Pseudodefect of the Capitulum

An abrupt contour change can be observed at the posterolateral margin of the capitulum at the junction of anterior capitulum and posterior lateral epicondyle. This contour change can be mistaken for an osteochondral lesion and has been termed the pseudodefect of the capitulum/capitellum.

The pseudodefect is most obvious on coronal images through the posterior aspect of the capitulum and on sagittal images on more lateral images.

The pseudodefect can be differentiated from an osteochondral lesion by noting that the latter occurs along the normally smooth convex surface of the anterior aspect of the capitulum and is associated with adjacent bone marrow edema. Increased bone marrow signal on T2-weighted images, however, can be simulated by filling of the pseudodefect with joint fluid or intraarticular contrast, as seen in this case.

References

• Chung CB. Chapter 12. In Chung CB and Steinbach LS. MRI of the Upper Extremity: Shoulder, Elbow, Wrist, and Hand. Lippincott Williams & Wilkins. 2010. p 462.
• Mulligan M. Medical terminology. AJR Am J Roentgenol. 2006 May;186(5):E10; discussion E10.
• Rosenberg ZS, Beltran J, Cheung YY. Pseudodefect of the capitellum: potential MR imaging pitfall. Radiology. 1994 Jun;191(3):821-3.