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Vol. 63, No. 12, December 2011, pp 4023–4030
DOI 10.1002/art.30589
© 2011, American College of Rheumatology
Association Between Cam-Type Deformities and
Magnetic Resonance Imaging–Detected Structural Hip Damage
A Cross-Sectional Study in Young Men
Stephan Reichenbach,1 Michael Leunig,2 Stefan Werlen,3 Eveline Nüesch,1
Christian W. Pfirrmann,4 Harald Bonel,5 Alex Odermatt,6 Willy Hofstetter,7
Reinhold Ganz,7 and Peter Jüni1
All MRIs were read for cam-type deformities, labral
lesions, cartilage thickness, and impingement pits. The
relationship between cam-type deformities and signs of
joint damage were examined using logistic regression
models adjusted for age and body mass index. Odds
ratios (ORs) and 95% confidence intervals (95% CIs)
were determined.
Results. Sixty-seven definite cam-type deformities
were detected. These deformities were associated with
labral lesions (adjusted OR 2.77 [95% CI 1.31, 5.87]),
impingement pits (adjusted OR 2.9 [95% CI 1.43, 5.93]),
and labral deformities (adjusted OR 2.45 [95% CI 1.06,
5.66]). The adjusted mean difference in combined anterosuperior femoral and acetabular cartilage thickness
was ⴚ0.19 mm (95% CI ⴚ0.41, 0.02) lower in those with
cam-type deformities compared to those without.
Conclusion. Our findings indicate that the presence of a cam-type deformity is associated with MRIdetected hip damage in asymptomatic young men.
Objective. Femoroacetabular impingement may
be a risk factor for hip osteoarthritis in men. An
underlying hip deformity of the cam type is common in
asymptomatic men with nondysplastic hips. This study
was undertaken to examine whether hip deformities of
the cam type are associated with signs of hip abnormality, including labral lesions and articular cartilage
damage, detectable on magnetic resonance imaging
Methods. In this cross-sectional, populationbased study in asymptomatic young men, 1,080 subjects
underwent clinical examination and completed a selfreport questionnaire. Of these subjects, 244 asymptomatic men with a mean age of 19.9 years underwent MRI.
Supported by the Swiss National Science Foundation (National Research Program 53 on Musculoskeletal Health grant 405340104778) and by the Deutsche Arthrose-Hilfe e.V. Dr. Jüni’s work was
supported by a PROSPER fellowship from the Swiss National Science
Foundation. The Clinical Trials Unit at Inselspital, Bern University
Hospital (CTU Bern) is supported by the Swiss National Science
Stephan Reichenbach, MD, MSc, Eveline Nüesch, PhD,
Peter Jüni, MD: University of Bern and Inselspital, Bern University
Hospital, Bern, Switzerland; 2Michael Leunig, MD: Schulthess Clinic,
Zurich, Switzerland, and University of Bern, Bern, Switzerland; 3Stefan Werlen, MD: Hospital Sonnenhof, Bern, Switzerland; 4Christian
W. Pfirrmann, MD: University Hospital Balgrist, Zurich, Switzerland;
Harald Bonel, MD: Inselspital, Bern University Hospital, Bern,
Switzerland; 6Alex Odermatt, PhD: University of Basel, Basel, Switzerland; 7Willy Hofstetter, PhD, Reinhold Ganz, MD: University of
Bern, Bern, Switzerland.
Drs. Reichenbach and Leunig contributed equally to this work.
Dr. Leunig owns stock or stock options in Pivot Medical.
Address correspondence to Stephan Reichenbach, MD, MSc,
Institute of Social and Preventive Medicine, University of Bern,
Finkenhubelweg 11, 3012 Bern, Switzerland. E-mail: [email protected]
Submitted for publication December 3, 2010; accepted in
revised form August 3, 2011.
Osteoarthritis (OA) of the hip is one of the major
causes of pain and disability (1,2), accounting for more
than 200,000 hip replacements annually in the US (3).
