Investigation of Systemic Metal Ion Concentration Following a Ceramic-on-metal Total Hip Arthroplasty

This is a pilot study to compare systemic concentrations of cobalt and chromium in patients
that have previously undergone total hip arthroplasties with ceramic on metal and metal on
metal bearing surfaces. Secondary goals include an assessment of osteolysis on radiographs,
potential long term analysis of implant survivability, and cancer rates in the two patient
populations.

Increased metal ion production has been documented in metal-on-metal arthroplasty
articulations. There are several concerns over metal ion production. First, even though
there is a decreased histiocytic response to metallic debris, a dose dependent cytotoxic
response with Interleukin 6, Prostaglandin E2, and Tumor Necrosis Factor alpha persists and
may cause osteolysis in the long term. Second, increased levels of cobalt, chromium and
nickel has been shown to correlate with increased cancer rates in several animal models, and
the carcinogenic risk in humans has not been fully elucidated as yet. Third,
hypersensitivity reactions to metal ion develop in up to 25% of these patients, and 60% of
patients with poorly functioning hip.

Ceramic on metal avoids many of these problems due to the improved wear characteristics. If
the level of metal ion production is significantly reduced and the implant survivability is
proven in long term studies, this articulation may become the preferred method.

Inclusion Criteria:

- Subject is 40 - 80, who has undergone a top hip arthroplasty with either metal on
metal or ceramic on metal articulation for a diagnosis of non-inflammatory
degenerative joint disease. We will also include subjects who have had bilateral hip
arthroplasties or a second arthroplasty performed since the initial surgery.

- Patient must be able to provide consent to participate

Exclusion Criteria:

- Diagnosis other than non-inflammatory degenerative joint disease, chronic renal
insufficiency, or any systemic inflammatory condition

- Evidence of active infections

- Patients whose occupations include welding or metal working

- A second arthroplasty performed since the initial will not be exclude, but their data
will be analyzed as a subpopulation

- unwillingness to comply with rehabilitation program or inability to return for
follow-up visits

- Any systemic steroid therapy within 3 months of surgery

- Subjects who are pregnant