Osteoporos Int (2006) 17: 143–149
DOI 10.1007/s00198-005-1947-8
O R I GI N A L A R T IC L E
Risk factors for fracture of the shafts of the tibia and fibula in older
individuals
Jennifer L. Kelsey Æ Theresa H.M. Keegan
Mila M. Prill Æ Charles P. Quesenberry Jr.
Stephen Sidney
Received: 13 October 2004 / Accepted: 10 May 2005 / Published online: 9 August 2005
International Osteoporosis Foundation and National Osteoporosis Foundation 2005
Abstract A case-control study to identify risk factors for
fracture of the shafts of the tibia and fibula among
persons 45 years of age and older was undertaken in five
Northern California Kaiser Permanente Medical Centers during 1996–2001. One hundred seventy-nine cases
of newly diagnosed fracture of the tibia/fibula shaft and
2,399 controls sampled from the membership lists of the
same five medical centers were included. Information on
potential risk factors was obtained by a standardized
questionnaire administered by trained interviewers. The
number of previous fractures was associated with an
increased risk [adjusted odds ratio (OR) (95% confidence interval) =1.49 (1.09–2.03) per previous fracture].
Attributes known or thought to be associated with
protection against loss of bone mass, including high
body mass index [adjusted OR =0.82 (0.69–0.97) per
5 kg/m2 increase], having ever used thiazide diuretics or
water pills for at least 1 year [adjusted OR =0.62 (0.38–
1.02)], and current use of menopausal hormone therapy
among females [adjusted OR =0.84 (0.53–1.32)] tended
to show decreased risks. Factors generally associated
with lower bone mass, such as current cigarette smoking
[OR =1.55 (1.01–2.39)] and, to some extent, lack of
physical activity [OR =1.31 (0.87–1.96) for the lowest
quartile compared to the upper three quartiles], tended
to demonstrate increased risks. The number of falls in
the past year and risk factors for falls were not associJ.L. Kelsey Æ T.H.M. Keegan Æ M.M. Prill
Department of Health Research and Policy,
Stanford University School of Medicine,
Stanford, CA, USA
J.L. Kelsey (&)
Division of Preventive and Behavioral Medicine,
University of Massachusetts Medical School,
55 Lake Avenue North, Shaw Building, Worcester,
MA 01655, USA
E-mail: Jennifer.Kelsey@umassmed.edu
Tel.: +1-508-8568549
Fax: +1-508-8562022
C.P. Quesenberry Jr. Æ S. Sidney
Division of Research, Kaiser Permanente Medical Care Program,
Oakland, CA, USA
ated with tibia/fibula shaft fractures, and indicators of
health status were weakly and inconsistently associated
with risk. Thus, this study suggests that risk factors for
low bone mass, but not health status or risk factors for
falls, may be important in the etiology of fracture of the
shaft of the tibia/fibula in older individuals.
Keywords Epidemiology Æ Fibula shaft
fracture Æ Osteoporosis Æ Risk factors Æ Tibia shaft
fracture
Introduction
Fractures of the shafts of the tibia and fibula in older
people are not common, but can be quite disabling when
they do occur. Based on data from the U.S. Medicare
population, Barrett et al. [1] estimated that among persons at an age of 65 years, 1.3% of White females, 0.5%
of White males and 0.9% of Black females will fracture
the shaft or proximal end of the tibia or fibula by the
time they reach age 85. Among older people, females are
at greater risk than males, and Whites are at slightly
higher risk than Blacks [1, 2, 3, 4, 5, 6, 7]. Most studies
show that incidence rates in females increase somewhat
with age starting at around 55–65 years, but little increase with age is seen for males at these older ages [2, 3,
6]. Across all ages, on average these fractures require a
stay in the hospital of more than a week [8].
Seeley et al. [9] have shown that in women of age
65 years and older, ‘‘leg’’ fractures (not including the
hip, foot, toe, patella, and ankle) are associated with low
bone mineral density and are usually caused by minimal
or moderate trauma. Honkanen et al. [10] found that
risk for fracture of the tibia (excluding the ankle) was
elevated in lactose-intolerant women of ages 38–
57 years, although it was unclear whether this was
attributable to the lower calcium consumption of the
lactose intolerant women. Otherwise, little is known of
risk factors for fracture of the shaft of the tibia/fibula in
144
older individuals. In this paper, we report the results of a
case-control study to identify risk factors for fracture of
the shaft of the tibia/fibula.
