The information on hip arthroplasties is based on data reported to the Norwegian Arthroplasty register. Data are reported directly by the surgeon, who usually fills in the form submitted to the register immediately after the operation. Even though this reporting of operations to the register is voluntary, we have reason to believe that the register is near-complete. Comparisons with information submitted to the Norwegian Patient Register (NPR) show that the number of primary hip arthroplasties reported to the Norwegian Arthroplasty Register constituted 97 % of the number of prosthetics reported to the patient register (21). This completeness of reporting has also been confirmed at the patient level in several hospitals (25) – (27). The validity of the reported information has also been investigated in one hospital and showed very satisfactory results with regard to the variables reviewed: side (left, right), type of operation (primary, revision) and the date of operation (25).
The fact that the patient’s reported place of residence was the current place of residence rather than the place of residence at the time of the operation could represent a weakness of the study design. However, in light of the age group in question, there is little reason to assume that many of the patients have moved to other counties or regional health enterprises (28).
The frequency of primary hip arthroplasties caused by idiopathic coxarthrosis has increased more than for the material as a whole. This could be due to improved access to surgery, but also to a change in indications for operation. It has been shown that if the operation is postponed and the patient’s condition deteriorates, then the outcome of the operation will be poorer (29, 30). This could probably to some extent explain why a higher number of operations than before are performed on young people with less assumed pain and better functional capability. Nevertheless, we found that the increase was most marked among the oldest patients. The increasing number of elderly people with good general health who are able to undergo hip arthroplasty, better anaesthetics and a general consensus of not using age as a contraindication for an operation, are factors that can explain this increase. It is crucial to investigate whether this change in indication for operation may change the results of hip arthroplasty surgery.
In recent years, we have seen that the frequency of primary hip arthroplasty has remained relatively constant, and one may ask whether existing surgical capacity is sufficient to cover demand for this type of surgery. A study published in 1999 showed that hip arthroplasty capacity in England fell six per cent short of demand (31). Comparable frequencies of primary hip arthroplasty have been reported for Norway and England (32), and if we assume that the prevalence of hip disorders that require implantation of a prosthesis also is similar, it is reasonable to claim that too few, rather than too many, are offered this type of surgery in Norway. Many studies estimate an increasing need for hip arthroplasty in the years to come, in light of an increasing proportion of elderly people in the population and also because an increasing number of young people (33) and elderly people undergo surgery (6, 33, 34). Further studies ought to be undertaken to clarify the need for future surgical capacity, with regard to Norway as well.
It has been shown that the frequency of primary total hip arthroplasties varies significantly in different countries (4). However, a study based on national registry data for the years 1996 – 2000 showed that the annual frequencies of arthroplasties caused by primary coxarthrosis were fairly similar in the Nordic countries (9). Differences could nevertheless be observed for groups of individuals. In concurrence with our study, Lohmann et al. (9) observed that the proportion with hip arthroplasty was twice as high among Norwegian women as among men, while this proportion was lower in the other Nordic countries, at 1.1 – 1.3.
Similar to the results of our study, considerable regional differences in the frequencies of primary total hip arthroplasties have been found in other countries as well (14) – (16). In a Danish study, differences related to diagnoses could not explain the regional variations (15). Investigating this issue in Norway is difficult, since generally little is known about the frequency of various diagnoses according to area of residence. Differences in the prevalence of coxarthrosis among various groups of the population have been demonstrated (35, 36), and it is conceivable that this can partly explain the low frequency of arthroplasty operations in some counties. For example, as of 1 January 2009, a total of 22 per cent of the population of Oslo had a non-Western background, compared to 8 per cent in the country as a whole (37). Another possible explanation includes the differences in attitudes to this type of operation among various groups of the population, reflected in surveys (38). For example, it has been shown that non-European patients have a higher level of discomfort before they undergo surgery, and that they assess this operation as dangerous to a higher extent than patients from a European ethnic background (39). Furthermore, studies have revealed a lower frequency of hip arthroplasty in large cities in countries such as England, Denmark, Sweden and Finland (14, 15, 17, 40). Attempted explanations refer to how the infrastructure and working conditions are better there than in rural areas, so that it is possible to cope without an artificial joint (14). A study from the US showed that low population density was correlated with a high frequency of hip arthroplasty (41), while other studies, on the other hand, show that regional differences cannot be explained by population density, or by factors such as density of orthopaedic surgeons, hospital costs and regional gross domestic product (14, 15, 17). In our study, we have not adjusted for factors such as differences in the extent of hospital coverage and surgical capacity, and further research should also investigate the effects of such factors in the Norwegian context. Geographical differences in the indication for an operation could also be a possible explanatory factor for the variations in frequency according to place of residence (14).