fractures occur when loads on the skeleton exceed the breaking strength of bone . among young adults , the skeletal loads causing rib fractures are generally due to high - energy traumatic events . in older adults , rib fractures often result from falls [ 1 , 2 ] , notably among alcoholic patients . however , most fractures in older individuals of both sexes are related also to impaired bone strength , as assessed clinically by bone densitometry , and an association between areal bone mineral density ( bmd ) and rib fracture risk was documented in the osteoporotic fractures in men ( mros ) cohort that was independent of other risk factors . associations of rib fractures with low bone density have also been observed among older women [ 5 , 6 ] , who account for the majority of all fractures in the population , but other potential risk factors have not been addressed in that group . this is an important limitation as interventions for bone loss and for other determinants of fracture risk ( e.g. , falls ) would likely differ . since rib fractures are associated with significant morbidity , mortality , and cost [ 79 ] , as well as an increased risk of subsequent fractures of other types [ 2 , 10 ] , it is important to evaluate the relative impact of bone density versus other contributors to rib fracture risk . we address this issue in an analysis of prospective data from a cohort of women and men randomly sampled from the community . after approval by mayo clinic 's institutional review board , subjects were recruited from age - stratified random samples of rochester , minnesota , women and men as described in detail previously . of 348 men who participated and provided full study data , there were approximately 50 subjects per decade of age from 2029 to 80 years and over ( mean age  sd , 55.4  19.6 years ; range , 22 to 90 years ) . among 351 participating women , there were also about 50 subjects per decade of age , including 138 premenopausal women ( age , 35.0  8.6 years ; range , 21 to 54 years ) and 213 women ( age , 67.8  13.2 years ; range , 34 to 93 years ) who were postmenopausal ( 6 or more months without menses and a follicle - stimulating hormone level > 20 subjects were interviewed by a study nurse using a standard protocol to collect clinical , demographic and lifestyle data . cigarette smoking and alcohol use were classified as ever / never , while self - reported heavy social or excessive alcohol consumption was considered heavy use . subjects were also queried about a history of prior fractures , and their complete ( inpatient and outpatient ) medical records in the community were reviewed by trained nurse abstractors to confirm fracture reports and collect information about a diverse array of conditions predisposing to secondary ( 2 ) osteoporosis ( e.g. , rheumatoid arthritis , hyperparathyroidism , malabsorption syndrome ) or to an increased risk of falling ( e.g. , stroke , epilepsy , parkinsonism ) [ 12 , 13 ] . height ( m ) and weight ( kg ) were measured , and body mass index ( bmi ) was defined as kg / m . physical activity ( kcal / week ) areal bmd ( g / cm ) was determined for the lumbar spine ( l2l4 in ap projection ) , femoral neck ( fn ) , and ultradistal radius using dual - energy x - ray absorptiometry ( dxa ) with the hologic qdr2000 device ( hologic , waltham , ma , usa ) and software version 5.40 . coefficients of variation ( cv ) for the spine , hip , and forearm bmd measurements were 0.6% , 1.8% , and 0.8% , respectively . ribs bmd was obtained from the ribs region of a total body scan on the same instrument . these subjects were then followed from baseline for the occurrence of any new fracture ( prospective cohort study ) by periodic interview and review of each subject 's medical record at every local medical care provider through 2008 . mayo clinic records , for example , contain the details of every inpatient hospitalization at its two affiliated hospitals ( st . marys and rochester methodist ) , every outpatient or office visit at the clinic , emergency room , or local nursing homes , as well as all radiographic and pathology reports , including autopsies . the medical records contained the clinical history and the radiologist 's report of each rib fracture , but the original x - rays were not available for review . because we reviewed all local inpatient and outpatient records for each subject , ascertainment of clinically evident fractures is believed to be complete , along with additional rib fractures found incidentally on x - rays taken for other purposes . recognizing that the actual skeletal loads involved are poorly defined , fractures were attributed to either ( 1 ) severe trauma ( e.g. , high velocity injuries like motor