- 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
– 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
- Non-uniform narrowing of joint space
- Subchondral sclerosis and cyst
- 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
- 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.
– Lower extremities: big joints eg knee, hip, ankle
– Upper extremities: shoulder, elbow, MCPs, whole wrist (DRUJ and carpal bones)
- Uniform narrowing of joint space
- Marginal bone erosions
- Periarticular osteopenia
- 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).
- Tophi (seen as soft tissue swelling)
- Sharply marginated erosions with overhanging edges
- 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
- Symmetrical involvement
- Can precede psoriatic skin manifestations.
- Involves distal extremities and spine (SI joint)
- Pencil in cup, sausage digit
- 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)