Greek Orthopaedic Association 2008

Introduction

The 64 ^th Panhellenic Orthopaedic Congress was held at the Athens Hilton Hotel and over 1000 delegates attended the meeting.

Invited Faculty

The invited international faculty included Martyn Porter from Wrightington Hospital ,   Professor John Fisher, Head of Bioengineering at Leeds University , Professor Ian Learmonth, Professor of Orthopaedics at Bristol , Dr Jim Waddell from Toronto , Canada , Dr Tad Vail, Head of Adult Reconstruction Surgery, San Francisco , USA and Professor Michael Morlock, Professor of Bioengineering from Hamburg , Germany .  

Martyn presented three talks: "Revision total knee replacement in relation to outcomes, complications and re-operations", "Changing Epidemiology of Total Hip Replacement" and "Technical Challenges in Reconstruction of the Acetabulum and Femur"

"Revision total knee replacement in relation to outcomes, complications and re-operations" Martyn Porter

Martyn described how the numbers of patients requiring revision of the total knee was increasing.   This was a reflection of the increased numbers of primary total knees being carried out globally.   The outcomes of revision of the total knee were not generally as good as revision of total hip and the complications were quite significant.   The types of problems that can be encountered requiring a revision include infection, stiffness, instability, pain, wear of polyethylene bearing, fracture and extensor mechanism failure.

Technical issues included implant selection and how much constraint and fixation to use.   Some of the best results are that described by Maybury from the Mayo Clinic (Journal of Arthroplasty 2007) with a 91 per cent survivorship at ten years.   Patients revised for stiffness are less likely to have a good outcome with only 66 per cent of patients satisfied as reported by Haidukewych in 2005 in the Journal of Arthroplasty.   When the indication for revision was deep infection the results were inferior.   Haleen from the Mayo Clinic in 2004 reported a 78 per cent survivorship at ten years.   Larger numbers of patients studied in the Finnish Arthroplasty Register indicated that the survivorship was only 79 per cent at ten years and the results were related to age with younger patients having a worse outcome than older patients.   Also patients being revised less than five years had a poorer outcome than patients being revised after five years.   In general when implants were fixed with cement the outcome was better than when cement was not used.  

The complications of revision total knee replacement can be as high as 34 per cent as described by Rand in Clinical Orthopaedics in 2004 and Saleh reported in the Journal of Arthroplasty a complication rate of 26 per cent.   In general complications after total knee replacement were generally more frequent, more severe and more difficult to manage than complications occurring after primary total knee replacement.   The results from Wrightington Hospital were presented, this experience being based on a database of over 650 cases and based on a series of presentations and publications from Wrightington.   The first paper (Pradhan, Porter et al, JBJS 2002) demonstrated that when patients had had more operations before the revision the outcome was inferior.   When patients had had only two previous operations the satisfaction rate was approximately 74 per cent whereas if three operations had been carried out the satisfaction rate dropped to 56 per cent.  

The second paper looked at the indications for revision and patients with aseptic loosening, implant failure and instability had results in the region of 70 to 80 per cent whereas the outcomes after pain and stiffness in flexion were in the region of 60 to 70 per cent.  

The third paper looked at a certain type of implant, the TC3 implant, and reported by Pradhan, Kay and Porter in the JBJS 2004, about 75 per cent of patients were excellent, good or fair following surgery and the cumulative survivorship was 95 per cent at eight years.

The final paper looked at the Endo-rotating hinge prosthesis as described by Pradhan, Kay, Porter et al in The Knee Journal 2004.   This included a group of patients with more severe and significant limiting deficiency who required the use of a more constrained implant.   Mobility post operatively improved significantly compared to the pre-operative mobility and 88 per cent of patients were satisfied when they received this type of knee.

It was concluded that revision total knee replacement was a challenging procedure and although results were not as good as after primary replacement, many patients improved after the procedure and with careful patient selection and attention to detail and appropriate patient counselling acceptable results could be achieved.  

"Changing Epidemiology of Total Hip Replacement" Martyn Porter

Various papers on the epidemiology of total hip replacement were discussed.   The first paper by Birrel 1999 projected that by 2026 there would be a 40 per cent increase in the demand for hip replacements due to demographic changes alone but this could be increased to 113 per cent if the indications for hip replacement matched that of the Swedish population.  

