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Orthopaedic Product News – For Today’s Orthopaedic Professional.

COMPANY INTERVIEW

Derek McMinn and Ronan Treacy

Mr Derek McMinn MD FRCS Consultant Orthopedic Surgeon, Mr Ronan Treacy MD FRCS consultant at the Royal Orthopaedic Hospital.

Q: Tell us a little of the history of the Birmingham Hip Resurfacing (BHR) device?

A: DM: Well, it would be remiss of us to discount the history leading up to the design and development of the BHR without paying homage to some key innovators from the past that in my mind contributed significantly to the success we now enjoy in hip arthroplasty. Professor Sir John Charnley‘s resurfacing design pre dated the now familiar hip replacement, his initial search took him into the field of polymers and his first attempt at hip arthroplasty in the early 1950’s was Teflon-on-Teflon resurfacing. Unfortunately the Teflon-on-Teflon bearings wore out within two years.

RT: It important to note that hip resurfacing has always been an attractive concept, and the theoretical advantages of hip resurfacings are numerous; minimal bone resection, normal femoral loading, avoidance of stress shielding, maximum proprioceptive feedback, restoration of normal anatomy, minimal risk of dislocation, and potentially easy revision to a primary hip replacement.

DM: Primary hip replacement is of course a hugely successfully operation. Around the same time that Charnley had discovered the usefulness of high density polyethylene and refined his cemented prosthesis, both Peter Ring and George Kenneth McKee had developed total hip replacements of their own both using chrome cobalt metal-on-metal in their articulations. Peter Ring distrusted bone cement and developed a self locking total hip replacement or ‘uncemented fixation’.

RT: Primary hip replacement was and still is today a resounding success. The problem we believe still lies with a group of patients who want to maintain a high level of activity. Professor Charnley was only too aware that active patients below the age of 65 did significantly less well with primary hip replacement.

DM: Satisfactory results had been published for the McKee metal-on-metal, the Charnley and most impressive, for the Ring metal-on-metal with 5% revision at 17 yrs! But as Ronan indicates these devices were rarely implanted in the active patient population. It seemed to us that all the theoretical advantages of the hip resurfacing concept could be realised using metal-on-metal, where thin metal shells can be used as the articulating parts. I designed the BHR following various prototypes between 1991 and 1996. The first BHR implantation took place in July 1997. I was very hands-on with the product, Ronan and I set up a company to manufacture the device, and in 1997 Midland Medical Technologies (MMT) was born.

RT: The need to set up on our own was to ensure the product was made to our exact specifications, with highly skilled and controlled manufacturing. During the development period Derek and I experienced a number of issues with the inconsistency in manufacturing which proved difficult to remedy with our original manufactures. With MMT we initially had a small following of surgeons and gradually selected more and more to use the technique. This core group had been trained by Derek or myself and understood the nuances of patient selection and sound operative technique. This way we ensured the results of the device, and maximised the benefits to the patients.

DM: We sold the company in 2004 to Smith & Nephew, and although with MMT our device had penetrated experienced hip arthroplasty surgeons in many countries around the world, Smith & Nephew planned to promote and distribute the device in the USA and absorb our existing infrastructure and global customers.

RT: The BHR received FDA approval in 2007. Because of the magnitude and quality of the clinical data which we and others had collected on the BHR device, the FDA approved the BHR for use in the USA without an IDE study. This is testament and thanks to the number of expert surgeons around the world who diligently recorded outcome studies and ensured the device was used in the correct patient groups implanted with a high level of surgical accuracy.

Q: What are the results of the BHR device in general and what should this mean to the surgical community?

A: RT: NICE guidelines in 2002 stated that for a device to justify its continued usage, its failure rate should be less than 1% per year up to 10 years. We’ve fulfilled that, for example, with our male patients both Derek and I see 98-99% survivorship at a 10-year minimum in osteoarthritis. The BHR is the only ODEP 10a rated resurfacing device and one of only a handful of hip systems (stem and cup) with this top rating.

DM: The problem now is that people don’t seem to be interested in the 10 year survivorship, the outstanding outcomes, and thousands of highly active BHR recipients. The community is focused on a very small, (in my series less than 1%) number of patients who not dissimilar to many arthroplasty devices exhibit a local tissue reaction of some sort. The phrase “pseudotumours” has been popularised in the clinical literature and linked directly to hip resurfacing. Not so long ago the community was up in arms concerning ALVAL. The point when using the term Pesudotumors is the negative connotation which is often taken out of context by many in the clinical and popular press.

Q: Yes, we’ve recently been hearing about these “pseudotumours” and the failure rate of metal-on-metal resurfacing, what are your thoughts on these findings?

A: RT: An academically linked institution has been publishing prolifically in the orthopaedic literature over the last 18 months. The findings are principally based on 20 female patients from their own and other centres, and the term Pseudotumors has been coined to describe abnormalities found around the implants. When reviewing these articles and listening to presentations we understand that x-ray evidence may not have been available in all of the cases and retrieval analysis shows that these implants have been subject to abnormal edge loading suggesting suboptimal component positioning.

DM: The failure rate of hip resurfacing from our standpoint is very device specific. Differences in the metal, geometry, and fixation seem to result in worse outcomes. Increased wear with all material types sets up a response in the soft tissues, which can damage them. This is not exclusive to metal-on-metal. Around the year 2000,
following our early experience with metal-on-metal resurfacing and encouraging results; hip resurfacing was becoming more popular very rapidly. It was never destined to displace Primary hip replacement but certainly bridge the gap affording the previously descried benefits to a notoriously difficult patient group.
During this period many orthopaedic companies designed and marketed their own devices. The BHR design was criticised in marketing campaigns and during this period many BHR users opted to try these newer devices, or became part of various design teams! Unfortunately for the patients some of these ‘improved’ designs have not faired well. We have witnessed less than encouraging registry data, device withdrawals, and MHRA advisory notices pertaining to certain device types. This is annoying as the damage that these devices cause is being generalised to all metal-on-metal hip resurfacing; this is simply not the case!

