Association between pain in the hip region and radiographic changes of osteoarthritis: Results from a population-based study

Abstract

The relationship between hip pain and radiographic change in the population is unclear due to lack of agreed definition for hip pain and difficulties in obtaining radiographs from asymptomatic random samples. Our objective was to assess the relationship between hip pain and radiographic change in osteoarthritis (OA) in a population sample aged over 45.
One thousand and seventy-one responders to a postal questionnaire using a recently validated approach to defining hip pain were stratified into hip pain-positive and -negative groups and samples of each were X-rayed and scored for OA using both minimum joint space and the Croft score. The association between pain and X-ray score was estimated, weighting back to the age and gender distribution of the original population.
Hip pain prevalence was 7% in males and 10% in females. Severe OA was present in 16% of those with and 3% of those without pain. Adjusting for age and gender, there was a very strong association of pain with severe OA [odds ratio (OR) 17.4, 95% confidence interval (CI) 3.0-102], but no association with mild/moderate OA (OR 1.4, 95% CI 0.4-4.7). By contrast, only 22% of men aged 45-54 with severe OA had current pain, though in older age groups the proportions with pain were higher (54-70%).
Hip pain is relatively infrequent in the general population compared with the published reports of other regional pain syndromes. Mild/moderate radiographic change is very frequent and not related to pain, whereas severe change is rare but strongly related. In younger males, severe radiographic change is much less likely to be associated with pain.

Full text

Rheumatology 2004; 1 of 5 doi:10.1093/rheumatology/keh458
Association between pain in the hip region and
radiographic changes of osteoarthritis: results from
a population-based study
F. Birrell
1,3
, M. Lunt
1
, G. Macfarlane
2
and A. Silman
1
Objectives. The relationship between hip pain and radiographic change in the population is unclear due to lack of agreed
definition for hip pain and difficulties in obtaining radiographs from asymptomatic random samples. Our objective was to assess
the relationship between hip pain and radiographic change in osteoarthritis (OA) in a population sample aged over 45.
Methods. One thousand and seventy-one responders to a postal questionnaire using a recently validated approach to defining
hip pain were stratified into hip pain-positive and -negative groups and samples of each were X-rayed and scored for OA using
both minimum joint space and the Croft score. The association between pain and X-ray score was estimated, weighting back to
the age and gender distribution of the original population.
Results. Hip pain prevalence was 7% in males and 10% in females. Severe OA was present in 16% of those with and 3% of
those without pain. Adjusting for age and gender, there was a very strong association of pain with severe OA [odds ratio (OR)
17.4, 95% confidence interval (CI) 3.0–102], but no association with mild/moderate OA (OR 1.4, 95% CI 0.4–4. 7). By
contrast, only 22% of men aged 45–54 with severe OA had current pain, though in older age groups the proportions with pain
were higher (54–70%).
Conclusions. Hip pain is relatively infrequent in the general population compared with the published reports of other regional
pain syndromes. Mild/moderate radiographic change is very frequent and not related to pain, whereas severe change is rare but
strongly related. In younger males, severe radiographic change is much less likely to be associated with pain.
Regional pain syndromes such as anterior knee pain are very
commonly reported in general population surveys [1, 2]. Although
in the majority of those subjects reporting pain there is considered
to be no underlying pathology, in clinical practice the reporting of
such pain is frequently a signal for radiographic examination to
exclude the presence of underlying degenerative disease as the
source of the pain. In population-based epidemiological studies,
any associations between pain reporting (for example, of the knee)
and the presence of osteoarthritic changes have been weak [3].
Pain in the hip region appears to be less common than other
regional pain syndromes [4]. Hip pain is, however, important
for the affected individual as it impacts on key functions, such as
walking. The importance of hip pain for health-care providers
results from its association with osteoarthritis (OA) and the
potential need for joint replacement. Hip OA is the most frequent
indication for hip arthroplasty [5] and unremitting pain the most
important clinical determinant of need for surgery [6]. The ‘hip’,
however, is a difficult region to define topographically compared
with, for example, the shoulder or knee. Referred pain from the
back and disorders of structures in and around the inguinal
and pelvic areas all might present with pain in similar areas to
that resulting from true hip disease. Similarly, compared with
more superficial joints, subjects have difficulty in localizing the
hip as the source of their pain. Indeed, there are no well-accepted
definitions of hip pain for epidemiological studies.
