Ten-year outcome of serum metal ion levels after primary total hip arthroplasty: a concise follow-up of a previous report*

Abstract

We previously reported on the metal ion concentrations of cobalt, chromium, and titanium that were found in the serum of patients three years after they had undergone primary total hip arthroplasty as compared with the concentrations found in the serum of control patients who did not have an implant. This study is a concise update on the serum metal levels found in a cohort of these patients ten years after the time of hip implantation. Of the original seventy-five subjects, metal ion levels were available for forty patients (53%). Ten patients (hybrid group) had received a hybrid total hip replacement that consisted of a modular cobalt-alloy femoral stem with a cobalt-alloy femoral head that had been inserted with cement and a titanium acetabular socket that had been inserted without cement. Nine patients (cobalt-chromium [CoCr] group) had received an implant with an extensively porous-coated modular cobalt-alloy femoral stem and femoral head along with a titanium acetabular socket; the femoral and acetabular components had each been inserted without cement. Eight patients (titanium group) had undergone insertion of a proximally porous-coated modular titanium-alloy femoral stem with a cobalt-alloy femoral head and a titanium acetabular socket; the femoral and acetabular components had each been inserted without cement. Thirteen patients (control group) from the original control group of patients who had not received an implant served as control subjects. Serum metal levels were measured with use of high-resolution sector field inductively coupled plasma mass spectrometry. The hybrid total hip arthroplasty group had mean cobalt levels that were 3.2 times higher at 120 months than they were at baseline, and the cobalt levels in that group were significantly higher than those in the titanium total hip arthroplasty group at thirty-six, sixty, eighty-four, ninety-six, and 120 months (p < 0.01). The hybrid group had mean chromium levels that were 3.9 times higher at 120 months than they were at baseline, and the CoCr total hip arthroplasty group had chromium levels that were 3.6 times higher at 120 months than they were at baseline. The serum titanium levels were higher in the titanium group at all follow-up time intervals as compared with the levels in all other groups, and the level in the titanium group at 120 months was eighteen times higher than it was at baseline (p < 0.01). Patients with well-functioning primary metal-on-polyethylene total hip replacements had elevated serum metal levels for as many as ten years postoperatively. Furthermore, metal release at the modular femoral head-neck junctions, rather than passive dissolution from porous ingrowth surfaces, was likely the dominant source of serum cobalt and chromium.

Fig. 1

Serum cobalt concentrations. Line graph showing the concentrations of cobalt in the serum, in nanograms per milliliter (ng/mL, parts per billion), as a function of time in the four groups investigated. The hybrid group had cobalt levels that were 3.2 times higher at 120 months than they were at baseline and had cobalt concentrations that were significantly higher than the levels in the titanium (Ti) group at thirty-six, sixty, eighty-four, ninety-six, and 120 months (p < 0.01). *Cobalt levels in the hybrid group were significantly different than those in the titanium group (p < 0.05).

Fig. 2

Serum chromium concentrations. Line graph showing the concentrations of chromium in the serum, in nanograms per milliliter (ng/mL, parts per billion), as a function of time in the four groups investigated. At 120 months, chromium levels were 3.9 times higher in the hybrid group than they were at baseline and 3.6 times higher in the CoCr group than they were at baseline. At sixty months, the hybrid group had elevated chromium levels as compared with the levels in the CoCr group (p < 0.01). *Chromium levels in the hybrid group were significantly different than the levels in the CoCr group (p < 0.01). Ti = titanium group.

Fig. 3

Serum titanium concentrations. Line graph showing the concentrations of titanium in the serum, in nanograms per milliliter (ng/mL, parts per billion), as a function of time in the four groups investigated. The titanium levels at 120 months were 8.9 times higher than they were at baseline in the hybrid group and 9.2 times higher than at baseline in the CoCr group. Serum titanium levels in the titanium (Ti) group were higher than those in all other groups at all follow-up intervals, and they were eighteen times higher than baseline levels at 120 months (p < 0.01). *Titanium levels in the titanium group were significantly different than those in the hybrid and CoCr groups (p < 0.01).