Natasja M. van Schoor, Johannes H. Smit, Jos W. R. Twisk, Lex M. Bouter, Paul Lips. Prevention of Hip Fractures by External Hip ProtectorsA Randomized Controlled Trial. JAMA. 2003;289(15):1957–1962. doi:10.1001/jama.289.15.1957
Author Affiliations: Institute for Research in Extramural Medicine (Drs Twisk, Bouter, and Lips and Ms van Schoor), Departments of Sociology and Social Gerontology (Dr Smit), Clinical Epidemiology and Biostatistics (Dr Twisk), and Endocrinology (Dr Lips), Vrije Universiteit Medical Center, Amsterdam, the Netherlands.
Context Several randomized controlled trials have been performed to examine
the effectiveness of external hip protectors in reducing the incidence of
hip fractures, but the results are controversial.
Objective To examine the effectiveness of hip protectors in reducing the incidence
of hip fractures in an elderly high-risk population.
Design, Setting, and Participants Randomized controlled trial of elderly persons aged 70 years or older,
who have low bone density, and are at high risk for falls. Participants lived
in apartment houses for the elderly, homes for the elderly, and nursing homes
in Amsterdam and surrounding areas in the Netherlands. They were enrolled
in the study between March 1999 and March 2001; the mean follow-up was 69.6
weeks. Of the 830 persons who were screened, 561 persons were enrolled.
Intervention External hip protector. Both groups received written information on
bone health and risk factors for falls.
Main Outcome Measure Time to first hip fracture. Survival analysis was used to include all
participants for the time they participated.
Results In the intervention group, 18 hip fractures occurred vs 20 in the control
group. Four hip fractures in the intervention group occurred while an individual
was wearing a hip protector. At least 4 hip fractures in the intervention
group occurred late at night or early in the morning. Both in univariate analysis
(log-rank P = .86) and in multivariate analysis (hazard
ratio [HR], 1.05; 95% confidence interval [CI], 0.55-2.03), no statistically
significant difference between the intervention group and control group was
found with regard to time to first hip fracture. In addition, the per protocol
analysis in compliant participants did not show a statistically significant
difference between the groups (HR, 0.77; 95% CI, 0.25-2.38).
Conclusion The hip protector studied was not effective in preventing hip fractures.
Worldwide, the annual number of hip fractures is expected to increase
from 1.66 million in 1990 to 6.26 million in 2050.1 This
is caused by not only the increasing number of elderly persons, but also an
increase in the age-adjusted incidence.2- 6 The
risk for hip fracture is higher among elderly persons who are institutionalized
than those living independently.7 The consequences
of hip fractures can be severe. During the year following a hip fracture,
the mortality rate is about 17% to 33%; after 1 year, 25% to 33% of patients
are severely disabled or cannot walk at all.8- 11 A
promising intervention in the prevention of hip fractures is the hip protector.12 When a person falls on the hip, the hip protector
is designed to absorb and/or shunt away the impact toward the soft tissues
to keep the force on the trochanter below the fracture threshold.
To date, 10 randomized controlled trials examining the effect of external
hip protectors on the incidence of hip fractures have been published to our
knowledge.13- 22 In
5 studies, hip protectors led to a statistically significant reduction in
the incidence of hip fractures13,14,16,17,19;
2 studies were borderline statistically significant15,22;
and 3 studies were not statistically significant.18,20,21 In
2 studies, only the fracture rate per fall was calculated.16,21 However,
4 of 10 studies were rather small (<200 participants)14,16,18,19;
and 5 studies did not use individual randomization to assign persons to the
hip protector or control group.13,15,17,19,22 In
2 relatively large studies that used individual randomization, hip protectors
were not effective in preventing hip fractures.20,21
The Amsterdam Hip Protector Study was designed to examine the effectiveness
of external hip protectors in the prevention of hip fractures. This large
randomized controlled trial used individual randomization to assign persons
to the intervention or control group to address some of the limitations of
The Amsterdam Hip Protector Study was designed as a randomized controlled
trial in which individuals were randomized to the hip protector group or to
the control group in a 1:1 ratio. The study enrolled residents of apartment
houses for the elderly, homes for the elderly, and nursing homes in Amsterdam
and surrounding areas in the Netherlands. Apartment houses for the elderly,
homes for the elderly, and nursing homes are characterized by increasing dependence
and care. Special adaptations, such as grip bars and adequate illumination,
are present in all 3 types of housing. In apartment houses, no nursing staff
is present, but home care can be provided.
