Sacroiliac Joint Flashcards
What is the orientation of the SIJ in the transverse plane?
Anterolaterally
What are the functions of the SIJ?
Transmit forces from lumbar spine to: - Femur (when standing) - Ischial tuberosities (when sitting) Relieves stress: - Point of max. torsional strain in pelvis
Why could the SIJ be classed as a diarthrodial joint?
2 articular surfaces
Separated by synovial fluid-filled cavity
Surrounded by joint capsule
Why is the SIJ an atypical diarthrodial joint?
Also has fibrocartilage
Posterior capsule absent
Articular surfaces not smooth
How could the joint be described in regards to the type?
Synovial in anterior 1/3
Fibrous in posterior 2/3
Describe the inner layer of the SIJ capsule?
Synovial membrane (intima) 2-3 cellular layers Contains synovial villi which extend into joint
What does the connective tissue of the outer fibrous layer of the SIJ capsule contain?
Fibroblasts
Blood vessels
Collagen fibres
How does the joint capsule change with age?
Becomes more fibrous
One part of the SIJ capsule is rudimentary/absent and the other is thin. Which is which?
Rudimentary/absent = Posterior capsule Thin = Anterior capsule
What does the study by Sakomoto et al., (2013) say about the SIJ capsule?
90% of mechanosensitive units are found in the joint capsule
Nerve fibres in joint capsule:
- Joint disturbance = Pain
What are useful references for overview of the SIJ and the joint capsule?
Bogduk, 2005
Cohen, 2005
Forst et al., 2017
What is the general shape of the articular surfaces of the SIJ?
L or C shaped
Describe the ‘undulating’ surfaces of the SIJ? What is its purpose?
Complementary depressions and elevations
- Increases stability by interlocking
- Protects from vertical shear force
Describe the cranial limb of the articular surfaces of the SIJ?
Shorter
More horizontal
Describe the caudal limb of the articular surfaces of the SIJ?
Longer
More vertical
How do the articular surfaces vary between the sexes?
Sacral surface is smaller in females:
- Only covers S1-S2 (vs S1-S3 in males)
What does the high coefficient of friction of the SIJ infer?
High stability
Describe the articular cartilage of the sacral surface of the SIJ?
Typical hyaline cartilage
White, glossy and smooth
1-3mm thick (2-3x thicker than iliac)
Doesn’t change much throughout life
How does Paquin, (1983) describe the iliac articular cartilage of the SIJ?
Special hyaline
How does Kampen and Tillmann, (1998) describe the iliac articular cartilage of the SIJ?
Fibrocartilage in childhood
Hyaline as it matures
How does Tuite, (2008) describe the iliac articular cartilage of the SIJ?
Both surfaces are hyaline inferiorly
Cartilage thinner on iliac surface (<1mm):
What reasons does Tuite, (2008) suggest may be why the iliac articular cartilage is thinner than the sacral cartilage of the SIJ?
It only absorbs forces (vs the sacral surfaces transmitting them)
Only stressed by vertical shear
How does the sacral articular surface appear histologically?
Thick
Similar to hyaline cartilage in limb joints
How does the iliac articular surface appear histologically?
Thin
Rich in perpendicular and oblique collagen fibre bundles
Where is an accessory SIJ found?
Posterior to true SIJ between:
- Medial aspect of PSIS and
- Transverse tuberosity lateral to 2nd sacral foramen
What is the incidence of accessory SIJ in CT scans and cadavers? (Reference?)
13/100 CT scans
9/56 cadavers
(Ehara et al., 1998)
In what populations are accessory SIJs more common? (Reference?)
Elderly
Obese patients
(Prassopoulos et al., 1999)
What variations of the SIJ are more common in women?
Iliosacral complex
Bipartite iliac bony plate
Crescent-like iliac bony plate
What are the two less common SIJ variations?
Semicircular defects on both surfaces of SIJ
Ossification centres
What are the prevalence rates of the 6 variations of the SIJ according to Prassopoulos et al., (1999)?
Accessory SIJ = 19.1% Iliosacral complex = 5.8% Bipartite iliac bony plate = 4.1% Crescent-like iliac bony plate = 3.7% Semicircular defects on both surfaces of SIJ = 3% Ossification centres = 0.6%
What is the course of the anterior sacroiliac ligament?
From ala and pelvic surface of sacrum
To adjoining margin of anterior surface of ilium
What is the anterior sacroiliac ligament an extension of?
Anterior joint capsule
What does the anterior sacroiliac ligament prevent?