The etiology of OA is multifactorial (4). Current classifications include “idiopathic” OA and “secondary” OA
in individuals with clearly visible deformities such as hip
dysplasia (5). More than four decades ago, however,
Murray suggested that most cases of idiopathic OA were
the result of frequently undetected deformities and were
therefore secondary OA (6). These deformities were
later suggested to cause femoroacetabular impingement
and signs of early hip OA (7). Two different types of
impingement were distinguished, cam and pincer. (An
illustration is available online at
Cam impingement is often seen in young male
athletes referred to orthopedic surgeons because of
groin pain (8), and internal rotation in flexion is usually
found to be diminished (9). It is caused by a nonspherical extension of the femoral head or a decreased offset
at the anterolateral transition of femoral head to neck
(8,10,11), which were referred to as cam-type deformities (7,12). The increased radius of the femoral head
entering the acetabulum may result in shear forces at the
acetabular cartilage, especially during flexion and internal rotation, and may lead to an abrasion of the acetabular cartilage and to cartilage avulsion at both the
labrum and the subchondral bone (13). Conversely,
pincer impingement occurs more frequently in women
and results from increased acetabular depth with overcoverage of the femoral head, while the femoral head–
neck configuration may be normal (14–16).
Cam-type deformities are common in asymptomatic young men (12), but their clinical relevance is
unclear. We therefore examined whether cam-type deformities, a nonspherical extension of the femoral head
and a decreased anterior head–neck offset, are associated with early signs of hip damage, including labral
lesions and decrease in articular cartilage, visible on
magnetic resonance imaging (MRI).
Participants. The Sumiswald Cohort is a populationbased inception cohort of consecutive young men undergoing
conscription for the Swiss army at a single recruiting center in
Sumiswald, Switzerland (12). In Switzerland, ⬃97.5% of men
of Swiss nationality are required by the army to attend a 3-day
recruitment session in specialized centers, regardless of their
health status. Consecutive males were asked to participate in
the baseline examination for this study, complete a selfadministered questionnaire, and undergo clinical examination.
We screened all individuals for hip pain using a modified
version of the question used in the first National Health and
Nutrition Examination Survey (17): During the past 3 months,
have you had pain in or around either of your hips? Individuals
who reported hip pain of ⱖ3 on a Likert scale ranging from 1
(no pain) to 5 (extreme pain) were excluded. Additional
exclusion criteria were previous surgery in either hip joint,
metabolic or inflammatory rheumatic disease or a history of
hemophilia, age younger than 18 years, and an inability to give
written informed consent. Self-report questionnaires included
the pain, stiffness, and function subscales of the Western
Ontario and McMaster Universities OA Index (WOMAC)
version 3.1 to quantify symptoms within the previous 48 hours
(18), as well as the EuroQol 5-domain questionnaire, which
includes 5 dimensions and a visual analog scale pertaining to
health-related quality of life (19). We measured internal
rotation using a recently developed examination chair (20),
which enabled us to accurately quantify internal rotation of the
hip in a sitting position with the hips and knees flexed 90° and
the lower legs hanging unsupported (20). The study was
approved by the Research Ethics Committee of the Canton of
Bern. All participants gave written informed consent prior to
any data collection.
MRI assessment. We used a central computergenerated randomization schedule for random selection of
participants for invitation for MRI. Stratification was performed according to the extent of internal rotation, with
oversampling in the strata with the lowest (⬍30°) and highest
(ⱖ40°) internal rotation. Only 1 hip per participant was
examined by MRI. In individuals whose hips had different
ranges of motion, the hip with the lower degree of internal
rotation was selected. When hips had similar internal rotation
(within 1°), the hip for MRI was randomly selected using a
concealed central computer-generated randomization schedule (12). All MRI studies were performed with a 1.5T highfield system (Magnetom Avanto; Siemens) using a flexible
surface coil and high spatial resolution protocol with patients
in the supine position with a neutral position of the hip joint.
Radial proton density–weighted sequences were acquired, with
all slices oriented parallel to the femoral neck axis, which was
used as the axis of rotation. Sequences were performed using
a sagittal oblique localizer, which was marked on the proton
density–weighted coronal sequence and which ran parallel to
the sagittal oblique course of the acetabulum (21).
Pulse sequence parameters of the turbo spin-echo
sequence were as follows: repetition time (TR) 2,000 msec,
echo time (TE) 15 msec, a field of view (FOV) of 260 ⫻ 260
mm, a matrix of 266 ⫻ 512, and a slice thickness of 4 mm with
a resulting voxel size of 0.98 ⫻ 0.51 ⫻ 4 mm. The acquisition
time for a complete set of 16 slices lasted 4 minutes 43 seconds.
