Hip Resurfacing vs THR by Mark Bloomfield
Posted by Mark Bloomfield on hipsrus Message board on April 20, 2009
Have not been here for a while, but thought it time to post something, especially after attending the recent British Hip Society meeting in Manchester.
Which, by the way, was poorly attended by what would be regarded as the doyens of UK hip surgery. Mostly new consultants, registrars or other 'training' grades. Not sure why. Maybe everyone is feeling fatigued by the credit crunch, the declining state of the NHS etc.
I have now done over 1000 hip resurfacings. Practically all the Birmingham device marketed by Smith & Nephew. So I thought I would share what I think about the technique right now. This is not a scientific paper and the views expressed are my own. I suppose I could 'prove' most of what is written below by suitable references in the literature, but some is instinct or gut feel. So it could be wrong, but chances are high the views expressed are accurate!
The 2 perceived 'flaws' or catches to metal-on-metal [MOM] hip resurfacing revolve around metal ion reactions on the part of the patient, and neck of femur fracture / collapse below the femoral component [the cap]. I have also had 3 cup failures where the device worked itself loose and tilted. These were probably my 'fault' as I did not realise they were poorly fixed at the time of the original surgery. It is easy to be fooled and I am now much more careful about testing the 'fix' of the cup to bone. If I have the slightest doubt, I augment the fixation with screws.
Taking each of the 2 perceived flaws in turn:
1. The metal ion story. This is potentially the most serious and; if you paranoid or fearful; the most worrying aspect of all MOM devices, be they resurfacings or Total Hip Replacements [THRs]. The concern is two-fold. First that metal ions may cause an allergic-type reaction [but NOT the same kind of allergy as a skin rash to cheap jewellery!] and second that they may cause cellular or chromosomal anomalies that may lead to an increased risk of cancers.
MOM devices are not new. At the time John Charnley developed his metal on polyethylene [plastic] hip replacement, McKee and Farrar in Norwich were attempting to perfect a MOM THR, many examples of which have survived to last 30 yrs or more. But there were so many early failures of the McKee-Farrar that it was eventually abandoned. This is NOT because MOM bearings are rubbish, but because the technology to make the bearings a perfect fit every time was not available. Those McKee-Farrars that were a perfect match and were implanted favourably, are the ones that lasted 2, 3 or more decades. In contrast, almost all Charnley metal on polyethylene hips started failing at 15 to 18 years, if not before. So metal on polyethylene does better at first, but is worse in the long run as compared to the 'best' McKee-Farrars.
Peter Ring, at Redhill in Surrey, developed a MOM THR which he placed in huge numbers - several thousand. Again, those that were a perfect match lasted a vey long time and most patients died with them in situ. But there were too many early failures if the fit was not perfect and Ring moved to polyethylene like Charnley. Ring metal on polyethylene hips did very badly - even worse than his MOM device or the Charnley version. He was later asked and recounted how he bitterly regretted moving away from MOM, but metal on polyethylene was the irresistible fashion at the time. So be aware that fads or fashions influence orthopaedic surgeons as well!
There are various other MOM THRs that came and went over the years. Most died out after being placed in relatively small numbers. In the early 90s, Sulzer [a prosthetic manufacturer] heavily promoted their Metasul MOM THR. This was machined with modern techniques to ensure an accurate fit every time. The results were good, but there was a significant percentage of unexplained pain and fluid-filled cyst formation which I now believe to be due to metal debris. The Metasul bearing was too small and the metallurgy not quite right to achieve 'fluid film' lubrication.
The point of all the above is to show that we have a combined clinical history of various MOM devices stretching over hundreds of thousands of patient-years. There is not a shred of epidemiological evidence that MOM devices cause an increased risk of cancer or other serious disease. There is, however, plenty of evidence that MOM bearings only work reliably if they are a) of large, rather than small diameter. In other words, the bigger the MOM bearing, the better. b) they are machined to be a perfect fit every time. That takes specialised knowledge and machinery. c) they are made of the right metal alloy, prepared and finished in the right way. d) they are implanted in near perfect position
When McMinn perfected his MOM resurfacing [the BHR], he knew where to go for the metal alloy he needed. He went to the men that made Peter Ring's sucessful MOM THRs. Some say McMinn was lucky. I say he instinctively knew the Ring hip alloy and the exact clearance that Ring was aiming for was the right one. Other makers of MOM hip resurfacing devices thought they could 'improve' the McMinn device. They were universally wrong. So be careful, some MOM hip resurfacings are [in my opinion] not as good as the S&N product. Some are only slightly worse. Others are truly terrible. I cannot say which here, as could be sued for libel!
