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Subchondral insufficiency fractures are more common in elderly women 1,4,6. Subchondral fractures due to trauma can occur at any age.
Associated injuries include 4-7:
- ligamentous injuries
- radial meniscal tears
Patients will usually present with pain on weight-bearing in the affected joint, improving with rest 2.
Subchondral fractures are usually a consequence of compressive forces, transmitted from the cartilage to the subchondral bone plate and from there to the trabeculae, which fail to resist that force and break or fracture 3. They can also occur in conjunction with twisting and ligamentous injuries.
Usually, subchondral fractures present as linear or curvilinear structures often paralleling the subchondral bone plate, with or without areas of subchondral collapse 2.
Sometimes visible as subchondral hyperlucency with a decrease in bone density. Sclerotic lines as a result of impaction or as slight deformities of the joint line in case of subchondral collapse can sometimes be seen particularly at a later stage 4.
- directly visible subchondral trabecular discontinuity on high resolution
- signs of subcortical impaction visible as subchondral hyperdensity
- subchondral bone marrow edema on dual-energy CT
The fracture can be seen as irregular linear or curvilinear subchondral low signal intensity structure near the subchondral bone plate of low signal intensity in T1-weighted images and also sometimes, but not always in T2-weighted images 1,2,4-8. The area between the fracture line and the articular surface should be of high signal in T2 weighted images 2,4.
Almost always there will be associated bone marrow edema best appreciated in fat-saturated T2 weighted and intermediate or proton-density weighted images 4.
- T1: low signal intensity fracture line, intermediate to a weak low signal of the surrounding stress reaction 2
- T2: low signal intensity fracture line, but not always visible 5
- IM/PDFS: high signal intensity stress reaction / bone marrow edema 2,5
A suggested grading system based on MRI findings is 9:
- grade 1: bone marrow edema
- grade 2: bone marrow edema with low signal intensity fracture line
- grade 3: fluid-filled fracture line and cysts
- grade 4: cortical collapse with a step off
Treatment and prognosis
Low-grade subchondral fractures in particular, if there is no collapse of the subchondral bone plate, can be treated conservatively with restricted weight-bearing 2,3 and non-steroidal anti-inflammatory drugs. Prostaglandin I-1 and/or bisphosphonates might be considered 5.
Joint preserving surgical treatments of subchondral fractures include microfracture, drilling, subchondroplasty 10, or in the hip joint: transtochanteric osteotomy 11.
- concave, smooth half-moon/crescentic appearing necrotic segment
- double line sign
- serpiginous line in the chronic phase
- also involves the cartilage
migratory transient bone marrow edema 2
- no subchondral fracture line
- subchondral cysts
- usually in conjunction with chondral damage
- usually affects all parts of the joint
- usually in adolescents
- osteoid osteoma
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