Subchondral insufficiency fracture
Subchondral insufficiency fracture refers to a type of stress fracture that occurs below the chondral surface on a weight-bearing surface of a bone due to mechanic failure of subchondral cancellous bone.
They tend to occur when normal physiological forces are repeatedly applied to an area of bone. Callus formation occurs along with non-mineralized osteoid and the absence of bone infarction.
- abnormal loading through the joint
Typical sites include:
- knee: can progress to spontaneous osteonecrosis of the knee
- femoral head
- femoral condyles
- tibial plateau
- metatarsal head
- secondary osteonecrosis
- osteonecrosis with cavitation (crescent sign)
- articular collapse
- destructive arthropathy
Plain radiography and CT
Radiographs are normal preceding the development of callus formation or collapse of the articular surface. Linear or patchy subchondral sclerosis may be present representing cancellous fracture.
- T1: may be characteristically low signal intensity band through the affected region
- parallels the subchondral bone plate whereas osteonecrosis is curvilinear
- preservation of the articular cartilage whereas an osteochondral defect is involved
- T2: florid marrow edema
The DDx of subchondral marrow edema includes: