Context The incidence of distal forearm fractures in children peaks around the
time of the pubertal growth spurt, possibly because physical activity increases
at the time of a transient deficit in cortical bone mass due to the increased
calcium demand during maximal skeletal growth. Changes in physical activity
or diet may therefore influence risk of forearm fracture.
Objective To determine whether there has been a change in the incidence of distal
forearm fractures in children in recent years.
Design, Setting and Patients Population-based study among Rochester, Minn, residents younger than
35 years with distal forearm fractures in 1969-1971, 1979-1981, 1989-1991,
and 1999-2001.
Main Outcome Measure Estimated incidence of distal forearm fractures in 4 time periods.
Results Comparably age- and sex-adjusted annual incidence rates per 100 000
increased from 263.3 (95% confidence interval [CI], 231.1-295.4) in 1969-1971
to 322.3 (95% CI, 285.3-359.4) in 1979-1981 and to 399.8 (95% CI, 361.0-438.6)
in 1989-1991 before leveling off at 372.9 (95% CI, 339.1-406.7) in 1999-2001.
Age-adjusted incidence rates per 100 000 were 32% greater among male
residents in 1999-2001 compared with 1969-1971 (409.4 [95% CI, 359.9-459.0]
vs 309.4 [95% CI, 259.3-359.5]; P = .01) and 56%
greater among female residents in the same time periods (334.3 [95% CI, 288.6-380.1]
vs 214.6 [95% CI, 174.9-254.4]; P<.001). The peak
incidence and greatest increase occurred between ages 11 and 14 years in boys
and 8 and 11 years in girls.
Conclusions There has been a statistically significant increase in the incidence
of distal forearm fractures in children and adolescents, but whether this
is due to changing patterns of physical activity, decreased bone acquisition
due to poor calcium intake, or both is unclear at present. Given the large
number of childhood fractures, however, studies are needed to define the cause(s)
of this increase.
Previous studies have shown that the incidence of distal forearm fractures
in children peaks during early adolescence around the time of the pubertal
growth spurt.1-3 This
observation has been explained on the basis of a transient increase in cortical
porosity that results from enhanced bone turnover in response to greater calcium
demand at the time of maximal longitudinal bone growth.4 Such
a process might be especially problematic given the thin cortex of the metaphyseal
region of the distal radius,5 and growth-related
structural changes in the metaphysis further compromise bone strength in the
distal forearm.6
Adolescence is also characterized by the increase in physical activity
necessary to maximize skeletal mass.7-9 Thus,
Parfitt4 has suggested that forearm fractures
in adolescence are "an inescapable consequence of an appropriate level of
physical activity, and [are] the price that has to be paid in order to maximize
bone accumulation during growth and minimize fracture risk in old age." To
some extent, then, forearm fractures in adolescence may represent a transient
imbalance between physical activity and acquisition of bone mass during puberty.
This relationship may have changed over the years, due either to changing
patterns of physical activity or to alterations in acquisition of bone mass,
related perhaps to changing dietary habits.
The incidence of distal forearm fractures among Rochester, Minn, residents
younger than 35 years in 1969-1971 was reported previously.10 The
purpose of the present investigation was to estimate the incidence of such
fractures among comparable Rochester residents 10, 20, and 30 years later
in 1979-1981, 1989-1991, and 1999-2001. In addition, we extended the newest
study in Rochester to include the remainder of Olmsted County, which is largely
rural. Thus, in addition to providing updated incidence rates for distal forearm
fractures in adolescence, and a comparison of urban with rural rates, we also
tested for possible changes in incidence over time.
Population-based epidemiologic research can be conducted in Rochester
because medical care is virtually self-contained within the community and
there are relatively few provider organizations. Through the medical records
linkage system provided by the Rochester Epidemiology Project, the details
of almost all of the medical care delivered to the residents are available
for study.11 We used this unique database to
identify all distal forearm fractures that occurred among community residents
younger than 35 years during the 3-year periods 1979-1981, 1989-1991, and
1999-2001, and we rereviewed previously published data for 1969-1971.10 Only a quarter of patients with forearm fracture
are hospitalized,12 but it was possible in
our data system to identify those treated solely on an outpatient basis. Moreover,
the indexing system is very redundant.