Subjects and Methods
This case-control study of fracture of the shaft of the
tibia/fibula was part of a larger case-control study to
identify risk factors for fractures of five sites: distal
forearm, foot, proximal humerus, pelvis and shaft of the
tibia/fibula. Cases and controls were identified during
the period October 1996 to May 2001 from five Northern California Kaiser Permanente Medical Centers:
Hayward, Oakland, San Francisco, Santa Clara and
South San Francisco. Details of the study design have
been described previously [11, 12] and will be presented
relatively briefly here. The study was approved by the
Institutional Review Boards of the Kaiser Permanente
Division of Research and the Stanford University
School of Medicine.
Cases
All fractures of the shafts of the tibia and/or fibula in
females and males of 45 years of age and older at the
time the fracture was diagnosed were identified each
week from computerized radiology reports and medical
records by a trained medical record abstractor. The
fracture had to be confirmed by X-ray, bone scan or
magnetic resonance imaging to be included. Persons
with previous fracture of the shaft of the tibia/fibula at
age 45 years and older were excluded from these analyses. Pathologic fractures resulting from diseases such as
Paget’s disease and cancer were also excluded. If a person had simultaneous fractures of multiple sites in
addition to the tibia/fibula shaft, only cases in which the
fracture of the tibia/fibula shaft was listed first on the
medical record among the five fracture sites considered
in this study were included in these analyses. Participation among eligible cases was 77.6%.
Controls
Controls were randomly selected within gender and age
groups from the membership lists of the same five Kaiser
Permanente medical centers over the same period of
time. Because the same controls were used for each of
the five fracture sites included in the overall study,
controls were not specifically matched to cases with tibia/fibula shaft fracture, but rather were chosen so that
there would be sufficient numbers across the age range of
the study. Every 3 months the computerized Kaiser
membership lists were stratified by gender and nine 5year age groups. Within each gender and age group the
members were randomly ordered and the first 34 females
and 7 males selected. All who belonged to a minority
group or were of unknown race/ethnicity and 39% of
white females and 78% of white males were randomly
chosen. Controls with a previous fracture of the shaft of
the tibia/fibula since age 45 years of older were excluded
from these analyses. The participation among the selected and eligible controls was 65.5%.
Collection of data on possible risk factors
Most information on possible risk factors was obtained
using a standardized questionnaire administered by
trained interviewers in English or Spanish. For the first
3 years of the study, most of the interviews were inperson; after 15 November 2000, most interviews were
conducted over the telephone in order to enhance participation and to increase numbers. No evidence was
found of effect modification by mode of interview; that
is, the associations between potential risk factors and
tibia/fibula shaft fracture were similar in those interviewed in-person (112 cases and 999 controls) and by
telephone (67 cases and 1,400 controls). The mode of
interview is included as a covariate in the analyses. Data
from proxy respondents (2 cases and 75 controls) are
included, but could not be considered as a separate
stratum because of the small numbers of cases.
The questionnaire covered the period of time before
the fracture for cases and before the interview for controls. Areas covered in the questionnaire were demographic characteristics; weight and height (used to
compute body mass index: weight in kilograms divided
by height in meters squared); handedness; a family history of hip fracture; a history of practitioner-diagnosed
medical conditions (diabetes; angina, a heart attack or
heart failure; stroke or a blood clot in the brain; epilepsy, seizures, convulsions, or fits; kidney disease; cataracts; glaucoma; Parkinson’s disease; arthritis;
depression; cancer; hyperthyroidism; hypothyroidism);
self-reported foot problems; a history of certain neuromuscular symptoms in the past year; a history of fractures; a history of use of selected medications (thiazide
diuretics, water pills, Tums, other calcium supplements,
multivitamins, melatonin, steroid pills, and seizure
medications) at least once per week for at least 1 year,
and recent use of medications to help sleep, calm nerves
or lift mood. Detailed questions, taken from the Women’s Health Initiative [13], were asked of women about
the use of menopausal hormone therapy for at least
3 consecutive months, and about age at last menstrual
period and prior hysterectomy and/or oophorectomy
[14]. Overall health status compared to others of similar
age was queried.
Measurement of physical functioning covered ability
in the past month to do heavy housework; walk up and
down stairs; walk half a mile without help; pull or push
objects; stoop, crouch or kneel; lift 10 lbs; extend the
arms above shoulder level; and write or handle small
objects. Ability to perform activities of daily living in the
145
past month covered using the telephone, getting groceries, getting to places outside of walking distance,
preparing meals, doing chores around the house, taking
medications, and handling finances.
