How do serum cobalt and chromium levels change after metal-on-metal hip resurfacing?

The results of primary Birmingham hip resurfacings at a mean of five years. An independent prospective review of the first 230 hips

We report an independent prospective review of the first 230 Birmingham hip resurfacings in 212 patients at a mean follow-up of five years (4 to 6). Two patients, one with a loose acetabular component and the other with suspected avascular necrosis of the femoral head, underwent revision. There were two deaths from unrelated causes and one patient was lost to follow-up. The survivorship with the worst-case scenario was 97.8% (95% confidence interval 95.8 to 99.5). The mean Harris hip score improved significantly (paired t-test, p < 0.05) from 62.54 (8 to 92) pre-operatively to 97.7 (61 to 100) at a mean of three years (2.1 to 4.3), then deteriorated slightly to a mean of 95.2 (47 to 100) at a mean of five years. The mean flexion improved from 91.5 degrees (25 degrees to 140 degrees) to 110.4 degrees (80 degrees to 145 degrees) at a mean of three years with no further improvement at five years (111.2 degrees; 70 degrees to 160 degrees). On radiological review at five years, one patient had a progressive lucent line around the acetabular component and six had progressive lucent lines around the femoral component. A total of 18 femoral components (8%) had migrated into varus and those with lucent lines present migrated a mean of 3.8 degrees (1.02 degrees to 6.54 degrees) more than the rest. Superolateral notching of the femoral neck and reactive sclerosis at the tip of the peg of the femoral component were associated with the presence of lucent lines (chi-squared test, p < 0.05), but not with migration of the femoral component, and are of unknown significance. Our results with the Birmingham hip resurfacing continue to be satisfactory at a mean follow-up of five years.

Does ion release differ between hip resurfacing and metal-on-metal THA?

Modern metal-on-metal hip resurfacing was introduced as a bone-preserving method of joint reconstruction for young and active patients; however, the large diameter of the bearing surfaces is of concern for potential increased metal ion release. We hypothesized there were no differences in serum concentrations of chromium, cobalt, and molybdenum between patients who had metal-on-metal hip resurfacing (Group A; average head diameter, 48 mm; median followup, 24 months) and patients who had 28-mm metal-on-metal THA (Group B; median followup, 25 months). Serum concentrations also were compared with concentrations in healthy subjects. We identified no differences in ion levels between Groups A and B. A distinction was made according to gender. Women showed a higher chromium release in Group A whereas men had a higher cobalt release in Group B. Values obtained from Group A were higher than those of the control subjects. Our data suggest metal-on-metal bearings for THA should not be rejected because of concern regarding potential increased metal ion release; however, patients with elevated ion levels, even without loosening or toxicity, could be at higher risk and should be followed up periodically.

LEVEL OF EVIDENCE

Level III, therapeutic study. See the Guidelines for Authors for a complete description of levels of evidence.

Serum ion level after metal-on-metal THA in patients with renal failure

We retrospectively reviewed cementless THAs with metal-on-metal bearings in five patients with chronic renal failure and investigated the relations between renal failure and elevated serum cobalt and chromium levels and the side effects of these elevations. Serum cobalt and chromium levels were measured by atomic absorption spectrophotometry at a minimum followup of 2.7 years (mean, 3.9 years; range, 2.7-6.2 years) in five patients with chronic renal failure and in six patients with normal renal function after THA. Mean serum cobalt concentration was 12.5 microg/L in patients with chronic renal failure; this was more than 100-fold higher than in patients with the same prosthesis type and similar followup period, but with no known renal disease. However, the mean serum chromium concentration was 5.1 microg/L, which was within the normal range in all 11 study patients. Side effects related to elevation of serum cobalt or serum chromium concentration were not identified and overall clinical results were good 4 years after surgery. The serum cobalt level was higher in patients with chronic renal failure. Longer followup is necessary to determine any clinical effects.

Chronic inflammation, joint replacement and malignant lymphoma

This paper considers the increased risk of the development of lymphoma in patients with chronic inflammatory disease who undergo metal-on-metal arthroplasty.

Can cobalt levels estimate in-vivo wear of metal-on-metal bearings used in hip arthroplasty?