The complete (inpatient and outpatient) medical records were reviewed
for all local residents with any diagnosis attributable to rubrics 813.4 through
813.9 in the International Classification of Diseases, Ninth
Revision, Clinical Modification.13 In
accordance with Minnesota privacy law that took effect in 1997,14 we
had authorization to review the 265 cases reported in 1969-1971 and all 944
potential cases in 1979-1981, 1595 of 1610 (99%) in 1989-1991, and 2362 of
2383 (99%) in 1999-2001. The study was approved by the Mayo institutional
review board.
Patients were excluded if they were not residents at the time of fracture,
if their fracture occurred outside the time frame of the study, or if it was
a fracture of the shaft rather than the distal forearm. Except for 36 patients
who declined to provide the research authorization, fracture ascertainment
is believed to be complete,15 and ascertainment
methods were consistent over time.
All fractures, including torus fractures, were radiographically confirmed
at the time of injury. Fractures were classified according to etiology using
information about each event that was recorded in the medical record: those
caused by a specific pathological process (eg, osteogenesis imperfecta), those
due to serious trauma (a category combining fractures clearly resulting from
severe trauma, eg, motor vehicle crashes or falls from a height, with an intermediate
category made up of recreational and occupational injuries), and those due
to moderate trauma (by convention, the equivalent of a simple fall from standing
height or less).
Olmsted County is a Metropolitan Statistical Area and contains 1 centrally
located city, Rochester, and 13 small towns or villages. We determined that
each child was a resident of either Rochester or the remainder of Olmsted
County on the date of fracture. Rochester had about 86 000 residents
in 2000 and was considered "urban" for the purposes of this study. The remainder
of the county is mostly farming country with a 2000 population of 38 000.
Although no one in Olmsted County is more than 23 miles from sophisticated
medical care available at Mayo Clinic, the population density of the area
outside of Rochester is only 61.7 people per square mile. Thus, the balance
of Olmsted County was considered "rural" for the purposes of this study, even
though 4% of the overall county population lived on the outskirts of Rochester
in 2000 and another 7% lived in one small town.
In calculating incidence rates, the entire population of Rochester (or
Olmsted County) younger than 35 years was considered to be at risk. Denominator
age- and sex-specific person-years were estimated from decennial census data.16 In order to estimate the underlying variability,
it was assumed that, given a fixed number of person-years, the number of fracture
cases follows a Poisson distribution. This allowed for the estimation of SEs
and the calculation of 95% confidence intervals (CIs) for the incidence rates.
Overall rates were directly age- or age-sex–adjusted to the population
distribution of US whites younger than 35 years in 2000. The SEs and CIs for
the adjusted rates were based on the same assumption as above.
The relationships of crude incidence rates to age, sex, and time period
(1969-1971 vs 1979-1981 vs 1989-1991 vs 1999-2001) or age, sex, and residence
(urban vs rural) were assessed using generalized linear models assuming a
Poisson error structure.17 Such models fit
the natural logarithms of the crude incidence rates as linear combinations
of sex, age group, residence, and time period. In our modeling, we first fit
sex and age group, testing for an interaction between them. Differences between
the 4 time periods were assessed using the subset of Rochester data alone.
Using the 1990-2001 data for all of Olmsted County, the difference between
residence (urban vs rural) was then assessed. Model fit was evaluated using
the model deviance, which is a measure of how well the observed and predicted
incidence rates agree. The model fits the data reasonably well if the expected
value of the deviance is approximately equal to its degrees of freedom. The
distributions of moderate and serious trauma fractures between Rochester residents
and residents of rural Olmsted County in 1999-2001 and between Rochester residents
in the various time periods were compared using the Pearson χ2 statistic.
All analyses were carried out in SAS version 8.02 (SAS Institute Inc, Cary,
NC), with P<.05 used to determine statistical
significance.
There were 1458 total fractures in these time periods. The number of
fractures increased from 265 in 1969-1971 to 469 in 1999-2001 (Table 1). The overall annual age- and sex-adjusted incidence of
distal forearm fractures per 100 000 Rochester residents younger than
35 years increased from 263.3 (95% CI, 231.1-295.4) in 1969-1971 to 322.3
(95% CI, 285.3-359.4) in 1979-1981 and to 399.8 (95% CI, 361.0-438.6) in 1989-1991
before leveling off at 372.9 (95% CI, 339.1-406.7) in 1999-2001. Overall,
comparably age- and sex-adjusted annual incidence rates were 42% greater (P<.001) in 1999-2001 compared with 1969-1971. The rates
per 100 000 were 32% greater among male residents in 1999-2001 compared
with 1969-1971 (409.4 [95% CI, 359.9-459.0] vs 309.4 [95% CI, 259.3-359.5])
and 56% greater among female Rochester residents in 1999-2001 (334.3 [95%
CI, 288.6-380.1] vs 214.6 [95% CI, 174.9-254.4]). The increase in incidence
was statistically significant for both male (P =
.01) and female residents (P<.001), but the rate
of increase did not differ significantly between the 2 groups (P = .31). As is evident from Table
1, the discrepancy was almost entirely due to differences in fracture
rates for Rochester residents younger than 20 years. However, the overall
age-specific pattern was relatively unchanged from one time frame to the next
(Table 1).
To obtain additional insight into the secular change in incidence, we
compared causes of the distal forearm fractures among Rochester residents
in the 4 time periods (Table 2).
There was a slight decline in the relative proportion of fractures due to
simple falls, but this was related to an absolute increase in fractures due
to serious trauma. In fact, the age- and sex-adjusted annual incidence of
distal forearm fractures due to moderate trauma in 1999-2001 was very similar
to the rate in 1969-1971 (72.7 per 100 000 [95% CI, 56.2-89.2] vs 69.6
per 100 000 [95% CI, 55.1-84.1]). The increase in fractures due to serious
trauma, eg, from 179.0 per 100 000 (95% CI, 152.2-205.8) in 1969-1971
to 293.8 per 100 000 (95% CI, 263.7-323.9) in 1999-2001, completely accounted
for the overall change in fracture rates between the 2 time periods. This
increase, in turn, was explained by an increase in the fractures associated
with recreational activities (Table 2).
The annual incidence of fractures due to recreational injuries doubled, from
114.7 per 100 000 (95% CI, 93.5-135.9) in 1969-1971 to 228.6 per 100 000
(95% CI, 202.0-255.2) in 1999-2001 (P<.001). However,
the distribution of recreational injuries by type was fairly comparable across
the time periods (Table 3), although
there was some increase associated with skiing and skating (especially skateboarding
and rollerblading) among boys and with basketball, soccer, and skating among
the girls. Injuries on playground equipment, included in the category of other
recreational causes, accounted for 10% of all distal forearm fractures in
1999-2001 and for a similar 6% in 1969-1971.
In the most recent 3-year period, 1999-2001, we had the opportunity
to compare urban with rural distal forearm fractures and to estimate the overall
incidence for Olmsted County as a whole. All together, 661 county residents
younger than 35 years experienced a total of 690 fractures, giving an overall
age- and sex-adjusted annual incidence rate of 361.6 per 100 000 (95%
CI, 334.6-388.6) for this age group. There were 385 fractures among male and
305 among female residents of Olmsted County. The annual incidence among male
residents was 394.1 per 100 000 (95% CI, 354.7-433.6) compared with 327.2
per 100 000 (95% CI, 290.4-363.9) among female residents, for a male
to female ratio of age-adjusted incidence rates of 1.2:1 (P = .01). The incidence of fractures varied strikingly with age in
both sexes (Figure 1), with the
highest rate among girls between the ages of 8 and 11 years and boys between
11 and 14 years. Peak annual rates were 1277 per 100 000 for girls aged
11 years and 1536 per 100 000 for boys aged 12 years. All together, 632
individuals (95% of the female and 96% of the male residents) experienced
a single distal forearm fracture during the 3-year study period, but 8 male
and 6 female residents had 2 separate fractures while 7 male and 8 female
residents experienced bilateral distal forearm fractures. For 332 male (90%)
and 259 female residents (89%), the initial distal forearm fracture observed
during the study period was the first such fracture that the individual had
ever experienced.