We have recently shown that the optimal definition of hip pain is
one that requires the subject both to use the word ‘hip’ in referring
to the site of their pain in addition to indicating the presence of
pain in the ‘bathing trunk’ area on a validated preshaded manikin
[7]. Such a stringent definition demonstrated much stronger
associations with indicators of hip disease, such as restriction in
movement and health-care utilization, than less rigid definitions
requiring either just the verbal or just the manikin definition [8].
However, the strength of the relationship between radiographic
change and hip pain in the general population is not known. Such
studies require the radiographic investigation of asymptomatic
subjects and, for this reason, there are few data. We have therefore
investigated the relationship between radiographic damage and hip
pain in a large population sample. We have specifically addressed
two related questions: (i) given the presence of radiographic
change, how frequent is hip pain? and (ii), given the presence of
hip pain, how frequent is radiographic change? Thus, we wanted to
determine from the first question what proportion of severe OA,
for example, would be missed by consideration of those only
with current hip pain; and from the second question the value
of undertaking a radiograph in those with pain.
Methods
Design
This was a two-stage population screening survey: subjects
completed a questionnaire asking about hip pain, and samples
of those with and without pain were invited for radiographic
Correspondence to: A. Silman: a.silman@manchester.ac.uk
1
arc Epidemiology Unit and
2
Unit of Chronic Disease Epidemiology, School of Epidemiology and Health Sciences, Manchester University Medical School,
Manchester M13 9PT, UK.
3
Present Address: University of Newcastle, Cookson Building, Framlington Place, Newcastle NE2 4NH, UK.
Submitted 5 July 2004; revised version accepted 30 September 2004.
Rheumatology ß British Society for Rheumatology 2004; all rights reserved
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assessment. Associations between pain and OA were then
calculated based on weighting the X-ray results of those
participating in the second phase to the population that were
initially sent a questionnaire.
Subjects
The sampling frame was the population listing from a general
practice population in the south of Manchester and has been
described in detail elsewhere [8]. This investigation was restricted
to subjects aged over 45, and a total of 1496 subjects were selected
for mailing a questionnaire.
Ascertainment of hip pain
The presence of current hip pain was determined using a postal
questionnaire. Two questions were used to determine the occur-
rence of hip pain. The subjects were asked (i) if they had had pain
in the hip for a period lasting more than 24 h in the previous
1 month, and (ii) to indicate on a manikin with a preshaded bathing-
trunk [7] area if they had had pain in that area during that period.
A positive respondent was one who reported hip pain using both
criteria. Subjects not responding to the questionnaire were sent a
postcard reminder within 2 weeks and a further questionnaire, if
necessary, after a further 2 weeks. The questionnaire also collected
data on a number of other aspects of hip pain and general health.
Radiographic follow-up
Random samples of those reporting and not reporting hip pain
were invited to attend a local hospital for a pelvic radiograph.
An anteroposterior pelvic film was taken in a standardized fashion
at a single centre. The X-rays were read blind to pain group by two
readers and graded using both the Croft modification of the
Kellgren and Lawrence (K&L) grading system [9]. The minimum
joint space (MJS) was also measured using a ruler, as previously
described by Croft et al. [9]. For the purposes of analysis, the scores
were stratified into three groups: (i) subjects with no OA (defined
as a K&L grade of <2 and MJS >2.5 mm); (ii) subjects with
mild to moderate OA (defined as a K&L score of at least 2 or
MJS <2.5 mm but not satisfying criteria for severe OA); and
(iii) subjects with severe OA (defined as a K&L score of at least 4 or
MJS <1.5 mm).
Analysis
The subjects invited for radiographic investigation were not a
random sample of the original population but were weighted
towards studying a greater proportion of hip pain-positive
compared with hip pain-negative subjects. Further, both age and
gender were strongly related to the presence of any radiographic
change. Thus, for the purposes of analysis, the subjects were
stratified by age (in 10-yr age groups) and gender. We therefore
assumed that in each of the two pain groups the distribution of
radiographic changes in those studied was the same as that in those
subjects with the same age and gender profile, who answered the
questionnaire but were not selected or attended for X-ray. We used
the sampling weights for these two variables to estimate the
population occurrence of radiographic change. The data are thus
presented first as the estimated population prevalence of radio-
graphic change in subjects with and without pain, and secondly as
the estimated population prevalence of hip pain in subjects with
and without radiographic change. The confidence intervals (CIs)
for the population prevalences were calculated using the ‘svytab’
procedure in Stata 8.0 (Stata Corporation, College Station, TX,
USA), which uses a standard formula for calculating the standard
error of a prevalence in a two-stage sampling design such as this
[10]. To examine the influence of pain on X-ray grade, logistic
regression analyses were undertaken, adjusting for age and
stratified by gender, where appropriate.
