E4852. Crack the Code! Imaging Characteristics of Lower Extremity Stress Injuries in Athletes and Clinical Implications
  1. Shruti Kumar; University of Arkansas for Medical Sciences
  2. Larry Balle; University of Arkansas for Medical Sciences
  3. Tarun Pandey; University of Arkansas for Medical Sciences
  4. Roopa Ram; University of Arkansas for Medical Sciences
  5. Kedar Jambhekar; University of Arkansas for Medical Sciences
  6. Gitanjali Bajaj; University of Arkansas for Medical Sciences
Stress fractures occur due to a mismatch between the strength of bones and the prolonged mechanical stress they endure. They are categorized into two main types: insufficiency fractures and fatigue fractures.

Educational Goals / Teaching Points
Insufficiency fractures occur because of usual stress on abnormal bones, and fatigue fractures occur due to unusual stress on normal bones. Based on the force distribution, some injury sites are considered high risk and others low risk. Radiography followed by MR are the imaging modalities of choice to evaluate potential stress injury. Knowledge of early imaging findings and typical locations aids in timely diagnosis and prevention of complications. Fredericson MRI classification system is used for grading tibial stress injuries. Grade of stress injury correlates with time to return to play.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
In cortical bone, stress fractures may be seen as the presence of an endosteal or periosteal edema without a fracture line, or a circumferential periosteal reaction with a fracture line through one cortex. In cancellous bone, stress fractures are even less well visible but may be appreciated as subtle areas of new bone formation some 2–3 weeks after the onset of pain. On MRI, Fredericson Grade 1 stress fractures show mild to moderate periosteal edema on STIR images but no marrow abnormalities. Grade 2 shows moderate to severe periosteal edema on STIR images, with added marrow edema on T2-weighted images. Grade 3 shows marrow edema on T1-weighted images, and in grade 4 stress injuries a fracture line is clearly visible. The choice of conservative treatment, prophylactic fixation versus surgical fixation depends upon the type of injury.

Stress fractures warrant early detection to reduce morbidity and prevent progression to complete fractures. A differential of stress fractures must be considered in MRI cases with nonspecific marrow edema.