Depict the MRI appearance of common normal variants of the shoulder, elbow, hip, and knee Compare the MRI appearance of common normal variant joint anatomy with the appearance of various joint pathologies

Recognition and discrimination of normal variant anatomy from pathology is essential for accurate diagnosis and appropriate patient management. Knowledge of the common normal variants that are often confused for pathology in the major joints can help avoid unnecessary follow-up testing or intervention. The typical MRI findings of normal variations in the shoulder, elbow, hip, and knee will be presented. In addition, a selection of common pathologiesthat can be confused with normal variants will be portrayed.

Normal Variants of the Shoulder: Os Acromiale (Fig. 1) Resulting from failure of fusion of the ossification centers at theacromial apophysis and base of the acromion Present in 7-15% of the population and bilateral in ~ 60% of cases Often asymptomatic, though can lead to pain, instability, orrotator cuffimpingement, best diagnosed on shoulder MR In symptomatic patients marrow edema and irregularity of the surface interface at the synchondrosis suggest motion Mimics an acromion fracture Sublabral Recess (Fig. 2) Recess between the superior portion of the...

Normal variants are commonly encountered on MRI of the large joints and can simulate clinically relevant disease. Although confident discrimination of variant anatomy from pathology may not be possible in every case, understanding and recognizing the most commonly confused variant anatomy can enhance image interpretation and potentially obviate the need for imaging follow-up and prevent unnecessary treatment.

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Dr. Eric Williams Diagnostic Radiology Resident Mayo Clinic Florida Jacksonville, Florida United States of America Dr. Hillary Garner Assistant Professor of Radiology Mayo Clinic Florida Jacksonville, Florida United States of America