The second paper by Crownenshield 2006 outlined the demographic "time-bomb" in the United States with the growth of the aging population.   It was explained that in 1960 there was 16.5m patients greater than 75 years of age but this would increase by 2030 to 70 million!   Life expectancy also increased in1960 from 70 years and by 2020 it will be 77.  

Obesity has increased significantly and now two thirds of patients in the age group of 65 to 74 are already overweight and patients with a body mass index of 39 had double the incidence of arthritis.  

The operation of total knee replacement had now rapidly exceeded that of total hip replacement.  

Other papers presented indicated that patients with more social depravation were less likely to receive the procedure of hip replacement and other papers suggested that the benefit of hip replacement may not be fully understood by primary care physicians - GPs or patients and that patients with arthritis may benefit from this procedure but unfortunately have not been counselled appropriately.

It was concluded that primary total hip replacement was on the increase and that revision total hip replacement was increasing at a greater rate.   The numbers were increasing as a result of aging population (baby boom, increase in life expectancy), change in threshold for surgery, meeting the unmet demand, change in patient demand).   It was concluded that if patients were living longer then more advanced bearings may be indicated to deal with the anticipated increased longevity of the implants.  

"Technical Challenges in Reconstruction of the Acetabulum and Femur" Martyn Porter

In this lecture Martyn explained that failure of total hip replacement was multi-factorial and there were considerable variations in the technical and anatomical challenges faced by the patient and surgeon alike.   Globally there was considerable variation in surgeons' experiences and preferences and dealing with problems and the academic literature is not always clear about which devices or techniques were superior.   The experience at Wrightington is now considerable with several hundred being carried out every year.   Historically very few revisions were carried out in the early 1960s and then by the late 1960s and early 1970s there were a few patients requiring revision, mainly for fracture of the femoral stem.   By the 1980s we saw more patients with socket and stem loosening and these predominantly dealt with simple implant exchanges secured with cement.   Over the last 15 years we have been dealing with defects using a combination of bone grafts on the femur and acetabulum and more recently we have been using other devices, uncemented devices and novel techniques to cope with bone deficiencies.   The general principles were to try and make a revision look like a primary operation, ie to restore bone where possible.   The general principles of revision operation are patient assessment and consent, to rule out infection, to try and improve bone stock, to correct the anatomy/biomechanics, to obtain good fixation but where necessary bypass weak areas of bone to prevent post operative fracture and finally, to always consider the potential of another operation should it be necessary.

Looking at the radiographs it is important to consider the mode of failure, develop a strategy for removing existing implants, to assess the quality of bone, to assess the size and location of bone defects and to assess the suitability of bone graft.   Having done than to plan a preferred procedure but also have available secondary procedures in case the preferred procedure does not go to plan during the operation.  

The key decisions were to decide whether to use cement or press fit fixation, the decision whether to use bone graft, use standard or long stems, whether to use a modular implant and to decide on bearing preferences.

Various classifications were discussed for the femur and acetabulum but essentially with Endo Clinic Grade 1 and 2 it was normally possible to obtain a metaphyseal revision (short stem).   With more severe degrees of bone loss in Grade 3 and 4 it was often necessary to go further into the femur in the diaphyseal region (long stem).  

In the acetabulum using the Paprosky classification there were really three major groups, the first two being relatively modest challenges where most of the acetabular bone was still present although thinned down.   The Grade 3 deficiencies with more than three centimetres of bone loss superiorly were more challenging as it was necessary to restore the buttress to the side of the acetabulum.

It was explained that the results of cemented revision could be highly acceptable and the paper by Raut 1995 illustrated the stem survival was 97 per cent at eight years when cement was used alone with a short stem and with more severe deficiency even with a long stem only 12 per cent had been revised.

Other methods of fixation were discussed, papers indicating that the results of cemented revision at ten years were in the region of 90 to 95 per cent in most series with cement in cement revision 100 per cent at two years, impaction bone grafting in the femur in the region of 90 per cent at ten years and similarly in the acetabulum.  

