= DEGENERATIVE JOINT DISEASE = ARTHROSIS

= predominantly noninflammatory degeneration of cartilage in synovial joints

◊Most common arthropathy ← repetitive articular cartilage damage

Age: prevalence increasing with age

Cause:

1. abnormal forces acting on a normal joint (eg, slipped capital femoral epiphysis)
2. normal forces acting on abnormal joint due to
   1. cartilage abnormality
   2. subchondral bone abnormality

Path:↓ chondroitin sulfate with age creates unsupported collagen fibrils → irreversible hyaline cartilage degeneration (= inability for regeneration)

• joint space narrowing (stage III) = inaccurate indicator of cartilage integrity
• subchondral sclerosis / eburnation in areas of stress
• subchondral cyst formation (geodes)
• increased joint fluid
• synovial inflammation (in severe osteoarthritis)
• osteophytosis at articular margin / nonstressed area

US:

• step-up prominences of cortex = peripheral marginal osteophytes ← new bone formation
• joint space narrowing, noted if marginal and severe
• joint effusion ± hyperemia of synovitis (on color Doppler)

MR:

• Cartilage
  Stages of damage to cartilage:
  1. cartilage swelling + softening (from damage to collagen matrix → decreased proteoglycan content + increase in water content)
  2. increased cartilage thickness (from proliferation of chondrocytes)
  3. cartilage loss → fibrillation + erosion + cracking of articular cartilage ← decrease in cellular proliferation of chondrocytes
  • increased SI of abnormal cartilage on T2WI (= increased amount of free water)
  • morphologic defects on surface of cartilage (best seen on fat-suppressed spoiled gradient-echo MR)
  
  Cartilage damage score on MR:
  • 0 normal
  • 1 increased T2 signal intensity
  • 2 partial-thickness defect <50%
  • 3 partial-thickness defect >50%
  • 4 full-thickness defect
• Bone
  • hyperintense subchondral bone marrow edema-like lesion on fat-suppressed T2WI / STIR ← increased fatty acid consumption
  • subchondral pseudocysts in weight-bearing areas (= contusional bone necrosis / intrusion of synovial fluid across damaged cartilage)
  • subchondral sclerosis (= stress-induced new bone deposition + trabecular microfractures + callus formation) hypointense on all sequences
  • osteophytes at joint margins ← stimulation of enchondral ossification in areas of low stress
  • flattening or depression of the articular cortex (= bone attrition)
• Synovium
  • synovial thickening with positive correlation between pain and degree synovitis
  • joint effusion
  • popliteal bursal fluid (common)
  • joint bodies
    Origin: chondral fragments, detached osteophytes, meniscal fragments, synovial osteochondromatosis
• Hand + foot
  Target area: 1^st MCP; trapezioscaphoid; DIP >PIP; 1^st MTP
  • loss of joint space, subchondral eburnation, marginal osteophytes, small ossicles in DIP + PIP:
    • Bouchard node = osteophytosis at PIP joint
    • Heberden node = osteophytosis at DIP joint: M÷F = 1÷10
  • radial subluxation of 1^st metacarpal base
  • joint space narrowing + eburnation of trapezioscaphoid area
• Shoulder
  • elevation of humeral head + lack of significant glenohumeral joint involvement (DDx to rheumatoid arthritis)
• Hip
  Predisposed: hip dysplasia, slipped capital femoral epiphysis, Legg-Calvé-Perthes disease, malunited femoral neck fracture, femoroacetabular impingement
  • femoral + acetabular osteophytes, sclerosis, subchondral cyst formation
  • thickening / buttressing of medial femoral cortex / calcar
  • migration of femoral head:
    • superolateral subluxation of femoral head
    • medial / axial subluxation ± protrusio acetabuli (in 20%)
    • primary hereditary protrusio = Otto pelvis (M <F)
• Knee
  Location: medial >lateral femorotibial >patellofemoral compartment
  • varus deformity (M>>F)
  
  Associated with:
  medial (66%), lateral (24%), bilateral (10%) meniscal tears (in 60% for asymptomatic + symptomatic patients alike), commonly associated with extrusion of meniscus from the joint line
• Spine
  • sclerosis + narrowing of intervertebral apophyseal joints
  • osteophytosis usually associated with diskogenic disease
• Sacroiliac joint
  • Most common disorder of sacroiliac joints
  
  Location: bi- / unilateral (contralateral SIJ with bad hip)
  • diffuse joint space loss
  • vacuum phenomenon
  • well-defined line of sclerosis, esp. on iliac side of articulation
  • prominent bridging osteophyte at superior + inferior limits of joint
  
  DDx: osteoblastic metastasis