience low back pain at some point in their lives, making it the second most common cause of absence in the workplace after the common cold.
• Mechanical stress and psychosocial factors contribute to low back pain.

This quiz covers the structure and characteristics of the lumbar spine, including vertebrae, intervertebral disks, primary and secondary curves, and the adaptation of the L5 vertebra for articulation with the sacrum.