Anterior diastasis of SIJ
What causes the greatest stress to the anterior sacroiliac ligament?
Axial loading
Where does the short posterior sacroiliac ligament lie?
Superiorly
Where does the long posterior sacroiliac ligament lie?
Inferiorly
What is the posterior sacroiliac ligament a continuation of?
Fibrous tissue (capsule)
How do the fibres of the posterior sacroiliac ligament compress the sacrum between the ilia?
FIbres run anterolaterally:
- Axial weight pulls ilia medially
- Compresses sacrum
- Locks congruent articular surfaces of SIJ
What is the course of the long posterior sacroiliac ligament?
Fibres run vertically:
- From PSIS
- To 3rd/4th transverse tubercles of sacrum
What is the function of the long posterior sacroiliac ligament?
Prevents excessive counternutation:
- Sacral promontory moving posterosuperiorly
- Ilia moving anteriorly on sacrum
What does the long posterior sacroiliac ligament work with to prevent SIJ separation?
Interosseous SIJ ligament
What is the course of the short posterior sacroiliac ligament?
Runs from 1st/2nd transverse tubercles
TO iliac tuberosity
What is the function of the short posterior sacroiliac ligament?
Limits nutation:
- Forward movement of sacral promontory
Resists anterior displacement of SIJ
Where does the interosseous sacroiliac ligament lie?
In recess between sacrum and ilium dorsal to joint cavity
What is the function of the interosseous sacroiliac ligament?
Infers multi-directional stability
Very important in limiting movement:
- Severing it in cadavers increased joint movement
What is the deepest ligament of the SIJ?
Interosseous sacroiliac ligament
What is the course of the sacrotuberous ligament?
From: - Posterior ilium - Lateral sacrum - Lateral coccyx To ischial tuberosity
What is the function of the sacrotuberous ligament?
Anchors inferior sacrum to ischium:
- Counterbalances rotation at superior sacrum
What is the course of the sacrospinous ligament?
From:
- Lateral sacrum
- Lateral coccyx
To ischial spine
What is the function of the sacrospinous ligament?
Perhaps acts as a fibrous part of coccygeus
Why are the sacrotuberous and sacrospinous ligaments important in high impact activities?
Superior sacrum receives great force via lumbar vertebrae
Weight transferred anterior to SIJ which would pull sacrum anteroinferiorly:
- Prevented by STL and SSL
What muscle, acting via the sacrotuberous ligament, stabilises the SIJ?
Long head of biceps femoris
What is the course of the iliolumbar ligament?
From tips of L4/L5 transverse processes
To posterior iliac crest
What are the functions of the iliolumbar ligament?
Strengthens relationship between ilium and vertebral column
Prevents L5 from anterior displacement on S1
Opposes gliding movements between vertebrae
What is the reference for the iliolumbar ligament?
Palanstanga, 2013
When does the SIJ develop?
Initially thought to develop in week 10
Recently suggested it develops in week 8
From what layers does the SIJ develop?
Three layers in pelvic mesenchyme:
- Sacral cartilage
- Iliac cartilage
- Interposed zone of mesenchyme
In what zone of mesenchyme does the early articular cavity form?
Interposed zone of pelvic mesenchyme
When does the synovial membrane form and from what?
Shortly before birth
Formed from mesenchyme surrounding edge of primordial central cavity
At what stage do bony ridges and bony grooves form on the bony surfaces of the SIJ?
Puberty
What is the arterial supply to the SIJ?
Anteriorly = Branches of iliolumbar artery
Posteriorly = Superior gluteal artery
Anteriorly and posteriorly = Lateral sacral arteries
Where do the venous draining the SIJ drain to?
Internal iliac vein
Where does lymph drain from the SIJ?
Internal iliac nodes
What is the anterior nervous supply to the SIJ?
L4-S2 ventral rami
What do earlier studies suggest give nervous supply to the anterior SIJ?
Obturator nerve
Superior gluteal nerve
Lumbosacral trunk
What is the posterior nervous supply to the SIJ?
Medial branches of L4-S3 dorsal rami
Some studies also suggest contributions from L3 and S4
What do some studies also suggest about the nervous supply to the SIJ?
Anterior SIJ is devoid of nervous tissue
What 4 movements are possible at the SIJ?
Rotation
Translation
Nutation
Counternutation
What movements of the SIJ are possible in the x (transverse) axis?
Sacral rotation in sagittal plane:
- Nutation
- Counternutation
What movements of the SIJ are possible in the y (longitudinal) axis?
