SI joint function:

  1. Keystone of the arch formed by both pelvis
  2. Works in unison with pubic symphysis in
    1. Shock absorbing
    1. Weight transfer
    1. Handling torsional stress

Anatomy

  • The joint has 2 parts:
  • Diarthrosis (Plane synovial)
  • Syndesmosis (interosseus membrane)
  • Capsule is present only anteriorly
  • C shaped synovial surface:
  • Ilium: fibrocartilage
  • Sacrum: Hyaline
  • Iliac faces anterior inferior medial
  • Sacrum faces posterior superior lateral
  • Important bony landmark:
    • ASIS, PSIS, Ischial Tuberosity, ischial spine, GT
  • Ligaments:Major
  • Other ligaments:
  • Sacrotuberous
  • Sacrospinous
  • Iliolumbar
  • Lumbosacral
  • Sacroiliac

Biomechanics

Movements:

Nutation: Sacral Nodding = posterior pelvic tilt/bilateral posterior innominate rotation: ASIS up PSIS down——–ilia come closer ischial tuberosities go further

Counter nutation: Sacral standing = anterior pelvic tilt/ bilateral anterior innominate rotation: ASIS down PSIS up——–ilia go further ischial tuberosities come closer

Movement of SIJoint with respect to hip motion:

Hip flexion: Posterior rotation of innominate= nutation= : ASIS up PSIS down,  ischial tuberosity go laterally

Hip extension: Anterior rotation of innominate= counter nutation= : ASIS down PSIS up,  ischial tuberosity come medially

Movement of SIJoint with respect to lumbar spine motion:

Bending forward:

  1. Innominate forward rotation
  2. Upto 60’ sacral nutation
  3. >60’ counter nutation

Extension= innominate posterior rotation, sacral nutation

Side flexion: innominate towards bent side, sacrum opposite side

Rotation: Same side nutation, opposite side counter nutation (Right side rotation= right pelvis nutates)

Pathomechanics

The following conditions may be due to postitonal faults or muscle tigntness.

  1. Upslope: ASIS & PSIS of affected side higher than the normal side
  2. Downslope: ASIS & PSIS of affected side lower than the normal side
  3. Anterior rotation deformity: ASIS lower and PSIS higher than the normal side. Sacrum goes for torsion- creates scoliosis. Also, acetabulum has gone down and posterior, so the affected side is longer in standing and shorter in long sitting in functional length.
  4. Posterior rotation deformity: PSIS lower and ASIS higher than the normal side. Sacrum goes for torsion- creates scoliosis. Also, acetabulum has gone up and anterior, so the affected side is shorter in standing and longer in long sitting in functional length.
  5. Inflare: ASIS of the affected side closer to midline
  6. Outflare: ASIS of the affected side further from midline
  7. Anterolateral shift of SIJ
  8. Posteromedial Shift of SIJ
  9. Compression of SIJ
  10. Gapping of SIJ

Assessment

  • History
  • Observation/palpation
  • Pelvic balance ins standing: for LLD
  • PSIS palpation for levels
  • ASIS palpation for levels
  • ASIS observation for flares (supine)
  • Standing flexion test

Management

SI Distraction

SIJ Compression

SIJ Posterior torsion

SIJ Anterior Torsion

SIJ Inflare

SIJ Outflare