hip fracture occurs primarily in the elderly , and is one of the most important causes of disability and death in this age group ( 1 ) . the number and mean age of the elderly continues to increase , and thus fracture incidence is likely to follow ( 2 - 5 ) . hip fracture is becoming a major health burden worldwide . rowe et al . ( 6 ) at our institute , reported the first epidemiological study on hip fracture in korea and provided much information . however , since the previous study conducted in 1991 ( reported in 1993 ) the socio - economic environment has changed and the number of elderly koreans has increased . the purpose of this study was to determine the incidence of hip fracture in 2001 , to compare this with that of 1991 . patients aged 50 yr or more , living in gwangju city and chonnam province , korea , and who sustained a fracture of the hip during the year 2001 were investigated . primary patient information was obtained from the health insurance review agency ( hira ) . as a crosscheck , all hospitals to which patients suspected of hip fracture might have been referred were visited . a total of 125 hospitals was visited , and medical records and radiographs were reviewed . all registered patients with a diagnosis of hip fracture or with a suspected diagnosis of hip fracture were reviewed . in this study , only patients who were admitted to hospitals for primary treatment of a first hip fracture were selected . we also interviewed patients or relatives by telephone to confirm post - fracture course or survival . the time from injury to interview ranged from 15 to 25 months with a mean of 18 months . only fractures of the femoral neck and intertrochanteric fractures were included , subtrochanteric fractures were excluded , since they usually caused by high energy trauma . information collected from the hospital records included age , sex , the nature of injury , the day of injury , location , the period from injury to hospital presentation , the method of treatment , the degree of osteoporosis , and the presence of concomitant medical conditions . location and type of fracture were determined from radiographs . the level of daily activity was graded into 4 groups according to a modification of halpin and nelson classification ( 8) . the semiactive group in his classification was subdivided into those with " moderate activity " and those with " limited activity " . in the present study , we described patients with full and moderate activity as having " good activity " , and those with limited activity or who were bedridden as having " poor activity " . age and sex specific annual incidences were calculated using the population of the gwangju city and chonnam province area as of 1 july 2001 . data were analyzed using the spss for windows v11.0 ( spss , chicago , il , u.s.a . ) . for all analyses , a p - value of < 0.05 was considered statistically significant . data were analyzed using the spss for windows v11.0 ( spss , chicago , il , u.s.a . ) . for all analyses , a p - value of < 0.05 was considered statistically significant . the population of the gwangju city and chonnam province , aged 50 yr or more in 2001 , was 864,966 , of whom 491,673 were female and 373,293 were male , giving a sex ratio of 1.3:1 . these individuals accounted for 25% of the total population ( 3,483,073 ) of this area . hip fractures occurred in 1,152 patients , an incidence of 0.133% ( 13.3/10,000 per year ) in this age group ; 15.0/10,000 in gwangju and 12.6/10,000 in chonnam . incidences were 3.1/10,000 in the age group 50 - 59 yr , 9.3 between 60 - 69 yr , 26.6 between 70 - 79 yr , and 62.8 in patients aged 80 yr or more . age specific incidence rates showed a gradual increase ( p<0.001 ) ( table 1 ) . no significant differences were found between the incidences in urban and rural areas . in the urban area ( gwangju , mokpo , yeosu , and suncheon cities ) , this was 14.2/10,000 and in the rural area 12.5/10,000 ( p=0.239 ) . the mean age of patients who sustained a fracture was 74.1 yr ( range 50 to 100 yr ) , and was 70.6 yr in men and 76.2 yr in women . the mean age for a fracture of the femoral neck was 74.1 yr and for an intertrochanteric fracture 74.2 yr . the mean age of patients from urban areas was 73.9 yr and from rural areas 74.4 yr . there was a 5.6-yr difference between the mean age of men and women ( p<0.001 ) , but no statistical difference was found between the two fracture types or between their incidences in urban and rural areas . in terms of sex distribution among those that experienced a fracture , 730 were females and 422 males , a ratio of 1.7:1 ( p<0.001 ) . the frequency of hip fractures among men was 11.3 per 10,000 per year ( 422/373,293 ) , and among women was 14.8 per 10,000 ( 730/491,673 ) , thus female patients predominated ( p<0.001 ) . fractures occurred in spring in 301 patients , summer in 276 , fall in 292 , and winter in 283 , which was not significantly different ( p=0.746 ) . 