|
European experts discuss the advantages of antibiotic-loaded bone cement for prosthesis and patient
Author: Heraeus Medical
The replacement of damaged hip and knee joints with artificial joints (arthroplasty) and the restoration of mobility by means of cemented joint replacements are regarded as one of the most significant medical achievements. The results are convincing: a lifetime of 10 years is achieved by more than 95% of implants. How to prevent multi-resistant micro-organisms that may cause revision in future and the extent to which antibiotic-loaded cement is used throughout Europe was one of the topics discussed at an international symposium in Maastricht (NL).
Experts from eight European countries introduced the latest scientific achievements and country-specific experiences in arthroplasty. By comparing the countries, significant differences can be seen in the choice of surgery methods as well as in the use and the route of delivery of antibiotics. Two-stage revision is preferred in almost all European countries. Its advantages are the second debridement and healing of the infection before the new implantation.
In Scandinavian countries and the Netherlands, antibiotic-loaded bone cement is the standard to prevent infections of the prosthesis even in primary arthroplasty. German surgical teams mainly use antibiotic-loaded cement. For revisions they tend to use antibiotic-loaded cement in combination with systemic antibiotics. In Italy, antibiotic-loaded bone cement is used in only 10% of cases, even in revisions. In France, Greece and the UK, surgeons prefer antibiotic-loaded spacers and autografts mixed with Vancomycin. In the southern countries, problematic bacteria such as Staphylococcus aureus are evident in 20-30% and coagulase-negative staphylococci in 30-40%.
The central theme of the symposium was the therapy of orthopaedic infections and the application of antibiotic-loaded carriers such
 |
| SEM micrograph of polymerized PALACOS R+G. Displayed in miscolours: Cement matrix (green), embedded Gentamycin (red) and zirconium oxide (blue) |
as antibiotic-loaded bone cements as well as classical gentamicin-PMMA (Polymethylmethacrylate) beads or spacers. There really are regional differences regarding the use of antibiotic bone cement as standard. Well-documented arthroplasty registers exist only in the northern countries, where clinical data about cemented and non-cemented arthroplasty are collected; comparison is difficult because more than 90% of the prostheses implanted in Sweden 1 or Norway 2 are cemented. With cemented prostheses, the revision rate in 10 years is 7% whereas it is 13% with uncemented implants 1. 89% of cemented prostheses and 72% of uncemented implants have a lifetime of 13 years.
The registers also show that PALACOS® R containing gentamicin is used in almost all cases in all hospitals and is one factor that helps to reduce the risk of revision significantly. Furthermore, the Swedish Hip Register shows that combined antibiotic prophylaxis – local in bone cement and systemic by injection – is the most effective 1,2,3. Four injections on the day of operation correlate with the lowest risk of revision 3.
History of bone cements
Fast regaining of patient mobility with cemented, sterile implanted endoprostheses presents a milestone in the history of medicine.
Several developments have led to this:
- 1943 Patent application for cold curing of MMA
- 1958 First implantation of a cemented total hip endoprosthesis (TEP) by Sir John Charnley
- 1959 Market approval of the first bone cement in Germany, PALACOS® R by Heraeus
- 1972 Market approval of the first antibiotic-containing PALACOS® R bone cement by Heraeus
The functions of PMMA bone can be summarised as follows:
- Fixing the endoprosthesis in the bone
- Transfer of the mechanical load from the implant to the osseous bed
- Reduction of mechanical loading of the bone by surface enlargement
- “Shock absorber”
- Support of the bone structure
- Local carrier function for antibiotics
Experimental tests in the early 1970’s demonstrated the effective release of bactericidal gentamicin. The high release rate of active substances in PALACOS® is due to the nature of the hydrophilic polymers contained in this bone cement, which facilitate the extraction of the antibiotic by diffusion processes. The excellent mechanical properties of the bone cement PALACOS® R remain uninfluenced by the additional antibiotics.