All persons included in the study had to have a high risk for hip fractures.
The follow-up duration was at least 1 year for all participants (those who
started first continued in the study until the last participants had been
followed up for 1 year). The ethical review board at the Vrije Universiteit
Medical Center approved the study and all respondents (or their proxies in
case of cognitive impairment) gave informed consent.
The screening consisted of a bone density measurement and a fall risk
assessment. Bone density was assessed by an ultrasound measurement (broadband
ultrasound attenuation [BUA]) of the calcaneus.23 In
addition, the risk factors of (1) 1 or more falls during the previous half
year; (2) dizziness while standing up from a chair in the last 2 weeks; (3)
having had a stroke in the past with sustained neurological impairment (ie,
hemiparesis); (4) urinary incontinence; (5) low physical activity; (6) impaired
mobility; and (7) cognitive impairment were assessed.24,25 The
first 5 risk factors were assessed by interviewing the participant. When it
was not possible to interview the participant (eg, in case of cognitive impairment),
a nurse of the ward in which the participant was living was interviewed. Physical
activity was assessed by asking the participant if he/she did some walking,
cycling, or heavy household tasks during the last 2 weeks. Low physical activity
was defined as not performing these activities. Mobility was assessed by the
walking observation scale, which ranges from 1 (he/she cannot walk) to 5 (he/she
is able to walk independently for 100 m on any surface including stairs).26 Impaired mobility was defined as a score of 3 or
less. Cognitive impairment was defined as a score of 23 or less on the Mini-Mental
State Examination (range, 0-30).27 Individuals
living on a psychogeriatric ward were assumed to have a cognitive impairment,
but the head of the department was also consulted for confirmation.
Persons were included when they were aged 70 years or older, had low
bone density, and/or a high risk for falling as determined by (1) BUA of 40
dB/MHz or less; or (2) BUA between 40 and 60 dB/MHz and at least 2 risk factors
for falling; or (3) BUA between 60 and 70 dB/MHz and at least 3 risk factors
for falling. Furthermore, persons who were completely immobile or persons
who had sustained a hip fracture or had a hip prosthesis on both sides were
excluded from the study. We conducted a substudy that validated that persons
who were included in the study sustained more falls and fractures than the
persons not included in the study because of being at low risk for fractures
(data not shown).
Each individual at high risk for hip fracture was randomized to the
intervention or control group. Randomization was performed in blocks of 4
after stratification for sex and for age in women (≤80 years vs >80 years).
Our statistical department generated randomization lists by computer. All
persons living in the same home were first screened by the research assistants,
and subsequently randomized by one of the authors (N.M.S.), in the same sequence
in which they had been screened. Randomization lists were not available to
the research assistants.
Both groups received written information on bone health (eg, diet, sunshine
exposure) and external risk factors for falls (eg, loose carpets). In the
intervention group, all participants received at least 4 hip protectors or
5 in case of urinary incontinence. In the control group, participants did
not receive a hip protector. Participants and nurses were taught about the
increased risk for hip fracture among institutionalized elderly, and about
the causes and consequences of hip fractures. In addition, information and
instructions about the use of hip protectors were given. These instructions
included information about the mechanism of the protector, the importance
of wearing the hip protector at night, and laundering. Newsletters were sent
to nurses to emphasize the importance of compliance. Participants were not
blinded to group assignment because it is difficult to design a sham protector
that does not have a small protective effect. In the intervention group, a
hip protector (Safehip) of the energy-shunting type was used (Tytex, Ikast,
Denmark). The hip protector consists of 2 shell-shaped protectors, made of
polypropylene, which are sewn into special underpants and cover the greater
trochanter. Hip protectors were replaced in case of loss or damage.
The primary outcome measurement was time to first hip fracture. Falls
and fractures were assessed prospectively by using a participant-kept calendar.
Hip fractures and pelvic fractures were verified by the general practitioner.
