Abstract
Purpose
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The aim of this study was to evaluate the development of the worldwide survival rate of primary total hip arthroplasty (THA). The hypothesis was that survival improved over the last decade in worldwide arthroplasty registers.
Methods
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THA registers were screened in 2022 and compared between different countries with respect to the number of primary implantations per inhabitant, age, fixation type, and survival rate, and compared to similar data from 2009. The data from these reports were analyzed in terms of number, age distribution, and procedure type of primary THAs. Survival curves and a comparative analysis with respect to the development over time were calculated.
Results
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We identified nine hip arthroplasty registers that contained sufficient data to be included. A large variation was found in the annual number of primary THA implantations per inhabitant, with more than the factor 4 for all age groups across regions. The procedure type varied strongly as well, e.g. in Sweden, 50% were cemented THAs, whereas in Emilia-Romagna (Italy), 96% of THAs were implanted cementless. We found an improved survival rate of 5%, with 90% of survival after 15 years in the cohorts from 2021 compared to 85% in the cohorts from 2009.
Conclusion
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The present study revealed a significant improvement in the survival of THA in worldwide arthroplasty registers within different countries and regions over the period of one decade. We believe that it is safe to state that the success of THA is still rising with respect to this main outcome.
Introduction
Arthroplasty registries are widely established in countries with advanced healthcare systems (1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21). The aim of these registries is to collect relevant data in order to assess and objectify the outcomes of implants in terms of implant-related factors, surgical technique, and patient-related factors. With the evolution of surgical concepts and implant technology over time, survival rates of implants have improved over the last decades (22). In the past, the Swedish Hip Arthroplasty Register, in particular, has provided data that significantly reduced revision rates by offering annual feedback on outcome data from the register (23, 24). The rationale was that analysis of register data was more likely to provide an objective estimate of the effectiveness of implants than a retrospective clinical trial and offers longer follow-up than conventional randomized controlled trials. The authors argued that registry data include results from all surgeons performing implantations, not just those from the originating center (24). This has led to the selection of safer and well-documented implants and the development of optimized surgical techniques (24, 25).
Meanwhile, total hip arthroplasty (THA) is considered the most successful operation of the century (26), leading to increased implantation numbers and modification in patients’ characteristics (27). This might partially be explained by further improvements during the last decades, e.g. standardized and optimized surgery techniques, which have become widely performed (28). Improved materials, such as new generation ceramic bearings and highly crosslinked polyethylene, which was patented in 1962 and introduced in the new millennium, might additionally have improved the durability of implants and therefore might lead to a positive outcome of surgical results (29). On the other hand, recent data suggest that the total number of primary and revision surgeries of the hip is continuing to increase (27).
Considering these numerous modified conditions, the aim of this study was to re-evaluate worldwide data on the survival of THA 10 years after a previous investigation with the same endpoints and data sources, to objectify possible changes in techniques and survival rates of THA within this period. The hypothesis was that worldwide survival of THA has substantially improved within one decade.
Materials and methods
A search in online databases, using the same terms ‘arthroplasty’ and ‘register’ or ‘registry’ as performed in 2012 in a previous study, was performed from 03/2022 to 04/2022 (30). THA registers of Australia, Denmark, Emilia-Romagna, New Zealand, England and Wales, Norway, Portugal, Slovakia, and Sweden were examined for data from 2012 to the present. England and Wales, Norway, and Sweden solely indicate the total incidence of THAs without specific distinction into different age groups. The findings of the remaining six THA registers were summarized in a table and compared to the study of 2012 in terms of the following endpoints: age at surgery, operation numbers, procedure type, and implant survival.
Age was classified according to the register of New Zealand into four classes: younger than 55, 55–64 years, 65–74 years, and older than or equal to 75 years. If age could not be extracted from the register, linear interpolation was used, as described earlier described by the study from 2012. Patients within the registers were normalized to the mean of the register period 2012–2022 by using national population estimates, which were sourced from official government agencies (1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21).
Fixation types were divided into four different groups: cementless, cemented, hybrid (cementless acetabulum and cemented femur resurfacing THA), and reverse hybrid (cementless femur and cemented acetabulum). Not all registries distinguish between reverse hybrid and hybrid and count those cases together. Since resurfacing THAs were not always listed separately either, three types of THA fixation were classified in this study: cementless, cemented, and hybrid, with hybrid including hybrid, reverse hybrid, and resurfacing THAs (1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21).
Statistical analysis
We estimated the survival rate of THAs using the Kaplan–Meier curve in those registers providing new data. In probability, the revision rate and survival rate are direct complements; thus, it was possible to convert these two parameters. We evaluated the survival curve by using the same registers as in 2012 (Australia, Denmark, Emilia-Romagna, New Zealand, Portugal, Slovakia) for all total hip arthroplasties, i.e. including all patient ages, implant types, diagnoses, etc., with revision as the failure endpoint, except for England and Wales, Norway, and Sweden where new data was not provided. As real-life data was analyzed, no probabilities were calculated, and therefore no P-values were relevant, as previously published (31). Significance was determined with respect to a deviation from the mean by a factor 3, as there exist a multitude of potential influencing factors in the included data, such as surgeons’ experience and expertise, demographic data of patients, surgical techniques, and different hospital environments. This method is in line with the Swedish and Danish hip arthroplasty registers. A difference in revision rates greater than 5% after 10 years was considered clinically relevant. The review process was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines.