Sacral rotation in the horizontal plane
What movements of the SIJ are possible in the z (sagittal) axis?
Sacral rotation in the coronal plane
How much does SIJ movement decrease with age?
~40-50% in males
~50% in females
How is the amount of movement of the SIJ measured?
Roentgen stereophotogrammetric motion analysis (RSA)
How much rotation is possible at the SIJ?
Maximum is 4 degrees (mean is 2.5)
How much translation is possible at the SIJ?
Maximum is 1.6mm (mean is 0.7mm)
What IV joints do nutation and counternutation affect?
Mainly L5-S1 (but also those superior to it)
What ligaments resist nutation?
Sacrotuberous ligament
Sacrospinous ligament
What ligament resist counternutation?
Long posterior sacroiliac ligament
How can pain at the SIJ arise with age?
Increased joint laxity with age
Therefore increased counternutation = Pain
What is the combined range of counternutation in individuals older than 72?
4 degrees (normal is <2 degrees)
What is force closure?
Anticipation for SIJ loading
Ligaments of SIJ tighten = Nutation
What induces force closure?
Sacral connections of erector spinae induce nutation by pulling ilia together
What is the course of the first pelvic trabecular system?
Arises from inferior auricular surface
Runs in an arc shape toward superior surface of acetabulum
What does the first pelvic trabecular system align with?
Vertical trabeculae bundle:
- Supports head and neck of femur
What is the course of the second pelvic trabecular system?
Begins at superior auricular surface
Runs to:
- Posterior border of greater sciatic notch
- Inferior border of acetabulum
What does the second pelvic trabecular system align with?
Arcuate bundle in femur
In what motion are the first and second pelvic trabecular systems important?
Bidepal motion
Why are there different pelvic trabecular system patterns in apes?
Different weight distribution
What is the alternate name for the third pelvic trabecular system?
Sacroischial trabeculae
What is the course of the third pelvic trabecular system?
Begins at auricular surface
Extends to ischium
When is the third pelvic trabecular system important?
When sitting:
- ischium supporting weight of body
At birth, the structure of the SIJ in humans is similar to that of quadrupeds. Why does it change with age?
Locomotion
How do the bony surfaces of the SIJ change after puberty?
Become rough
Fibrous plaques form in some areas
What age related changes of the SIJ are seen in a person’s 20s?
Fusion of sacral vertebrae
What age related changes of the SIJ are seen in a person’s 30s and 40s?
More grooves
Bony ridges on articular surface of ilium to increase stability
What age related changes of the SIJ are seen in a person’s 50s?
Degeneration begins:
- Synovial articular surfaces erode
- Synovial cleft narrows to 1-2mm
What age related changes of the SIJ are seen in a person’s 60s?
Capsule becomes more collaginous
What age related changes of the SIJ are seen in a person’s 70s?
Synovial cleft only 0-1mm
Ankylosis often present
What age related changes of the SIJ are seen in a person’s 80s?
Erosions and plaques:
- Inevitable
- Pervasive
When does SIJ pain arise in pregnancy?
Week 18 of gestation
What causes SIJ pain in pregnancy?
Increased oestrogen and relaxin:
- Relaxation of ligaments
- Less SIJ interlocking
- Increased pelvic rotation
- Increased lordosis
What does SIJ ligament relaxation allow?
Increased SIJ diameter by 10-15% for passage of baby
In what women are SIJ changes during pregnancy more prominent?
Multiparous women
How does a sacroiliac belt reduce pain? (Reference?)
Reduces SIJ mobility
Mens et al., 2006
What can cause a lateral compression injury to the SIJ?
RTAs
Fall from height (>15 feet)
Sports injuries
Crush injuries
What is the most common mechanism of injury to the SIJ?
Lateral compression
What does the mortality of a SIJ fracture depend on?
Severity of bleeding
Presence of thoracic/abdominal injures
In what individuals are low energy stress fractures more common in?
Females
In what individuals are high energy fractures (lateral compression, AP compression or vertical shear) more common in?
Males
What conditions are SIJ fractures related to?
Osteoarthritis
Ankylosing spondylitis
What are the three types of lateral compression and anterior pelvic rami fracture?
Type I = Ipsilateral sacral fracture
Type II = Ipsilateral crescent fracture
Type III = Ipsilateral Type I/II and contralateral open-book fracture
What are the three types of AP compression and symphysis diastasis injuries?
Type I = Minor opening of symphysis and anterior SIJ
Type II = Anterior SIJ opening but intact posterior ligs.
