Hip Resurfacing News - Metal Ion Issues

Metal Ion Study 2002

nospam@example.com (Patricia Walter) — Fri, 03 Aug 2007 06:31:53 -0700

Medium Term Serum Cobalt and Chromium Levels in Patients with Metal-metal Resurfacing

NOTE: This paper was presented at the New Trends of Joint Reconstructive Surgery 2002 Meeting, comparing serum levels in a control group, conventional THR, McKee Farrar, MOM Hip Resurfacing, and MOM THR (Sulzer), which concluded that metal ion levels are higher at 1 year with a small diameter MOM THR (Sulzer) than with resurfacing. As the Sulzer device has been in use for over 15 years with no associated problems reported to date, this is further evidence that this is currently not an issue.

V Reddy MD† J Dorairajan MD† J Nevelos PhD* S Krikler PhD FRCS(Orth)†.
† University Hospitals Coven try & Warwickshire NHS Trust * Corin Medical†

Introduction
The conservative principles of hip resurfacing combined with very low wear metal-metal bearing technology may provide a very attractive solution for the younger arthritic hip. The long-term effects of the inevitable metal ion release however, remain a concern. Serum ion levels from metal-metal resurfacing hip patients were measured pre-operatively and then every year for up to five years.

Materials and Methods
All patients had had either a McMinn (1995-1996) or Cormet® (1997-) hip resurfacing (both manufactured by Corin Medical, UK) implanted by a single surgeon. Blood was collected using a standardised technique to ensure no metallic contamination. Chromium analysis was by graphite furnace atomic absorption (ETA-AAS) using a 4100ZL or A800 Perkin Elmer instrument. Cobalt was analysed by inductively coupled plasma mass spectrometry (ICP-MS). Measurements were taken from 39 patients with 7 of those having bilateral resurfacings. Pre-operative levels were only taken from 15 patients, and these were universally low (below 20nmol/l).

Results – General Population
In all patients the serum levels of cobalt and chromium increased following resurfacing although the extent of the increase varied greatly between patients. There was a general decrease in ion levels from ~2 years. The data shows a definite trend of decreasing ion levels after 3 years. This may be consistent with running-in wear and healing of the peri-prosthetic tissues providing a smooth, stable joint. The decline in serum level seems to start slightly earlier in younger patients (<40) than older patients (>60).

Discussion – General Population

Ion levels increase over the first two years before dropping to a generally low level.
Younger patients’ ion levels peak earlier than older patients – probably related to activity level.
There was no difference in ion levels between the McMinn and Cormet devices.
Bilateral resurfacings did not appear to elevate the ion levels significantly.
Insufficient sample numbers for statistical analysis.

Results – Outliers
The vast majority of patients studied had similar ion level release which remained below 250nl/l. There were, however three individual patients who had much higher ion levels which may cast light on possible causes of increased wear.

Case 1. Patient AP. 22 year old female at primary operation – Steep Acetabular Cup

Case 2. Patient LB. 42 year old female at primary operation Post operative Dislocation and Steep Cup

Case 3. Patient SM. 35 year old male at primary operation.

Discussion – Outliers
These cases were performed before the start of this study and so ion levels were not taken pre-operatively. Their levels were one or two orders of magnitude higher than the general population. (Note scale on the respective graphs). Also the ion levels show no sign of decreasing with time unlike the general population. Steep acetabular cup angles have been shown to be related to increased wear in hard-hard hip bearings (16) . Steep cups will also inevitably lead to an increased chance of dislocation (as in case 2). The large diameter heads used for hip resurfacing are naturally resistant to dislocation and Case 2 of this series remains the only dislocation to date in the senior author’s personal series of over 250 operations.

Conclusions
In the vast majority of patients with metal-metal hip resurfacing there is a small but early rise in serum metal ions over the first 2-3 years but the levels then gradually diminish over time .

Steep cups seem to be associated with increased levels, which could be due to wear and therefore increased ion release into the body.

READ COMPLETE STUDY

Dr. Schmalzried discusses the ASR

nospam@example.com (Patricia Walter) — Tue, 16 Mar 2010 06:50:51 -0700

Advice to patients concerning the ASR

I suggest a few points that, I think, everyone can agree to (for any hip, including an ASR):

1. If you have pain or are in any way concerned - go see your surgeon.

2. There are some screening tests. Based on current experience, if blood (or serum) ion levels of Cr and Co are <5ppb, the likelihood a problem with the implant is low. If the level of either is >10ppb, the likelihood of a problem with the implant is increased. In either event, the next step would be an imaging study (ultrasound or MRI) to look for a fluid collection, or a cystic or solid mass - as evidence of an adverse local tissue response.

3. An aspiration of the joint may be appropriate a) to exclude infection as a cause of the joint dysfunction and b) the characteristics of the fluid may help in the differential diagnosis of a problem related to the metal-metal bearing.

I think that the first point is the most important. If you are concerned, go see your surgeon.

Thomas P. Schmalzried, M.D.

Larger Cups and Optimal Positioning Produce Lowest Ion Levels Medical Study

nospam@example.com (Patricia Walter) — Fri, 08 Jul 2011 18:57:38 -0700

Larger cups and optimal positioning produced lowest ion levels and wear

In a review of 585 blood serum evaluations following hip resurfacing, only femoral size and cup inclination were found to have an effect on ion levels, according a study by orthopedic investigators.

The findings were presented at the 2010 Annual Meeting of the American Academy of Orthopaedic Surgeons.

David J. Langton, MRCS, and his colleagues also found that the size of the coverage angle of the acetabular component contributed significantly to its tolerance of suboptimal positioning.

"Larger joints, it must be emphasized, tolerated suboptimal cup position," he said. "This must be taken into account in all analyses."

Inverse relationships

Using routinely obtained blood serum metal ion levels from patients under the care of the two senior authors of the paper being presented - both highly experienced hip resurfacing surgeons - metal ion results were analyzed regarding their relationship to femoral and acetabular component size and orientation, UCLA activity score, age, time post surgery and postoperative femoral head/neck ratios.

Langton reported an inverse relationship between metal ion levels and femoral size. A smaller acetabular coverage arc was associated with higher metal ion levels.

Another significant inverse correlation was noted by Langton between metal ion levels and contact patch to rim (CPR) distance. CPR is a measurement that relates the position of the articular contact patch with the patient in standing position to the cup rim. According to the abstract, CPR less than 5 mm is associated with a 50% chance of ion levels greater than 30 mg/L.

Words of warning

Langton warned the audience, "To increase metal ion levels as quickly as possible, use as small a bearing diameter as possible, use a cup with the smallest coverage arc, and combine very high anteversion with high inclination."
He concluded, "Cups placed with angles between 40° and 50° inclination and 10° to 20° anteversion have the lowest ion levels and the lowest rates of volumetric wear."

Reference:

Langton D, Jameson S, Joyce T, et al. A review of 585 serum metal ion results post hip resurfacing: cup design and position is critical. Paper 006. Presented at the 2010 Annual Meeting of the American Academy of Orthopaedic Surgeons. March 9-13. New Orleans.

Langton has received research or institutional support from DePuy, a Johnson & Johnson Company, DJ Orthopaedics; he has also received miscellaneous non-income support (e.g., equipment or services) from DePuy, a Johnson & Johnson Company.