Some uncemented stems were now giving results of 90 to 95 per cent with the follow up varying from 5 to 14 years and some uncemented acetabular components were achieving nearly 100 per cent results in the region of 7 to 14 years. Several case examples were presented including cemented revision using a medium length long stem, impaction bone grafting with a short stem to the femur, a long stem with impaction bone grafting and a variety of techniques to address acetabular reconstruction using structural head allograft, jumbo cups, medium length uncemented stems and trabecular metal dealing with severe pelvic deficiencies.   Finally a case report was demonstrated where there had been such severe loss of bone that it was necessary to replace the whole of the femur.   It was summarised that there were considerable challenges in revision surgery and surgeons had different views about how to obtain best fixation but it was certainly our view to be conservative where possible using bone graft and conservative stems but where necessary to use longer distal fitting stems.   It was thought the use of trabecular metal in particular looked promising in the acetabulum but the key was to understand and apply the relevant techniques appropriately.  

Instructional Course on Metal on Metal Articulation Saturday 11 ^th October 2008.

Jim Waddell from Toronto , an advocate of ceramic on ceramic bearings outlined the positive attributes of ceramic on ceramic.   New ceramics are very hard, have very good surface finish, high wetability and very low co-efficient of friction and therefore theoretically an ideal bearing surface.   The concerns were about durability but present fracture rates are in the region of four in 10,000, so the overall incidence of fracture is now very low.   Dr Waddell from St Michael's Hospital, Toronto described his own series of 3,000 implants from which he had only had one fracture.   He explained that the wear of ceramic on ceramic was the lowest of any bearing surface but the wear particles are abrasive and if revision surgery is necessary the surgeon has to carry out a complete capsulectomy/synovectomy and remove all membrane and ideally revise to another ceramic.

He then discussed a randomised controlled trial of ceramic on ceramic versus Alumina on polyethylene.   This study was commenced nearly ten years ago and was a double blinded randomised controlled study of 55 patients in 56 hips.   26 hips were ceramic on ceramic and 30 were ceramic on polyethylene.   All patients were well matched.   There were only two revisions, one for instability and one for sepsis.   There was only one case of osteolysis and that was in the group of ceramic on polyethylene.   The mean penetration of the ceramic on ceramic was 0.02mm per year and this was significantly less than the ceramic on polyethylene which was 0.14mm per year.   The mean follow up was nine years.   There were no differences in outcomes or patient satisfaction as identified on a detailed outcome assessment.   Although the ceramic on ceramic had worked well Dr Waddell conceded that the potential problems with ceramic were noise, breakage and the reduced liner options.   There were also concerns about stripe wear and revision could be difficult.   However, in his experience these were not significant clinical problems

He felt the ideal indications were that of small anatomy, particularly female patients.

Professor Learmonth then discussed the biological responses to metal on metal articulations and the potential for mutagenic changes.   He described the histology as lymphoid neogenesis and it was uncertain whether this was a response to metal particle overload or hypersensitivity reaction.   He described the histology in detail explaining metal particles were coated with calcium phosphate and the characteristics were not entirely well defined but he felt the response to this material could potentially have a long latency similar to asbestos particles.  

There was some evidence that the metal particles could cause chromosomal damage and there were concerns about corrosion products and there was lack of clarity regarding the transport mechanisms and the toxicity threshold of these metal particles as well as the excretion characteristics.   The evidence so far clinically was that there were no risks of metal on metal but the histological and particle characteristics were not yet fully understood.

The final talk of this session was from Professor Michael Morlock from Hamburg who talked about the lessons learned from retrievals of failed hip resurfacing.   He started off by demonstrating that the evidence from the Australian Hip Register indicated that hip resurfacing generally had a higher failure rate in the early years but most of this failure was in the first year and after the first year the failure really paralleled that of hip replacements in general.

Professor Morlock has an extensive experience with hip resurfacing retrievals and has now analysed 276 hip resurfacing retrievals.   He carried out wear analysis,   studied x-rays for cup inclination, morphology, cement thickness penetration, histology and revision reasons.

In relation to problems he defined four problems.   Type 0 was no acute fracture but neck thinning and revision for neck thinning alone.   Type 1 failure was a head fracture which was inside the hip resurfacing head.   Type 2 was a rim fracture extending up the rim of the head.   Type 3 was cup loosening.   From the retrievals the wear was significantly greater if there was rim loading.   In the rim loading cases the wear was 15.8mm³ /year.   If it was not rim loading it was 0.6mm³ /year.   Those wear levels were in the cup.    

