Unit 5 - Lumbopelvic Spine IV including SI Joint

Sacroiliac Joints (SIJ)

• Junction between caudal end of axial skeleton and lower appendicular skeleton

• Designed for stability

  • Sacrum “wedged” between ilia

  • Effective transfer of large forces between vertebral column, lower extremities, and ground

Pelvic Ring

Components

• Sacrum

• SIJs

• Hemipelvis (ilium, pubis, ischium)

• Pubic Symphysis Joint

Pelvic Ring

Transfers body weight force bidirectionally between pelvic ring, trunk, and femurs

SI Joint Structure

• Just anterior to palpable posterior-superior iliac spine (PSIS)

• Matching auricular (little ear) surfaces of sacrum and ilium

• Semicircle “boomerang” shape

  • Concavity facing posterior

SI Joint Structure Changes

• during puberty from

  • Diarthrodial (synovial)

    • Freely movable

  • to modified Synarthrodial

    • Immovable (pg. 29)

  • Smooth to Rough surfaces

    • Enhances friction, resistance to vertical shear force

• 85% in 60s show degenerative changes, asymptomatic

• 80s, 10% of population completely ossified/fused

Ligaments

Anterior aspect

• Anterior Sacroiliac

  • Thickening of anterior / inferior regions of capsule

• Iliolumbar

  • Blends with Ant. Sacroilia

    

Ligaments

Within

Interosseous

• Strongest of SIJ

• Dense, short fibers fill gap of posterior / superior margins

• Similar to syndesmosis of distal tibiofibular joint

  

Ligaments

Posterior aspect

• Posterior Sacroiliac

  • Short and long

  • From posterolateral aspect of sacrum to iliac tuberosity and PSIS of ilium

• Sacrotuberous

  • Large

  • O: PSIS, lateral aspect of sacrum, coccyx

  • I: Ischial tuberosity

  • Blends with biceps femoris (lat. Hamstring) tendon

    

• Sacrospinous

  • Deep to sacrotuberous

  • From caudal end of sacrum and coccyx to ischial spine

    

Sacrotuberous and Sacrospinous Ligaments do not directly cross the SIJ, but do provide articular stability

Innervations

• Sensory nerve fibers within periarticular connective tissues of SIJ

  • Presence of Substance P and calcitonin-gene related polypeptides

  • Potential source of Nociception

• Spinal Innervation

  • Most consistently from dorsal rami of L5-S3

  • Less often ventral rami of L4-S2

Thoracolumbar Fascia

• Dynamic mechanical stability to lumbar spine and SIJs

• Anterior and Middle Layers (surround QL)

  • Anchor medially to TP of lumbar spine, inferiorly to iliac crests

• Posterior Layers (covers Erector Spinae, Multifidus, Latissimus Dorsi)

  • Anchor to all lumbar SP, sacrum, and ilium near PSIS

• Lateral Raphe

  • Lateral fusion of posterior and middle layers

  • Blends with Transverse Abdominus and Obliquus Internus Abdominus

Kinematics

• Rotation: 1-4 degrees

• Translation: 1-2 mm

• Nutation

  • “to nod forward”

  • Anterior sacral tilt relative to

  • Posterior iliac tilt

• Counternutation

  • Posterior sacral tilt relative to

  • Anterior Iliac tilt

• Defined as

  • Sacral-on-iliac rotation

  • Iliac-on-sacral rotation

  • Or simultaneous

• Not to be confused with Anterior and Posterior Pelvic Tiltin

  

Kinematics

SIJ Function

1. Stress Relief within pelvic ring

   1. Same for pubic symphysis

2. Load transfer between axial skeleton and lower extremities

Kinematics

Walking

• Small, oppositely directed torsions at R and L iliac crests

• Dissipates stress

Kinematics

Childbirth

• Mobility / joint laxity increases during last trimester

• Especially notable during 2nd pregnancy

• Weight-gain + increased lordosis + hormone-induced ligamentous laxity

Nutation Torque

• Increases stability at SIJ

  • Gravity

  • Passive tension from stretch ligaments

  • Muscle Activation

• Increases compression and shear forces between surfaces

• Full Nutation = “close-packed”

• Counternutation = “loose-packed

  

Nutation Torque: Gravity

• From Body Weight passes downward

  • Anterior to SIJs

  • Posterior to femoral heads

  • Rotates sacrum anteriorly

• Femur through Acetbula

  • Upward-directed counter force

  • Rotates ilium posteriorly

• “Locks” SI

  

Nutation Torque: Ligaments

• Tension

  • Interosseous Ligament

  • Sacrospinous Ligaments

  • Sacrotuberous Ligaments

• Slackened

  • Long Posterior Sacroiliac Ligament (not pictured

    

Nutation Torque: Muscles

• Based on attachments to

  • Thoracolumbar fascia

  • Sacrospinous & Sacrotuberous Ligaments

• Stability generated by

  • Active compression forces against articular surfaces

  • Increasing nutation torque, “active locking mechanism”

  • Tensing connective tissues that directly or indirectly reinforce joint

  • Combination of above

Nutation Torque: Muscles

Directly

• Rotate Sacrum anteriorly

  • Lumbar Multifidi

  • Erector Spinae

• Rotate Ilium posteriorly

  • Rectus Abdominus

  • External Oblique

  • Biceps Femoris (hamstring)

  • Gluteus Maximu

    

