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Bone stress injuries (BSIs) occur when there’s an imbalance between bone microdamage & remodeling. Without sufficient recovery time, an accumulation of microdamage leads to bone stress injury. 


BSI exists on a spectrum of severity, which is part of the reason their presentation can vary so widely from one individual to the next - some people experience pretty severe pain and sit out from sport for months, while others have mild pain and are back to running after a few weeks. (This recovery time also has to do with the site of injury, not just the severity - more on that later). 


There are a few classification systems to grade the level or severity of bone stress injury, and these were compared in a chart by Hoenig et al. as you can see below. MRI is used for bone stress injury grading as many will not show up on X-ray for several weeks after the onset of pain.

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Chart from Hoenig et al. 2022

Though there are many proposed classifications, a gold standard classification system for bone stress injuries hasn’t been determined yet. We don’t have one specific system that factors in both radiographic & clinical characteristics of the injury, can be applied to all fracture sites, and is easily accessible, safe and widely applicable. 


With that said, the Fredericson classification system & Arendt classification systems are the most commonly used, so we’ll go into a little more detail on each of them. 


The Fredericson system was initially created to classify medial tibial bone stress injuries and grades are as follows, as seen on MRI:

  • Grade1: periosteal edema with no bone marrow abnormalities

  • Grade 2: periosteal edema, mild bone marrow edema only on T2-weighted images

  • Grade 3: periosteal edema, extensive bone marrow edema on both T1 & T2-weighted images

  • Grade 4: 

    • A: all of the above + multiple focal areas of intracortical signal changes

    • B: all of the above + linear region of intracortical signal change e.g. fracture line

Here's an easier-to-comprehend graphic of BSI grading based on the Fredericson classification:







The Arendt grading system was created using various sites of bone injury and modified the Fredericson with the addition of STIR (short tau inversion recovery) which suppresses the signal from fat tissue. Their grades are:

  • Grade1: bone marrow signal change on STIR

  • Grade 2: bone marrow signal change on STIR and T2-weighted images

  • Grade 3: bone marrow signal change on STIR, T2-weighted images and T1-weighted images with no definite fracture line

  • Grade 4: all of the above + visible fracture line on T1 or T2-weighted images


As you can see, the presence or absence or periosteal edema does not change the grading in the Arendt system which differs from the Fredericson. 


It is possible though rare for a stress fracture to progress to a complete fracture if left untreated, particularly at high-risk sites like the femoral neck - this is why it’s important to catch these early, to both prevent more serious injury from happening and to facilitate faster recovery timelines. 


All bone stress injuries are not created equal. They exist on a pretty broad spectrum - which is one reason why pain presentation and recovery can vary so significantly from one individual or injury to the next. 


Your recovery should be individualized based not only on your specific grade & site of injury, but also your injury history, current health status and future goals. 


If you’re concerned about recurrent bone stress injuries or looking for help rehabbing from one, let’s chat! Click the button below to reach out.

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Hoenig, T., Tenforde, A. S., Strahl, A., Rolvien, T., & Hollander, K. (2022). Does magnetic resonance imaging grading correlate with return to sports after bone stress injuries? A systematic review and meta-analysis. The American Journal of Sports Medicine, 50(3), 834-844.


Kaeding, C. C., & Miller, T. (2013). The comprehensive description of stress fractures: a new classification system. JBJS, 95(13), 1214-1220.


Fredericson, M., Jennings, F., Beaulieu, C., & Matheson, G. O. (2006). Stress fractures in athletes. Topics in Magnetic Resonance Imaging, 17(5), 309-325.

Miller, T., Kaeding, C. C., & Flanigan, D. (2011). The classification systems of stress fractures: a systematic review. The Physician and sportsmedicine, 39(1), 93-100.

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