A healthy fifty-seven-year-old man had undergone a minimally invasive right total hip arthroplasty via a two-incision approach because of degenerative arthritis; the arthroplasty components included a uncemented hemispherical acetabular shell (Trilogy; Zimmer, Warsaw, Indiana) with a highly cross-linked polyethylene liner (Longevity; Zimmer), a fully porous-coated uncemented cylindrical stem (VerSys Beaded FullCoat; Zimmer), and a 32-mm cobalt-chromium femoral head. The patient had had an uneventful recovery, and the hip had remained asymptomatic through regular follow-up for the first seven years after surgery.
The first symptoms regarding the hip occurred approximately seven years postoperatively. The patient noted mild thigh discomfort without start-up pain, as well as numbness and tingling over the anterolateral aspect of the thigh, both of which were associated with vigorous activity. He reported no change in activity level and was still jogging up to four miles at a time and playing eighteen to thirty-six holes of golf on a regular basis. Other than some subjective tingling in the distribution of the lateral femoral cutaneous nerve, the physical examination and radiographs were normal. Naproxen was quite effective in providing relief.
Five months after the pain began, the patient returned with substantially elevated serum cobalt (7.2 ng/mL; reference, 0.16 ng/mL) and chromium (5.4 ng/mL; reference, 0.24 ng/mL) levels, which had been determined from tests ordered by the primary care physician. These tests were obtained because of a three-year history of migraine headaches and occasional bilateral tinnitus without a clear etiology and because there have been numerous case reports in the medical and orthopaedic literature of neurologic symptoms associated with metal ion release following total hip arthroplasty15-23. Since there have been reports of corrosion at the modular head-neck junction causing elevated metal levels and adverse local tissue reactions with this type of implant13, the patient was evaluated with a more extensive workup. Radiographs remained unremarkable and demonstrated well-fixed components in appropriate position with no evidence of wear or osteolysis (Fig. 1). Serum metal levels were repeated at our institution’s trace metal analysis laboratory according to previously described methodology24, and the patient underwent magnetic resonance imaging (MRI) with a metal artifact reduction sequencing protocol. Repeated tests to determine metal levels again demonstrated substantially elevated serum cobalt and chromium (Table I). These levels exceeded thresholds that have been used to suggest the potential for implant failure or adverse local tissue reaction6,10. An MRI demonstrated an anterior fluid collection consistent with psoas bursitis, but there was no apparent reactive tissue around the hip. The patient was sent to a board-certified medical toxicologist for evaluation.
At the recommendation of the toxicologist, the patient stopped taking over-the-counter supplements, which included a multivitamin (Centrum Silver Adults 50+; Wyeth, Madison, New Jersey), a B-complex vitamin (Super B-Complex; Nature Made, Mission Hills, California), and a B-12 (cobalamin) vitamin (Vitamin B-12, 1000 mcg; Nature Made) (Table II). He had been taking the multivitamin for approximately five years, the B-complex vitamin twice daily for approximately three years, and the B-12 vitamin daily for approximately two years. The patient remained off these supplements for fifteen weeks before the serum metal levels were redrawn at our laboratory. No other changes to diet or medications were made. Repeat testing (Table I) demonstrated normalization of the serum cobalt and near-normalization of the serum chromium. On follow-up, he saw a leading migraine expert who thought that the migraines and tinnitus were unrelated to the total hip arthroplasty or to the previously elevated cobalt and chromium levels. The hip remains minimally symptomatic, with thigh pain and numbness appearing only after prolonged activity. He reports no appreciable change in the symptoms from when the serum metal ion levels were substantially elevated.
Disclosure: One or more 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 an aspect of this work. In addition, one or more of the authors, or his or her institution, has had a financial relationship, in the thirty-six months prior to submission of this work, with an entity in the biomedical arena that could be perceived to influence or have the potential to influence what is written in this work. 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.