What's the Diagnosis - Case 26

History 45 year old woman with long standing hip pain.

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Findings AP radiograph in the first case demonstrates symmetric, marked axial migration of the femoral heads and protrusio deformity. There is marked deformity of both femoral heads. CT examination shows an obliteration of the joint space with erosive and subchondral cystic change. Soft tissue attenuation is prominently filling the joint space.

MRI of the second case shows moderate-sized joint effusions containing a dense degree of synovitis with edema of the left acetabulum. Further, there is erosive change with global cartilage loss, and an anterosuperior labral tear.

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Diagnosis: Hemophilia Rheumatoid arthritis is an inflammatory arthropathy that yields synovial proliferation and synovitis, accounting for the dense synovitis seen on the MRI. Inflammation leads to erosion of bone as well as cartilage loss, accounting for the joint space loss and articular findings seen well on both the CT and MRI. Rheumatoid is a diffuse process and, as such, typically involves joints in a symmetric pattern with uniform joint space narrowing.

This uniform joint space narrowing is what leads to the concentric or axial type narrowing seen of the hip joints in rheumatoid arthritis. The finding of protrusio is not unique to rheumatoid but is related to the joint remodeling often seen in inflammatory arthropathies. Although strictly diagnosed via medial displacement of the acetabular line relative to the ilioischial line, an easier substitute is the femoral head crossing the ilioischial line.

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Resources

• Resnick. Diagnosis of Bone and Joint Disorders. 4th Ed. 2002.

• Brower. Arthritis in Black and White. 2nd Ed. 1997. www.ajronline.org/cgi/content/abstract/189/6/1502

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