Biomech

6/24/1999

Facets

• Limit motion of the spine
• Protect the disc
• Disc rotates 4-8° before tearing
• Uncinate process limit flexion/extension
• Cervical facets appear like a ski lift
• Compression forces
• Cervical spine carries 1/3 of the weight
• Lumbar spine carries none of the weight—facet is straight up and down
• Rotation—shoulder to nose—C1 has most of it
• Thoracic spine—turn up a little harder and turn outward
• Bigger the disc, the more motion
• Fig 10-6 Biomechanics of Lumbar Spine
• Fig 3.2-3.2 B&T
• Fig 7.7 B&T
• Rotation of the lumbar spine
• Facet on one side stops and prevents further rotation
• To go farther have to break the facets
• Only get about 4° of rotation before tearing could begin

Fig 3.5

• L4-5-- 45° protects in almost all areas—B
• L1-2 15°
• L5-S1 45°
• Do not know exactly where the facets are oreinted, and cannot tell on plan x-ray
• Every pt will be differetn
• Motion palpate will be different for everyone
• End feel is the most important

• Tropism—the facets are oriented in different planes of the same vertebrae
• Common finding
• At L5 is runs about 50%
• T12 about 40%
• Problems because transition areas of the spine

• Sagittal at birth
• 1-2 y/o much change
• flatten out by age 8

Lordosis of Cervical Spine

Kyphosis of Thoracic Spine

Lordosis of Lumbar Spine

• what affects the normal curves
• the way the discs are shaped
• bodies are shaped that way
• muscles can also influence
• cervical bodies are smaller in the front than the back—by itself it would be kyphotic
• the shape of the disc is what makes it lordotic—larger in the front
• thoracic is from the shape of the bodies—smaller in the front
• the discs are flat
• increased kyphosis would look for fracture of the bodies

• lumbar—L1 and L2 are smaller in the front, L3 and L4 are equal, L5 is larger in the front
• study at Logan had L1, L2, L4 were flat
• disc height if very important
• look from the bottom and work your way up
• look at the sacral base angle
• compensation
• direct energy in the right planes
• strength of something w/curves
• 2N+1
• normal spine is 7
• most cases has no or very little curves; therefore have little strength