907 patients ( 78% ) were injured by slipping at ground level , 101 by falls from more than one meter , 79 in road traffic accidents , and 65 from other causes . the average period elapsed between injury and presentation at hospital was 2.7 days , ranging from the day of injury to 180 days after injury . the subtypes were subcapital in 278 ( 50% ) , transcervical in 160 ( 29% ) and basicervical in 119 ( 21% ) . and there were 595 intertrochanteric fractures ; type i of the tronzo classification ( 9 ) was found in 43 ( 7% ) , type ii in 153 ( 26% ) , type iii in 269 ( 45% ) , type iv in 116 ( 19% ) , and type v in 14 ( 2% ) . radiographic examinations showed definite osteoporosis ( singh grade i - iii ) in 70% , borderline osteoporosis ( grade iv or v ) in 29% , and 1% were normal ( grade vi ) . definite osteoporosis was seen in 48% of patients aged 50 - 59 yr , in 65% of those aged 60 - 69 yr , in 70% of those between 70 - 79 yr and in 81% in those aged 80 yr or more ( table 2 ) . definite osteoporosis was identified in 63% of males and in 73% of females ( p=0.000 ) . osteoporosis was observed in 73% of fractures of the femoral neck and in 67% of intertrochanteric fractures ( p<0.012 ) . operations included replacement arthroplasty of the femoral head in 434 , total hip replacement in 39 , and osteosynthesis in 537 . the types of fixation used in osteosynthesis were a compression hip screw in 341 , multiple pins in 83 , an ender intramedullary nail in 5 , a rowe plate in 2 , a gamma nail in 101 , and an angled blade plate in 5 . arthroplasty was performed in 393 of 490 operations for a fracture of the femoral neck , and in 80 of 520 procedures for intertrochanteric fracture ( table 3 ) . of 1,010 patients ( 88% of all patients ) who received an operation , 374 ( 37% ) achieved full activity postoperatively , 245 ( 24% ) moderate activity , 180 ( 18% ) limited activity , and 211 ( 21% ) were bedridden . in 142 patients that received non - operative management 33 ( 23% ) showed full activity , 9 ( 6% ) moderate activity , 17 ( 12% ) limited activity , and 83 ( 59% ) were bedridden . postinjury activity was good in 61% of the operated group and in only 30% of the non - operated group ( p<0.001 ) . of the 1,152 patients , 172 died within 12 months of injury , a mortality rate of 14.9% . the age and sex adjusted mortality rate in the general population was 5.8% in this age group . in detail , the mortality rate in the operated group was 5.5% within 3 months of injury , 7.7% within 6 , 10.5% within 9 , and 12.3% within 12 . the mortality rate in the non - operated group was 16.2% within 3 months of injury , 23.2% within 6 , 32.4% within 9 , and 33.8% within 12 ( p<0.001 ) . thus the annual mortality rate of patients that experienced fracture ( 14.9% ) was 2.6 times higher than in the general population ( 5.8% ) . to determine significant changes during the 10-yr period from the year of 1991 , when the first korean epidemiological study of hip fracture was conducted by our institution in the same area ( 6 ) , the year 2001 and 1991 results were compared . the total annual number of hip fractures rose considerably during the 10-yr period from 247 in the year 1991 to 1,152 in 2001 , an average increase of 36.6% per year . the fracture incidence also increased remarkably from 3.3 per 10,000 in 1991 to 13.3 in 2001 , representing a 4-fold increase over 10 yr ( p<0.001 ) . in 1991 , the total population of gwangju city and chonnam province area was 3,685,283 and the population aged 50 yr or more was 757,417 , accounting for 20.6% of the total population . in the year 2001 , there was a 5.5% decrease in the total population versus 1991 , but the population aged 50 yr or more increased by 14.2% ( p<0.001 ) . the mean age of the elderly that experienced a hip fracture also rose during this 10-yr period from 70 yr in 1991 to 74 yr in 2001 . in women this increase was from 73 yr to 76 yr , and in men from 67 yr to 71 yr . although seasonal incidences were not significantly different , there was a difference between the observed seasonal increases . increases in incidence of fractures were higher in winter ( 4.7-fold increase ) and spring ( 4.4-fold increase ) than in fall ( 3.8-fold ) and summer ( 3.6-fold ) , suggesting that the elderly people are becoming at higher risk of falling in the cooler seasons . regarding fracture pattern , a definite increase was observed in unstable intertrochanteric fracture ( tronzo type iii , iv , v ) , which is usually caused by a severe fall . in 1991 , the proportion of unstable intertrochanteric fractures was 54% , which increased to 66% in 2001 ( p=0.006 ) . a significant increase in definite osteoporosis was noted , from 50% in the year 1991 to 70% in the year 2001 ( p<0.001 ) . a remarkable increase was observed in two age groups : 27% in the year 1991 to 48% in the year 2001 in those aged 50 - 59 yr ( p=0.012 ) and 37% in the year 1991 to 65% in the year 2001 in those aged group of 60 - 69 yr ( p<0.001 ) ( table 2 ) . to determine significant changes during the 10-yr period from the year of 1991 , when the first korean epidemiological study of hip fracture was conducted by our institution in the same area ( 6 ) , the year 2001 and 1991 results were compared . the total annual number of hip fractures rose considerably during the 10-yr period from 247 in the year 1991 to 1,152 in 2001 , an average increase of 36.6% per year . the fracture incidence also increased remarkably from 3.3 per 10,000 in 1991 to 13.3 in 2001 , representing a 4-fold increase over 10 yr ( p<0.001 ) . in 1991 , the total population of gwangju city and chonnam province area was 3,685,283 and the population aged 50 yr or more was 757,417 , accounting for 20.6% of the total population . in the year 2001 , there was a 5.5% decrease in the total population versus 1991 , but the population aged 50 yr or more increased by 14.2% ( p<0.001 ) . the mean age of the elderly that experienced a hip fracture also rose during this 10-yr period from 70 yr in 1991 to 74 yr in 2001 . in women this increase was from 73 yr to 76 yr , and in men from 67 yr to 71 yr . although seasonal