Leisure-time physical activity was assessed by questioning participants about the frequency and duration of
walking/hiking, gardening, exercise classes, swimming,
bicycling, tennis, calisthenics/weight training, social
dancing, jogging, bowling, golfing, stretching exercises
or yoga, Tai Chi, and heavy housework in the past year.
Questions modified from the Physical Activity History
questionnaire [15] were used. The data obtained were
converted into metabolic equivalent hours of exercise
per month [16]. A calcium-validated food frequency
questionnaire [17], to which a few ethnic foods were
added, was used to assess dietary calcium intake. Data
on cigarette smoking, alcohol consumption, a history of
falling, and the immediate cause and circumstances
surrounding the fracture were also obtained. Vision was
assessed by asking participants whether they could see
well enough to recognize a friend across the room and
by a short test of visual acuity. Hearing loss was assessed
by two questions about use of a hearing aid.
Ten percent of participants agreed to a slightly
abbreviated interview that did not include questions on
dietary calcium intake, physical activity, cigarette
smoking, and part of the medication history. Because of
the reduction in sample size for these variables, analyses
involving them are based on somewhat smaller numbers
than other analyses.
Statistical analysis
Data were analyzed using SAS version 8.2 software. The
odds ratio, which approximates the relative risk, was
used as a measure of the magnitude of the association
between putative risk factors and fracture of the shaft of
the tibia/fibula. All odds ratios were adjusted by
unconditional logistic regression for the sampling variables 5-year age group, gender, and race/ethnicity as
recorded in Kaiser records (white versus nonwhite or
unknown), and whether the interview was conducted in
person or by telephone. Age in years and self-reported
race/ethnicity (White, Native American or other; Asian
or Pacific Islander; Black; Hispanic) were also included
to control more tightly for these variables. Unconditional logistic regression was also used to control for
several other variables associated with fracture of the
shaft of the tibia/fibula. When odds ratios are shown
according to quartiles, the distribution of the variable in
the control group was used to create the quartile
boundaries.
Effect modification by gender, age, race/ethnicity,
and selected other variables was assessed both by visual
inspection and by including cross-product terms in logistic regression models. Because of the relatively small
number of cases, we had little power to detect effect
modification, but little evidence of it was apparent.
Consequently, all subgroups are combined in the analyses.
Results
One hundred seventy-nine cases and 2,399 controls were
included (Table 1). The number of female cases (n
=103) exceeded that of male cases (n =76). About 90%
of the cases were younger than 75 years of age. There
were fewer members of minority racial/ethnic groups
among the cases than controls, but in this study minority
controls were oversampled, whereas all cases of tibia/
fibula fracture were included.
Seventy-three percent of tibia/fibula shaft fractures
occurred as a result of a fall. Eighteen percent were
attributed to motor vehicle accidents, 5% to recreational
accidents, 3% to the bone just breaking, and 1% to
other causes. Little difference was seen between odds
Table 1 Number (and percentage) of cases (n =179) and controls (n =2,399) by gender, age and race/ethnicity
Characteristic
Females
Males
Cases
Age (years)
45–54
55–64
65-74
75–84
85+
Total
Race/ethnicity
White, Native American and Other
Asian/Pacific Islander
Black
Hispanic
30
37
24
8
4
103
Controls
(29.1)
(35.9)
(23.3)
(7.8)
(3.9)
(100.0)
Cases (females
and males)
118
10
24
27
(65.9)
(5.6)
(13.4)
(15.1)
513
456
451
363
102
1885
Cases
(27.2)
(24.2)
(23.9)
(19.3)
(5.4)
(100.0)
Controls (females
and males)
1,268
480
415
236
(52.9)
(20.0)
(17.3)
(9.8)
34
25
11
6
0
76
Controls
(44.7)
(32.9)
(14.5)
(7.9)
(0.0)
(100.0)
120
130
119
107
38
514
(23.4)
(25.3)
(23.1)
(20.8)
(7.4)
(100.0)
146
ratios computed with and without the inclusion of
fractures in which the immediate cause was a multiple
vehicle accident. Therefore, all cases were included in
subsequent analyses in order to maximize sample size.