Participants were instructed to complete the calendar on a weekly basis and
to mail the pages to the institute at the end of every 3 months for at least
1 year. When a participant was unable to complete the calendar, a nurse acted
as a proxy. When the calendar was not fully completed, completed incorrectly,
or not returned to the institute at the end of the 3 months, the participant
or nurse was contacted by 1 of the authors or research assistants.
Compliance with wearing hip protectors was assessed by unannounced visits
by one of the research assistants at 1, 6, and 12 months after inclusion in
the study. At this visit, the participant was checked to see if he/she was
wearing the hip protector and was interviewed about hip protector use.28 In addition, at the end of each period of the fall
and fracture calendar (1 period is 3 months), participants were asked whether
they were wearing the hip protectors when they fell.
According to our power calculation, 700 elderly persons had to be followed
up for 1 year to detect a clinically important reduction in the incidence
of hip fractures from 4% in the control group to 1% in the intervention group
(1-sided α = .05, β = .20). However, we enrolled only 561 participants,
so the power to detect a clinically important reduction (from 4% to 1%) in
the incidence of hip fractures was 74%. To increase the number of events and
therefore the power, the follow-up duration was extended (mean, 69.6 weeks).
This resulted in an incidence of hip fractures of 7% in the control group.
The power to detect a reduction (from 7% to 2%) in the incidence of hip fractures
was 89% (risk reduction of about 75%).
To examine the effect of external hip protectors on the incidence of
hip fractures, the intention-to-treat principle was followed. The unadjusted
relationship between the intervention (use of hip protectors) and time to
first hip fracture and time to death was examined using Kaplan-Meier survival
analysis. Second, the risk ratio for recurrent falling was calculated using
the Cox proportional hazards model with equal survival time for all participants.
The risk ratio was calculated instead of the odds ratio because the incidence
of recurrent falling was higher than 10% and therefore, the odds ratio would
have overestimated the effect. Individuals who fell recurrently were defined
as participants who fell at least twice within 6 months.29 Third,
type of institution, cognitive impairment, age, sex, and stratum (1 = men;
2 = women aged ≤80 years; 3 = women aged >80 years) were examined to determine
if they modified the relationship between the use of hip protectors and time
to first hip fracture using the Cox proportional hazards model. When an interaction
was statistically significant (P<.10), an interaction
term was added to the model. Fourth, potential confounders were added to the
model: type of institution, cognitive impairment, age, sex (if no interaction
was present), BUA, risk factors for falling, and recurrent falling. Fifth,
a per protocol analysis was performed. In this analysis, participants from
the intervention group were included in the analysis if they were compliant
at all unannounced visits (n = 78). In addition, participants and nurses from
the control group were asked to report when a participant from the control
group started wearing hip protectors. These persons were excluded from the
per protocol analyses (4 persons excluded; 281 included). Finally, the fracture
rate per fall was calculated for both the intervention and control groups.
The fracture rate per fall was also calculated for those who fell in the intervention
group who were reported to not have been wearing hip protectors during any
of the periods on the fall and fracture calendar vs those who fell who were
reported to have been wearing hip protectors during 1 or more periods. All
analyses were performed using SPSS statistical software (version 9.0.1, SPSS
Inc, Chicago, Ill).
In total, 830 elderly persons from 45 homes or apartment houses for
the elderly and nursing homes were screened for risk for hip fracture between
March 1999 and March 2001 and followed up for hip fracture through March 2002
(Figure 1). Of these, 561 persons
had a high risk for hip fracture and were assigned to the intervention (n
= 276) or control (n = 285) group by individual randomization. The hip protectors
were marked prior to distribution with the name and room number of the participant
(median time between randomization and start was 2 weeks). Both groups started
with the follow-up when the hip protectors were distributed. Eight persons
in the intervention group and 4 persons in the control group died before distribution
of the hip protectors in the intervention group. In addition, one person from
the intervention group was not able to start wearing hip protectors because
of a hip fracture on the day before randomization and then died. All persons
who were randomized to the intervention or control group were included in
the survival analyses. Total follow-up time was 357 person-years for the intervention
group and 398 person-years for the control group. The baseline characteristics
of both groups are presented in Table 1.
There was no significant difference between the intervention and control
groups with regard to time to first hip fracture in univariate analysis (log
rank P = .86; Figure
2). In the intervention group, 18 hip fractures occurred in 18 persons
(fracture rate of 5/100 person-years); and in the control group, 20 hip fractures
occurred in 19 persons (fracture rate of 5/100 person-years). In both groups,
one of the hip fractures occurred between randomization and distribution of
the hip protector. When excluding these hip fractures, the log-rank P value was .85.