The overall age- and sex-adjusted annual incidence rate in 1999-2001
was 10% greater among the residents of the central city of Rochester (372.9
per 100 000; 95% CI, 339.1-406.7) compared with those living in the rural
portion of Olmsted County (340.2 per 100 000; 95% CI, 294.7-385.8) as
shown in Table 4 (P = .58). Age-adjusted rates were 13% greater among urban than among
rural male residents (P = .81) and 5% greater comparing
female residents of Rochester with female residents of rural Olmsted County
(P = .58), but neither difference was statistically
significant. There was also no significant difference in the distribution
of causes when comparing Rochester residents with the residents of rural Olmsted
County (P = .45). All together, 79% of the distal
forearm fractures among young Olmsted County residents in 1999-2001 resulted
from serious trauma. Again, this was mostly in conjunction with recreational
activities, which accounted for 420 fractures. An additional 72 fractures
were caused by falling from greater than standing height, while 18 were due
to motor vehicle crashes and 38 to occupational and other injuries. One hundred
twenty-six fractures (18%) were due to moderate trauma. The final 16 forearm
fractures could not be confidently ascribed to a specific injury.
These results demonstrate a significant increase in the incidence of
distal forearm fractures among children in Olmsted County, Minnesota, between
1969-1971 and 1989-1991, with a leveling off in 1999-2001. Although the increase
could be partly due to more aggressive treatment of these injuries in recent
years, this is unlikely to account for an overall increase in distal forearm
fractures of 56% in female and 32% in male residents. Moreover, investigators
in other settings have made similar observations. Landin1 documented
an overall increase in distal forearm fractures of roughly 60% in girls and
35% in boys in Malmö, Sweden, between 1950 and 1979, and a subsequent
study revealed a further 31% increase in girls but no change in boys between
1975-1979 and 1993-1994.18 Likewise, Danish
investigators estimated that fracture rates had increased 33% in girls and
5% in boys between 1975-1979 and 1985.2 Overall,
Jónsson and colleagues19 reported a
60% increase in distal forearm fractures among Swedish boys aged 10 to 19
years between 1953-1957 and 1991-1992, although they saw no increase among
girls in Malmö. In the comparable time frame, 1989-1991, annual Rochester
rates for 10- to 19-year-old boys and girls were similar to those reported
for Malmö (for boys, 85 in Rochester vs 57 per 10 000 in Malmö
and, for girls, 34 vs 29 per 10 000, respectively). By contrast, there
was no change in rates of distal forearm fracture among Rochester residents
35 years and older between 1969-1971 and 1989-1991.15 This
has been confirmed by other investigators who found no change in incidence
even among children.20
As have others,1,3,19,21-25 we
documented a greater incidence of distal forearm fractures in boys than in
girls. There was little difference between the sexes before age 5 years, but
fracture rates rose rapidly thereafter to peak among girls aged 8 to 11 years
and boys aged 11 to 14 years. These results are consistent with those of other
researchers2,3 who have found
that the peak incidence of distal forearm fractures spans the pubertal growth
spurt, which reaches its maximum around age 12 years in girls and age 14 years
in boys.8 Moreover, the greater height velocity
in boys than in girls (4.9 vs 2.9 cm per year) may help explain the excess
of distal forearm fractures in boys,3 although
different injury patterns may also contribute. Generalized deficits in bone
density have been reported for girls with distal forearm fractures.26,27 However, the subsequent rapid decline
in fracture rates, which also was observed by Bailey and colleagues,3 points to a more transient process. According to Parfitt,4 the pubertal growth spurt entails a dramatic increase
in the requirement for calcium that is met by an increase in intracortical
bone turnover; when growth velocity slows, the cortical porosity is corrected
with a concomitant increase in bone mass. Thus, the cessation of longitudinal
growth in the distal radius after age 12 years in girls and age 14 years in
boys is accompanied by a rapid increase in cortical thickness and bone strength.6
Since cortical porosity5 and increased