RT: We have learnt over time from having implanted many thousands of hip resurfacings between us which patients do well and those in whom an alternative device may be more suitable and have published extensively on this. Male patients universally do well, but caution needs to be exercised in small females particularly with dysplasia.

DM: That’s true, the combined anteversion in this particular group is critical, again resurfacing may not be the best treatment option if we as surgeons cannot accurately account for such abnormalities.

RT: Of course you need to use an implant which has been designed using sound principles and understanding of what has worked in the past and more importantly what has not worked! And whether its metal-on-metal or another bearing couple, if it’s put in at the wrong angle it will not perform as the manufacture or designer intended!

DM: Component placement is a major issue, if the head articulates on the edge of a metal-on-metal device it produces an increased amount of metal wear – there can be a localised reaction of the patients soft tissues which can appear as a swelling around the hip joint. I have personally not experienced aggressive destructive soft tissue lesions but I believe Ronan has revised a case recently. I will not deny it occurs; it has been reported in the literature elsewhere, notably in the North of England with the ASR device (Articular Surface Replacement), which in our opinion has a number of design issues. And secondly, it is seen in the growing number of poorly positioned components, implanted by inexperienced and / or untrained surgeons.

RT: The key to all this is if you have a reasonable surgeon who puts the implant in a reasonable position (which none of us can completely guarantee), with a reasonable implant, you’ll get a reasonable outcome. The literature and registry data tells us if you have a well trained experienced surgeon using a Birmingham Hip implant, you’ll get a good outcome. If you have a reasonable surgeon using a poorly designed implant, you may well get an unexpected outcome. Similarly a poorly implanted device of whatever provenance will struggle to perform consistently within its designer intended parameters!

Q: What are the difference in design between for example the ASR and the BHR?

A: RT: The difference in the design of the BHR and ASR may appear subtle; With the Birmingham cup, everything you see on the internal surface is available for the articular surface. The cup introducer mechanism for the BHR doesn’t remove any of the articular surfaces as wires go through the wall of the component. With the ASR, the design team went down a different route and used some of the internal equatorial edge (bearing surface) of the cup to attach a cup introducer. In doing so some of the available articulating surface was lost. This made the device more sensitive to sub optimal component positioning. Combine this with different material grades for the metal articulation, alternate cement philosophy and acetabular ongrowth features, what appears to be yet another hip resurfacing is in fact quite different from the Birmingham design!

Q: Is training a contributing factor to failure do you think?

A: DM: Certainly! Between us, we’ve trained many hundreds of surgeons from around the world; following the acquisition, Smith & Nephew provided a stringent training course for the core group of American Surgeons which formed part of the FDA approval requirement. This training we believe is key to the understanding and successful implantation of the BHR device. Ronan and I have visited many institutions all over the world and made some great friends during our careers to date, we feel disappointed that what is an excellent device and procedure is currently being confused with poorly designed and implanted products. We hope that even minded surgeons can help prevent the baby being thrown out with the bath water!

Q: So why should we keep to metal-on-metal as a bearing device?

A: RT: I think it is important to differentiate between metal-on-metal resurfacing and metal-on-metal THR; metal-on-metal THR has represented less than 1% of my metal-on-metal practice. At the present time I see no viable alternative to metal-on-metal for resurfacing and as emphasised, I am very happy with this technology for the majority of my younger active patients. I hear early reports of poorer results with some metal-on-metal THR’s compared with resurfacings and am hopeful that surgeons will be sufficiently inquisitive to distinguish between the results of these devices and the BHR.

DM: When I designed the device over 20 years ago there was no other viable material option. Ceramic-on-ceramic was a non-starter, the components were too thick for a conservative arthroplasty and brittleness and fracture was an issue. Polyethylene had been tried but the volumetric wear associated with the necessarily large head for resurfacing resulted pseudotumors of the day- osteolysis – and the 5 year survivorship was less than 50%. Now, 10 yr survivorship in male patients with BHR is 98% If we wish to continue to treat young active patients with the same degree of success as we have seen with the Birmingham Hip Resurfacing, it is currently difficult to recommend an alternative bearing material.

Mr Derek McMinn MD FRCS qualified from St Thomas’s Hospital in London. Practicing as a Consultant Orthopedic Surgeon since 1988, his special interest has been joint reconstruction surgery. He always loved taking on the challenge of patients with complex hip and knee problems – complexities that often demanded improvisation and innovation. His pioneering of the Birmingham Hip Resurfacing has for many revolutionized the management of hip arthritis in young active patients. In addition to his busy Private Practice, he works part-time in the UK National Health Service at the Royal Orthopedic Hospital, Birmingham.

Mr Ronan Treacy MD FRCS became a consultant at the Royal Orthopaedic Hospital in 1994. With more than 15 years experience with metal-on-metal hip resurfacing devices, Mr Treacy has performed over 4500 hip resurfacings, the largest single surgeon experience in the world! He now performs hundreds of hip resurfacings per year, in addition to other hip and knee surgery, as well as training domestic and international surgeons. Mr. Treacy’s international practice and his presence on the global lecture circuit enable him to discuss his vast experience in the treatment of the active patient population with Key opinion leading surgeons the world over.

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