Eighty-three persons died in the intervention group and 79 persons died
in the control group. Survival time until death was similar in the intervention
and control groups (P = .31). Furthermore, there
were 100 individuals who experienced recurrent falls in the intervention group
compared with 119 in the control group (risk ratio, 0.87; 95% confidence interval
[CI], 0.67-1.13). Also, the incidence of other fractures was comparable between
groups. In the intervention group, 16 other fractures occurred (including
2 pelvic fractures), and in the control group, 14 other fractures occurred
(including 3 pelvic fractures).
In multiple analyses, no effect modification was found. After adjustment
for confounding, no significant difference between participants from the intervention
and control groups was found with regard to time to first hip fracture (hazard
ratio, 1.05; 95% CI, 0.55-2.03). To test the assumption of proportionality,
an interaction term of treatment × 70 weeks was added to the model.
A cut-off value of 70 weeks was chosen to test whether the effect of hip protectors
on hip fractures was significantly different before and after 70 weeks (in Figure 2, the effect appears to be slightly
different before and after 70 weeks). This interaction term was not statistically
significant (P = .68), which indicates that the effect
of hip protectors on hip fractures was not significantly different before
and after 70 weeks.
Compliance with hip protectors at unannounced visits was 132 (61%) of
217 individuals after 1 month (42 individuals were visited too late and not
included), 110 (45%) of 246 after 6 months, and 85 (37%) of 230 after 12 months.28 Individuals who died before the compliance visit
were not included in the compliance calculation. During the interview, fewer
than 16% of the participants were found to be using the hip protectors at
While the overall compliance was moderate to good in this study, 4 of
18 persons from the intervention group were wearing hip protectors while fracturing
their hip (13 persons were not wearing hip protectors and in one hip fracture,
it was not clear). In 9 of 13 hip fractures that occurred without a hip protector
in the intervention group, the circumstances are known. One person fell immediately
after randomization before the hip protectors were distributed; 4 persons
fell late in the evening or early in the morning; 1 person was not wearing
hip protectors because the hip protectors were being washed; 1 person stopped
wearing hip protectors while bedridden and fell out of bed afterward; and
2 persons fell during the day (1 had stopped wearing hip protectors because
of aesthetic reasons).
In the per protocol analysis, 78 compliant participants from the intervention
group were compared with 281 participants from the control group. In the intervention
group, 4 hip fractures occurred in 102 person-years (fracture rate of 3.9/100
person-years). In the control group, 20 hip fractures occurred in 19 persons
in 394 person-years (fracture rate of 5.1/100 person-years). After adjustment
for confounding, persons from the intervention group had a 23% lower probability
of fracturing a hip than persons from the control group (Figure 3). However, this difference was not statistically significant
(hazard ratio, 0.77; 95% CI, 0.25-2.38).
Finally, the fracture rate per fall was calculated. In the intervention
group there were 18 hip fractures in 727 falls (fracture rate per fall of
2.5%) and in the control group there were 20 hip fractures in 1075 falls (fracture
rate per fall of 1.9%). In Table 2,
the hip fracture rates per fall are presented according to the number of periods
that participants from the intervention group (or their nurses) reported to
be compliant on the fall and fracture calendar.
Hip protectors were not effective in preventing hip fractures in this
study according to the intention-to-treat analysis. To examine whether this
was due to low compliance, a per protocol analysis was performed including
only those participants who actually wore hip protectors. In this analysis,
a 23% nonsignificant reduction in the incidence of hip fractures was observed
in the intervention group compared with the control group. In addition, a
lower fracture rate per fall was found for those who fell, in the intervention
group, and reported compliance for more calendar periods. However, the latter
2 analyses should be interpreted with caution because of low statistical power.
Finally, there were 4 persons in this study who fractured a hip while wearing
the hip protector, indicating that the impact efficacy of the studied hip
protector was less than expected.
