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Vertebral Column > Sacroiliac joints > Flashcards

Sacroiliac joints Flashcards

1
Q

Describe the sacroiliac joint

A
  • Point of articulation between the ilia and the sacrum
  • Largest axial joint in the body
  • Orientated anteriorly and laterally in the transverse plane
  • Acts to revlieve stresses and transmit forces from the lumbar spine
  • Located at the point of maximal torsional stress in the pelvic ring
  • Multiplanar joint - 3 axes
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2
Q

Discuss the classification of the sacroiliac joint

A
  • There is debate
  • More recent studies classified it as a diarthrodial synovial joint.
  • Most likely:
    • Synovial in its anterior 1/3
    • Fibrous in its posterior 2/3
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3
Q

Describe the capsule of the sacroiliac joint

A
  • Composed of 2 layers in the first decade of life
  • Surrounds entire joint attaching to articular margins
  • Becomes fibrous with increasing age
  • Anterior capsule is very thin
  • Posterior capsule is rudimentary / absent
  • Nerve fibres within the capsule
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4
Q

Describe the 2 layers of the sacroiliac joint capsule

A
  • Inner layer - synovial membrane (intima). Composed of 2-3 cellular layers. Contains synovial villi which extend into the joint.
  • Outer layer - Fibrous. Composed of connective tissue containing fibroblasts, blood vessels and collagenous fibres.
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5
Q

Describe the articular surfaces of the sacroiliac joint

A
  • Auricular L- or C- shaped undulating articular surfaces - enhance stability and help protect from vertical shear force.
  • Lateral aspect of the sacrum
  • Medial aspect of the ilium
  • Sacral articular surface smaller in females
  • Cranial limb - shorter and more horizontal
  • Caudal limb - longer and more vertical
  • Articular portions surrounded by synovial membrane
  • High coefficient of friction
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6
Q

What is meant when the articular surfaces of the sacroiliac joint are described as undulating?

A

They have complementary depressions and elevations which contribute significantly to the stability of the joint by an interlocking mechanism.

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7
Q

Describe the articular cartilage on the sacral surface of the sacroiliac joint

A
  • Debate in the literature
  • Generally described as typical hyaline cartilage
  • White, glossy and smooth
  • Between 1-3mm thick
  • Often remains relatively unaltered from infancy until okd age
  • 2-3x thicker than iliac articular cartilage
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8
Q

Describe the articular cartilage on the iliac surface of the sacroiliac joint

A
  • Generally characterised as fibrocartilage
    • Histological and biochemical analysis contradict this
  • Duller in colour than sacral and appears striped
  • Bundles of collagen fibres
  • Appears like fibrocartilage but histologically is more similar to hyaline cartilage
  • Typically less than 1mm thick
  • Exhibits morphological changes during ageing, resembling osteoarthritic degeneration.
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9
Q

What is the likely reason for the iliac articular cartilage being thinner than the sacral articular cartilage?

A

Because the sacral cartilage is involved in transmitting forces, whereas the iliac cartilage absorbs these forces.

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10
Q

Discussion of the sacral and iliac cartilages in the literature

A
  • Paquin (1983) concluded that the iliac cartilage represents a special form of hyaline cartilage.
  • Kampen and Tillmann (1998), however, state that iliac joint surface is fibrocartilaginous only in early childhood, becoming more hyaline with maturation.
  • Tuite (2008) states that both iliac and sacral surfaced are covered with hyaline cartilage, but concedes that cartilage is thinner on the iliac surface.
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11
Q

Describe the accessory sacroiliac joint

A
  • Anatomic variant
  • Found posterior to the true sacroiliac joint, between the medial aspect of the posterior superior iliac spine and a transverse tuberosity lateral to the second sacral foramen (rudimentary).
  • Aetiology is unclear
  • Common - 13/100 CT scans
  • Prassopoulos et al. (1999) - found that accessory joints are more common in elderly and obese patients.
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12
Q

List some ‘normal’ variation patterns of the sacroiliac joints

(not considered pathologies)

A
  • Iliosacral complex (5.8%)
  • Bipartite iliac bony plate (4.1%)
  • Crescent-like iliac bony plate (3.7%)
    • ​More common in women than men and not associated with increasing age
  • Semicircular defects on both iliac and sacral sides (3%)
  • Ossification centres (0.6%)
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13
Q

What is the main function of the ligaments of the sacroiliac joint?