Table 2 presents the prevalence in the control group
of several characteristics of interest, and Table 3 shows
odds ratios for the relation between these characteristics
and tibia/fibula shaft fracture, first adjusted for the design variables only (third column) and then adjusted for
the design variables and all the other variables in the
table (fourth column). Among factors that may be in
part markers of low bone mass or to affect fracture risk
through their effect on bone mass, the number of previous fractures since age 45 was associated with increased risk. High body mass index, use of thiazide
diuretics or water pills, and current use of menopausal
hormone therapy, generally thought to be protective
against loss of bone mass, were associated with decreased risks, although the use of menopausal hormone
Table 2 Percent prevalence of selected characteristics among 2,399
controls
Characteristic
Percent
prevalence
At least one fracture since age 45
Body mass index (kg/m2) ‡25.0
Ever used thiazide diuretics/water pills
Current use of menopausal hormone
therapy (females only) a
Current smokerb
Leisure-time physical activity <18 MET
hours per month in past yearb
Dietary calcium <800 mg/day in past yearb
Ever used calcium supplements for ‡1 year
Fell at least twice in past year
Self-reported poor or fair health status
Has at least one neuromuscular symptomc
Has difficulty performing one or more
physical functionsd
Needs help or unable to do at least one
activity of daily livinge
Self-reported history of one or more
practitioner-diagnosed diseasesf
5.6
53.6
20.2
21.3
11.6
25.1
60.6
32.1
11.4
16.5
59.5
37.3
41.1
66.0
therapy was based on only the 103 women and did not
reach statistical significance. Current cigarette smoking
and to some extent lack of leisure-time physical activity,
thought to be associated with low bone mass, were
associated with increased risks. Higher dietary calcium
intake and use of calcium supplements, which would be
expected to be associated with higher bone mass, did not
have much effect on risk.
The number of falls in the past year was not associated with tibia/fibula shaft fracture. Factors thought to
increase the risk for falls, such as vision problems,
hearing problems, and epilepsy or use of seizure medication, were also not associated with risk (data not
shown).
No clear picture emerged of the relation between
general health status and risk for fracture of the tibia/
fibula shaft. Self-reported fair or poor health, number of
neuromuscular symptoms reported, and difficulty with
or inability to perform various physical functions were
associated with somewhat decreased risks, although the
association for physical functioning was not as strong in
the multivariate-adjusted analysis as in the analysis adjusted only for design variables. In contrast, needing
help or inability to perform activities of daily living was
associated with a slightly increased risk, an association
that was somewhat stronger in the multivariate-adjusted
analysis than in the analysis adjusted only for design
variables. As noted above, lack of physical activity,
which may be an indicator of poorer health, was also
associated with a slightly increased risk. Number of
diseases reported was not associated with risk, and none
of the individual diseases queried was associated with an
elevation or reduction in risk (data not shown). Use of
physical aids was also not associated with tibia/fibula
shaft fracture (data not shown).
Other variables, including height, vision problems,
hearing problems, foot problems, other lower extremity
problems, maternal history of hip fracture, oophorectomy or hysterectomy, alcohol consumption, and use of
any of the other medications queried, were not associated with risk.
a
Current use refers to use in the month before fracture for cases and
before interview for controls and continuously used for at least
3 months. bExcludes 16 cases and 265 controls who were given
abbreviated interviews. See Methods for explanation of abbreviated interview. cNeuromuscular symptoms include numbness or
weakness in the feet or legs, problems with balance or unsteadiness,
limping, tremors or shakes, dizziness or lightheadedness, difficulty
walking in dim light and pain, numbness, burning or tingling in the
legs or feet when not walking. dHas some or a lot of difficulty or
unable to perform one or more physical functions including heavy
housework, walking up and down stairs, walking half a mile
without help, pulling or pushing objects, stooping, crouching or
kneeling, lifting 10 lbs, extending arm above shoulder level, writing
or handling small objects. eActivities of daily living include using
the telephone, getting groceries, getting to places beyond walking
distance, preparing meals, doing chores around the house, taking
medications and handling finances. fDiseases queried were diabetes,
angina, a heart attack or heart failure, stroke or a blood clot in the
brain, epilepsy, seizures, convulsions or fits, kidney disease, cataracts, glaucoma, Parkinson’s disease, arthritis, depression, cancer,
hyperthyroidism and hypothyroidism
Discussion
These results suggest that among older individuals,
fracture of the shaft of the tibia/fibula may tend to occur
among those who have low bone mass, but who do not
show any particular propensity to fall, and whose health
status, on balance, is not much different from people
who do not fracture.
