Total joint replacement has been recognized as a highly efficacious and cost-effective procedure for the treatment of advanced hip and knee osteoarthritis (OA) in its capability to relieve pain, increase mobility, and improve the quality of life 123. The majority of knee and hip replacements are performed for OA 4. Since OA is not a life-threatening disease, total joint replacement is an elective option available to patients for the purpose of improving their quality of life.

The racial and ethnic disparities in the rates of total joint replacement have been well documented in the US, where African-Americans and Hispanics have substantially lower rates of hip and knee joint replacement compared with Caucasians 5678910. The origins of these disparities are complex. The differences in the rates of total hip and knee replacement cannot be attributed to differences in the prevalence of OA since there is evidence that the prevalence of OA is similar among these ethnic groups 1112. Potential sources of the disparities may include access to health care, physician bias, patient-physician communication, and patient-level factors 131415161718. Studies on the ethnic disparity of joint replacement other than in the US population are limited. Although the prevalence of symptomatic hip and knee OA in Italy and Greece is similar to that of other countries 19, there are some data to suggest that Italian people in Italy have a low rate of joint replacements 20.

Overseas migration has played a key role in shaping Australia as one of the most culturally diverse nations in the world. According to preliminary estimates for 2005, 24% of the Australian population was born overseas 21. After migrants from the UK and New Zealand, those from Italy and Greece are among the most common migrant groups 21 and accounted for 1.1% and 0.6%, respectively, of the total Australian population in the 2005 census 22. Italian and Greek immigration increased dramatically after World War II. Italian and Greek migrants arrived at Australia in the largest numbers in the decades immediately following. World War II. They were among the main groups targeted by Australian Government Migration Schemes in the 1950s and 1960s to deal with labour shortages in Australia. To be accepted, individuals needed to be of European ancestry, reasonably healthy, and without a criminal record. Most of the immigrants who arrived in Australia in those decades were unskilled and had little or no formal education, and only a minority had higher levels of education. Most migrants arriving in the 1950s were in their twenties. Thus, people coming from Italy and Greece represent the older migrant streams 22.

The aims of this study were to use the Melbourne Collaborative Cohort Study (MCCS) to examine whether Australian-born people and migrants to Australia from Italy or Greece had different rates of primary joint replacement performed for OA and to determine whether any differences could be accounted for by socioeconomic factors and known risk factors for OA. We hypothesize that Italian and Greek migrants to Australia have a lower rate of joint replacement compared with Australian-born individuals and that this discrepancy is not explained by differences in risk factors for OA or in education.

In this prospective cohort study, participants born in Italy or Greece had a significantly reduced rate of primary joint replacement for OA compared with Australian- or UK-born individuals, which was independent of age, gender, BMI, education level, self description of health status, and physical functioning. This was consistent when primary hip and knee replacements were analysed separately. Moreover, the reduced rate was observed for joint replacements performed in private hospitals, but not for joint replacements performed in public hospitals.

The racial and ethnic disparity in the rates of joint replacement has been well documented in the US. Although the disparity is generally thought to be largely due to lack of access and to social disadvantage, factors such as treatment preference, patient perception, and sociocultural beliefs may also contribute 131415161718. For example, Caucasians are more likely to undergo total knee and hip replacement compared with African-Americans 5678910. Total knee replacement rates among Hispanics are higher than among African-Americans but are lower than among Caucasians 7. Hispanics with Medicare receive total hip replacement at lower rates than non-Hispanics 27. We also observed ethnic disparity in joint replacement rates in this cohort study. Although the prevalence of symptomatic hip and knee OA in Italian and Greek people is similar to that of other populations 19, we found a significantly reduced rate of primary joint replacement among those born in Italy and Greece compared with those born in Australia, independent of age, gender, BMI, and educational level.

There are a number of possible explanations for the lower rate of joint replacement for migrants from Italy and Greece. In our study, Italian and Greek migrants had more severe physical function limitation and worse self-described health status in comparison with Australian-born people, suggesting that the former may have higher or at least similar levels of need. However, they had lower rates of joint replacement than Australian-born people. It is possible that the observed differences were a result of inequalities in access to health care. This is supported by the difference in the rates of joint replacement performed in private hospitals for those born in Italy or Greece, each of which requires the patient to have private health insurance or very substantial 'out of pocket' costs for this procedure. This was more evident in the Greek migrants, who had an HR of 0.08 for joint replacement performed in private hospitals but an HR of 0.92 for joint replacement performed in public hospitals when compared with Australian-born participants. Australia has a publicly funded universal health insurance system (Medicare) and people who do not have private health insurance have access to quality health care service under this system. If the need for joint replacement were similar between Italian and Greek migrants and Australian-born people and if differential access to health care were the only explanation for the lower rate of joint replacement in Italian and Greek migrants, we would expect that any unmet need may have been reflected in a disproportionate increase in the rate of joint replacement in the public hospital system for this group. However, this was not observed in our study; the standardized incidence ratio in those born in Italy and Greece was very low at 0.38 (95% CI 0.32 to 0.45) and they had a similar rate of joint replacement performed in public hospitals compared with Australian-born people. It does raise issues of whether there are other patient-related factors that affect the utilization of joint replacement in those with an Italian or Greek background.

