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Erosions of dens, uncovertebral joints, facet joints
Atlantoaxial instability in 20-86% patients with RA
Atlantoaxial subluxation in 5% of cervical RA
Cranial settling occurs in 5-8% of RA patients
Lower cervical spine: Facet and uncovertebral joint erosions, instability
Neutral, flexion, and extension lateral radiographs performed for evaluation of instability
Normal = 2 mm between inner margin anterior ring of C1 and dens
If distance ≥ 9 mm, high correlation with neurologic symptoms
Pannus is mass-like and surrounds and erodes dens, facet joints, uncovertebral joints
Low signal on T1WI
Heterogeneous signal on T2WI, STIR
Enhances avidly with gadolinium
Seronegative spondyloarthropathy
Calcium pyrophosphate dihydrate deposition (CPPD) disease
Juvenile chronic arthritis
Osteoarthritis
Degenerative disc disease
50-60% of RA patients have involvement of cervical spine
Never involves spine before hands &/or feet
May develop radiculopathy, myelopathy
Instability → significant morbidity, mortality
Calcifying mass with odontoid erosions is not RA
Indicates crystalline arthropathy, usually CPPD
Rheumatoid arthritis (RA)
Location
Cervical spine: Approximately 50-60% of RA patients
C1-odontoid articulations, occipital condyles
Facet and uncovertebral joints
Severity of craniovertebral junction (CVJ) involvement is factor of disease duration and severity
Rarely involves sacroiliac joints or lumbar spine
Hands &/or feet involved if spine involved
Radiography
Erosions of dens, uncovertebral joints, and facet joints
Dens may be completely eroded
Neutral, flexion, and extension lateral radiographs to evaluate for instability
Voluntary movement of neck to maximum range of motion possible for patient without technologist assistance
Subluxation(s) assessed in flexion; reducibility assessed in extension
Subluxation(s) primarily seen in flexion
Extension views useful to assess reducibility of subluxation
Craniocervical instability
Due to erosions of occiput-C1 facets
Transverse ligament synovium-lined bursa susceptible to pannus formation
C1-C2 instability
Normal: < 2 mm between inner margin anterior ring of C1 and dens (anterior atlantodental interval [AADI])
Neurologic symptoms usually present if distance ≥ 9 mm
Spinal canal < 14 mm at C2 (posterior atlantodental interval [PADI]) also correlates with neurologic symptoms
Instability seen in 5% of patients with cervical RA
Atlantoaxial instability (AAI) in 20-86% of patients with RA
Extension view is useful to determine if pannus precludes full reduction
Acquired basilar invagination (BI): Decreased distance occiput to C2
Used synonymously with cranial settling
Bony erosions of occipital condyles and C1 lateral masses where cranium moves downward (settles) relative to dens
Dens may protrude through foramen magnum
C1 maintains normal relationship with clivus
Alar and apical ligaments involved
Occurs in 5-8% of RA patients
Due to facet joint erosions
Acquired basilar impression (BI)
Used synonymously with cranial settling
High vertebral column indents skull base
C1 maintains normal relationship with C2
Measurements
McRae: Positive if tip of dens extends beyond line drawn from basion to opisthion
McGregor line: Positive if dens > 4.5 mm above line from posterior hard palate to inferior point of occipital curve
Redlund-Johnell: Line from mid caudal surface of C2 body to McGregor line
Positive if < 34 mm in males or < 29 mm in females
Instability may also be present at lower levels of cervical spine
Often multilevel (“stepladder”) subluxations
Ankylosis of spine not seen in adult RA
Osteopenia: Difficult to reliably detect on radiographs
Not radiographically evident unless severe
Can be masked by or mistaken for senile osteoporosis
Can be absent (“robust RA”)
Sacroiliitis
Erosions 1st seen on iliac side of joint
May be unilateral or bilateral
Rarely progress to fusion
Disc and adjacent vertebral body destruction (extremely rare)
Synovitis extends from apophyseal joint
Bone CT
Increased conspicuity of odontoid erosions compared to radiographs
Pannus around dens may be seen; never calcifies
Pannus is mass-like, surrounds and erodes dens, facet joints, uncovertebral joints
Erosions of uncovertebral and facet joints
Preoperative planning and postoperative follow-up
CT of craniocervical junction (CCJ) can also be performed in flexion/extension
Pannus
Low signal intensity (SI) on T1WI
Heterogeneous SI on fluid-sensitive sequences
May be predominantly low SI
Usually predominantly intermediate SI
Contrast-enhanced T1WI MR may be able to discriminate between joint effusion and various forms of pannus
Hypervascular pannus is distinguished from hypovascular and fibrous pannus on T2WI MR
Joint effusion and pannus are detected in patients with negative radiographic findings
No concordance between MR findings and clinical symptoms
Enhances avidly with gadolinium
Subluxations may lead to spinal stenosis
Myelopathic changes are common
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