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Relationship of Plasma Metal Ions and Clinical and Imaging Findings in Patients with ASR XL Metal-on-Metal Total Hip Replacements
Eric Y. Chang, MD1; James L. McAnally, MD2; James R. Van Horne, MD3; James G. Van Horne3; Tanya Wolfson, MA4; Anthony Gamst, PhD4; Christine B. Chung, MD1
1 VA San Diego Healthcare System, 3350 La Jolla Village Drive, San Diego, CA 92161
2 Medford Radiological Group, 842 East Main Street, Medford, OR 97504
3 Paragon Orthopedic Center, 702 S.W. Ramsey Avenue #112, Grants Pass, OR 97527
4 University of California, San Diego Medical Center, 200 West Arbor Drive, San Diego, CA 92103
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  • Disclosure statement for author(s): PDF

Investigation performed at the VA San Diego Healthcare System, San Diego, California



Disclosure: None of the authors received payments or services, either directly or indirectly (i.e., via his or her institution), from a third party in support of any aspect of this work. None of the authors, or their institution(s), have had any financial relationship, in the thirty-six months prior to submission of this work, with any entity in the biomedical arena that could be perceived to influence or have the potential to influence what is written in this work. Also, no author has had any other relationships, or has engaged in any other activities, that could be perceived to influence or have the potential to influence what is written in this work. The complete Disclosures of Potential Conflicts of Interest submitted by authors are always provided with the online version of the article.

Copyright © 2013 by The Journal of Bone and Joint Surgery, Inc.
J Bone Joint Surg Am, 2013 Nov 20;95(22):2015-2020. doi: 10.2106/JBJS.L.01481
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Abstract

Background: 

Plasma metal ion levels are commonly used in the postoperative follow-up evaluation of patients who have had a metal-on-metal hip arthroplasty. However, the relationship between these levels and clinical and imaging findings is not well known.

Methods: 

We evaluated 156 consecutive patients who received a unilateral ASR XL total hip replacement. Patients presented, regardless of symptoms, in response to a voluntary recall of the hip replacement by the manufacturer and were assessed with regard to the presence and type of symptoms and plasma cobalt-chromium levels. In addition, radiographic and magnetic resonance imaging studies were performed and analyzed.

Results: 

Eighty patients were asymptomatic, and seventy-six patients were symptomatic. The median cobalt level was 1.8 ppb, and the median chromium level was 1.0 ppb (at or below measurement threshold). Pseudotumors that could be detected on magnetic resonance imaging were seen in 69% (107) of 156 patients, and radiographic osteolysis was evident in 7% (eleven patients). At a threshold of 5 ppb, no association was detected between abnormal metal ion levels and patient symptoms, prosthetic femoral head size, or acetabular cup inclination. An abnormal cobalt level was significantly associated with the presence of periprosthetic lucency on radiographs and pseudotumor on magnetic resonance imaging (p < 0.05). An abnormal chromium level showed a similar pattern, but the relationships did not reach significance. Both abnormal plasma cobalt and chromium levels were associated with larger sizes of pseudotumor when present (p < 0.05).

Conclusions: 

In our sample, with a threshold of 5 ppb, abnormal plasma metal ions were associated with larger sizes of pseudotumors when present, but were not predictive of patient symptoms. Abnormal plasma cobalt levels have a significant association with periprosthetic lucency and presence of pseudotumor. Plasma chromium shows a similar pattern of association with lucency and presence of pseudotumor, although the relationships were not significant. Metal ion analysis should be used in conjunction with clinical and imaging evaluation and not as a sole indirect screening test when evaluating patients following metal-on-metal hip arthroplasty.

Level of Evidence: 

Diagnostic Level III. See Instructions for Authors for a complete description of levels of evidence.

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    References

    Accreditation Statement
    These activities have been planned and implemented in accordance with the Essential Areas and policies of the Accreditation Council for Continuing Medical Education (ACCME) through the joint sponsorship of the American Academy of Orthopaedic Surgeons and The Journal of Bone and Joint Surgery, Inc. The American Academy of Orthopaedic Surgeons is accredited by the ACCME to provide continuing medical education for physicians.
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