The mean cup inclination in the rim loading specimens was 58.5 degrees and with no rim loading it was 49.8 degrees.   On the basis of this information Professor Morlock felt that under load the wear was low if the inclination was less than 55 degrees but high if greater than 55 degrees but even in cases where the cup inclination was greater than 55 degrees there were several specimens where wear was low and he postulated that in those cases the anteversion angle may have been beneficial and he thought that the wear was a combination not just of the inclination angle but also the anteversion and the stability of the hip.   This was later confirmed by Professor Fisher from his own experiences.

In terms of cement thickness he felt the ideal cement thickness was less than five millimetres but in the specimens analysed 84 per cent had a cement thickness of greater than five millimetres and he felt this was detrimental to the blood supply of the femoral head.   He then described the different types of head fracture and the Type 1 failure when the fracture was inside the head the AVN occurred around 262 months but when there was a rim fracture which he thought was probably related to notching failure was early, the mean failure was 99 months.   However, when the cup failed which he thought was related to high frictional torque of the device the failure was later and the mean failure was 423 months.

He finished his talk by explaining that he thought whilst there was some vulnerabilities of hip resurfacing he thought the main problem was failure of surgical technique and if the surgeon could properly align the component and correctly tension then he thought there was a good chance that the wear rate would be very low.   He also thought it was important that appropriate press fit and seating of the cup was more difficult than non-resurfacing cups because of the resurfacing cups were more rigid and technically more difficult to insert and the surgeon could not really be sure that it had bottomed out fully because there was no pilot hole.   Therefore, the combination of the correct implant and the correct surgical technique was important.

During the discussion the faculty were asked which bearing   combination they would choose in younger high demand patients.   Dr Waddell indicated that he would use a ceramic on ceramic in younger active patients under 55 and ceramic on cross link polyethylene on patients over 65.   Professor Learmonth indicated that it would depend on the patient demand, patient profile and cost issues.   Professor Morlock indicated that thought the metal on metal hip resurfacing was rather like a Formula 1 car.   It was quite difficult and rather unforgiving and there were greater margins for error but done correctly it could have considerable benefits.   Dr Vale indicated that the surgeon's experience and numbers of resurfacing were important for a satisfactory result.  

Professor Fisher has already presented on ceramic metal articulation, the metal being the acetabular component and the ceramic being the femoral head.   He felt that differential materials have advantages in terms of wear debris.   Wear volumes are close to ceramic on ceramic but it has the advantage of significantly reducing metal debris.  

Professor Morlock gave a lecture on Biomechanics in Total Hip Replacement.   He described a series of patients who had hip replacements carried out with special telemetry devices, whereby the loads in the artificial hip could be recorded.   This series was described by Bergman in 1991.   Although loads could be calculated theoretically this series was important as it indicted the real loads experienced during certain activities.   During walking peak loads were in the region of two and a half times body weight and crouching 3.75 times body weight.    He also reported that Nordin in 1989 reported on the movement required for certain activities of daily living.    He also explained that the large diameter femoral head increased the range of movement but had the downside of increasing the frictional torque of the cup.   He discussed the influence of cup angle inclination as reported by Dr Williams et al in JBJS 2008 and the presence of stripe wear in ceramic material was described by Nevelos et al, Journey of Arthroplasty in 2001 and Stuart in 1991.

John Fisher gave a lecture entitled,   "Understanding Tribology".   Professor Fisher started off by saying that the lifetime osteolysis threshold was in the region of 400 mm³   as described by Ingham and Fisher in the Journal of Engineering and Medicine 2000 and Biomaterials 2005.   Young active patients have a ten fold increase in lifetime demand and 200 million steps over a 40 to 50 year period.   Joints of bigger head size have an increased sliding distance and have a larger head area contact, both of which are bad for wear under dry conditions.   Ceramic on ceramic articulations can exhibit strip wear as described by Nevelos et al in the Journal of Arthroplasty 2001.   This is thought to be the result of microseparation in that the head is not always located centrally in the cup but makes contact with the rim of the socket before relocating centrally, the cup guiding the head into position.   This rim contact leads to edge loading.   Under simulated conditions the edge loading produces wear in the region of the 1 mm³ per million cycles but with newer ceramics such as Delta this may be as low a 0.5 mm³ , whereas Biolox Forte is in the region of 1mm³ .   In comparison ceramic and cross link polyethylene is in the region of 5 mm³ .   Metal on metal articulations are in the region of 1 to 2 mm³ .   However, he emphasised that the wear debris was different in the metal metal compared with the ceramic on ceramic articulations.   He also explained that ALVAL was an adverse response although it was not clear whether this was related to hypersensitivity or to an increased burden of cobalt and chromium ions.  

