Analysis of 118 second-generation metal-on-metal retrieved hip implants

H.-P. Sieber, C. B. Rieker, P. Köttig; from the Regionalspital, Biel, Switzerland; J Bone Joint Surg [Br] 1998;80-B:46-50.
Received 20 April 1998; Accepted after revision 8 July 1998

Download full Scientific Paper – Click here

Reading this paper is fascinating – problems with metal on metal hips have been around since the 1930’s and seem to have gone out of favour in metal – polyethylene hips in the 1960’s.

The first use of metal-on-metal surfaces was by Wiles in 1938 with a stainless-steel implant. The unsatisfactory results induced McKee to employ cast cobalt alloy. From 1962 onwards metal-on-metal prostheses were increasingly rivalled by the metal-on-polyethylene implant of Charnley. Both prostheses contributed to the success of THR in the 1960s. The better results achieved with metal-on-polyethylene implants almost led to discontinuation of the use of metal-on-metal prostheses.

However, the wearing of the polyethylene over time led to its own problems and:

Osteolysis is due to particulate wear debris and is mainly responsible for the long-term failure of total hip replacement (THR). The Charnley THR has been shown to give satisfactory clinical results with a survival rate of 85% at 20 years. When radiological evidence of loosening was added to that seen at revision operations, 22% of the acetabular and 7% of the femoral components were considered to be unstable.

Polyethylene wear was shown to be significantly related to acetabular loosening and resorption of the femoral neck in nearly two-thirds of cemented THRs in patients younger than 20 years at the time of operation.

About half a million polyethylene wear particles are produced at each step due mainly to abrasive wear.

Contact of particle-laden articular fluid with the surrounding bone could be a key factor in the development of osteolysis. Joint fluid under pressure invades soft tissues and bone and expands the effective joint pace. As a result, activated macrophages may be found in cysts around the
prostheses.

… There have been many attempts to find a solution to the problem of wear. Trials of an improved polyethylene have not been convincing…

So it is not just metal-on-metal which causes problems in hip replacements – it is “wear particles” in general which can lead to osteolysis, tissue damage and bone resorption. Also, interesting to note that:

Polymethylmethacrylate (PMMA) cement alone is less harmful if it does not contain radiopaque additives. In vitro, monocytes and macrophages responding to particles of bone cement are capable of differentiation into osteoclastic cells. Their capacity for bone resorption is activated only when radiopaque additives are introduced with the cement particles, with a doubling of the rate for Ba2SO4 compared with ZrO2.  Osteolysis therefore has a multifactorial pattern and the biological activity of all possible wear particles has to be considered when introducing new implants.

And following on in the article:

Based on their findings of low wear and minimum osteolysis with retrieved Müller-Huggler prostheses, Weber and Fiechter developed a new metal-on-metal implant called Metasul (Sulzer Orthopedics Ltd, Winterthur, Switzerland). This second-generation prosthesis has been used
in over 60 000 THRs since 1988.

And they note that:

… found that the metal wear particles from McKee-Farrar and Metasul implants had a smaller diameter (<0.1 μm) than polyethylene particles from conventional implants (about 0.5 μm). Although the metal-on-metal implants have a lower volumetric wear, the calculated number of wear particles is higher than for the same volume of polyethylene wear. The granulomatous inflammatory reaction and the presence of foreign-body giant cells, however, were less pronounced around the metal-on-metal implants.

And this is fascinating:

In an experimental study on rabbits, Goodman et al  showed that the presence of Co-base alloy particles may inhibit bone growth, and Allen et al  reported that Co [i.e. Cobalt; my note] was toxic to osteoblast-like cell lines and inhibited the production of type-I collagen, osteocalcin and alkaline phosphatase [emphasis added].

And then Alumina rises in popularity:

In 1970, Boutin developed an alternative alumina-on-alumina implant. Although this combination has very low wear and is still used in Europe, its popularity remains limited because of the possible fracture of the brittle components.

… After its introduction in the 1970s alumina has been used widely for the head to articulate with a polyethylene cup. It has maintained its position despite reports of fractures of the head and has proved successful in reducing the amount of polyethylene wear. The introduction of ceramic-on-ceramic articulating surfaces did not achieve the same success. There are many reports of problems related to the brittle material, insertion and design. Studies in France on cemented alumina implants revealed problems of fixation of the acetabular cup and early deterioration of the cement mantle giving rise to third-body wear. Since this wear was attributed to the zirconia particles  (my emphasis) used to opacify the bone-cement particles and not to the alumina particles, uncemented fixation has been recommended.

