Development and application of a Japanese model of

Authors: S Fujiwara T Nakamura H Orimo T Hosoi I Gorai A Oden H Johansson J A Kanis

Publish Date: 2008/02/22

Volume: 19, Issue: 4, Pages: 429-435

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Abstract

The present study estimated the 10year probability using the Japanese version of WHO fracture risk assessment tool FRAX™ in order to determine fracture probabilities that correspond to intervention thresholds currently used in Japan and to resolve some issues for its use in JapanThe objective of the present study was to evaluate a Japanese version of the WHO fracture risk assessment FRAX™ tool to compute 10year probabilities of osteoporotic fracture in Japanese men and women Since lumbar spine bone mineral density BMD is used preferentially as a site for assessment and densitometers use Japanese reference data a second aim was to investigate the suitability and impact of this practice in JapanFracture probabilities were computed from published data on the fracture and death hazards in Japan Probabilities took account of age sex the presence of clinical risk factors and femoral neck BMD Fracture probabilities were determined that were equivalent to intervention thresholds currently used in Japan The difference between Tscores derived from international reference data and that using Japanesespecific normal ranges was estimated from published sources The gradient of risk of BMD for fracture in Japan was compared to that for BMD at the lumbar spine in the Hiroshima cohortThe 10year probabilities of a major osteoporosisrelated fracture that corresponded to current intervention thresholds ranged from approximately 5 at the age of 50 years to more than 20 at the age of 80 years The use of femoral neck BMD predicts fracture as well as or better than BMD tests at the lumbar spine There were small differences in Tscores between those used for the model and those derived from a Japanese reference populationThe FRAX™ tool has been used to determine possible thresholds for therapeutic intervention based on equivalence of risk with current guidelines The approach will need to be supported by appropriate health economic analyses Femoral neck BMD is suitable for the prediction of fracture risk among Japanese However when applying the FRAX™ model to Japan Tscores and Zscores should be converted to those derived from the international referenceFractures related to osteoporosis have become a major health and economic burden in Asian countries just as they have in North America and Europe An estimated 117900 cases of hip fracture occurred in 2002 1 and the incidence in Japan has increased in the past 10 years 1 2 Asia will be expected to have the highest absolute increase in fracture number because it has the largest population Early detection of individuals with high fracture risk using clinical risk factors would have a substantial impact on reducing the burden of fractures in AsiaA series of metaanalyses on prospective populationbased cohorts has identified a number of clinical risk factors that contribute to fracture risk independently of BMD at the femoral neck 3 The integration of these risks would therefore enhance the predictive value of BMD 4 The risk factors comprise age sex bone mineral density body mass index BMI longterm use of glucocorticoids parental history of hip fracture history of fragility fracture smoking alcohol consumption 3 or more units/day and secondary osteoporosis such as rheumatoid arthritis A WHO scientific group has proposed that the 10year probability for fracture is used to express fracture risk for clinical assessment 5 and to determine intervention thresholds 3 The aim of this study was to create a fracture probability model based on the methodology of the WHO risk assessment tool FRAX™ 6 calibrated to the epidemiology of JapanIn addition several problems need to be resolved before the FRAX™ model is applied to Japan First the FRAX™ tool inputs femoral neck BMD and the Zscore or Tscore is based on the NHANES III reference data base In Japan BMD at the lumbar spine is widely used clinically because the physical size of Japanese people is smaller than that of Western people giving rise to a view based on little evidence that the reproducibility of measurements at the femoral neck BMD would be poorer than that at the lumbar spine Furthermore data on the young adult mean YAM and the mean at each age are installed in the DXA systems in Japan and programmed to calculate T and Zscores from Japanese reference data In addition the Japanese Society for Bone and Mineral Research 7 8 provide recommendations for the diagnosis of osteoporosis and intervention based on YAM and these are widely used in clinical practice

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