Chapter 1 Background to the study
1.2 Epidemiology of osteoporotic hip fractures
There is a wide geographic, ethnic and gender variation in the incidence of hip fractures. While the incidence of hip fractures has been extensively reported in developed countries, data from developing countries are limited. The highest rates of osteoporotic hip fractures are seen in Norway, Sweden and the USA [32-34].
There is a north to south gradient with latitude with decreasing incidence southwards. Intermediate rates have been reported in Latin America [4] and Asia [35, 36], and the lowest rates in Africa [37-40] and the Middle East [28]. In Europe and America the prevalence of fractures is greater in women, with the lifetime risk for sustaining a hip fracture for a women being 15% and for men 5% [41]. In contrast, in the developing world the prevalence of hip fractures is similar for both men and women with fractures occurring at a lower rate [42].
Varying hip fracture rates have been reported in Asia. In a recent study from India the crude hip fracture incidence rate in over 50 year olds was 129 per 100 000 persons and rates of 105 per 100 000 and 159 per 100 000 in men and women respectively, were reported [43]. The rate increased exponentially with age to reach 962 per 100 000 in the 90 - 94 year age group. Despite a lower incidence, osteoporotic fractures occur 10 - 20 years earlier in Indians as compared to Caucasians [44]. While the above rates are similar to those from South East Asia, they are lower than that seen in more developed Asian countries such as Japan or Singapore and that in northern Europe and North America (NA) [36, 42].
1.2.1 Hip fractures in Africa
There are few published studies from Africa and early studies failed to document a significant hip fracture incidence. The first study from rural Gambia found that African women had lower bone mineral density (BMD) compared to United Kingdom (UK) women but no hip fractures were noted [45]. A further study confirmed the lower rate of hip and forearm fractures in Nigeria compared to the USA [40].
Possible reasons postulated for the lower incidence include reduced longevity in developing nations and a possible under-reporting [40, 46-48].
Recent studies show that incidence rates have increased nine-fold for women and five fold for men with age specific incidence rates increasing exponentially. The rates however remain lower than in Europe [49]. In contrast to Europe and USA the mean age of fracture is lower and male to female ratio fairly similar.
The first study to report a change in hip fracture trends in Africa was a study from Morocco in 2002, in which the rate of hip fractures was 52.1 per 100 000 persons [50]. Although higher than previously reported this was still not comparable to the USA (80.5 per 100 000 persons). A subsequent retrospective hip fracture study from Nigeria (2002 - 2008) found the mean age of fracture remained younger compared to developed countries. The female to male incidence rate had also changed to 1.7:1 unlike earlier studies which showed a similar incidence rate in men and women in Africa [37, 40, 51].
The only longitudinal hip fracture study in Africa from Rabat, Morocco (2006 – 2009) reported that age and sex specific hip fracture incidence trends were stable, but projected that a doubling would occur in the period between 2010 and 2030 [47]. In keeping with previous studies from Cameroon men were significantly younger (73.3
± 11.0 years vs. 75.0 ± 10.7 years; p = 0.014) and hip fracture rates increased with age.
1.2.2 Osteoporotic hip fractures in South Africa
In SA although studies have looked at risk factors and prevalence of osteoporosis in the different ethnic groups, few studies have documented incidence rates or risk factors for hip fractures. In the landmark study by Solomon, published over forty years ago, an extremely low prevalence of hip fractures in Africans (5.2 per 100 000 persons) was seen [39]. The reason for this was not well understood, as a subsequent study showed no significance difference in BMD between Africans and
Whites [52]. Schnaid et al., in 2000 reported a higher rate of hip fractures in Nelspruit, but this study had several limitations as it excluded subjects with osteoporosis and was limited to small geographic area [39, 52, 53].
However, a recent study showed a similar prevalence of VF’s in African and White subjects suggests that the pattern of osteoporosis may be changing [54].
In keeping with the worldwide demographic change, the older population of SA is expected to increase exponentially despite population growth remaining static. The number of elderly will increase from the present 8 million (16%) aged 50 years and over and 1.6 million (3%) aged 70 years and over to 13.6 million (28%) and 4 million (8%) respectively by the year 2050 [28]. In addition there is significant urbanization and change in dietary and lifestyle factors. It is therefore expected that there will be a commensurate increase in osteoporotic fracture rates.
The effects of urbanization on osteoporosis are well documented. In Asia, urbanization has had a marked increase in the rate of hip fractures [55]. A high protein diet is associated with a negative calcium balance and there is strong correlation between animal protein intake and hip fracture rates [49, 50]. In post- apartheid SA, there has been a massive shift from rural to urban areas with associated lifestyle and dietary changes. Whilst the intake of calcium has decreased there has been an associated increase in the intake of animal protein. This combined with a decrease in physical exercise may contribute to a decrease in bone mass. Whether the effects of the increased body mass found in the African
population and the inherent genetic predisposition can counteract the urbanization effects needs further study [56].