References
- Ann. Report 2004; The Swedish National Hip Arthroplasty Register, Dep. of Orthopaedics Sahlgrenska Univ. Hospital 2005
- Havelin LI et al: The effect of cement type on early revision of Charnley total hip prothesis. J Bone Joint Surg (Am) 1995; 77A:1543-50
- Engesaeter et al: Prospective studies of hip prosthesis and cements. A Presentation of the Norwegian Arthroplasty register 1987 – 1999. Scientific Exhibition presented at the 67th Annual Meeting of the American Academy
The Optetrak Knee - Why I Made The Switch
Author: M El-Shazly, Droitwich Knee Clinic
A popular myth that has propagated among patients over the years is that Total Knee Replacements (TKR) do not do as well as hip replacements. While this may have been true some years ago, it is no longer the case.
Total Knee Arthroplasty has evolved over the years to produce a large number of systems and commercial brands. While most have been successful some have produced disastrous results and have had to be taken off the market.
The development of the total condylar and then the posterior stabilized TKR’s has really laid down the principles that eventually most commercial companies have applied to their products with quite reasonable results and longevity at least in the medium term. However the results of the Insall Burstein (IB) TKR reported from the Hospital for Special Surgery (HSS) have yet to be excelled, with over 90% survivorship at over 20 years1,2.
This led to my reluctance for a long time to change from the IBII TKR which I had been using quite happily for years. It was obvious to me however particularly when performing revisions that the IBII kits were being phased out and when I found I had to change, I started looking at a number of systems, staying as close as possible to the principles of the posterior stabilized knee laid down by John Insall et al3. Several things led me eventually to the Optetrak knee (Exactech, Gainsville Fl, USA), having tried a number of other options at the time. Mainly, I found that it was the TKR that had been most true to these principles.
There were only minor alterations to the basic design, which has stood the test of time. Decreasing the conformity in the sagittal plane while increasing it in the coronal plane appears to have given it a better average range of motion (ROM) (table 1)4, and perhaps better stability in the coronal plane. After all TKR is a compromise between conformity and mobility. It was also reassuring to know that the main designer Al Berstein was the same engineer involved for years with the development of the IB series at the HSS.
Table 1: Literature review: Reported range of motion4-7
| Range of Motion |
| IB II PS: Mean P Aglietti |
116° (65-133°) |
| Optetrak: multicenter trial |
121.6° (9.7°) |
| Optetrak PS: Robinson RP 2005 |
118° |
| Optetrak CR & PS: I Gradissar |
114° |
| LCS: Beuchel 2001 2y, 7y |
104, 107° |
| Rotaglide S Brooks |
112° |
|
| Figure 1a An IBII TKR at three weeks postoperatively |
From my own experience in the past few years the Optetrak seems to have got this balance right. Of course the single most important factor in achieving a good ROM is the patient’s pre-operative range (fig 1a)
Also there was evidence that at least in the lab, the molded polyethylene used in the Optetrak knee had less than one third the wear rate of its predecessors8. If this translates into clinical results in the long term, then perhaps we should be braver putting in TKR’s for the younger more active individual. Of course polyethylene wear is only one factor in eventual failure of any given TKR.
However, I was not about to use a system on my patients without seeing some long term clinical results. Again when I compared systems, I found that in fact the Optetrak Knee had the longer follow-up with 97% good & excellent results4,6 (table 2), with 97% survivorship at over seven years with an average ROM of 118° (table 1). More recently Gradissar et al presented similar ten year results in 1700 TKR’s7,9 with an average ROM of 117° even though most of his early cases were posterior cruciate retaining.
Table 2 |
|
| Results: HSS scores |
|
| IB : |
71% exc |
25% good |
| IBII: |
64% exc |
31% good |
| Optetrak: |
77% exc |
20% good |
| • Robinson RP 2001 |
|
|
 |
|
 |
Figure 1b
Severe valgus OA |
Figure 1c
Postoperative appearance after Optetrak PS-TKR with tibial augment and stem |
It was not really until I actually started using the instrumentation in theatre that I made the decision to switch. I found the kit very user friendly. As I carry out the usual checks for external rotation of the femoral cut using Leo Whiteside’s line, overall alignment, balancing of the flexion /extension gaps and ligament stability I find consistently that the cuts are very precise and accurate. The instrumentation is very cleverly designed to cut on inventory and the nurses in theatre love it for that reason (well after they have used it a couple of times). I am particularly fond of the Maudlin tool which seems to do everything!