High levels of cobalt and chromium ions are detected in the blood and urine of patients with metal-on-metal (MoM) hip replacement. These elements are released as a result of wear at the bearing surfaces. Wear rates depend on a multitude of factors, which include the bearing geometry, carbon content, manufacturing processes, lubrication, speed and direction of sliding of the surfaces, pattern of loading, and orientation of the components. In-vivo wear of MoM bearings cannot be reliably measured on X-rays because no distinction can be made between the bearing surfaces. Hip simulator studies have shown that wear rates are higher during the initial bedding-in phase and subsequently drop to very low levels. Accordingly, metal ion levels would be expected to decrease with the use of the bearing, measured as implantation time following surgery. However, several clinical studies have found that metal ion levels either gradually rise or fluctuate instead of decreasing to lower levels. Moreover, hip simulator studies predict that large-diameter bearings have lower wear rates than small-diameter bearings. In clinical studies, however, metal levels in patients with large-diameter bearings are unexpectedly higher than those in patients with small-diameter bearings.

As a consequence, high cobalt ion levels in patients do not necessarily imply that their MoM bearings produce much wear debris at the time that their levels were measured; it may simply be due to accumulation of wear debris from the preceding time. Exercise-related cobalt rise may overcome this limitation and give a better assessment of the current wear status of a MoM bearing surface than a measure of cobalt levels only.

Hip resurfacing arthroplasty: the Australian experience

In the last 10 years, resurfacing hip arthroplasty has become a popular option again for treating hip disorders in younger, active patients in some parts of the world. We report the Australian experience with this operation based on the Australian National Joint Replacement Registry and the literature available on the Australian experience in Resurfacing.

Chromium and cobalt ion release following the Durom high carbon content, forged metal-on-metal surface replacement of the hip

We evaluated the concentrations of chromium and cobalt ions in blood after metal-on-metal surface replacement arthroplasty using a wrought-forged, high carbon content chromium-cobalt alloy implant in 64 patients. At one year, mean whole blood ion levels were 1.61 μg/L (0.4 to 5.5) for chromium and 0.67 μg/L (0.23 to 2.09) for cobalt. The pre-operative ion levels, component size, female gender and the inclination of the acetabular component were inversely proportional to the values of chromium and/or cobalt ions at one year postoperatively. Other factors, such as age and level of activity, did not correlate with the levels of metal ions. We found that the levels of the ions in the serum were 1.39 and 1.37 times higher for chromium and cobalt respectively than those in the whole blood.

The levels of metal ions obtained may be specific to the hip resurfacing implant and reflect its manufacturing process.

Hip resurfacing: a technology reborn

In recent years there has been a resurgence of interest in the concept of hip resurfacing. Much of this interest has stemmed from the work of McMinn in the West Midlands. Hip resurfacing is now emerging as a viable alternative to conventional hip replacement. In this article, we discuss the conceptual advantages offered by hip resurfacing and review the early clinical results and the ongoing clinical concerns regarding this technology.

The effect of the diameter of metal-on-metal bearings on systemic exposure to cobalt and chromium

The recent resurgence in the use of metal-on-metal bearings has led to fresh concerns over metal wear and elevated systemic levels of metal ions.

In order to establish if bearing diameter influences the release of metal ions, we compared the whole blood levels of cobalt and chromium (at one year) and the urinary cobalt and chromium output (at one to three and four to six years) following either a 50 mm or 54 mm Birmingham hip resurfacing or a 28 mm Metasul total hip replacement. The whole blood concentrations and daily output of cobalt and chromium in these time periods for both bearings were in the same range and without significant difference.

Long-term results with the Wagner metal-on-metal hip resurfacing prosthesis

The purpose of this study was to report the long-term results of the metal-on-metal Wagner resurfacing prosthesis. Between January 1991 and August 2004, 54 Wagner resurfacing prostheses were implanted in 52 patients. There were 45 female patients (1 bilateral case) and 7 male patients (1 bilateral case). All the operative procedures were performed using the anterior approach. Of those cases available, the average time to follow-up was nine years. The average Merle dAubign score improved from 8.3 preoperatively to 17.3 postoperatively (p-value < 0.001). Seventeen prostheses required revision. Radiographic evidence of femoral neck narrowing was seen in three prostheses that remained in situ. Combined with a stricter diagnosis and an exact operating technique, the Wagner metal-on-metal surface replacement of the hip joint may offer an alternative surface replacement option.

The development of the DuromTM metal-on-metal hip resurfacing

The poor results of conventional total hip replacement in young and active patients have led to a renewed interest in alternative interventions and bearing material combinations. Con-temporary metal-on-metal resurfacing of the hip has emerged as an attractive option. This procedure utilises a low wear producing bearing which minimises the risk of periprosthetic osteolysis, preserves femoral bone stock should subsequent procedures become necessary, and, due to the increased stability and range of motion, allows the rapid resumption of an active lifestyle. We describe the development of the DuromTM metal-on-metal hip resurfacing and report the preliminary results of the first 100 consecutive cases.