vehicles accidents or falls from a height ) , ( 2 ) no more than moderate trauma ( low velocity injuries , by convention , the equivalent of a fall from standing height or less ) , which encompassed a wide range of presumptive skeletal loads including those rib fractures that appeared to have been  spontaneous  ( e.g. , secondary to a fit of coughing ) , or ( 3 ) a specific pathological lesion ( e.g. , metastatic malignancy ) . in this context ,  trauma  is considered synonymous with the forces on bone regardless of the exact nature of the precipitating event . the association of rib fractures with bmd and other potential risk factors was evaluated using two basic methods of analysis , both carried out in sas ( sas institute , cary , nc , usa ) . the cumulative incidence of a new rib fracture was first estimated for up to 15 years using the kaplan - meier method . andersen - gill time - to - fracture regression models   were then used to assess the impact of various covariates ( e.g. , bmd , prior fracture history , heavy alcohol use , etc . ) on the relative risk ( hazard ratio ( hr ) ) of a subsequent rib fracture , separately for women and men . these models allow for multiple rib fracture episodes per subject , while accounting for the correlation structure . the dependent variable was time until rib fracture , and the independent variables were age , bmd , and the clinical characteristics at baseline . for both univariate and age - adjusted models , the assumption of proportional hazards was not violated for the variables considered . subsequently , 56 of them had 67 rib fracture episodes ( more than one rib could have been fractured in each episode ) during 8560 person - years ( p - y ) of followup ( median , 13.9 years per subject ; range , 1 day to 17 years ) . forty - six people had a single event , while nine had two and one individual had three separate rib fracture episodes . these included 33 women ( 9% ) with at least one rib fracture and 23 men ( 7% ) . counting episodes , the overall crude incidence of rib fracture was 7.8 per 1000 p - y ( 8.8 per 1000  p - y in women and 6.6 per 1000 p - y in men ) , while the estimated cumulative incidence of a rib fracture 15 years after baseline was 9.5% ( 10.1% in women and 9.0% in men ) . the median age at the first rib fracture during followup was 83 years for the women and 70 years for the men . the majority ( 73% ) of rib fractures were due to injuries conventionally attributed to no more than moderate trauma ; these included falls from a standing height or less in 23 cases , but no specific traumatic event was acknowledged in nearly 40% of the episodes , most of which were classified as  spontaneous  ( e.g. , coughing ) . severe trauma accounted for the remaining fractures ( 25% ) , including 7  rib fractures that occurred as the result of falling from greater than standing height . of note , 52% of the women with a rib fracture , as well as 26% of the men , had at least one traditional osteoporotic fracture ( i.e. , hip , spine , or distal forearm due to moderate trauma ) during followup . rib fracture risk increased with age ( hr per 10 years , 1.7 ; 95% ci , 1.52.0 ) and was slightly less in men than women ( p = 0.331 ) . the determinants of a rib fracture varied somewhat by sex , although adjustment for age substantially reduced associations with most risk factors ( table 2 ) . there was a significant age - adjusted association with previous rib fractures in women but not men , as 20 women had experienced a rib fracture prior to baseline compared to only four men . cigarette use , but not alcohol consumption , was associated with rib fracture risk among the women . however , there was an increased risk of rib fracture episodes with heavy alcohol use among both sexes in the unadjusted analysis . this was not independent of age , although heavy alcohol users ( 13% of the cohort ) accounted for 24% of all those with a rib fracture and a third of the subjects with multiple rib fracture episodes . in univariate analyses , greater bmi was protective , while less physical activity increased the risk of a rib fracture . likewise , diseases associated with a greater likelihood of falling or with secondary osteoporosis , as described in methods , were associated with an increased risk of rib fracture , but none of these associations was statistically significant after adjustment for age . among the women but not the men , low bmd at the fn , lumbar spine , and ultradistal radius also predicted an increased likelihood of a rib fracture during followup , as did ribs region bmd from the total body scan . in multivariable analyses , the independent predictors of a rib fracture among the women included age ( hr , 1.5 ; 95% ci , 1.12.1 ) , cigarette smoking ( hr , 2.2 ; 95% ci , 1.044.7 ) , and ultradistal radius bmd ( hr 1.8 ; 95% ci , 1.12.9 ) ; among men , age was the only independent risk factor ( hr , 1.5 ; 95% ci , 1.21.9 ) . for example , women who smoked were more likely to consume alcohol ( 94% ) or be heavy alcohol users ( 12% ) compared to never smokers ( 78% and 3% , resp . ) . likewise , ultradistal radius bmd was highly correlated with fn bmd ( r = 0.81 ; p < 0.001 ) , and the age - adjusted analysis revealed a statistically significant 1.7-fold overall increase in rib fracture risk per sd decrease in fn bmd among the women . in this group , however , the association was as strong for the 10 rib fractures attributed to severe trauma ( hr , 3.0 ; 95% ci , 0.99.4 ) as for the 31  rib fractures attributed to no more than moderate trauma ( hr , 1.5 ; 95% ci , 0.82.5 ) , although statistical power was correspondingly limited . even so , there was a significant 4.6-fold ( 95% ci , 1.514 ) increased risk of a severe - trauma rib fracture for each sd decrease in ribs region bmd . no overall age - adjusted association with bmd was observed among the men with rib fractures due to severe trauma , although they were somewhat younger than the women at the time of fracture ( median , 60.3 years versus 78.2 years ) . among men age 50 years and over , however , each sd reduction in ribs region bmd was associated with a 3.9-fold ( 95% ci , 1.212 ) increase in the risk of a rib facture attributed to severe trauma . despite the fact that they represent the most frequent clinically - evident fracture in older people [ 2 , 20 ] , rib fractures have received little attention relative to other common fractures . rib fractures do appear to be increasing with aging of the population ; and , like more traditional osteoporotic fractures , the risk of rib fractures increased with age and bmd among randomly sampled women in this prospective study . in this group , the age - adjusted hr per sd decrease in fn bmd was 1.7 , consistent with the 1.6-fold increase in rib fracture risk among women in the study of osteoporotic fractures , as well as the relative risk of an osteoporotic fracture ( 1.6-fold per sd decrease in fn bmd ) among white women generally . somewhat lower relative risk estimates by fn bmd were made in perimenopausal women . among the men in this study , there was no overall increase in rib fracture risk with lower fn bmd , nor was there any association between rib fractures and fn bmd among men in the dubbo osteoporosis epidemiology study . this contrasts with a recent report from mros , where there was a statistically significant relative rib fracture risk of 1.4 per sd decrease in total hip bmd , even after adjusting for other potential risk factors . other population - based studies have generally found more rib fractures in men [ 16 , 20 , 25 , 26 ] , but we found no male excess . moreover , just 25% of the rib fractures in our study population were attributed to severe trauma . noteworthy , however , is the finding that bmd appeared to be as strongly associated with the rib fractures attributed to severe trauma as with those attributed to no more than moderate trauma . it must be recognized , however , that the distinction between  severe  and  moderate  trauma in the bone field is only a convention aimed at countering early criticism that the impact of osteoporosis was exaggerated by including fractures resulting from trauma sufficient to break anyone 's bones ; the specific forces involved in these different fracture etiologies have not been well quantified . indeed , even among better studied wrist fractures , which almost invariably are described as caused by a fall forward on the outstretched arm ,  the actual orientation of the fall , and presumably the resultant forces , varies substantially . moreover , other studies have documented the fact that bmd predicts fractures attributed to high trauma events ( e.g. , motor vehicle accidents ) as well as it does to those resulting from presumed lower trauma such as falls [ 29 , 30 ] . the majority of rib fractures in this study were attributed to lesser degrees of trauma , especially falls from standing height and activities of daily living . because biomechanical loading ( e.g. , falling ) dominates bone strength with respect to fracture pathogenesis , interventions directed solely at improving bone density are unlikely to be completely effective in reducing the fracture burden in the population . in fact , osteoporosis and/or osteopenia only account ( i.e. , attributable risk ) for a quarter of the rib fractures observed among older women in the population , so other factors are clearly involved in the etiology . indeed , body sway was