MRI OCD Knee
In a patient with a known OCD lesion on x-ray, an MRI of the knee is an option to characterize the OCD lesion or when concomitant knee pathology is suspected such as meniscal pathology, ACL injury, or articular cartilage injury.

Rationale
AAOS conducted a systematic review that identified two diagnostic studies40, 41 addressing this recommendation. One of these studies evaluated the diagnostic performance of clinical examination with radiographs and of selective MRI in the evaluation of intra-articular knee disorders by comparing these findings with arthroscopic findings.40 The clinical diagnosis (from the initial visit), MRI diagnosis (from the MRI report), and the arthroscopic diagnosis (from the operative report) were retrospectively reviewed and compared.  Since only a subset of all patients that underwent evaluation of intra-articular knee disorders proceeded to arthroscopic evaluation, this diagnostic study does not universally apply the reference standard of arthroscopy.  Consequently, this retrospective diagnostic study without a universally applied reference standard was evaluated as a Level II study.

Similarly, the second diagnostic study identified in the systematic review, prospectively evaluated all consecutive patients undergoing knee arthroscopy who had a preoperative MRI.41 Again, this study only reports on the subset of patients that required surgery; therefore, this diagnostic study does not universally apply the reference standard of arthroscopy.  Consequently, this prospective diagnostic study without a universally applied reference standard is also evaluated as a Level II study.

These Level II studies, when considered together, may have supported a moderate strength of recommendation.  However, these studies found that both x-ray and MRI are good rule in tests and do not address the incremental diagnostic value of an MRI in the setting of known OCD determined by x-ray.  That is, these studies do not compare the diagnostic performance of clinical examination with standard radiographs to clinical examination with standard radiographs and an MRI; therefore we downgraded the strength of this recommendation to limited.

In addition to identifying the presence of OCD lesions and distinguishing OCD lesions from other intra-articular pathology, an MRI may be used as an adjunct to clinical examination with radiographs to provide additional information that will guide therapeutic decision-making.  Of the 5 therapeutic studies42-46 that were included in the development of this guideline, three studies 42-44 report the acquisition of an MRI at enrollment and three studies42, 44, 45 report the acquisition of an MRI at follow-up evaluation. Further, one prognostic study19 predicts the healing potential of stable OCD lesions, utilizing a multivariable logistic regression model. Of all of the variables that were considered (including sex, side, location, symptoms, knee dimensions, and lesion dimensions), only knee symptoms as well as normalized length and normalized width of the OCD lesion as measured on MRI were found to be predictive of healing potential.

Of note, three studies47-49 correlated MRI findings with arthroscopic findings in patients with OCD of the knee. The evidence for assessment of stability of an OCD lesion was inconsistent.

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