Biomechanics (Ch 9)

Spinal regions

33 vertebrae: 7 cervical, 12 thoracic, 5 lumbar, 5 fused sacral, 4 fused coccygeal.

Atlas (C1)

First cervical vertebra.

Axis (C2)

Second cervical vertebra; helps enable head rotation.

Motion segment

Two adjacent vertebrae and their associated soft tissues; functional unit of the spine.

Facet joints

Posterior gliding joints that guide and limit spinal motion and help bear compressive loads.

Intervertebral disc

Fibrocartilage structure that cushions adjacent vertebral bodies.

Nucleus pulposus

Fluid-rich, gel-like center of an intervertebral disc.

Annulus fibrosus

Outer fibrocartilaginous ring that holds vertebral bodies together.

Primary spinal curves

Thoracic and sacral curves; present at birth and concave anteriorly.

Secondary spinal curves

Cervical and lumbar curves; develop as children begin supporting the body upright.

Lordosis

Exaggerated lumbar curvature.

Kyphosis

Exaggerated thoracic curvature.

Scoliosis

Abnormal lateral curvature of the spine.

Spinal movements

Flexion, extension, lateral flexion, rotation, and circumduction.

Erector spinae

Iliocostalis, longissimus, and spinalis; extend and laterally flex the spine and assist rotation.

Rectus abdominis

Bilaterally flexes the lumbar spine and assists posterior pelvic rotation.

External oblique

Bilaterally flexes the trunk; unilaterally rotates the trunk to the opposite side.

Internal oblique

Bilaterally flexes the trunk; unilaterally rotates the trunk to the same side.

Spinal loading forces

Body weight, ligament tension, muscle tension, intra-abdominal pressure, and external loads.

Spinal bending and disc loading

Bending creates tension on one side of a disc and compression on the other; rotation creates shear stress.

Spondylolysis vs. spondylolisthesis

Spondylolysis is a pars interarticularis fracture; spondylolisthesis is forward vertebral displacement.