Another possible explanation for this ethnic disparity may relate to health beliefs and preferences for treatment 1516171828. A recent study showed that there were significant differences in health-related beliefs, in particular in relation to reduced perceived benefits of total joint replacements, and more perceived barriers to total joint replacement for African-Americans compared with Caucasians 29. There are no data available as to whether such barriers might exist in those of Italian or Greek background and thus result in a reduced access to joint replacement surgery. In addition, it may be that differences in family support arrangements enable Italian and Greek migrants to cope better with significant OA and either avoid or delay the onset of joint replacement. We were unable to examine these factors in this study. A language barrier for Italian and Greek migrants may also provide a possible explanation for the observed ethnic disparity for joint replacement. There is evidence that language is a common barrier in health care settings, affecting medical comprehension and increasing the risk of adverse medication reactions 303132. Breaking the language barrier is the critical first step to reduce health care disparities 33. It is likely that, due to a language barrier, Italian and Greek migrants lack good communication with health care providers, are less familiar with joint replacement surgery, or have greater perception of risk and thus would not prefer joint replacement as a treatment for severe OA.

A further potential explanation is that, although the OA prevalence in Italian and Greek people is similar to that in other populations 19, it is possible that those born in Australia or the UK have a higher rate of more severe or end-stage OA requiring a joint replacement. It is possible that genetic or environmental factors (such as diet) of the migrants from Italy and Greece may confer a protective effect on the progression of hip and knee OA, despite their relative obesity. For example, the notion of the beneficial effects of the Mediterranean diet is well described in the area of cardiovascular disease 3435 and recent work has suggested that diet, in particular increased vitamin C and reduced fatty acids, has a beneficial effect on joint health 3637.

Strengths of our study include the large sample size and prospective study design. Our results are further strengthened by the prospectively collected demographic data and the directly measured height and weight, which are more reliable than self-reported data. However, there are a number of potential limitations in this study. There may be a selection bias. The MCCS is a healthy volunteer cohort with lower rates of mortality, cardiovascular disease, and cancer compared with the general population 23. The participants are likely to be more health conscious than the general population, as in most voluntary cohort studies. Migrants to Australia from Italy and Greece were deliberately oversampled to extend the range of lifestyle exposures and to increase genetic variation, making the MCCS a heterogeneous cohort. Greek and Italian migrants are likely to be different from the home population in terms of health status and socioeconomic status. In particular, there is likely to be a 'healthy migrant effect' resulting from a self-selection process that includes people who are willing to migrate and excludes those who are sick or disabled. Most of the immigrants who arrived in Australia during the decades after World War II were unskilled and had little or no formal education, and only a minority had higher levels of education. However, representativeness is not necessary for the estimation of associations between exposures and subsequent health outcomes with a high degree of internal validity, but we cannot use the MCCS to derive population estimates of disease prevalence and incidence. There is no selection bias in terms of ascertainment of joint replacement since the identification of joint replacement is based on linkage to the AOA NJRR, which has very comprehensive coverage in Australia.

The recruitment of MCCS participants and data collection commenced in 1990 to 1994. The NJRR started joint replacement data collection in Victoria in 2001. Thus, we do not have complete and reliable joint replacement data for the study population prior to 2001. Although we excluded those MCCS participants who reported a joint replacement prior to 2001 at the second follow-up, this information may be unreliable and is known for only 68% of the original cohort. As a result, some misclassification of joint replacement status may have occurred, although it is likely to have been nondifferential in relation to the studied risk factors, subsequently underestimating the strength of any observed associations. In addition, participants born in Australia or the UK had a joint replacement incidence similar to the general Australian population over the same time period.

People born in Italy or Greece had a lower rate of primary joint replacement in this cohort study compared with those born in Australia, and this difference could not be explained merely by factors such as education level, physical functioning, and weight. Although access to health care may play a role, it may be that social factors and preferences regarding treatment or different rates of progression to end-stage OA in this population are important. This warrants further investigation since it is unclear whether efforts aimed at education regarding potential benefits of joint replacement are needed to deal with this difference, or alternatively, it may be that genetic or lifestyle factors in the Italian or Greek population identify novel factors that prevent progression to end-stage OA despite their relative obesity.

AOA: Australian Orthopaedic Association; BMI: body mass index; CI: confidence interval; HR: hazard ratio; MCCS: Melbourne Collaborative Cohort Study; NJRR: National Joint Replacement Registry; OA: osteoarthritis.

The authors declare that they have no competing interests.

YW participated in the design of the study, performed the statistical analysis and the interpretation of data, and drafted the manuscript. JAS participated in the acquisition of data, helped to perform the statistical analysis, and reviewed the manuscript. AEW and DMU helped in the interpretation of data and reviewed the manuscript. DRE and GGG participated in the design of the study and the acquisition of data and reviewed the manuscript. SG participated in the design of the study and the acquisition of data, helped in the interpretation of data, and reviewed the manuscript. FMC participated in the design of the study, helped in the interpretation of data, and reviewed the manuscript. All authors read and approved the final manuscript.