Type III = Complete SIJ disruption
What pelvic injury can a vertical shear force result in?
Displacement of hemipelvis
What is the classification system of pelvic fractures called?
Young-Burgess Classification
What is a crescent fracture?
Combination of:
- Vertical iliac fracture
- SIJ dislocation
What is a crescent fracture characterised by?
SIJ disruption:
- Extended proximally as a fracture of posterior iliac wing
What are the three types of crescent fractures?
Type I = Less than or equal to 1/3 of SIJ dislocated
Type II = 1/3-2/3 of SIJ dislocated
Type III = More than or equal to 1/3 of SIJ dislocated
How long would a pelvic injury take to recover?
8-12 weeks
What are the benefits of ORIF for a pelvic fracture?
High success rate
How can the pelvis be stabilised prior to ORIF?
External fixation via pins in ilia
When might external fixation be enough in pelvic fractures?
If minimal displacement
What are the downsides of ORIF?
Long recovery Risk of re-displacement Surgical risks: - Haemorrhage - Infection - Nerve damage
How is ORIF carried out in SIJ disruptions?
Plates
How is ORIF carried out in crescent fractures?
Screws
How is ORIF carried out in sacral fractures?
Screws
What can improve outcomes in pelvic injuries?
Early stabilisation of pelvic ring
What injury has a worse prognosis; SIJ injuries of iliac wing fractures?
SIJ injuries
What can pelvic injuries predispose the patient to?
SIJ dysfunction syndrome
What did Borg, (2011) find regarding the prognosis of pelvic injuries?
30% satisfied with QoL post-surgery:
- 20% less than those who did not require surgery
10% unsatisifed
In pelvic fractures, what injuries can the strong ligaments cause?
Avulsion fractures
What SIJ ligaments are most likely to be ruptured with pelvic fractures? What ligaments require a severe fracture to be disrupted
Anterior sacroiliac ligaments
Posterior sacroiliac ligaments
Why are NSAIDs prescribed in pelvic fractures?
Ligament damage results in inflammation
Inflammation results in pain
NSAIDs reduce inflammation
What percentage of lower back pain cases are due to SIJ dysfunction?
15-25%
What injury mechanism tends to result in SIJ dysfunction?
Combination of:
- Axial loading and
- Abrupt rotation
What are some intra-articular causes of SIJ dysfunction?
Arthritis
Inflammatory conditions
What are some extra-articular causes of SIJ dysfunction?
Enthesopathy
Fracture
Ligamentous damage
What factors can predispose to SIJ dysfunction?
Leg length discrepancy Gait abnormalities Prolonged vigorous exercise Scoliosis Spinal fusion to sacrum Lumbar spine surgery Pregnancy
What are the SIJ pain criteria?
- Pain in region of SIJ
- Stressing SIJs in clinical tests reproduces pain
- Selectively infiltrating SIJ relieves pain
Where does SIJ pain radiate?
Buttocks (94%) Thigh Leg Ankle/Foot Groin Abdomen
Why is SIJ dysfunction difficult to diagnose?
Cannot be diagnosed by:
- Examination
- Osteopathic or chiropractic techniques
- Imaging
What physical exam tests can be used to attempt to diagnose SIJ dysfunction?
Compression test
Bilateral internal hip rotation test
How sensitive and specific is radionucleotide bone scanning for SIJ dysfunction?
13% sensitive
100% specific
Why can CT be useful in SIJ dysfunction?
Can find other potential pathologies
What does Bogduk, (2005) suggest is the only reliable way to diagnose SIJ dysfunction?
Analgesic response to small-volume local anaesthetic block
What is the basis of management of SIJ pain?
Target underlying pathology and alleviate symptoms
What conservative therapies can be used for SIJ dysfunction?
Shoe insoles if: - Leg length discrepancies - Gait abnormalities Physiotherapy/Chiropractic techniques Mobilisation-stabilisation Pelvic belt
When is radiofrequency ablation used to treat SIJ pain?
If positive response to diagnostiv block
When might radiofrequency ablation not be successful in relieving pain?
If pain is from ventral SIJ
How else can SIJ pain be relieved?
Intra-articular hyaluronic acid injections
Surgical arthrodesis
Why is the SIJ the 1st joint affected in ankylosing spondylitis?
Clefts in iliac cartilage allow osteophyte invasion
What is the most common SIJ disorder (especially if 40 years old +)? Is it usually unilateral or bilateral?
Osteoarthritis
Unilateral
