Neurosurgery notes/Spine/Spinal biomechanics/Alignment goals

Alignment goals

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Spinal biomechanics
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Cervical spine

Cervical spine

 

Thoraco-lumbar spine

  • General
      • Under/over correction of deformity
        • Under-correction of lumbar lordosis can lead to
          • Compensatory pelvic retroversion
            • causing dorsally directed forces at the uppermost instrumented vertebra (UIV) and ventrally directed forces in the non-instrumented spine, increasing the risk of proximal junctional failure (PJF).
          • Tension rather than compression through the instrumented construct, particularly in the lower lumbar spine, → pseudarthrosis
        • Over-correction of lumbar lordosis (the body attempts to achieve a C2 Tilt of 0)
          • Results in a negative global sagittal alignment, leading to
            • Pelvic anteversion OR
            • PJK (more common)
  • SRS-Schwab Alignment goals
    • PI-LL < 10°
    • PT < 20°
    • SVA < 4 cm
  • GAP scoring system
    • Ideal Lumbar lordosis = PI x 0.62 + 29
    • Ideal Sacral slope = PI x 0.59 + 9
    • Ideal Global tilt = PI x 0.48 - 15
    • Lower lumbar lordosis ratio: 50%-80%; L4-S1/L1-S1x100
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