A
  • Act to limit motion in all planes
  • Contribute significantly to overall stability
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14
Q

Describe the anteiror sacroiliac ligament

A
  • Broad, flat ligament comrpised of several bands
  • Ala and pelvic surface of sacrum → adjoining margin of the anterior surface of the ilium.
  • Extension of the anterior joint capsule
  • Does not make a contribution as significant as that of the posterior ligament
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15
Q

Describe the posterior sacroiliac ligaments

A
  • Several distinct bands. Split into:
    • Short posterior (superiorly)
    • Long posteior (inferiorly)
  • Is a continuation of the posterior fibrous joint capsule
  • Their function is effectively to compress the sacrum between the ilia.
  • Fibres run obliquely upward and outward from the sacrum.
  • Te axial weight pushing down on the sacrum pulls the ilia medially so that they compress the sacrum between them, locking the congruent surfaces of the sacroiliac joint together.
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16
Q

Describe the short band of the posterior sacroiliac ligament

A
  • Fibres run obliquely
  • 1st/2nd transverse tubercles → iliac tuberosity
  • Resists forward movement of the sacral promontory
  • Shown in red
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17
Q

Describe the long band of the posterior sacroiliac ligament

A
  • Most superficial fibres
  • Fibres run almost vertically
  • From the posterior superior ilac spine → 3rd/4th transverse tubercles of the sacrum
  • Shown in blue
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18
Q

Describe the interosseous sacroiliac ligament

A
  • Deepest ligament
  • Thick and extremely strong
  • Lies in recess between sacrum and ilium, dorsal to the joint cavity
  • Multidirectional stability
  • ‘Axial joint’ enclosed within the ligament
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19
Q

What happens when the interosseous sacroiliac ligament is severed?

A

Cadaveric study showed severing of ligament leads to increased sacroiliac joint motion - this shows the importance of this ligament in limiting movement.

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20
Q

List the accessory ligaments of the sacroiliac joint and state their function

A
  • Sacrotuberous ligament
  • Sacrospinous ligament
  • Iliolumbar ligament
  • Although these ligaments are situated at a distance from the joint, they confer vital added stability against unwanted movements.
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21
Q

Describe the sacrotuberous ligament

A
  • Posterior ilium, lateral sacrum and lateral coccyx → ischial tuberosity
  • Anchors inferior sacrum to ischium, counterbalancing the rotation at the superior aspect of the sacrum
  • Shown in red
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22
Q

Describe the sacrospinous ligament

A
  • Lateral sacrum and lateral coccyx → ischial spine
  • Deep to sacrotuberous ligament
  • Important when high force is applied, such as landing after high jumping / weight lifting.
  • So closely associated with coccygeus that it can be considered a fibrous part of the muscle.
  • Shown in blue
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23
Q

What is the role of the long head of biceps femoris in the sacroiliac joint?

A

Acts to stabilise the sacroiliac joint via the sacrotuberous ligament.

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24
Q

Describe the iliolumbar ligament

A
  • Transverse processes of L4/L5 → posterior iliac crest
  • Not associated with the sacrum
  • Strengthens the connection between the ilium and the vertebral column
  • Prevents L5 from anterior displacement from S1 and opposes gliding movements between the vertebra
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25
Q

Describe the development of the sacroiliac joint

A
  • Develops in week 8 from a 3-layered structure in pelvic mesenchyme.
  • Central cavity forms when in-utero movements begin - week 10.
  • Complete development of joint cavity finished by the 8th month when the joint becomes capable of movement.
  • Synovial membrane formed shortly prior to birth via mesenchyme.
  • Bony surfaces of the joint are smooth until puberty, after which combinations of bony ridges and grooves appear.
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26
Q

Describe the arterial supply of the sacroiliac joint

A
  • Anteriorly - branches of iliolumbar artery
  • Posteriorly - superior gluteal artery
  • Anteriorly and posteriorly - lateral sacral arteries
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27
Q

Describe the venous drainage of the sacroiliac joint

A

Corresponding veins to arterial supply which collectively drain to the internal iliac

28
Q

Describe the lymphatic drainage of the sacroiliac joint

A

Follows arterial supply to drain to the internal iliac nodes

29
Q

Describe the nervous innervation of the sacroiliac joint

A
  • Extremely complex - major discrepancies in literature
  • Largely believed to be:
    • Anterior innervation - L4-S2 anterior rami
    • Posterior innervation - medial branches of L4-S3 dorsal rami
  • Some papers say that the sacroiliac joint has posterior innervation only.
    • Some authors even suggest that the anterior sacroiliac joint is devoid of nervous tissue.
30
Q

List the 4 movements of the sacroiliac joint

A
  • Rotation
  • Translation
  • Nutation
  • Counternutation
31
Q

Describe the 3 axes of the sacroiliac joint

A
  • X-axis - sacral rotation in the sagittal plane (ant. post.)
  • Y-axis - sacral rotation in the horizontal plane (medial lateral)
  • Z-axis - sacral rotation in the coronal plane
32
Q

What happens to movement of the sacroiliac joint with age (in men and women)?

