20
The Future Role of Cemented Total Hip Arthroplasty
Henrik Malchau, Steffen J. Breusch
Future Burden of Ageing Population
The World Health Organisation estimates that in the next 20 years the elderly population will increase 4 fold, which will greatly increase the demand for total hip arthroplasty as the population seeks to remain more active [9]. Total hip arthroplasty has enjoyed tremendous success and has gained worldwide popularity, but with this continued growth comes an impending epidemic of failures neces- sitating revision surgery. This revision burden can be tempered by knowing which hip systems have enjoyed clinical success and those that have poor outcomes.
The most effective data must be obtained by more pro- spective clinical trials comparing implants and using reproducible outcomes measurements. Other methods, including larger scale-joint registries as have been cre- ated in Sweden and Norway, have shown enormous utility in tracking the results of all implants placed in those countries. Registries such as these are significantly important in tracking the early, midterm and late results of many implants which are not reported in the literature but widely used today. Due to the enormous volume of patients being tracked in these registries, we can detect early component failures with relative ease. Therefore, it will be extremely important to implement similar regis- tries throughout Europe as well as in the United States where huge volumes of unproven and newly designed hip systems are being implanted and are poorly tracked. The financial burden on society due to revision-hip surgery is extremely large and will continue to rise with the increas- ing number of hip replacements being done, but these costs can be dramatically cut with the implementation of a registry that can efficiently detect implants that are destined to fail in a timely manner.
Evaluation of New Implant Systems
The question which fixation technique is optimal and most durable has been debated for many years. Several new cements, implant designs and bearing surfaces have been introduced in the past 10–15 years, but surprisingly often without appropriate scientific, clinical documenta- tion. The Bonelock cement, Capital hip system and heat- treat polyethylene (Hylamer) are only some examples, which have created major clinical problems with unac- ceptable failure rates. Decisions about medical treatment should be based on a careful appraisal of the best evidence available. In order to increase evidence-based decision- making in the evaluation of new surgical techniques and implants a stepwise introduction is necessary to expose as few patients as possible to the risk of failure.
The history of development of total hip arthroplasty could have been different if the introduction had been more careful and performed in a stepwise manner. Inferi- or properties would have been revealed earlier thus reduc- ing the number of failures and allowing the necessary improvements. It is therefore desirable that the profession agree on a standardised way to introduce new implants.
Market Introduction
Based on the Swedish experience the following schedule for stepwise clinical introduction [4–7] of new implants is suggested (
⊡Fig. 20.1):
▬ The initial step is a preclinical testing.
▬ The first clinical step is the open prospective and
preferably randomised trial including a minimum of
patients to obtain a valid evaluation. The strict rules
of prospective randomised trials should be addressed.
In this first clinical level, high accuracy methods such as radiostereometric analysis (RSA) and dual energy X-ray absorptiometry (DEXA) are required to detect potential early problems. Within 6 months to 2 years these methods have the potential of identifying implants with inferior/superior fixation, extreme wear or unfavourable/favourable bone remodelling. Results from these methods determine if further clinical evalu- ation is worthwhile. It should be noted and underlined that all types of complication cannot be predicted and further follow up is necessary and should be done.
If migration analysis is performed with conventional methods (less accurate than RSA), larger cohorts is needed, exposing more patients for potential risks.
▬ Step 2: If favourable results are obtained in step 1, the second step, a multi-centre trial exposing the new procedure to a broader aspect of the orthopaedic com- munity can be initiated. The implant will then be exposed to various surgical techniques and hospital environments. In step-1 investigations there is a risk for susceptibility and performance bias as the inventors often perform these first introductory investigations.
The protocol of the multi-centre study must be carefully prepared and agreed upon by all participating inventors.
A sufficient number of patients must be included in or- der to allow statistical analysis. The witnessed or written patient consent is essential, as is an approval by ethical committee. The ultimate goal will be to make even the multi-centre trial randomised using a well-documented implant as the golden standard on baseline control.
▬ Step 3 in the evaluation is a continuous quality control effected by register studies based on large population to reveal early or unusual and potential catastrophic complications. In a comparable small community, e.g. Sweden, the register should be nation-wide and include all units in a specific field.