Our finding that indicators of low bone mass may be
associated with an increased risk is consistent with the
report of Seeley et al. [9] of a strong correlation between
measured bone mineral density and risk for fractures of
the lower leg exclusive of the hip, foot, toe, patella, and
ankle. A history of fractures since age 45 years, which, it
should be noted, has been found to be associated with a
risk for fractures above and beyond its association with
Yes/no, one or more physical functionsh
Per activity
Per disease
Yes/no
Yes/no
Yes/no
Lowest quartile vs. all othersf
Per 500 mg/day
Yes/no
Per fall
Fair/poor vs. good/excellent
Per symptom
1.49 (1.09–2.03)
1.53 (0.80–2.92)
1.94 (0.72–5.23)
0.82 (0.69–0.97)
0.80 (0.56–1.16)
0.67 (0.43–1.05)
0.62 (0.38–1.02)
0.84 (0.53–1.32)
1.55 (1.01–2.39) e
1.31 (0.87–1.96) e
1.04 (0.84–1.28) e
0.86 (0.59–1.26)
1.01 (0.98–1.03)
0.70 (0.43–1.13)
0.86 (0.77–0.96)
0.90 (0.61–1.34)
0.59 (0.40–0.88)
0.71 (0.49–1.04)
1.17 (1.00–1.37)
1.02 (0.89–1.17)
Adjusted
(179 cases, 2,399 controls)
(0.38–1.14)
(0.49–1.37)
(0.99–2.45)
(0.91–2.23)
(0.85–1.31)
(0.60–1.39)
(0.99–1.04)
(0.36–1.20)
(0.75–1.01)
0.83 (0.52–1.34)
1.29 (1.04–1.61)
1.06 (0.89–1.26)
0.66
0.82
1.56
1.42
1.05
0.91
1.01
0.66
0.87
0.81 (0.66–0.99)
1.53 (1.09–2.15)
Multivariate-adjusted
(154 cases, 1,997 controls)
Odds ratio (95% confidence interval)
c
Adjusted for gender, 5-year age group, Kaiser-reported race/ethnicity, in-person vs. telephone interview, age in years and self-reported race-ethnicity. bAdjusted for gender, 5-year age
group, Kaiser-reported race/ethnicity, respondent status (self vs. proxy), in-person vs. telephone interview, age in years, self-reported race/ethnicity and all the other variables in the
table. cExcludes cases and controls with missing values for the variables included in the tables. See Methods for explanation of abbreviated interviews, which account for most of the
missing values. dCurrent use refers to use in the month before fracture for cases and before interview for controls and continuously used for at least 3 months. eExcludes 16 cases and
265 controls who were given abbreviated interviews. See Methods for explanation of abbreviated interview. fLowest quartile: <18 MET hours per month of leisure-time physical
activity. gNeuromuscular symptoms include numbness or weakness in the feet or legs, problems with balance or unsteadiness, limping, tremors or shakes, dizziness or lightheadedness,
difficulty walking in dim light and pain, numbness, burning or tingling in the legs or feet when not walking. hHas some or a lot of difficulty or unable to perform one or more physical
functions including heavy housework, walking up and down stairs, walking half a mile without help, pulling or pushing objects, stooping, crouching, or kneeling, lifting 10 lbs,
extending arm above shoulder level and writing or handling small objects. iActivities of daily living include using the telephone, getting groceries, getting to places beyond walking
distance, preparing meals, doing chores around the house, taking medications and handling finances. jDiseases queried were diabetes mellitus, angina, a heart attack or heart failure,
stroke or a blood clot in the brain, epilepsy, seizures, convulsions or fits, kidney disease, cataracts, glaucoma, Parkinson’s disease, arthritis, depression, cancer, hyperthyroidism and
hypothyroidism
a
Per fracture
Number fractures since age 45
1 fracture versus none
2+ fractures versus none
Body mass index (BMI) (kg/m2)
BMI 25.0–29.9 versus <25.0
BMI ‡30.0 versus <25.0
Ever thiazide diuretic/water pill use for ‡1 year
Current use of menopausal hormone therapyd
Current smoker
Leisure-time physical activity (MET hours per month in past year)
Dietary calcium intake (mg per day, past year)
Ever used calcium supplements for ‡1 year
Number of falls in past year
Self-reported health status
Number neuromuscular symptomsg
1 symptom versus none
2+ symptoms versus none
Has difficulty performing
Number of activities of daily living with which needs help or unable to doi
Number of diseases reportedj
Per 5 units
Unit
Variable
Table 3 Adjusteda and multivariate-adjustedb odds ratios (and 95% confidence intervals) for the associations between selected variables and fracture of the shaft of the tibia/fibula
147
148
low bone mineral density [18], was associated with an
increased risk in this study. A protective effect of greater
body mass index, as suggested by these data, is probably
attributable to the higher endogenous estrogen and testosterone concentrations in obese individuals and to the
greater mechanical stress on weight-bearing bones [19].