But Alumina has led to tissue and bone problems too:

In retrieved implants, a rate of wear of 8 μm per year was measured for the cup and head.

Alumina particles were found to be widespread in periarticular lymphatic tissues, but the tissue reaction proved to be low. By contrast, zirconia particles produced marked activation of macrophages and an inflammatory reaction (I have added the big bold italics).

Although alumina wear has been said to be substantially inert, there has been a recent report of a spontaneous fracture of the distal femur in a patient with an uncemented ceramic-on-ceramic THR. Material obtained from the area of fracture showed abundant histiocytes and spectrography revealed concentrations of aluminium ten times higher (my emphasis added) than those of Co and Cr. The
fracture was attributed to the foreign-body reaction to the large amount of ceramic particles and the subsequent osteolysis.

SO – all forms of hip replacement have problems

– but what really interests me is that I have a Smith & Nephew Birmingham Spectron Cobalt Chrome Total Hip Replacement (THR) – which by the way is bloody painful as I write this – and I think that we all know the issues emerging with Cobalt Chrome – higher levels than normal in the blood & tissues, osteolysis (tissue damage) and bone resorption.

So metal-on-metal is not performing well if you have a DePuy THR – and for lucky low-percentile types like me – the Smith & Nephew Cobalt Chrome is just as nasty it seems…

So what are Smith & Nephew touting now … OXINIUM (Smith & Nephew Registered TM) – which is:

Oxidized Zirconium – which is ZIRCONIA...

Now, according to Wikepedia:

Zirconium dioxide (ZrO₂), sometimes known as zirconia (not to be confused with zircon), is a white crystalline oxide of zirconium.

Now didn’t I read somewhere (above) that:

Since this wear was attributed to the zirconia particles… AND

zirconia particles produced marked activation of macrophages and an inflammatory reaction …

So I ask myself a very simple question – why would someone make an articulating surface (hip joint) which is effectively made of a metallic “sand paper” – surely one would have to expect wear – even though it is in theory “diamond hard”

A few things stand out for me:

1. Zirconium may well be bio-compatible like titanium – but according to the scientific paper above oxidised zirconium (zirconia) IS NOT…
2. As the Zirconia in the ball joint of the THR wears, surely it will shed zirconia particles – these produced marked activation of macrophages and an inflammatory reaction… AND
3. wear was attributed to the zirconia particles…
4. AND… wear with Oxinium, while less, may lead to to more inflamatory reaction – less may produce more – will have to research the literature further to see what is said.

So call me a bloody skeptic, but we may well end up with yet another accident going somewhere to happen…

And you will note below:

Smith & Nephew say “excellent fracture toughness like cobalt chrome” – WELL, that answers another of my questions about S&N Birmingham Spectron Cobalt Chrome THR’s – they MUST have “heat treated” the cast Cobalt Chrome alloy as cast Cobalt Chrome according to the literature I have read is brittle – have a look at the post where I highlight the scientific study that shows – click here to go to it. And here is the Scientific Paper Click here.

AND when you heat-treat cast Cobalt Chrome, you decrease the carbide content –

“carbide content can be reduced from a volume percentage of seven down to 0.03.”

So as reduced carbide content reduces toughness, but gives more flexibility (less fractures), it also increases wear, and the rate of release of cobalt and chromium ions into the surrounding bone and tissue – leading to osteolysis, tissue and bone damage, bone resorption and many metabolic problems at higher levels.

So it seems safe to assume (may I?) that the Smith & Nephew Cobalt Chrome THR that I have has heat treated Cobalt Chrome – hence the cobalt chrome damage to my hip tissues and bone.

Note the earlier reference:

Co [i.e. Cobalt; my note] was toxic to osteoblast-like cell lines and inhibited the production of type-I collagen, osteocalcin and alkaline phosphatase…

So cobalt is toxic to the very cells that produce new bone….

Here’s what Smith & Nephew have to say about OXINIUM:

Related articles

• Visit to the Surgeon Monday 18th July 2011 (earlsview.com)
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• Sadwin Doesn’t buy the BHR Story … (earlsview.com)
• Cell biology surrounding metal on metal hips (earlsview.com)