The Benchmark
Based on existing figures, a chance of at least 92–95%
can be promised to the average patient, requiring a total hip replacement, to still have their original implant after 10 years. This is a benchmark hard to beat. It is estimated that approximately 4330 patients are needed in a com- parative study with a valid statistical approach (a = 0.05, power = 0.95) to show an improvement from 95% survival to 95.5%. It will therefore be difficult for any new implant or technology to prove that it will perform better than es- tablished designs with a long-term track record. However, there is always room for further improvement and we should continue to thrive to achieve better and even more consistent outcomes for our patients, but under controlled and scientific circumstances as outlined above.
Current »Trends« in THA
It is both intriguing and worrying with how much vehe- mence and marketing efforts new implant technologies drive both so-called »champion surgeons« or »opinion leaders« as well as the industry, often despite the lack of long-term evidence. It is long-term evidence, which is required before we can offer a new technique of implant to our patients. We not only stand on much firmer ground, but also owe this to our patients. It is not enough to »think«
that the proposed method »may« be of benefit.
Currently, metal-on-metal resurfacing and minimally invasive hip surgery (MIS) are advocated, considered
»trendy« and hence rapidly gained popularity. These are already included in treatment algorithms that lack scien- tific support [1, 2]. Yet, the public is led to believe that these »modern« methods are better. It will take decades to determine if the benefits of metal-on-metal bearings or MIS outweigh the associated risks [1, 3, 8]. Hence, it is
20
Register Studies
Multicenter Studies Prospective
Randomized Studies
Preclinical Testing Initial Step
Clinical Step I
Clinical Step II
Clinical Step III
retrieval and explant analysis
⊡ Fig. 20.1.
368 Part VI · Future Perspectives
369
long to go before enough data will be available to draw any firm conclusions. The jury is still out!
Until then it is questionable whether these techniques should be offered on a larger scale and tested by the aver- age arthroplasty surgeon and treatment centres, which lack the infrastructure to conduct clinical trials.
The Value of Cemented THA
It is not an issue in our opinion to further fuel the long and ongoing debate about uncemented or cemented fixa- tion. The future arthroplasty surgeon needs to be familiar with both techniques. Based on the experience gained from cemented fixation over the past four decades, it is probably not unreasonable to state that this concept has been driven to a very high standard with reproducible outcome.
The basic science, operative technique and outcome data have been compiled for this book to give a compre- hensive background of current knowledge and state of the art of cemented THA. It is a method – if performed well – which is highly successful, reproducible and cost-effec- tive. It is based on this knowledge, that we believe that a well-performed cemented THA still remains the treat- ment of choice for the average patients with osteoarthritis of the hip over the age of 60–65 with average activity.
Younger patients and those with high demand activity will have to accept a higher chance of earlier failure irrespec- tive of the mode of fixation and choice of implant.
It is important to realise and accept, that surgical tech- nique is most important and that the future for cemented THA should be seen in continued and improved training of young surgeons with an interest in arthroplasty.
References
1. Berry DJ. »Minimally invasive« total hip arthroplasty. J Bone Joint Surg 2005; 87-A:699–700
2. Carr AJ, Morris RW, Murray DW, Pynsent PB. Survival analysis in joint replacement surgery. J Bone Joint Surg 1993;75-B(2):178–82 3. Fehring TK, Mason JB. Catastrophic complications of minimally
invasive hip surgery. J Bone Joint Surg 2005; 87-A:711–14 4. Gross M. Innovations in surgery. A proposal for phased clinical tri-
als. J Bone Joint Surg 1993; 75B:351–354
5. Malchau H. On the importance of stepwise introduction of new hip implant technology. Thesis, Göteborg University, 1995 6. Malchau H. Introduction of orthopaedic devices to the market-
place. Presidential guest lecture The Hip Society, AAOS, Anaheim, USA, February 7, 1999
7. Malchau H. Introducing new technology: a stepwise algorithm.
Spine 2000; 25(3): 285
8. Silva M, Heisel C, Schmalzried TP. Metal-on-metal total hip replace- ment. Clin Orthop 2005; 430:53–61
9. Woolf AD, Pfleger B. Burden of major musculoskeletal conditions.
Bull World Health Org 2003;81:646–656
Chapter 20 · The Future Role of Cemented Total Hip Arthroplasty