In addition, we used a transverse T1-weighted sequence (FOV
200 ⫻ 200 mm, slice thickness 4 mm, TR 650 msec, TE 20
msec); transverse fast low-angle shot sequence (FOV 120 ⫻
120 mm, section thickness 2 mm, TR 650 msec, TE 20 msec,
flip angle 90°); sagittal true fast imaging with steady-state
precession (FISP) 3-dimensional (3-D) sequence (FOV 130 ⫻
130 mm, section thickness 1.5 mm, TR 8.87 msec, TE 3.23
msec, flip angle 28°); sagittal inversion recovery sequence
(FOV 180 ⫻ 180 mm, section thickness 3 mm, TR 4,800 msec,
TE 32 msec, time to inversion 160 msec); and a coronal
trueFISP 3-D sequence (FOV 180 ⫻ 180 mm, section thickness 1.5 mm, TR 8.16 msec, TE 2.89 msec, flip angle 28°). For
ethical reasons, neither intraarticular nor intravenous contrast
was injected.
To determine the presence of cam-type deformities,
we graded the maximal offset at the head–neck junction on the
radial sequences using a semiquantitative scoring system. This
system consisted of grades ranging from 0 to 3, where 0 ⫽
normal, no evidence of a nonspherical femoral shape (cam
deformity) on any sequence; 1 ⫽ possible deformity with
cortical irregularity and a possible mild decrease in the anterior head–neck offset; 2 ⫽ definite deformity with an established decrease in the anterior head–neck offset (cam deformity of ⬍10 mm); and 3 ⫽ severe deformity with a large
decrease in the anterior head–neck offset (cam deformity of
⬎10 mm) (12). The mean ⫾ SD alpha angle was 44.8 ⫾ 8.4° for
grade 0, 48.4 ⫾ 10.1° for grade 1, 57.7 ⫾ 12.7° for grade 2, and
Figure 1. Magnetic resonance images (MRIs) showing different types of joint damage. A,
Labral deformity on radial proton density–weighted MRI. The labrum is deformed, and the tip
has an oval shape (arrowheads) instead of a triangular shape. B, Labral avulsion on sagittal true
fast imaging with steady-state precession (FISP) MRI. The labral tear can be seen at the
transition between the labrum and acetabular cartilage (arrows). C, Intralabral signal alteration
on radial proton density–weighted MRI. The alteration is seen as a hyperintense linear signal
change in the body of the labrum (arrowhead). D, Intralabral ganglion (arrow) on coronal true
FISP sequence. E, Impingement pit on radial proton density–weighted MRI. An oval defect of
the femoral neck with decreased signal intensity in the adjacent bone marrow (arrow) is shown.
F, Sagittal true FISP sequence showing the combined thickness of the femoral and acetabular
cartilage (distance between the tips of the arrowheads) in the anterosuperior location.
76.4 ⫾ 9.7° for grade 3 deformities (P for trend ⫽ 0.001) (12).
Grades 2 and 3 were prespecified to indicate a definite
cam-type deformity. We used a clock face system to record the
localization of cam-type deformities and signs of joint damage
on MRI, such as labral disorders on radial sequences, with 12
o’clock denoting a superior location, 3 o’clock an anterior, 6
o’clock an inferior, and 9 o’clock a posterior location (12).
Figure 1 shows all disorders that were scored. The
normal labrum has a pointed, triangular shape with sharp
margins. Deformed labra (Figure 1A) were defined as those
with any shape other than triangular (i.e., oval, round, or
irregular) at 12 o’clock (21,22). The prespecified primary
outcome was the presence or absence of a labral lesion at any
location from 1 o’clock to 12 o’clock, defined as a linear band
of high signal intensity detected in the labrum. We distinguished 2 types of labral lesions: labral avulsion if detected at
the basis, i.e., at the transition between labrum and acetabular
cartilage (Figure 1B), and intralabral signal alterations if
detected in the body of the labrum (Figure 1C). In a labral
avulsion, the linear signal change reaches the surface, whereas
in an intralabral signal alteration the linear signal intensity
remains within the labrum and does not reach the surface
(22,23). Labral ganglia (Figure 1D) were recorded at any
location from 1 o’clock to 12 o’clock (21). Impingement pits,
formerly called herniation pits (Figure 1E), are well delineated, round to oval fibrocystic changes in the femoral neck,
with increased or decreased signal intensity (24–26). These
alterations are deemed to be a consequence of repetitive
microcontusions of the femoral neck against the acetabular
rim. We recorded the presence and locations of such cysts. We
measured the combined thickness of the femoral and acetabular cartilage in the anterosuperior location in millimeters
using the sagittal trueFISP sequence, where the section
through the center of the femoral head was selected (Figure
1F). Separate measurement of the femoral and acetabular
cartilage was not possible due to the lack of intraarticular
All MRIs were read by an experienced radiologist
(SW). A random sample of 30 MRIs were also read by 2 other
experienced radiologists (CP and HB). Weighted kappa values
for intrarater agreement (27) were 1.00 (95% confidence
interval [95% CI] 0.49, 1.00) for both labral lesions and
impingement pits and 0.59 (95% CI 0.09, 1.00) for labral
ganglia, whereas the intraclass correlation coefficient for cartilage thickness was 0.67 (95% CI 0.47, 0.86). Weighted kappa
values for interrater agreements were 0.51 (95% CI 0.16, 0.86)
for labral lesions, 0.63 (95% CI 0.27, 0.99) for impingement
pits, and 0.74 (95% CI 0.25, 1.00) for labral ganglia, whereas
the intraclass correlation coefficient for cartilage thickness was
0.74 (95% CI 0.59, 0.91).
