How are stress and insufficiency fractures diagnosed on MRI?
The most sensitive MR imaging sequences for demonstrating these injuries are fluid-sensitive ones, in which both stress and insufficiency fractures appear as linear low signal intensity foci surrounded by high signal intensity bone marrow edema. These fractures can be complete (involving the entire circumference of the cortex) or incomplete (involving only one side of the cortex) most commonly along the compressive surface in the medial aspect of the femoral neck.
MRI is also highly sensitive for radiographically occult milder or earlier forms of stress injuries, stress reaction, and microtrabecular stress fracture. Stress reactions appear as focal bone marrow edema in the medial femoral neck without linear signal abnormality; microtrabecular stress fractures may in addition demonstrate linear low signal intensity similar to stress fractures but isolated to the spongy bone and not involving the cortices.
These injuries are commonly associated with a hip joint effusion and adjacent soft tissue edema, which demonstrate hyperintense signal intensity on fluid-sensitive sequences.