The kit is just as modular as it needs to be. I have a real issue with companies producing ten trays in order to please every possible surgeon, often sacrificing the original principles of the system. It is backed up by a robust revision system (constrained condylar) which can be used whenever there are bony & ligamentous deficiencies with femoral & tibial augments of different sizes and an innovative easy to use system of attachment for both the trials and the definitive prostheses. In cases where there is ligament insufficiency but no significant bony deficiency exists, the “intermediate” non modular constrained (NMC) system comes in handy with a smaller box cut on the femur when no femoral stem is necessary.
 |
| Figure 1d 3 days post-op |
 |
| Figure 1e16 wks post-op |
Does it have any flaws? There are minor problems with the design of the distal femoral cutting block, which can slip into the plus 2 or 4 mm position too easily, Similarly one of the the extra-medullary jig designs for the tibial cut allows changing the posterior slope of the tibial cut and again this can alter easily if you are not careful before pinning the cutting block. This may have to do with overuse of the particular kit at our institution and both of these are being addressed. There are also alternatively designed cutting jigs available.
Also, the edges of the femoral prosthesis have been chamfered off to reduce tension on the patellar retinaculae. The depth of the groove has been increased (and elongated)8. While this design has nearly eliminated post-operative patellofemoral crepitus and entrapment4, as a result the edges of the trochelar groove are now more prominent and pointy. Although this has not produced any clinical problems for me, it allows overhang over the edges in larger patellae, as seen on postoperative skyline x-rays, particularly when patellar resurfacing was not performed. An easy solution to this is to reduce the size of the lateral facet of the patella.
Our short term results have been re-assuring. We have been looking prospectively at our first 50 Optetrak TKR’s, a single surgeon’s experience at the Droitwich Knee Clinic, with an average age of 69 years and a mean follow-up of 27 months. These included four revisions and another four complex reconstructions requiring augments and stems. The rest were all standard posterior stabilized implants. There have been no aseptic loosenings, no deep infections and no re-operations. Nine patients reported residual pain (18%). The mean Borg pain score was 1.6 (on a scale of 0 to 10). Two patients registered a pain score of 7 & 8 respectively. The rest registered a pain score of 0 to 3. Their mean American Knee Society (AKS) functional score10 was 79.13 (range: 40-100), with 69% recording a score of 80 - 100. A significant number returned to light sporting activity including cycling, swimming, rambling, golf, yoga and rowing. One patient returned to regular jogging. The mean Tegner activity score was 3.
 |
 |
Figure 1f-h
post-op x-rays |
 |
What about the future? Well, like many of us I am now learning about Computer Assisted Orthopaedic Surgery and understand the dedicated software to this particular prosthesis is now available. This should assist with increasing the accuracy of the cuts, particularly in minimally invasive surgery.
Having said all this, let me end by borrowing a quotation from Dr Siegel of Cincinnati: “The typical Orthopedic surgeon uses a study like a drunk uses a lamp post … for support rather than illumination”.
So I guess that I have been as guilty as everyone else when using the above data to support what I actually do. The fact is most major knee replacements do very well nowadays and have remarkable similarities. Have you ever wondered why there are hardly any real comparative randomized clinical trials out there comparing one system to another? I believe Dr Siegel has the answer to this one.
Acknowledements
The author would like to acknowledge the help of Miss Ellen Beales of the Knee Foundation for her assistance with data collection and the preparation of this manuscript.
References
- Scuderi G, Insall J, Windsor R, Moran M. Survivorship of cemented knee replacement. J Bone Joint Surg 1989;71-B:798-803.
- Font-Rodriguez D, Scuderi GR, Insall J. Survivorship of cemented total knee arthroplasty. Clin Orthop 1997;345:79-86.
- Insall J, Lachiewicz P, Burstein A. The posterior stabilized condylar design, two to four year clinical experience. J Bone Joint Surg 1982;64-A:1317.
- Robinson R. Five year follow-up of Primary Optetrak Posterior Stabilized Total Knee Arthroplasties in Osteoarthritis. J Arthroplasty 2005;20-7:927-31.
- Indelli PFA, P. Buzzi, R. Baldini, A. The Insall-Burstein II prosthesis: a 5- to 9-year follow-up study in osteoarthritic knees. J Arthroplasty. 2002;17-5:544-9.
- Robinson R. Advances in Bone & Joint Restoration. Hip & Knee Replacement Course. , Miami, Florida, 2001.