To date, results of 11 randomized controlled trials have been published,
of which 4 studies (including our own) did not observe a statistically significant
reduction in the incidence of hip fractures.18,20,21 The
Cochrane review by Parker et al12 concludes
that hip protectors appear to reduce the risk for hip fracture within a selected
population at high risk for sustaining a hip fracture. However, the 4 negative
studies were not included in this review. When considering the type of hip
protector, the Safehip hip protector was used in 6 randomized controlled trials.
In 3 studies, the Safehip hip protector reduced the incidence of hip fractures
(1 at borderline statistical significance)13,19,22;
and in 3 studies it did not (including ours).18,20
Our study was performed among institutionalized elderly persons at high
risk for hip fracture. We believe that the results of this trial can be generalized
to most institutionalized elderly persons, because two thirds of the screened
population (561/830 persons) were at high risk for hip fracture. According
to our screening criteria, more than half of our patients were cognitively
impaired (the nursing home patients included were almost all cognitively impaired
patients because most patients with chronic medical conditions only were excluded
due to immobility). Cognitively impaired patients are an important group to
study because they are at high risk for hip fracture. It is unclear how the
compliance will be in psychogeriatric patients.19,30 In
the first study, it was reported that when demented patients acquire the habit
of wearing the hip protector, they usually continue to wear it. In the second
study, it was reported that dementia reduces the compliance.
The main strength of our study is that it was a large randomized controlled
trial (N = 561) that used individual randomization to assign persons to an
intervention (hip protector) or control group. In 2 other studies that were
both relatively large (N = 384 and N = 548, respectively) and used individual
randomization, hip protectors were also not effective in preventing hip fractures.20,21 However, in the second study, half
of the population was selected at random by the head of nursing, which may
have resulted in selection bias. In addition, in both studies fewer than 10
hip fractures occurred, indicating that the statistical power may have been
insufficient. Another important feature of our study is that it resembles
daily practice. The study was performed in 45 different homes for the elderly
and nursing homes in which nurses had to supervise the wearing of the hip
Some of the other studies concluding that hip protectors were not effective
in preventing hip fractures indicate that this may be due to a lack of power.
The realized power of our study to detect a clinically important reduction
from 4% to 1% in the incidence of hip fractures was 74%. We chose an expected
risk reduction of 75% because in 2 large studies that were performed before
we started our trial, risk reductions of 56% to 67% were found with a compliance
lower than 50%.13,15 However,
now that more studies are published, this risk reduction probably was overestimated.
The compliance in our study was moderate to good and similar to the
compliance in most other studies.13,15- 18,21,28 Compliance
was aided by newsletters, which emphasized points such as the importance of
wearing hip protectors at night. In addition, the unannounced visits may have
had a small positive effect because noncompliant participants were encouraged
to wear hip protectors at the end of the visit. The compliance at the unannounced
visits changed from 61% to 37% during follow-up. At the moment of hip fracture,
22% of the participants were wearing a hip protector (4/18 participants).
An important reason for this discrepancy in compliance is that fewer than
16% of the participants were wearing hip protectors at night, and 4 hip fractures
in the intervention group occurred late in the evening or early in the morning.
In the study by Jantti et al,31 which was performed
in nursing home residents, 59 of 207 falls occurred during the night. Compliance
at night might increase if the hip protector is made more comfortable. Another
possibility is to combine the hip protector with other interventions, such
as a movement sensor, which alerts the nurse when the patient is getting out
of bed; a softer hip protector during the night; or fall prevention strategies.32
Another problem we encountered is that the number of hip protectors
provided was not always sufficient. In some homes, it was not possible to
wash the hip protectors during the weekends and sometimes this resulted in
a shortage, especially in persons who were incontinent of urine. In our study,
1 person fractured a hip while all hip protectors were being washed. It is
possible that persons who were noncompliant at night or due to a shortage
of hip protectors were compliant during the unannounced visits and were included
in the per protocol analysis. This may have diluted the effects of this analysis.
In future research, it would be interesting to examine whether the use
of hip protectors influences the activity level of the participant. None of
the studies to date used a sham hip protector. Because the participants and
their nurses were not masked to the intervention, it is possible that the
presence of the hip protector changed the person's activity level, and subsequently
the risk for falls and fractures.
In conclusion, the studied hip protector was not effective in preventing
hip fractures in this study. Possible causes for this lack of effectiveness
include compliance, which was moderate to good during the day, but low at
night; and lower impact effectiveness than expected.