A
  • Decreases with age
    • ~40-50 in men
    • ~50 in women
33
Q

Only very small movements are permitted at the sacroiliac joints. Why?

A
  • Due to:
    • Strong ligamentous connections
    • Surrounding muscle tone
    • Undulating iliac and sacral articular surfaces
  • Even in joints with known pathologies and lax ligaments, movement is still relatively limited.
34
Q

Goode et al. (2008) on rotation and translation in each axis

A
  • X axis
    • ​Rotation: -1.1 - 2.2°
    • Translation: -0.3 - 8mm
  • Y-axis
    • Rotation: -0.8 - 4°
    • Translation: -0.2 - 7mm
  • Z-axis
    • ​Rotation: -0.5 - 8°
    • Translation: -0.3 - 6mm
35
Q

What is nutation of the sacroiliac joint?

A

Relative anterior tilt of sacral base (between L5/S1) in relation to the ilium

36
Q

What is counternutation of the sacroiliac joint?

A

Relative posterior tilt of the sacral base (between L5 / S1) in relation to the ilium.

37
Q

Which ligaments resist nutation?

Which ligaments resist counternutation?

A
  • Nutation:
    • ​Sacrotuberous ligament
    • Sacrospinous ligament
  • Counternutation:
    • ​Long band of posterior sacroiliac ligament
38
Q

What induces nutation?

A

Sacral connection of erector spinae muscles

39
Q

Describe the first pelvic trabecular system

A
  • Arises from lower auricular surface of ilium and passes in an arc shape to the superior surface of acetabulum.
    • Here, it aligns with the vertical trabecular bundle, which is one of the main systems supporting the head/neck of femur.
  • Shown as ①
40
Q

Describe the second pelvic trabecular system

A
  • Begins superiorly at the auricular surface of the ilium to both the border of the greater sciatic notch and the inferior border of the acetabulum.
  • This aligns with an important trabecular bundle in the femur - the arcuate bundle.
  • Shown as ②
41
Q

Describe the third pelvic trabecular system

A
  • Called the sacroischial trabeculae
  • Extend from the auricular surface to the ischium
  • Important during sitting when the ischium is supporting the body weight
  • Shown as ③
42
Q

What causes the pelvic trabecular systems?

A
  • Thought to be caused by locomotion
  • Cunningham and Black (2009) found progressive patterns in developing juvenile skeletons, suggesting that density patterns may develop in-utero, before they have been exposed to any weight bearing function.
    • This development is said to be in response to early limb movements.
43
Q

Describe the age related changes to the sacroiliac joint

A
  • At birth, SIJ form is similar to quadrupeds, but changes occur with locomotion.
  • Bony surfaces of joint are smooth until puberty.
  • After puberty, bony surfaces become roughened and in some areas firbous plaques can form.
  • 20s - fusion of sacral vertebrae.
  • 30s and 40s - changes accelerate - more groove formation, bony ridges on iliac articular surface (increase stability).
  • 50s - synovial articular surfaces erode and synovial cleft narrows to 1-2mm.
  • 60s - capsule becomes increasingly collagenous.
  • 70s - synovial cleft only 0-1mm and ankylosis often present.
  • 80s - erosions and plaques become inevitable and pervasive.
44
Q

Desribe the change of the sacroiliac joint which comes with locomotion

A
  • The sacrum enlarges laterally
  • Articular surfaces form a more adult-like curvature
  • Caused by factors related to weight-bearing, loads on the femur and strain at the pubic symphysis
45
Q

Describe the sacroiliac joint in pregnancy

A
  • SIJ cited as underlying cause of pelvic pain during pregnancy.
  • Usually pain begins around 18 weeks gestation.
  • Increased levels of sex hormones:
    • Increased osetrogen
    • Increased relaxin
  • Cause the pelvic ligaments to relax allowing the pelvic joints to relax.
  • Relaxation of ligaments causes the interlocking mechanism of the SIJ to become less effective.
  • Relaxation of ligaments = risk of dislocation in late pregnancy.
  • More pronounced in multiparous women.
46
Q

What causes a low energy sacroiliac joint fracture?

A
  • Stress
  • Insuffucient support
47
Q

What causes a high energy sacroiliac joint fracture?