The study was approved by the Local Research Ethics
Committee and written subject consent was obtained.
Results
A total of 1496 subjects were mailed a questionnaire and, after the
two reminders, completed questionnaires were received from 1071.
A further 123 were notified as being sent to the wrong address.
Thus, the final adjusted response rate of those receiving the
questionnaire was 78%. The responders comprised 556 males and
515 females. The age- and gender-specific hip pain prevalences are
shown in Table 1. Overall, the prevalence was 6.8% in the males
and 10.3% in females. As shown, the prevalence was higher in
females at all ages except for those over the age of 75. A total of 82
subjects with hip pain and 308 without hip pain were invited
to attend for radiographic screening (women aged <50 were not
invited), of whom 56 (68%) and 147 (48%), respectively, attended.
An analysis within each pain group, comparing those who
attended for X-ray with those who did not, showed no evidence
of any participation bias in relation to the severity indicators
derived from the questionnaire. Thus in the hip pain group,
compared with those who did not, those who attended for X-ray
had similar visual analogue pain scores as well as similar
proportions of those using analgesics and requiring a walking
stick for their pain.
The distributions of radiographic score between those with and
without pain are shown in Table 2. There was a marked difference
between the two groups, as expected (
2
¼ 12.9, P ¼ 0.002). The
frequency of severe change was substantially larger in the group
with pain (16 vs 3%), and the absence of change was more common
in those without pain. However, mild/moderate OA was very
common in this population, with an equal high frequency of such
changes in both those with and without pain.
Age and gender were expected to have powerful effects on the
likelihood of radiographic change. Indeed, there were substantial
differences in the occurrence of radiographic change (independent
of pain frequency) between the genders and with age. Allowing
for the proportions with and without hip pain, the estimated
population prevalence of radiographic change by age and gender,
together with their 95% CIs, are shown in Table 3. These data
show that severe change was exceptionally rare in women at
TABLE 1. Prevalence of hip pain by age and gender
Men Women
Age group (yr) n Hip pain % n Hip pain %
45–54 220 10 4.6 227 22 9.7
55–64 169 12 7.1 140 14 10.0
65–74 117 7 6.0 95 12 12.6
75–84 50 9 18.0 53 5 9.4
TABLE 2. Frequency of radiographic change by presence/absence of pain
Radiographic severity
No OA
n (%)
Mild/moderate OA
n (%)
Severe OA
n (%)
No pain (n ¼ 147) 60 (41) 83 (56) 4 (3)
Pain (n ¼ 56) 16 (29) 31 (55) 9 (16)
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all ages. Further, and unexpectedly, there was very little influence
of age on the occurrence of OA in men. It should be noted,
however, that these prevalences, once stratified by age and gender,
are based on very small numbers and as a result the CIs are wide.
The estimated prevalences of radiographic change in the
population were then stratified by pain status (Table 4). Women
were excluded from this analysis, given the virtual absence of
severe OA from this group. The data show that in each age group
those men with pain were substantially more likely to have severe
OA, with no influence on the likelihood of mild to moderate OA.
A weighted multinomial logistic regression analysis was under-
taken, adjusting for age, and this showed that the odds ratio (OR)
for mild/moderate OA in those with pain was 1.4 (95% CI 0.4–4.7),
with a much greater association with severe OA (OR 17.4, 95%
CI 3.0–102).
The final analysis was to evaluate the estimated population
prevalence of hip pain in those with and without evidence of OA
(Table 5). As discussed above, despite the higher prevalence of
pain in the women, there were virtually no women in this sample
with severe OA. In men, hip pain was more likely to be reported in
those with severe OA, but not by those with mild OA. Hip pain
was much less frequent in young men with severe radiographic
change (estimated prevalence 22%) and much higher in the other
age groups. The age-adjusted ORs for reporting pain in those with
mild to moderate OA and for those men with severe OA are the
same as above. The data for women, by contrast, do show an
association between mild to moderate OA and pain: OR 2.8, 95%
CI 0.94–8.6.
