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Fryette's Laws & Spinal Mechanics
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Fryette's Laws & Spinal Mechanics

Type I (neutral, group) vs Type II (non-neutral, single segment).

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◆Fryette's First Law (Type I — Neutral)

  • •In NEUTRAL position, side-bending and rotation occur to OPPOSITE sides
  • •Involves a GROUP of vertebrae (≥3 segments)
  • •Compensatory, usually chronic, asymmetric posture
  • •Example: T5–T8 NSRRL (neutral, side-bent R, rotated L)

◆Fryette's Second Law (Type II — Non-neutral)

  • •In FLEXION or EXTENSION, side-bending and rotation occur to the SAME side
  • •Involves a SINGLE segment
  • •Often acute, traumatic, painful
  • •Example: T4 FRSR (flexed, rotated R, side-bent R)
  • •Type II dysfunctions get priority for treatment

◆Fryette's Third Law

  • •Motion in one plane modifies (limits) motion in the other planes
  • •Practical: if a segment is held in flexion, side-bending and rotation will be reduced

◆Applies to thoracic & lumbar ONLY

  • •Cervicals follow different rules (especially C0–C2)
  • •C2–C7 typically: side-bending and rotation are coupled to the SAME side (Type II-like)
  • •OA (C0–C1): side-bending and rotation OPPOSITE
  • •AA (C1–C2): essentially pure rotation (no side-bending coupling)

Type I vs Type II

FeatureType I (Neutral)Type II (Non-neutral)
PositionNeutralFlexed or extended
CouplingSide-bending opposite rotationSide-bending SAME side rotation
SegmentsGroup (≥3)Single segment
OnsetChronic, compensatoryAcute, often traumatic
Treatment priorityLowerHIGHER
ExampleT5–T8 NSRRLT4 FRSR or T4 ERSL

High-yield pearls

  • ◆Mnemonic: Type I — 'opposite' (neutral); Type II — 'same' (flexed/extended)
  • ◆Treat Type II FIRST when both are present
  • ◆Cervical spine doesn't follow Fryette's laws (C2–C7 = same-side coupling regardless of position)
  • ◆OA reversed: side-bend and rotation are OPPOSITE
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