a more important determinant of rib fracture risk than was fn bmd in the dubbo osteoporosis epidemiology study , whereas falling and fn bmd predicted rib fractures comparably among men in the mros cohort . in the present investigation , risk factors for falling were somewhat more strongly associated with rib fracture risk than was bmd in the unadjusted analysis . both variables are strongly age - related , however , and the association with risk factors for falling was not statistically significant after adjusting for age in either sex . one particular risk factor for falling , heavy alcohol use , was associated with a 2-fold age - adjusted increase in rib fracture risk though this did not achieve statistical significance . the relation of bone density to social drinking is equivocal , but bone density may be impaired in alcohol abusers [ 3335 ] , who are also at increased risk of other fractures [ 33 , 36 ] . nevertheless , only one - quarter of the subjects with rib fractures in this study were considered heavy drinkers so prophylaxis focused solely on alcoholism would also be incomplete . in particular , it was a prospective study of randomly sampled community women and men with long followup and superior ascertainment of subsequent fractures . indeed , fracture ascertainment was likely more complete than for community residents generally   since we reviewed all community radiographic reports for each subject . the risk factors were recorded before any knowledge of resultant fractures , and fractures were documented in detailed medical records that spanned each subject 's entire period of residency in the community . the main limitation is the relatively small sample size , with correspondingly low numbers of rib fractures and reduced statistical power . in addition , only 13% of all subjects reported heavy alcohol use , as such individuals are typically underrepresented in community studies . also , our results are not generalizable to nonwhites because the study cohort and the underlying rochester population are largely white , although rib fractures appear to be less common in the non - white population . moreover , the local population is largely of northern european extraction , but age - adjusted hip fracture incidence rates from rochester are comparable to those for us whites generally . finally , the focus here is on fractures among older adults . as noted in the introduction , rib fractures in younger patients often are due to high - energy trauma , and premenopausal women and men under 50 years of age are not generally recommended for osteoporosis assessment . these limitations notwithstanding , from a clinical perspective , our findings indicate that older women presenting with a rib fracture should generally have a careful evaluation for osteoporosis and be prescribed pharmacologic therapy if appropriate . this is especially important as half of them did not experience a traditional osteoporotic fracture ( hip , spine , or wrist ) that might otherwise have prompted such a workup . even those older patients who present acutely in the emergency department with fractures resulting from severe ( ~high velocity ) trauma should be followed up with an osteoporosis evaluation as would be expected for women who present with a hip fracture due to a fall . finally , almost half of all rib fractures observed were precipitated by falls of various types . consequently , fall prevention strategies should also be considered in both women and men with a rib fracture .
to address the epidemiology of rib fractures , an age- and sex - stratified random sample of 699 rochester , minnesota , adults age 2193 years was followed in a long - term prospective study . 
 bone mineral density ( bmd ) was assessed at baseline , and fractures were ascertained by periodic interview and medical record review . during 8560 person - years of followup ( median , 13.9 years ) , 56 subjects experienced 67 rib fracture episodes . 
 risk factors for falling predicted rib fractures as well as bmd , but both were strongly age - related . 
 after age - adjustment , bmd was associated with rib fractures in women but not men . 
 importantly , rib fractures attributed to severe trauma were associated with bmd in older individuals of both sexes . 
 self - reported heavy alcohol use doubled fracture risk but did not achieve significance due to limited statistical power . 
 bone density , along with heavy alcohol use and other risk factors for falling , contributes to the risk of rib fractures , but no one factor predominates . 
 older women with rib fractures , regardless of cause , should be considered for an osteoporosis evaluation , and strategies to prevent falling should be considered in both sexes .