Discussion
In summary, these data have highlighted that the frequency of hip-
region pain as defined in the community is low compared with
other regional pain syndromes, such as those affecting the knee
[1, 2]. The criteria for hip pain used were stringent, though, as
others have shown, the prevalence of hip pain, using a broader-
based question, was much higher. Thus, a study from Oxford [4]
in subjects over 65 revealed a prevalence of 19%, approximately
twice that observed in the same age group in the present study.
Similarly, the frequency of severe radiographic change in the
population is low, especially in women, whereas the frequency of
mild to moderate OA changes are more common in this age group
than a ‘normal’ X-ray appearance. The major findings relate to the
limited association between pain and X-ray. As an example,
despite an obvious relationship between severe change and pain in
males, we estimate that 1 in 20 men aged 45–54 without current hip
pain have severe radiographic OA. Examining the results the other
way round showed that important proportions of men, especially
in the youngest age group investigated (45–54), with severe
radiographic OA do not have current pain. By contrast, there
is no important relationship between current pain and milder
forms of OA.
There are a number of limitations in interpreting these
data. First, and most importantly, the numbers in each age and
gender group with X-ray data are small. Age and gender did have
substantial influences on both the occurrence of radiographic
change and probably the relationship between pain and OA.
The number of individuals in this community survey who were
X-rayed was too small to provide robust estimates in the
age–gender groups, and such strata-specific proportions are subject
TABLE 4. Estimated prevalence of radiographic damage by hip pain status: men
Severity
No pain Pain
Age group (yr) None Mild Severe None Mild Severe
45–54 34 (8, 74) 61 (24, 89) 5 (1, 33) 23 (3, 76) 45 (10, 85) 33 (6, 78)
55–64 53 (27, 77) 47 (22, 73) 1 (0, 6) 38 (12, 74) 38 (12, 74) 24 (5, 64)
65–74 56 (29, 80) 42 (19, 70) 1 (0, 7) n/a 71 (29, 94) 29 (6, 71)
75–84 44 (27, 63) 53 (34, 71) 3 (1, 13) 44 (14, 80) 30 (7, 71) 26 (6, 67)
Data are % (95% CI). n/a, numbers too small for calculation.
TABLE 3. Estimated (weighted) population prevalence of radiographic change
Radiographic severity
Men Women
Age group (yr) None Mild Severe None Mild Severe
45–54 33 (9, 72) 60 (25, 88) 7 (1, 30) 45 (23, 70) 55 (30, 77) 0
55–64 52 (27, 75) 46 (23, 71) 2 (1, 8) 33 (19, 50) 67 (50, 81) 0
65–74 53 (28, 77) 45 (21, 70) 3 (1, 9) 55 (31, 78) 43 (21, 68) 1 (0, 9)
75–84 35 (13, 67) 52 (35, 69) 5 (2, 12) 28 (7, 67) 72 (33, 93) 0
Data are % (95% CI).
TABLE 5. Estimated (weighted) prevalence of hip pain in subjects with
and without radiographic damage
Prevalence of hip pain: % (95% CI)
Age group (yr) None Mild Severe
Men
45–54 3 (0, 28) 3 (1, 17) 22 (2, 84)
55–64 5 (1, 19) 6 (1, 21) 70 (12, 98)
65–74 n/a 10 (3, 28) 67 (11, 97)
75–84 22 (5, 64) 6 (3, 37) 54 (6, 95)
Women
45–54 n/a 15 (5, 38) n/a
55–64 18 (7, 38) 5 (2, 15) n/a
65–74 4 (1, 19) 20 (7, 44) n/a
75–84 n/a 14 (4, 44) n/a
n/a, numbers too small for calculation.
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to wide CIs. It is, however, not easy to obtain pelvic X-rays from
true population samples, which is why alternative strategies have
been used, such as reading films from intravenous urograms [9].
Secondly, and perhaps surprisingly, we found only one woman
from the 109 with X-rays who had severe OA, and as a
consequence we are unable to usefully comment on the relation-
ship between pain and severe OA in women. Clinical experience
demonstrates that severe hip OA clearly exists in women and
the virtual absence of this state in the current cohort might reflect
the population scarcity of this grade of OA, or possibly a selective
non-response or non-participation of those women with the worst
disease. The latter seems intuitively unlikely as typically it is
those with the relevant health problem who are more likely
to respond to survey participation.