When it comes to positioning in the body, this is also crucial. This is the factor that most depends on the surgeons insight, experience and innate ability to work well with tissues or bone. To be done well the operation needs good exposure and adequate releases. Doing this SAFELY is a knack some learn easily and quickly, some more slowly and some not at all. Hip resurfacing must be done perfectly or nearly perfectly every time to be reliable. It does not forgive errors that would be seen as relatively minor in the context of THR. It is why I am very, very wary of 'mini incision' resurfacing. Wounds heal side to side, not end to end. They hurt from end to end, but that is usually temporary! As a result of my website and hipsrus, have seen a number of patients unhappy with their resurfacings. Almost all had mal-positioned cups. The other problem is that plain x-rays nearly always under-estimate or 'hide' the true extent of mal-positioning. Bad position = increased metal ion formation = pain and inflammation. True 'allergy' seems exceptionally rare and skin patch testing is useless for detecting this. Ditto the Melissa test.
2. The fracture neck of femur story. This is also a question of surgeon experience, technical skill and judgement. I have done both hips [BHR] in a woman who is now 84. She is exceptional and should not be seen as the rule. In my first 500 resurfacings, I had 5 fractures I know about. There could have been 1 or 2 more that occurred after I left the NHS. In the last 500, there has not been a single fracture, despite doing patients that other surgeons would dismiss out of hand. So it is a combination of physiological not chronological age, surgeon technique, bone quality and aftercare that allows hip resurfacing to be done 'out of the box' . Much has been written about the surgical approach and fractures. I.e. anterior, posterior, trochanter detachment etc. It is a sterile debate as it largely does not matter. DESPITE research that suggests it does. It just shows how research or theory and practice do not always match. But the trochanter detachment causes too many problems for me to adopt it. Non-union, painful screws, bursitis etc. It also takes more time and this is a cardinal sin as operation time and infection rates are directly correlated. The quicker, slicker the operation - whilst respecting safety - the lower the infection rate.
What is not widely recognised are the more subtle advantages of resurfacing. THR invades the femoral bone canal and embolises the fatty marrow into the bloodstream. This marrow is filtered by the lungs but it still causes a reaction that is generally considered harmful. This effect is greatly reduced by resurfacing. So I notice how - in general- resurfacing patients bounce back from surgery quicker and have fewer metabolic complications or reactions. Resurfacing preserves your own bone and we probably do not yet fully understand the neural or tiny nerve network in bone. Too many of my colleagues regard bone as essentially inert or stupid. It is not. It knows the difference between resurfacing and having its head amputated, then a great piece of metal and/or cement shoved none too gently down its throat! So resurfacing feels more natural in a way that is difficult or impossible to quantify scientifically. And all the research and literature is based on scoring systems that cannot fully measure this.
Then there are the issues of offset, leg length and version. No time to go into detail, but all are easier to get right with BHR.
The alternatives to resurfacing are not without their own unique problems. Ceramic-on-ceramic can break. Or squeak. So loudly the patient is constantly embarrased. It is also a very hard bearing couple with no 'give' at all. MOM resurfacing has a tiny amount of give that makes all the difference because it is one metal surface 'floating ' on another. It can slightly absorb shocks by displacing the fluid. The hip bones do not likle ceramic-ceramic and they never fully adapt. Again the effect is very subtle and the patient is usually so grateful to be free of pain and able to walk that scientists cannot measure the slight downside. Do not get me wrong, I do use ceramic-ceramic when I cannot resurface with MOM. But it is not my first choice.
Metal or ceramic on polyethylene THR is improving. Newer 'cross-linked' polyethylene looks promising as it wears less than the older versions. BUT and this is a big but, we have been here before and been disappointed by newer 'improved' polyethylene. There was a disastrous 'improved' polyethylene a few years back. Not sure of name but relieved to tell you I never used it. Whatever you do, plastic remains plastic. I prefer metal wherever possible. I hear a ceramic on ceramic resurfacing is being developed. I hope it does not suffer from the present drawbacks of ceramics.
Resurfacing cannot correct every pre-operative deformity. So some patients are unsuitable even if bone quality is OK. Knowing who can and who can't be resurfaced for this reason goes back to surgeon intuition.
So in summary:
I like to resurface whenever I think it will work. Based only loosely on CHRONOLOGICAL age or SEX. It is physiological age and activity that counts. It seems it is never a bad idea to preserve bone if this can be done with a low risk of complications related to resurfacing.
Much of the critical press vs resurfacing is hopelessly ill-informed. And there is some hysteria emerging, much like the MMR vaccine scare. It is a difficult operation to do well and the learning curve is not steep. It is flat, so getting really skilled takes time.
'Bad' MOM bearings, either because mal-positioned or wrong metallurgy/design are occasionally seriously destructive of surrounding tissues. Such hips need revising sooner rather than later. Diagnosing what is wrong early and accurately is important. Knowing how to fix the situation even more so.
Men do better with BHR than women for 2 reasons. First their bone is generally stronger. Men are resistant to osteoporosis. Second, their hips are larger so the bigger bearings are less likely to suffer if slightly mal-positioned. But all other things being equal, I believe there is no difference between the sexes and therefore excluding women from having BHR is nonsense. It does mean that large women with small bones and small hips are a particular technical challenge to get it near perfect! Hence no apologies for making a really big incision in this group.
Hope this helps. Email me directly if queries or comments. And Chris, before you ask, yes please cross-post to other fora. But verbatim please, as the disclaimers are legally important.
Mark