Statistical analysis. The study was set up as an inception cohort study. Assuming 80% followup, an incidence of
hip pain of 5% in those without deformity, and a 25% frequency
of cam-type deformity, a sample size of 240 patients to be
Table 1. Characteristics of the subjects with and those without
cam-type deformity*
Definite cam-type deformity
on MRI
Age, years
Height, cm
Weight, kg
BMI, kg/cm2
Internal rotation, no. (%)
of patients
ⱖ30° and ⬍40°
WOMAC scores‡
EuroQol health state index‡
EuroQol VAS‡
(n ⫽ 67)
(n ⫽ 177)
20.0 ⫾ 0.7
178.8 ⫾ 7.6
77.4 ⫾ 13.7
24.3 ⫾ 4.2
19.9 ⫾ 0.7
178.1 ⫾ 6.9
71.9 ⫾ 11.6
22.6 ⫾ 3.4
40 (60)
17 (25)
10 (15)
43 (24)
64 (36)
70 (40)
0.2 ⫾ 0.5
0.2 ⫾ 0.8
0.4 ⫾ 1.1
0.2 ⫾ 0.5
9.4 ⫾ 1.2
8.3 ⫾ 1.2
0.2 ⫾ 0.4
0.2 ⫾ 0.6
0.7 ⫾ 1.7
0.1 ⫾ 0.4
9.3 ⫾ 1.4
8.5 ⫾ 1.2
* Except where indicated otherwise, values are the mean ⫾ SD.
MRI ⫽ magnetic resonance imaging; BMI ⫽ body mass index;
WOMAC ⫽ Western Ontario and McMaster Universities Osteoarthritis Index; VAS ⫽ visual analog scale.
† By one-way analysis of variance for numeric variables and by
chi-square test for categorical variables.
‡ Scores were standardized to range from 0 to 10.
included at baseline would yield ⬎80% power to detect a 16%
difference in the incidence of hip pain between those with and
those without cam-type deformity, and ⬎90% power to detect
a 20% difference. Associations between the presence of definite cam-type deformities and signs of joint damage (any labral
lesions as primary outcome, labral avulsions, intralabral signal
alterations, labral ganglia, labral deformities, and impingement
pits) were determined using crude univariable and multivariable logistic regression models adjusted for age and body mass
index (BMI). Sensitivity analyses were restricted to cam-type
deformities and signs of joint damage in the anterosuperior
location between 1 o’clock and 3 o’clock. An odds ratio (OR)
Table 2.
of ⬎1 indicates that hips with cam-type deformities are more
likely to have signs of joint damage than those without.
Differences in cartilage thickness between hips with
and without cam-type deformities were determined using
crude univariable and multivariable linear regression models
adjusted for age and BMI. A negative difference in cartilage
thickness indicates that cartilage thickness is smaller in hips
with cam-type deformities. As a graphical display of the
distribution of cartilage thickness, we plotted cumulative frequencies of cartilage thickness separately for hips with and
without cam-type deformities.
Baseline characteristics of the participants according to
the presence or absence of cam-type deformities were compared using one-way analysis of variance for continuous data
and chi-square tests for categorical data. WOMAC scores were
standardized to range from 0 to 10, with higher values indicating more severe symptoms. The dimensions of the EuroQol
were mapped onto a single health status index based on the
European value set and standardized to range from 0 to 10
(28), with higher values indicating better health-related quality
of life. P values are 2-sided. Statistical analyses were performed
using Stata version 11 software (StataCorp).