- Gradisar I. Ten year clincal results - a 1700 patient study. Optetrak Total Knee System. Belfry & Droitwich Knee Foundation, UK, 2005.
- Burstein A. congruency and polyethylene wear in total knee replacement. Optetrak Total Knee System. Belfry & Droitwich Knee Foundation, 2005.
- Edwards J, Gradisar I, Nadaud M, Kovacik M, Askew M. Eight and one half year clinical experience with the Optetrak Total Knee Prosthesis. American Academy of Orthopedic Surgeons. 71st annual meeting. San Francisco CA, 2004.
- Insall J, Dorr L, Scott R, WN S. Rationale of the Knee Society clinical rating system. Clin Orthop 1989;248:13-4.
Clinicians and procurement personnel working together
to support long term joint survival
Authors: Liz Green, Director of Marketing, Summit Medical Ltd.
Debjani Duncan , Head of Nursing, Clinical Evaluations and Networks, Healthcare Purchasing Consortium
On what basis should procurement decisions be made when it comes to relatively low profile single use medical devices which support long term joint survival?
Changes in the NHS are highlighting the need to balance the preferred options of the clinicians with the needs of the procurement professionals, whose agenda, in simplest terms, is to limit the number of suppliers and reduce overall costs. However, because a device is supplied free of charge with the implant, or at a large discount, is it necessarily best for the long term result?
There has been much debate lately at various conferences and in published articles, about how to ensure innovative products are introduced in to the NHS. An integrated approach between clinicians and procurement personnel is needed in order to ensure that both the clinical and economic benefits of devices can be realised.
Increasingly procurement professionals are being advised internally by clinical staff whose role is to bridge the gap between the functions and move the agenda more towards a long-term approach rather than solely seeking to achieve ‘in year’ cash releasing savings. These clinical staff are looking at innovative products and services that promote efficiency, reduce dependence on the NHS (e.g., reduced pharmaceutical bills, reduced length of stay/readmission rates, reduced infection/co-morbidity etc) and also to deliver improved or equivalent clinical outcomes to those already in use.
Likewise, tried and tested products, which are well-supported with evidence to prove their efficacy, must be considered on their merits, not just seen as commodities, with purchasing decisions being made based on price alone.
The procurement professionals and clinical staff are seeking to ‘add value’ through collaborating with local development agencies, SME’s and such forums as the Health Industries Task Force (HITF).
The challenge for manufacturers is to ensure that they are supplying both clinicians and procurement specialists with enough information on which to make informed decisions.
The information provided should be tailored to the audience – the clinician and the procurement professional need to know different things. Using health economics to demonstrate the long-term potential of a product to improve efficiencies as well as improved clinical outcomes is a must in the current climate – clinicians and procurement staff will be reluctant to advocate changing to a product that does not help deliver other ‘added value’ such as helping a Trust to achieve their goals in terms of service reform (10 High Impact Changes, Efficiency Map, Integrated Service Improvement Plans).
The National Joint Registry 2nd Annual Report (NJR) issued in September 2005 relates to information collected during 2004 and shows reported data of approximately 49,000 THR and 45,000 TKR performed per annum in England and Wales. This Registry also shows that most procedures used cement. For primary hip replacements, 77% used femoral cement and 56% used acetabular cement.
Vacuum mixing of bone cement has been practised for over twenty years and it has been proven that this improves the mechanical properties of the bone cement. There are now a variety of vacuum mixing devices available on the market. When choosing a vacuum mixing device it is therefore important to consider a number of key points:
- According to the National Joint Registry 2005 the most common indication for a hip revision was aseptic loosening, present in 79% of patients.
- According to the National Joint Registry 2005 the most common indication for a knee revision was aseptic loosening, present in 59% of patients.
- The majority of aseptic loosening is due to cement mantle failure
- Revisions incur high direct and human costs
- Correct mixing and administering of the bone cement is a vital part of the cemented joint procedure.