Results
We identified nine hip arthroplasty registers that comprised sufficient data to be included (Australia, Denmark, Emilia-Romagna, England and Wales, New Zealand, Norway, Portugal, Slovakia, and Sweden) (Table 1). Within these registers, we explored a large variation in the annual number of primary THA implantations per inhabitant, with a factor of more than 4 for all age groups across regions. The highest number was observed in Denmark (186/100k inhabitants), while the lowest was in Portugal (43/100k inhabitants) (Fig. 1). This was different in the age group <55 years, where the highest implantation numbers were observed in Norway (35/100 000 inhabitants) and the lowest numbers in Portugal (3/100 000 inhabitants).
Annual total number of primary total hip arthroplasty (THA) implantations per 100 000 inhabitants in worldwide arthroplasty registers in collectives until 2012 and from 2012 to 2022.
Citation: EFORT Open Reviews 9, 8; 10.1530/EOR-23-0080
Arthroplasty registers including time periods of total THA number, THA age distribution, THA procedure type, and THA survival/revision data considered in the present study.
| Register | Total number | Age distribution | Procedure type | Survival data |
|---|---|---|---|---|
| Australian Orthopaedic Association National Joint Replacement Register | 2022 | 2021 | 2021 | 1999–2021 |
| Danish Hip Arthroplasty Register (in Danish) | 2021 | 1995–2017, 2018, 2019, 2020 | 2021 | 1995–2020 |
| Emilia-Romagna Register of Orthopaedic Prosthetic Implants | 2016 | 2000–2016 | 2016 | 2000–2016 |
| National Joint Register for England and Wales | 2020 | 2003–2020 | 2020 | 2003–2020 |
| New Zealand Joint Register | 2020 | 1999–2020 | 2020 | 1999–2020 |
| Norwegian Arthroplasty Register | 2020 | 2020 | 2020 | 1987–1990, 1991–1993, 1994–1998, 1999–2005, 2006–2012, 2013–2020 |
| Portuguese Arthroplasty Register | 2013 | 2012 | 2013 | NA |
| Slovak Arthroplasty Register (in Slovakian) | 2011 | 2011 | 2011 | Only for specific implants |
| Swedish Hip Arthroplasty Register | 2020 | 2000–2020 | 2020 | 1997–1991, 1992–2009, 2008–2010, 2012–2014, 2018–2020 |
The fixation type also varied strongly within regions (Fig. 2): Emilia Romagna had the highest rate of cementless fixations, with 96% of all THAs. In contrast, Portugal had the lowest rate of cementless fixations (7%) but the highest rate of hybrid fixation. Cemented fixation was predominant in Sweden (50%), while Emilia-Romagna used the lowest amount of cemented (1%) and hybrid THAs (3%) among all regions.
Fixation type distribution of primary total hip arthroplasties in collectives in worldwide arthroplasty registers from 2012 to 2022 (THAs).
Citation: EFORT Open Reviews 9, 8; 10.1530/EOR-23-0080
Survival rates were extracted up to 20 years postoperatively from the registers, except for Emilia-Romagna, with a follow-up of 17 years after surgery (Fig. 3). During the first 5 years, the New Zealand register revealed the highest survival rate, with almost 97%, while Denmark had the highest revision rate, namely 4.5%. After 10 years, Australia revealed the highest survival rate of implanted THAs (95%), whereas Denmark had the lowest, namely 92.8%. Fifteen years after implantation, 94% of THAs in Australia had no revision. In comparison, Denmark presented a much lower survival rate of 89%. After 20 years of follow-up, Australia had the best outcome (91% survival rate), while Denmark had the worst outcome among the included countries with 83%. Worldwide cumulative survival improved by 5% within one decade, representing a 90% survival after 15 years in the cohorts from 2021, compared to an 85% survival after 15 years in the cohorts from 2009.
Kaplan–Meier survival curve including total hip arthroplasties (THAs) with revision as failure in collectives from 2012 until 2022 from Australia, Denmark, Emilia-Romagna, and New Zealand and cumulative survival of THAs in collectives until 2012 (30).
Citation: EFORT Open Reviews 9, 8; 10.1530/EOR-23-0080
Discussion
The aim of this study was to re-evaluate worldwide data on the survival of THA 10 years after a previous investigation with the same endpoints and data sources, in order to objectively assess possible changes in patient characteristics, techniques, and the survival rate of THA within this period.
The hypothesis was that the worldwide survival of THA has substantially improved within one decade.
We found that the worldwide cumulative survival improved by 5% within one decade, with 90% survival after 15 years in the cohorts from 2021 vs 85% survival after 15 years in the cohorts from 2009 (30).