In relation to metal on metal bearings Professor Fisher indicated that wear was not dependent on metallurgy as long as high carbon cobalt chrome was used.   It was dependent on diametrical clearance, head diameter and on component position.  

Experimentally with cup inclination angles of 45 degrees typical wear volumes was in the region of 1mm ³ per million cycles but when the cup inclination was 60 degrees this was increased five to seven fold.   However, clinically the observed levels are increased 40 to 50 times and so when they use the effects of microseparation of 0.5mm they found cup inclination of 55 degrees, the increase in wear volume was about 20 fold and therefore he felt that in the simulator they now replicated the important factors explaining what happens in vivo.   He therefore concluded that wear was a result of steep cup inclination and the effects of microseparation.   He then reported the series of Issac et al, presented at the AHKS in 2007 when it was found that some patients with steep cups still had wear levels below 100 micrograms/litre and this was probably explained by lack of hip separation occurring in these high inclination hips, therefore confirming the previous observations that the wear was a combination of inclination and stability of the joint.

He then discussed ceramic on metal and he felt from an engineering point of view there were distinct advantages of using materials of different hardness, the ceramic being harder than the metal.   The wear of ceramic on metal is about double that of ceramic on ceramic but avoids stripe wear and the squeaking.   Fracture is less likely as fracture is potentially more vulnerable on the acetabular liner rather than the large diameter femoral head made of modern ceramics.  

He reported the early results of a clinical series in South Africa which were now out to about two years.   The metal ion levels in the series of patients who received   ceramic on metal joints were about half of that of metal on metal joints.   Reference value was about 0.6 with the metal on ceramic being in the region of 0.4 and metal on metal in the region of 0.8.

Dr Waddell described his experience of cementless stems in revision surgery using extensively coated cobalt chrome stems.   The series was of 93 patients which had data on 82 patients.   The femoral component alone had been revised in 22 and the femoral and acetabular components in 60.   Patients were assessed radiologically and clinical outcome measures including WOMAC and SF36.  

There was an improvement in limb length equality.   X-rays indicated that 74 stems were fully integrated, five had subsided but were now stable, three were subsided and were loose.   There were two intra-operative fractures, two deep infections which were treated by debridement, irrigation and retention of implants, three stems subsided and there were four dislocations.   Of the three subsided stems one fractured and two were under-sized. There were four dislocations, three treated by closed means and one with a constrained liner.   He emphasised that the outcome was inferior compared to primary total hip replacement but he felt that his experience of the extensively coated femoral stems were indicated in about 90 per cent of all revision cases.  

Professor Babis from the First Orthopaedic Unit, Attikon University Hospital , Athens described his experiences of using acetabular reconstruction cages.   He felt the main indications were in Paprosky three type defects and the cages had the advantages of restoring the hip centre, that they had large contact surfaces, they provided load distribution and could restore early motion.   However, he felt they were quite difficult to insert and there was no potential for ingrowth and he felt they could fail with time as describes by Berry et al, Clinical Orthopaedics 2004 as some series had indicated a failure rate in the region of 17 per cent, Berry 2007.   However, Professor Babis felt there was an indication for this device in some difficult acetabular deficiencies.

Finally Professor Zenakis from the University of Ioannina described his experiences in dealing with deep infection.   He outlined that the accepted incidence of deep infection was in the region of one per cent but in some American series the incidence was as high as 2.2 per cent and in revision cases it was between 7 and 16 per cent.

He described four stages of infection, the first stage being infection in the first six weeks of primary surgery, Stage 2 being delayed with chronic symptoms that could occur at any period subsequently, Stage 3 an acute infection with previously good hip function and Stage 4 being a bacteria or positive culture at revision surgery in previous unsuspected case.  

He reported that the CRP had a sensitivity of 96 per cent and a specificity of 92 and a high ESR of sensitivity of 82 and a specificity of 85.   He also reported that TNF, alpha and pre-calcitonin test had a 30 per cent sensitivity and a 98 specificity.   He also outlined leucoscans and a PET scan which he reported as a sensitivity of 91.7 per cent and specificity of 96.6 per cent.   The results of debridement and retention of implants were reported to be in the range of 26 to 76 per cent.

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