A
  • Lateral compression
  • Anterior posterior compression
  • Vertical shear
48
Q

List the causes of lateral compression injuries

A
  • Motor vehicle collisions and pedestrian-vehicle crashes.
  • Falls from height, generally greater than 15 feet.
  • Sport injuries
  • Crushing injuries
49
Q

List the lateral compression (LC) pelvic fractures of the Young-Burgess classification

A
  • LC1 - sacral fracture on side of impact
  • LC2 - crescnent fracture on side of impact
  • LC3 - type 1 or type 2 injury on side of impact with contralateral open-book injury
50
Q

List the anterior-posterior compression (APC) pelvic fractures of the Young-Burgess classification

A
  • APC1 - minor opening of the symphysis and SI joint anteriorly.
  • APC2 - opening of anterior SI joint, intact posterior SI ligaments.
  • APC3 - Complete disruption of SI joint.
51
Q

List the vertical shear (VS) pelvic fractures of the Young-Burgess classification

A
  • Vertical displacement of hemipelvis with symphysis distasis or rami fractures anteriorly

AND

  • Iliac wing, sacral fracture or SI joint dislocation posteriorly.
52
Q

Describe a crescent fracture

A
  • Combination of vertical iliac fracture and dislocation of the SIJ.
  • Characterised by the disruption of the sacroiliac joint extending proximally as a fracture of the posterior iliac wing.
  • Injury to posterior ligaments varies.
  • 3 types:
    • Type 1 - 1/3 or less of SI joint dislocated
    • Type 2 - 1/3-2/3 of SI joint dislocated
    • Type 3 - 2/3 + of SI joint dislocated
53
Q

Describe treatment for a minor SI joint fracture

A
  • Bed rest, painkillers and anti-inflammatory drugs.
  • Physical therapy and possibly crutches
  • Recovery - 8-12 weeks
  • If pain persists, surgery may be considered
54
Q

Describe treatment for a major SI joint fracture

A
  • Must act quickly - resuscitation where necessary.
    • Fluid replacement and cauterising vessels.
  • Pelvis is stabilised before other treatments are considered.
  • If still highly unstable, surgical intervention is considered:
    • Open reduction internal fixation (ORIF).
    • High success rate, but carries high risk.
55
Q

Describe ligament damage due to trauma

A
  • Variable severity / type of injury = ligamentous damage is highly variable.
  • Some fractures result in the tearing away of bone by the strong ligaments associated with the sacroiliac joint.
  • Damage of ligaments causes imflammation resulting in painful disruption at the joint.
  • Ligaments of the SI joint can also be damaged or torn over time with age, or during pregnancy.
56
Q

Describe sacroiliac joint dysfunction

A
  • Cause of lower back pain in 15-25% of patients
  • Injury - combination of axial loading and abrupt rotation
  • Can be either intraarticular or extraarticular.
  • Predisposition - gradual development of pain due to increased stress borne by SI joints.
57
Q

What are the intraarticular causes and extraarticular causes of of sacroiliac joint dysfunction?

A
  • Intraarticular - arthritis and inflammation.
  • Extraarticular - enthesopathy, fracture or ligament damage.
58
Q

Pain referral from sacroiliac joint dysfunction

A
  • Pain in buttocks - 94%
  • Pain in thigh - 48%
  • Pain in lower leg - 28%
  • Pain in ankle / foot - 13%
  • Pain in groin - 14%
  • Pain in abdomen - 2%
59
Q

Diagnosis of SI joint dysfunction

A
  • Dozens of physical examination tests but not easily reproducible and very poor inter-observer reliability.
  • Challenging with many limitations
60
Q

What are the reasons for poor reliability of tests of sacroiliac joint dysfunction?

A
  • SI joint is not easily palpated / manipulated
  • Tests don’t really isolate the SI joint
  • Scans are often normal (even in the presence of SI joint dysfunction).
  • Several other conditions cause the same symptoms.
61
Q

What is (supposedly) the only way to diagnose true SI joint dysfunction?

A

To see a positive response to a local block injected into the joint.

  • Challenging procedure
  • Limitations:
    • Placebo effect
    • Extravasion of block into surrounding pain-generating structures can cause a false positive.
62
Q

What are the 2 major treatment methods for sacroiliac joint dysfunction?

A
  • Targeting underlying pathology
  • Alleviating symptoms
63
Q

What are the non-interventional treatments for SI joint dysfunction?

A
  • Shoe insoles for those with leg length discrepancies or gait abnormalities.
  • Physiotherapy / osteopathic / chiropractic manipulation.
  • Mobilisation
  • Stabilisation - pelvic belt
64
Q

What are the common related pathologies of sacroiliac joint dysfunction?

A
  • Ankylosing spondylitis
  • Osteoarthritis
  • Sacroiliitis
65
Q

Sacroiliac joint is one of the first affected by ankylosing spondylitis. Why?

A

It is suggested that this is because of the clefts in the iliac cartilage (as it is much thinner) which allows for easier invasion of osteophytes.

Vertebral Column (13 decks)

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