MRI grading system for bone stress injuries

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MRI grading system for bone stress injuries​ is a useful tool in assessing the extent of clinical findings related to bone stress injury and predicting the time to return to full activity, the latter being especially important for athletes.

Classifications

Fredericson grading system

Fredericson et al. created an MRI grading system initially developed to grade medial tibial stress injuries but has since been applied elsewhere :

  • grade 1: periosteal edema with no associated bone marrow abnormalities
  • grade 2: periosteal edema with mild bone marrow edema visible only on fat-suppressed T2WI
  • grade 3: periosteal edema and extensive bone marrow edema visible on T1 and fat-suppressed T2WI
  • grade 4
    • grade 4a: periosteal edema, extensive bone marrow edema visible on T1WI and fat-suppressed T2WI and multiple focal areas of intracortical signal changes
    • grade 4b: periosteal edema, extensive bone marrow edema visible on T1WI and fat-suppressed T2WI and linear region of intracortical signal change (i.e. a fracture line)
Arendt grading system

Arendt et al. assessed bone stress injuries in athletes at different skeletal sites and modified the Fredericson grading system, adding STIR sequence to the assessment :

  • grade 1: positive marrow signal change on STIR
  • grade 2: positive marrow signal change on STIR and T2WI
  • grade 3: positive marrow signal change on STIR, T2WI and T1WI, no definite cortical break
  • grade 4: grade 3 findings plus visible fracture line on T1WI or T2WI

In contrast to Fredericson grading system, the absence or presence of periosteal reaction does not affect the injury grade.

The estimated time of treatment (rest) required to return to sports activity based on this classification is :

  • grade 1: 3 weeks
  • grade 2: 3-6 weeks
  • grade 3: 12-16 weeks
  • grade 4: 16+ weeks
Nattiv grading system

Nattiv et al. assessed bone stress injuries in athletes at different skeletal sites and combined the criteria of the above two grading systems. As a result, both bone marrow edema and periosteal reaction affect injury grade :

  • grade 1: mild marrow edema on fat-suppressed T2WI (but not on T1WI) or periosteal edema
  • grade 2: moderate marrow edema on fat-suppressed T2WI (but not on T1WI) or periosteal edema
  • grade 3: severe marrow edema on both fat-suppressed T2WI and T1WI or periosteal edema, without a fracture line
  • grade 4: severe marrow edema on both fat-suppressed T2WI and T1WI or periosteal edema plus visible fracture line on T1WI or T2WI

Practical points

Due to the presence of several grading systems, the radiological report may be unclear if only an injury grade is given, without any further details. For this reason, it is advisable to:

  • talk to the orthopedic surgeons at the institution to reach a consensus regarding the used grading system
  • report the findings in a descriptive manner, adding in brackets the grade and the author of a grading system (e.g. Arendt grade 3 bone stress injury)