Osteoporosis is a growing public health problem in China and worldwide, particularly in the aged population. China has the largest population of aged people in the world, and it is increasing at an annual rate of more than 3.2% [1]. According to a census in China in 1994, there are 110 million aged people in China, comprising about 9.5% of the total population. The figure will reach 130 million (l0% of the total population) by the end of this century. If the death rate and birth rate remain in their present proportion, the number of aged people will increase to more than 400 million (25% of the population) by the middle of the next century. This trend will arouse increasing social concems about osteoporosis and related fractures. Diagnosis of Primary OsteoporosisWehave found that the present diagnostic criteria for osteoporosis (bone mineral density or content 2.5 standard deviations or more below comparable norms), as used in most countries in the world, may not be suitable for the Chinese [2]. A comparison of DXA data from studies in China and elsewhere demonstrates that the peak bone mass of the Chinese is 5-15% lower than that of Caucasians (Table 1).Osteoporosis is characterized as a progressive diminution in bone mass [2]. The balance of bone resorption and bone formation mountains bone mass throughout life, but many factors can disturb this balance. In early adulthood, bone formation is dominant, peak bone mass (PBM) being reached at round 25 years of age. Women begin losing bone mass at an annual rate of 0.2-0.5% after the age of 40 years [3]. After the menopause, estrogen deficiency can increase the bone tumover, which results in a fast rate of bone loss of 2-3% annually. This trend continues für about 10 years. A 59-year-old woman, without any treatment, would already have lost about 22.8-37% of her PBM. According to the above criteria, women diagnosed as osteoporotic are mostly over 70 years old. We compared the PBM and Correspondence and offprint requests to: G. Z. Ding,

From January to December 2008, balloon kyphoplasty was performed on 45 consecutive female patients with primary single-segment vertebral compression fractures as an inpatient procedure. All of the treated vertebral bodies were located within the thora-columbar region (T11-L2). Demographic data such as age, body mass index, fracture age, hospital stay, lumbar spine bone mineral density, and amount of bone cement injected per vertebrae were recorded. Patients were analyzed clinically by ambulatory status and the visual analog scale (VAS) for pain. Lateral radiographs were used to measure changes in anterior vertebral height. Mean anterior vertebral height increased from 58.9%+/-12.50% pre-kyphoplasty to 79.8%+/-7.12% post-kyphoplasty (P<.001).Two groups were defined based on the percentage of height restoration achieved: group A (18 patients) with a height restoration of at least 20%, and group B (27 patients) with a height restoration of 0% to 19.99% post-kyphoplasty. Mean anterior vertebral height restored in groups A and B was 28.2%+/-7.2% and 12.1%+/-6.2%, respectively (P<.05). Four patients in group A and none in group B had height loss at the treated vertebral level (P<.05). Both VAS and ambulatory status were improved after treatment (P<.05) with no significant difference between the 2 groups. Kyphoplasty can restore the collapsed vertebral height, but patients with greater height restoration were more vulnerable to a loss of corrected height.