Although the overall incidence of THA implantations was similar to our 2012 study (30), it still varied significantly between the included countries and regions during the detected time period as follows. The largest discrepancy in comparison was Denmark, where four times the number of implanted THAs compared to Portugal was observed. One explanation for this observation could be that the healthcare systems have different financial limits on THA in different countries. Furthermore, attention must be paid to the differing availability of surgical capacities in different countries as a reason for the variety of incidences of THA implantations. When comparing incidences of THA implantations, age distribution is an important influencing factor in each country. However, since the specific parameters for each individual country have not been accurately determined by the investigated THA registries, the cause remains largely unexplained.
The presented study also revealed that the types of fixation vary greatly depending on the detected country. While in Emilia Romagna, 96% of THAs were implanted without cement, Sweden used cement in 50% of their cases. Portugal, with the highest amount of hybrid fixations, namely 70%, further strengthened the described variability of different types of fixation depending on the country. If these values are compared with the study from 2012, it stands out that a trend developed towards cementless implantation of THAs. This could mainly be due to the fact that the materials and coatings of the cementless prosthesis have improved significantly in quality due to scientific progress (32). For the long-term survival of such prostheses, a well-established coating is most important, so that ingrowth into the bone is guaranteed (33). A possible increase in material-associated durability can be targeted by monitoring and documentation in prosthesis registers like those we investigated in this study. Since functioning techniques and implants are highlighted, factors that worsen the outcome can be recognized and improved immediately (34). A further argument for using cementless implants is that a rare but possible cement reaction of patients does not occur. Since the rates of failure and the associated revision interventions have decreased significantly, both a progress in science and a possible profit from arthroplasty registers can be derived.
The present study showed that long-term durability is best in Australia with 91% and worst in Denmark, although the ‘cementless’ type of fixation dominated in both countries. This illustrates that not only the fixation type of the prosthesis itself but also other parameters such as age and surgical technique might have a major impact on the outcome. Comparing Emilia-Romagna with Denmark, it is also noticeable that Emilia-Romagna has a superior long-term outcome, although cementless fixation dominates in both countries. An age-related difference as a revision factor could not be evaluated due to the lack of specific data in the investigated THA registries. Although Denmark used the hybrid fixation system in 24% compared to Emilia-Romagna with just 3%, it cannot be stated that cementless fixation has the better outcome. This would be in contrast to data from Australia, where the best long-term outcome was reported and mostly ‘hybrid’ fixation of THA was performed. However, since there is no information available concerning other factors that play a key role in the durability of the prosthesis, such as the patient's age, gender, body mass index (BMI), or the patient’s state of health, it is very difficult to identify the best fixation type from our data. For further investigations, it could be recommended to record parameters preoperatively and analyze the data with respect to these additional factors worldwide. However, since the individual durability of the prostheses only varies by a few percent in different countries, a high-quality standard in each of the countries examined can be assumed.
When comparing durability to the 2012 study, there is a clear increase in durability, from 85% to 90% after 20 years. There are many factors that account for this progress. In addition to the factors already mentioned, such as better materials for implants, scientific progress, and precise feedback from the prosthesis register, additional technical progress in the operating room itself must also be mentioned. Since the beginning of these registers, there has been a significantly higher level of cleanliness in the operating room, which efficiently prevents infections and the revision procedures associated with them (33). Especially the intervention of the laminar airflow technique had a high impact on the revision rate of THAs (35). Furthermore, the pre- and intra-operative procedures were standardized and therefore have clearly improved in quality. Technical aids such as preoperative measurement of X-ray images or navigated operations might further improve the accuracy and therefore long-term survival rates of THA in the future (36).
A further factor for a reduction in revision rates could be the improvement of surgical skills. A trend toward specialization has led to an increased focus and the establishment of specific sections for hip surgery. On the other hand, the implantation of THA has become a well-standardized and described procedure, including step-by-step instructions for optimal workflow, which have positively developed over the years. In addition, worldwide surgical training become more standardized and improved over time. As a result, the establishment of specific training centers and cadaver labs could have led to fewer complications for surgeons during their learning curve.
The study possesses various limitations: Like any analysis based on register data, findings hinge upon the quality of primary databases, which are subject to commonly acknowledged challenges, including the comprehensiveness of performed procedures, lack of patient-reported outcome measurements (PROMs), stratification of patients, and standardization relating to reported age, actual numbers of revisions, or fixation type (37).
Finally, the postoperative care and rehabilitation had an additional positive impact on patient outcomes and certainly improved over a decade.
Conclusion
The present study revealed a significant improvement in the survival of THA in worldwide arthroplasty registers across different countries and regions over the period of one decade. We believe it is safe to state that the success of THA is still rising with respect to this main outcome.
ICMJE Conflict of Interest Statement
All authors of this article declare that they have no financial and personal relationships with other people or organizations that could inappropriately influence (bias) this work, such as employment, consultancies, stock ownership, honoraria, paid expert testimony, patent applications/registrations, and grants or other funding.
Funding Statement
This work did not receive any specific grant from any funding agency in the public, commercial, or not-for-profit sector.
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