Nutation Torque: Muscles

Indirectly

• Connected through Thoracolumbar Fascia

  • Latissimus Dorsi

  • Gluteus Maximus

  • Erector Spinae

  • Internal Oblique

  • Transverse Abdominus

• Valsava Maneuver

  • Diaphragm

  • Pelvic Floor Muscles

Why Terminology Matters

• Outdated terms create confusion

• Consistency improves communication

• Diagnostic accuracy requires precise language

Pain Classifications

• Nociceptive pain

• Referred pain (from adjacent structures) 

• Central sensitization

Pain Mechanism Revisited

Nociceptive

localized, predictable

Pain Mechanism Revisited

Referred

segmental, mimics SIJ

Pain Mechanism Revisited

Central

diffuse, unpredictable, non-mechanical

Hallmarks of SIJ Related Pain

• PSIS tenderness

• Pain with load transfer tasks

• Negative centralization

• Negative hip signs

• Symptom duration >3 months

Contemporary vs. Outdated Terms

• Stop saying: 'upslip', 'rotation', 'inflare'

• Start saying: 'SIJ-related nociceptive pain'

• Use functional and pain-based descriptors

Where SIJ Fits in Chronic LBP

• SIJ accounts for ~15-30% of chronic LBP

• Often coexists with myofascial or lumbar issues

• Not always the primary pain source

Chronic Pain = Multidimensional

• Biopsychosocial contributions

• Fear, beliefs, deconditioning

• Don’t ignore mood, sleep, or stress

Why Rule Out First?

• Most LBP is lumbar or hip in origin

• SIJ rarely acts alone

• Rule-out prevents misdiagnosis and false positives

Clinical Priority: Rule Out the Lumbar Spine

• Centralization with repeated motions (McKenzie)

• Neurological screen: strength, sensation, reflexes

• Facet loading patterns

• Pain with extension, prolonged sitting, or flexio

  

Impairment-based Classifications Lumbar Spine

• Movement Coordination Deficits

• Mobility Deficits

• Referred Pain

• Radiating Pain (neuropathic)

Now Rule Out the Hip

• ROM testing (especially IR <15°)

• FABER and FADIR provocation tests

• Capsular pattern: IR > Flexion > Abduction

• Pain with stairs, squatting, prolonged sitting

  

Hip Pathology Patterns

• Hip OA: age >50, stiffness, IR loss

• FAI: sharp anterior pain with flexion and rotation

• Labral pathology: clicking, catching, instability

Rule-Out Summary

• Step 1: Centralization or neuro signs = treat spine

• Step 2: IR <15°, FABER/FADIR = treat hip

• Step 3: No spine/hip findings? Consider SIJ

Laslett’s Cluster Overview

• ASIS Distraction Test

• ASIS Compression Test

• Thigh Thrust

• Sacral Thrust

• Gaenslen’s Test
  3 out of 5 = SIJ likely

ASIS Compression Test

• applies medial force to the ASIS, which compresses the anterior SI joint and gaps the posterior surface

  

ASIS Distraction Test

• lateral force is applied to the anterior-superior iliac spines, which distracts or opens the anterior aspect of the SI joint and simultaneously compresses the posterior aspect

  

Thigh Thrust

• patient is laying supine

• position the hip at 90 degrees and apply an axial load through the femur

  

Sacral Thrust

• the patient is laying prone and you apply a vertical force from P to A over the sacrum

  

Gaenslen’s Test

• should be performed on both sides

• The setup creates opposing rotational forces across the pelvis

• One leg is flexed, promoting posterior rotation of the ilium

• The opposite leg is extended off the table, encouraging anterior rotation of the contralateral ilium

• Since each side of the pelvis is stressed differently, testing both sides is essential to assess for SI joint related pain in either direction

  

Clinical Application Tips

• Confirm symptom location and type

• Apply pressure gradually

• Use consistent technique

• Be cautious with highly irritable patients

Why Not Just One Test?

• Single test sensitivity/specificity is too low

• Multiple tests increase diagnostic accuracy

• Evidence supports 3/5 positive as threshold

Limitations of the Cluster (Laslett’s)

• Not validated in acute LBP

• Can’t rule in central sensitization

• False positives if spine or hip not ruled out

CPG Informed Treatment Priorities

• Stabilization training

• Lumbopelvic motor control

• Manual therapy for symptom modulation

• Patient education and reassurance

Motor Control: Core Activation

• Start with deep stabilizers: TA, multifidus

• Train in neutral spine positions

• Incorporate breath and pelvic floor control

Stabilization Progression: Early to Advanced

• Phase 1: Isometric bracing, supine activation

• Phase 2: Bridges, side planks, bird-dogs

• Phase 3: Anti-rotation, single-leg stability

• Phase 4: Load-bearing and dynamic movement

Manual Therapy: When and Why

• Use to modulate pain, not 'realign joints'

• Mobilization: SIJ, lumbar, thoracic, hip as needed

• Soft tissue: glutes, piriformis, QL

Pain Science and Patient Beliefs

• Pain ≠ damage

• Reframe beliefs about alignment and instability

• Build self-efficacy through graded exposure

When to Refer or Reassess

• No progress after 6–8 weeks

• Increasing disability or fear

• Imaging or medical referral if red flags

The Treatment Mindset

• SIJ is a regional contributor, not always primary

• Treat movement, not just tissue

• Progress gradually, educate constantly

• Help patients reclaim confidence and control