1. Backflow from a Metallosis-Induced Intrapelvic Mass into a Revision Hip Arthroplasty by Yasuo Yoshihara, Yuichiro Shiromoto, Masato Tatsumi, Masamoto Hirano, Tomoki Kawano, Hiroshi Arino, Motohiko Osako, and Koichi Nemoto JBJS Case Connect Volume 3(3):e66 July 10, 2013 ©2013 by The Journal of Bone and Joint Surgery, Inc.

2. Anteroposterior radiograph of the pelvis showing eccentric wear of the right polyethylene liner with no evidence of loosening of either the acetabular or femoral metal component. Yasuo Yoshihara et al. JBJS Case Connect 2013;3:e66 ©2013 by The Journal of Bone and Joint Surgery, Inc.

3. Axial T1-weighted (Fig. 2-a) and T2-weighted (Fig. 2-b) MRI images of the pelvis showing a large inhomogeneous mass in the right iliac fossa. Yasuo Yoshihara et al. JBJS Case Connect 2013;3:e66 ©2013 by The Journal of Bone and Joint Surgery, Inc.

4. Axial T2-weighted MRI images showing the trochanteric cystic lesion (Fig. 3-a) connected to the hip joint space (white arrow). Yasuo Yoshihara et al. JBJS Case Connect 2013;3:e66 ©2013 by The Journal of Bone and Joint Surgery, Inc.

5. The operative findings showed a black globular cystic mass underneath the iliopsoas fascia in the pelvic cavity. Yasuo Yoshihara et al. JBJS Case Connect 2013;3:e66 ©2013 by The Journal of Bone and Joint Surgery, Inc.

6. The cystic mass had a thick fibrous wall and contained muddy black metallic debris. Yasuo Yoshihara et al. JBJS Case Connect 2013;3:e66 ©2013 by The Journal of Bone and Joint Surgery, Inc.

7. Pathological examination of the mass wall revealed many black depositions suggestive of metal debris in addition to foam cells and multinucleated giant cells in the connective tissue (hematoxylin and eosin stain, 400× magnification, scale bar = 20 μm). Yasuo Yoshihara et al. JBJS Case Connect 2013;3:e66 ©2013 by The Journal of Bone and Joint Surgery, Inc.