incidences were not significantly different , there was a difference between the observed seasonal increases . increases in incidence of fractures were higher in winter ( 4.7-fold increase ) and spring ( 4.4-fold increase ) than in fall ( 3.8-fold ) and summer ( 3.6-fold ) , suggesting that the elderly people are becoming at higher risk of falling in the cooler seasons . regarding fracture pattern , a definite increase was observed in unstable intertrochanteric fracture ( tronzo type iii , iv , v ) , which is usually caused by a severe fall . in 1991 , the proportion of unstable intertrochanteric fractures was 54% , which increased to 66% in 2001 ( p=0.006 ) . a significant increase in definite osteoporosis was noted , from 50% in the year 1991 to 70% in the year 2001 ( p<0.001 ) . a remarkable increase was observed in two age groups : 27% in the year 1991 to 48% in the year 2001 in those aged 50 - 59 yr ( p=0.012 ) and 37% in the year 1991 to 65% in the year 2001 in those aged group of 60 - 69 yr ( p<0.001 ) ( table 2 ) . our results confirm a rising trend in the absolute number of hip fractures from 247 in 1991 to 1,152 in 2001 , which is equivalent to a fracture incidence from 3.3 persons per 10,000 population in the year 1991 to 13.3 in 2001 , and an age - adjusted incidence from 3.74 persons per 10,000 population in the year 1991 to 13.3 in the year 2001 . this study also confirms rising trends in age - specific incidences of women and men , as illustrated in table 1 . an increase of 4.8-fold was observed in women and 3.1-fold increase in men in terms of fracture incidence during the 10-yr period from the year 1991 to 2001 . in the first limitation , there were patients who were not treated in the hospitals after hip fractures . as their number is very small compared with the number of hospital admission in the present medical system , the resulting underestimation of the incidence of these fractures is negligible . in the second limitation , patients developed the hip fracture in our study area were transferred to the other region in any cause . informations obtained from the hira were included all the patients who had hip fractures in our country . because we selected all the patients registered in the gwangju city and chonnam province among the above mentioned patients , the loss of patients who were transferred to outside the gwangju city and chonnam province could be prevented . in most industrialized countries ( 1 ) reported a 2.7-fold increase in fracture incidence over 27 yr in finland . ( 10 ) reported an increase of 59.7% in women and 42.2% in men in annual hip fracture numbers during the period 1972 - 1984 . in singapore , fracture incidences in 1957 - 1963 , were 106/10,000 in women and 148/10,000 in men for ethnic chinese and 44 in women and 52 in men for ethnic malays ( 11 ) . according to studies made in 1991 - 1998 ( 12 ) , these incidences increased to 410 in women and 168 in men for chinese and 264 in women and 71 in men for malay . these data mean that the increase in fracture incidence was from 3.7- to 6.0-fold in women and from 1.1- to 1.4-fold in men . in the present study , an increase in fracture incidence of 4.8-fold was observed in women and 3.1-fold in men during the 10-yr period from the year 1991 to 2001 . thus , our study demonstrates that the number of hip fractures in gwangju city and chonnam province , korea has increased at a rate that can not be explained by demographic changes alone . the precise reason for this are not known , but increases of osteoporosis and injurious falls of the elderly could partly account for the difference . the incidence of osteoporosis and an increased propensity for injurious falls have been proposed as factors frequently in the literature ( 1 , 13 - 16 ) . these factors include increased body height , greater occurrence of associated systemic diseases , poorer nutrition including calcium and vitamin d , more frequent use of drugs ( particularly psychotropic drugs ) , greater consumption of tobacco and alcohol , a less active life style , poorer general mobility including an impaired gait , balance , proprioception , reaction times , and muscle strength ( 1 , 13 , 15 , 17 ) . as a possible explanation for the rising incidence observed in the present study , three factors are suggested by our results . firstly , there was an increase in the elderly population from 20.6% of the total population in the year 1991 to 24.8% in the year 2001 . secondly , bone weakness increased due to osteoporosis . patients with definite osteoporosis increased substantially from 50% in the year 1991 to 70% in the year 2001 . a remarkable increase was observed in two age groups , i.e. , 27% in the year 1991 to 48% in the year 2001 for those aged 50 - 59 yr , and 37% in the year 1991 to 65% in the year 2001 for those aged 60 - 69 yr . as compared with the year 1991 figures in the year 2001 fractures increased more so in winter ( 5.5-fold ) and in spring ( 5.3-fold ) than in the summer ( 4.0-fold ) and fall ( 4.2-fold ) , suggesting that the elderly people are becoming at higher risk of falling in the cooler seasons . in addition , the proportion of unstable intertrochanteric fracture increased from 54% in 1991 to 66% in the year 2001 . in conclusion , the reasons for this rising trend of hip fracture in gwangju city and chonnam province , korea , were not fully explained . however , an increase in the elderly population , an increase in osteoporosis , and an increase in injurious falls could partly account for the observed increase .