Thirdly, the nature of the study design meant that hip pain
subjects were more likely to be sampled for radiological examina-
tion. As one aim was to ascertain the relationships between pain
and X-ray change in the whole population, we assumed that that
the former would be the same between those who were and were
not X-rayed. It is difficult to be certain about the correctness of
this assumption, though analysis of certain characteristics related
to hip pain severity in those with hip pain who were and were not
X-rayed does not suggest any important selection bias.
The response rates to the questionnaire were high and should
not have influenced the external validity of these results. The
participation rates for those selected for X-ray were lower and
selectively different when those with and without pain were
compared. It is obviously difficult to encourage those who were
pain-free to attend for radiographic examination. It is possible that
those who did may have selected themselves on characteristics
such as previous injury [11], family history [12] or obesity [13],
all of which might have resulted in a bias towards those with
OA changes. The study population was also drawn from a
single general practice population, and again the associations
between hip pain and X-ray change may not be applicable to other
groups, which might have a different underlying prevalence of
disorders leading to either hip pain or OA. Thus, farming com-
munities have been shown to have a higher prevalence of OA
hip [14].
There are a number of strengths of the present study. First,
we used a validated definition for hip pain which has been
demonstrated to have greater construct validity with measures
of hip disease than definitions relying either on the use of the
word ‘hip’ or on a pain manikin alone [9]. Secondly, the X-rays
were taken and read in a standardized and blinded fashion; we
have previously reported on our reliability of reading hip X-rays
[7]. Thirdly, the population answering the first questionnaire
was large, with a high response. It was also possible within the
present study to obtain a number, albeit limited, of X-rays on
those with pain-free hips, a task of increasing difficulty as
both ethical and population concerns about X-rays increase in
society.
The prevalence of mild to moderate OA changes was, as noted
above, very high and indeed such change was more common than
a ‘normal’ radiograph. Further, such changes were not associated
with pain. The major conclusion from such observations is that
these degrees of radiographic change, although they might
represent an underlying anatomical change, are perhaps inappro-
priately considered as representing the disease state of clinical OA.
Therefore, the term ‘mild–moderate OA’ to describe such changes
is probably misleading.
It was interesting to note that the likelihood of reporting pain,
given the presence of severe OA, was substantially less likely in
younger men. This observation would add weight to the concept
that other factor(s) other than the degree of radiographic damage
contribute to pain. One explanation, impossible to test in a cross-
sectional study, is that age is a surrogate for ‘disease duration’
and that the younger men have had changes for a shorter period,
and it is the longevity of the change that contributes to pain.
This, however, would not explain why the rates of pain are not
highest in the oldest ages. Ageing itself may be accompanied by an
increase in pain perception, although in population surveys the
increased reporting of musculoskeletal pain with ageing is only
modest [15].
As noted in the Introduction, there are few studies with which
to compare these results. A study of intravenous urograms
from 1315 men aged 60–75 was used to provide a population
surrogate for identifying the frequency of different aspects of
radiographic hip OA. In total, 29% of a subset of 759 of these men,
who provided information, reported ever having had hip pain,
though again it was only in those with radiographic appearances
at the extreme (2%) end of the radiographic severity spectrum
that there was an association between pain and radiographic
feature [9].
There are, however, some interesting messages that emerge.
First, it would be inappropriate to conclude that an elderly patient
with hip region pain is inevitably likely to have OA. Secondly,
even severe radiographic change is relatively infrequently accom-
panied by continuing hip pain, and it is important to be cautious
before linking the pain with the X-ray. Thirdly, the majority of
younger male subjects in the community with severe OA will be
pain-free, and in subjects with other indicators of hip disease,
such as known childhood hip disorder, prior injury or limitation in
movement, severe OA could still be present.
Acknowledgements
This study was funded by the UK Arthritis Research Campaign
(arc) and F.B. was an arc research training fellow in
epidemiology. We are grateful to Dr Coope (The Waterhouse,
Bollington Medical Practice) and Dr Sanders (Cheadle Medical
Practice) and their staff for access to their patient population.
The survey was coordinated by Liz Nahit, who also assisted in
the reading of the radiographs.
The authors have declared no conflicts of interest.
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