Posttraumatic Subchondral Injuries

Posttraumatic subchondral injuries affect the articulating surface with intact articular cartilage. They are both associated with lysis and liquefaction of medullary fat and can be further classified as contusions (bruises) and fractures (impaction).

• Subchondral bone contusions: These are trabecular microfracture or infractions with hemorrhage and edema. MRI reveals poorly defined, reticulated, heterogeneous T1-hypointensity and T2-hyperintensity. The area of signal abnormality is usually larger on T2-weighted images compared to T1-weighted images.
  
  Differential considerations for this appearance include:
  • Osteonecrosis
  • Fat necrosis
  • Osteoarthritis
  • Normal variant (e.g., in children)
  
  
  
• Subchondral fractures: These are linear or curvilinear fractures that extend through the subchondral bone without violation or depression of the subchondral bone plate. There may be thickening of the black line of the subchondral bone plate and/or geographic or linear areas of signal abnormality in the subchondral bone marrow. When geographic, there is a coalescent area of low T1 signal that abuts the subchondral plate. When linear (shown above), the signal abnormality can be vertical, oblique or parallel to the cartilage.
  
  Differential considerations include:
  • Osteonecrosis
  • Stress fracture
  • "Spontaneous osteonecrosis of the knee"

References

• Bohndorf K. Imaging of acute injuries of the articular surfaces (chondral, osteochondral and subchondral fractures). Skeletal Radiol. 1999 Oct;28(10):545-60.
• Vellet AD, Marks PH, Fowler PJ, Munro TG. Occult posttraumatic osteochondral lesions of the knee: prevalence, classification, and short-term sequelae evaluated with MR imaging. Radiology. 1991 Jan;178(1):271-6.