bone turnover28 could both be expected to impair
bone strength at an age when physical activity is high,3 these
fractures may well represent an imbalance between the demands placed on the
skeleton by the increase in physical activity and the ambient bone mass.4 However, the increase in incidence that we observed
between 1969-1971 and 1999-2001 also suggests either that the pattern of physical
activity has changed, that acquisition of bone mass is being impaired, or
both. Previous investigators linked both the increasing incidence of distal
forearm fractures and the convergence of female with male rates to greater
participation in sports and recreational activities.1,2,18 Similarly,
we found an increase in fractures due to recreational activities, and the
fact that forearm fractures were more frequent in the summer months reinforces
this notion. This indicates that at least part of the explanation for our
findings may lie with changes in physical activity. Indeed, national data
indicate a substantial number of distal forearm fractures attributable to
rollerskates or in-line skates in recent years.29 Others
have suggested instead that decreasing physical activity may be more important
by inducing overweight; thus, the increase in distal forearm fractures could
relate to skeletal overloading by obesity,27 which
is also increasing among children.30 In other
countries, where obesity is less prevalent, reduced physical activity in recent
years has been associated with fewer forearm fractures.18
Although we were unable to directly address the issue in a retrospective
study such as this, these data also raise concerns about whether acquisition
of bone mass may be impaired in the later time periods, perhaps related to
changing dietary habits. Over the past 20 years, there has been a dramatic
increase in the consumption of carbonated soft drinks, with a corresponding
decline in milk consumption.31,32 Among
girls aged 12 to 19 years, for example, consumption of soft drinks increased
from 207 to 396 g per day between 1977-1978 and 1994-1996, while milk consumption
fell from 303 to 189 g daily; overall, daily calcium intake declined slightly
from 784 to 771 mg/d for girls and remained unchanged at 1145 mg/d for boys.33,34 Both values are below the recommended
dietary allowance for calcium of 1200 mg/d for adolescents,35 the
1300 mg/d recommended for maximizing peak bone mass in this age group,36 or the 1300 mg/d recommended as an adequate intake
in the new dietary reference intake values.37 In
addition to changing dietary habits, other lifestyle factors, such as smoking
or other drug use, may also impair acquisition of bone mass; however, our
study was not designed to study these problems. We also were not able to study
the severity of fractures because different classifications were used over
the period.
In summary, our study demonstrates a significant increase in distal
forearm fractures in children and adolescents between 1969-1971 and 1999-2001,
although the results are based on estimates made at specific points in time.
The comparison is a fair one because we used comparable methods throughout
and rereviewed the 1969-1971 fractures previously reported,10 reassigning
diagnoses and etiologies as needed for consistency with the new data. Moreover,
these data are population-based and complete. However, Rochester is a small
midwestern community that is predominantly white and better educated than
the white population of the country as a whole.11 To
the extent that increasing rates of forearm fracture in childhood are a more
generalized phenomenon, there may be cause for concern. This is because distal
forearm fractures are a harbinger of additional osteoporotic fractures, at
least among adults,38-40 and
because impairments in childhood growth rates are associated with a dramatic
increase in risk of hip fracture later in life.41 Indeed,
a quarter of the bone mass in adult women and men is accumulated during the
adolescent growth spurt42 and it is essential
that adequate nutrition in childhood be ensured.43 Suggestions
for accomplishing this in practice have been published by the American Academy
of Pediatrics.44 In addition, further studies
are needed to determine whether the changes in the incidence of distal forearm
fractures are due primarily to increased physical activity, decreased acquisition
of bone mass, or both.
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