The mixing devices chosen need to fulfil the following key objectives:
- Easy to use for all types of bone cement formulation
- Reproducible mixing action to ensure a low level of variability of mix quality across operators, in various theatre conditions/temperatures, thus giving high surgical confidence
- Demonstrable mechanical properties of bone cement produced, in excess of the ISO standards set for bone cement
- A cost effective range of devices to meet all mixing needs from small joints to revision hips
- Training support from the manufacturer
The design of the mixing device can have a significant effect on the quality and reproducibility of the cement produced. It is therefore important when making purchasing decisions that the choice of system is based on sound scientific data, not just price, as different systems have been proven to give significantly different results. The objective is to minimise the variability caused by different levels of user skill and experience. This variability is dependant on mixer design and the operator’s technique.
Vacuum mixing removes air from the cement, thereby reducing the number of voids and leading to an improvement in the strength and fatigue properties of the cement and thus a decrease in the number of potential crack initiation sites (Wixson 1992, Lewis 2000). Not all vacuum mixing systems provide the same levels of mix quality and manufacturers should be able to present data to both the surgical team members and the procurement managers, in order to support their mixing devices and demonstrate fatigue data of bone cement mixed in their devices, compared to competitors’. In addition to the data showing average mechanical properties it should also demonstrate the variability in mix quality achieved by that design. Examining the standard deviation in mechanical results can indicate the range of mix quality that can be achieved even with the same user. There is little value in achieving one off mixes of high quality if some patients are going to receive poor quality cement. The design of the device can influence mix variability significantly and should be a key consideration.
Fatigue failure begins with a small crack that develops slowly under cyclical loading leading eventually to sudden failure. The initial crack is likely to start in an area of weakness within the cement. Culleton et al (1993) found evidence of fatigue cracking originating from defects in the cement, and Topoleski et al (1990) examined 12 failed cement arthroplasties and identified fatigue crack growth as being the most likely mode of failure of the cement.
There have been many studies to show that the level of vacuum applied to the mixing of the bone cement can affect it’s shrinkage. During polymerisation, bone cement heats up and then shrinks. If the shrinkage is large, the cement will form micro cracks, which can open up during loading and lead to fatigue failure. Test work conducted at the Queens University in Belfast (2001) indicates that the optimal vacuum for mixing bone cement is around 550mmHg, providing the optimal balance between basic mechanical strength and excessive shrinkage and the formation of micro-cracks. It is therefore important that users ask the manufacturer at what vacuum level their mixing systems operate in order to ensure that the cement is mixed to reach its maximum fatigue life.
The design of the mixing device has also been shown to have an influence on the integration of the PMMA liquid and powder. For example, Kurdy et al (1986) demonstrated that a fixed axis mixing bowl produced significantly inferior results to a rotational axis design or even to hand mixing. A fixed axis bowl is one where the blades of the mixer rotate on the same track on each turn, compared to a rotational axis design where the whole paddle moves around the bowl. With a fixed axis there was greater unmixed powder and higher levels of porosity.
 |
| Fixed axis |
Hand mixing |
Rotational Axis |
|
|
Kurdy et al 1996 |
This is an example where it is important that the clinicians and procurement managers are working together in order to fully appreciate the long term benefits of a product. Weaknesses in the bone cement caused by poor integration of the powder and monomer can lead to future joint implant failure, with its associated revision rates, high human costs and high direct costs for the NHS.
References
- Culleton TP, Prendergast PJ, Taylor D 1993. Fatigue failure in the cement mantle of an artificial hip joint. Clinical Materials 12 95-102
- Dunne NJ, Orr JF, 2001 The effects of porosity on acrylic bone cement shrinkage after polymerization. European Society for Biomaterials
- Kurdy NMG, Hodgkinson JP, Haynes R, 1996 Acrylic bone-cement: influence of mixer design and unmixed powder Journal of Arthroplasty 11 (7) 813-819
- Lewis G, 2000 Relative roles of cement molecular weight and mixing method on the fatigue performance of acrylic bone cement: Simplex P versus Osteopal Journal of Biomedical Materials Research 53 (1) 119-130
- National Joint Registry for England and Wales. 2nd Annual Report. www.njrcentre.org.uk
- Topoleski LDT, Ducheyne P, Cuckler JM, 1990 A fractographic analysis of in vivo poly(methyl methacrylate) bone cement failure mechanisms Journal of Biomedical Materials Research 24,135-154
- Wixson RL, 1992 Do we need to vacuum mix or centrifuge cement? Clinical Orthopaedics and Related Research 285 84-90
|