The mechanism for a possible protective effect of thiazide diuretics, if such an effect exists for fractures of the
shaft of the tibia/fibula, is not known with certainty, but
is believed to be related to lower calcium excretion [19].
Current use of menopausal hormone therapy is known
to protect against loss of bone mass and fracture of most
sites [19, 20], but the number of women in this study was
not large enough to show a statistically significant effect.
An increased risk from cigarette smoking is consistent
with the findings that smoking is associated with lower
endogenous estrogen concentrations and lower bone
mass [21]. Lack of physical activity may be a risk factor
because of its association with lower bone mineral
density [22]. It can also be considered a marker of frailty,
but other indicators of frailty were not strongly associated with tibia/fibula shaft fracture in this study.
The lack of association in our study with previous
falls and with fall-related risk factors finds some support
from the European Vertebral Osteoporosis Study.
Among the 30 centers included in that study, a moderate
correlation was noted between the incidence of falls and
the incidence of upper limb fractures, but little correlation was found between the incidence of falls and the
incidence of lower limb fractures [23].
Although a propensity to fall may not be a risk factor
for tibia/fibula shaft fracture, how a person falls when
she/he does fall appears to be of significance. In a previous publication from this study, Keegan et al. [24]
reported that among controls who had fallen at least
once in the previous year and cases who attributed their
fracture to a fall, tibia/fibula shaft fractures were associated with non-vigorous outside activity, falling from
more than a standing height, falling sideways, straight
down and particularly falling in multiple directions
(such as backward and sideways) and tumbling or rolling. Wearing high-heeled shoes was associated with an
increased risk, while putting out a hand or grabbing or
hitting something with the body to break a fall was
protective. Also, as noted above, 18% of fractures of the
shaft of the tibia/fibula in this study were attributed to
motor vehicle accidents. Thus, common sense measures
such as avoiding situations in which one falls from a
substantial height, wears high-heeled shoes, or is involved in a motor vehicle accident, as well as breaking a
fall with an outstretched hand or other means, may reduce the incidence of these fractures. Breaking a fall with
an outstretched hand would, however, increase the risk
for a distal forearm fracture [24].
To our knowledge no previous studies have considered health status in relation to risk for fracture of the
shaft of the tibia/fibula. In the present study, the associations were weak and varied according to the indicator
of health status used. Although more study is needed
before any conclusions are reached, health status does
not appear to be a major risk factor for fracture of the
shaft of the tibia/fibula. The relatively modest increase in
incidence rates with age reported in other studies [2, 3, 6]
also suggests that fracture of the shaft of the tibia/fibula
is not mainly a fracture of frail, elderly people.
There are several limitations to this study. It was a
case-control study, and was therefore dependent upon
participants to remember and report past events.
Undoubtedly some inaccuracies in remembering and
reporting occurred. However, a prospective study of a
relatively uncommon occurrence such as fracture of the
tibia/fibula shaft would require a very large study population. Although the 179 cases included in this study
make it by far the largest study to date of risk factors for
fracture of the shaft of the tibia/fibula, we had limited
power to detect small associations or to examine subgroups. We did, however, have adequate power to detect
moderate or strong associations. For instance, power
was 92% to detect an odds ratio of 2.0 if only 10% of
the controls were exposed to a factor, and 81% to detect
and odds ratio as low as 1.7 for factors to which 15% of
the controls were exposed.
In summary, the study of Seeley et al. [9] and the
present study indicate that people with low bone mass
may be at increased risk for tibia/fibula shaft fractures,
but otherwise these fractures may be hard to predict.
Thus, on the basis of the limited available information,
preventive measures include preservation of bone mass
and employing general common sense to avoid hazardous situations created by falling from more than a
standing height, wearing high-heeled shoes and being
involved in motor vehicle accidents. Further study is
needed, however, before firm conclusions can be reached.
Acknowledgements This study was supported by grants from the
National Institute of Arthritis and Musculoskeletal Diseases (R01
AR42421 and T32 AR07588). We thank Beverly Peters and Luisa
Hamilton for project management, Michael Sorel for computing
and database management and Carolyn Salazar for medical record
abstraction.
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