Joint Diseases Radiology

Osteoarthritis

  • Loss of hyaline cartilage –> two ends of bones to collapse towards each other
    – in X ray, we can’t see cartilage directly, we can only see it indirectly via the joint space
  • Involves
    – Lower extremities: knee (medial narrowing), hip (superior narrowing), 1st MTP ** it spares ankle joint
    – Upper extremities: thumb base (CMC and STT joint), DIPs
    – Lower C-spine and lumbar spine

Imaging features:

  1. Non-uniform narrowing of joint space
  2. Osteophytes
  3. Subchondral sclerosis and cyst

Erosive OA

  • A form of osteoarthritis where, as the name implies, there is an additional erosive/inflammatory component.
  • Normally involves post-menopausal women.
  • Differ to normal OA: symmetrical involvement

Imaging features: gullwing and sawtooth erosion

RA

  • Inflammation of synovial cavity (pannus) causing hyperemia and increased inflammatory cells (one of which is osteoclast). Hyaline cartilage is destroyed causing joint space narrowing.
  • Osteoclast causes bone resorption causing erosions and peri-articular osteopenia.
  • Involves
    – Lower extremities: big joints eg knee, hip, ankle
    – Upper extremities: shoulder, elbow, MCPs, whole wrist (DRUJ and carpal bones)
    – C1-2

Imaging features

  1. Uniform narrowing of joint space
  2. Marginal bone erosions
  3. Periarticular osteopenia

Gout

  • Crystals deposition (uric acid) in synovial cavity, causing inflammation to the joint and bone.
  • because the synovial space is filled with something, the joint space does not narrow even though cartilage is destroyed.
  • Random distribution, though favours 1st toe (podagra).

Imaging feature

  1. Tophi (seen as soft tissue swelling)
  2. Sharply marginated erosions with overhanging edges

CPPD

  • Also known as pseudogout, but with different imaging features and distribution.
  • Distribution: atypical to OA
    – Commonly involves patello-femoral compartment (knee: lateral narrowing)
    – MCPs, entire wrist

Imaging features: resemble OA

  1. Symmetrical involvement
  2. Chondrocalcinosis

Psoriatic arthritis

  • Can precede psoriatic skin manifestations.
  • Involves distal extremities and spine (SI joint)

Imaging features

  1. Pencil in cup, sausage digit

  2. Asymmetrical narrowing of SI joint

** Milwaukee shoulder: calcium hydroxyapatite deposition causing destructive shoulder arthropathy

  • Commonly after trauma
  • Imaging features
    – Destruction of articular surface with subchondral sclerosis and debris (loose bodies) **3Ds mnemonic: destruction, density, debris (similar to Charcot joint)

Summary

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