The flow of participants through the study has
been described previously (12) and is available online at Of 1,080 eligible individuals, 430 asymptomatic participants were invited for
MRI examination and 244 attended (57%). Sixty-seven
participants showed definite cam-type deformities (adjusted prevalence of 24%) (12). Table 1 presents a
comparison of the participants with and those without
cam-type deformity; those with the deformity had a
larger BMI and decreased internal rotation.
Table 2 presents crude and adjusted ORs for the
association between cam-type deformity and signs of
joint damage on MRI. The primary outcome of labral
lesions was found in 57 of 67 participants with a camtype deformity (85%) and 118 of 177 participants with-
Associations between cam-type deformity and signs of joint damage on MRI*
Definite cam-type
Labral lesions
Intralabral signal alterations
Labral avulsions
Labrum deformity
Impingement pits
Labral ganglion
(n ⫽ 67)
(n ⫽ 177)
Crude OR
(95% CI)
Adjusted OR
(95% CI)
57 (85)
32 (48)
51 (76)
12 (18)
20 (30)
21 (31)
118 (67)
54 (31)
102 (58)
15 (8)
21 (12)
44 (25)
2.85 (1.36, 5.98)
2.08 (1.17, 3.71)
2.34 (1.24, 4.43)
2.36 (1.04, 5.34)
3.16 (1.58, 6.33)
1.38 (0.74, 2.56)
2.77 (1.31, 5.87)
2.12 (1.17, 3.83)
2.24 (1.17, 4.28)
2.45 (1.06, 5.66)
2.91 (1.43, 5.93)
1.26 (0.67, 2.38)
* Values are the number (%) of patients. MRI ⫽ magnetic resonance imaging; OR ⫽ odds ratio; 95%
CI ⫽ 95% confidence interval.
Figure 2. Distribution of the localization of different morphologic signs
associated with hip joint damage. The top panel shows the localization of
definite cam-type deformities. Labral lesion is the composite of labral
avulsions and intralabral signal alterations. The localization of the deformities and damages was recorded in a clockwise manner, where 12 o’clock
corresponds to the superior position, 3 o’clock to the anterior, 6 o’clock to
the inferior, and 9 o’clock to the posterior position.
out a cam-type deformity (67%), yielding a crude OR of
2.85 (95% CI 1.36, 5.98). The association remained
unchanged when adjusting for age and BMI (OR 2.77
[95% CI 1.31, 5.87]). Labral avulsions were observed in
76% of those with a cam-type deformity and 58% of
those without, with a crude OR of 2.34 (95% CI 1.24,
4.43) and an adjusted OR of 2.24 (95% CI 1.17, 4.28).
Intralabral signal alterations were found in 48% of
subjects with a cam-type deformity versus 31% of those
without, with a crude OR of 2.08 (95% CI 1.17, 3.71) and
an adjusted OR of 2.12 (95% CI 1.17, 3.83). Labrum
deformities were found in 27 of 244 MRIs (11%) and
were more frequent in those with a cam-type deformity
than in those without (18% versus 8%, adjusted OR 2.45
[95% CI 1.06–5.66]). The labrum was oval in 7 participants, round in 6, and of an irregular shape in 14.
Impingement pits were found in 30% of the subjects
with a cam-type deformity versus 12% of the subjects
without (adjusted OR 2.91 [95% CI 1.43, 5.93]), whereas
labral ganglia were detected in 31% of the subjects with
cam-type deformity versus 25% of those without (adjusted OR 1.26 [95% CI 0.67–2.38]).
Figure 2 shows the localization of definite camtype deformities and signs of hip damage. Of 67 definite
cam-type deformities, 61 were located in the anterosuperior position between 1 o’clock and 3 o’clock (91%).
Similarly, most labral abnormalities were located in this
position. One hundred thirty-five of 175 labral lesions
(77%), 112 of 134 labral avulsions (84%), 57 of 86
intralabral signal alterations (66%), 30 of 41 impingement pits (73%), and 44 of 65 labral ganglia (68%) were
located between 1 o’clock and 3 o’clock. The results of a
sensitivity analysis restricted to cam-type deformities
and signs of joint damage in the anterosuperior location
between 1 o’clock and 3 o’clock are available online at Estimated associations
were similar to those observed in the main analyses, even
though 95% CIs crossed the line of no difference at 1 for
cartilage avulsion and labrum deformity.
The mean ⫾ SD cartilage thickness of anterosuperior femoral and acetabular cartilage combined was
3.96 ⫾ 0.74 mm in those with a cam-type deformity and
4.21 ⫾ 0.77 mm in those without, with a crude difference
of ⫺0.24 mm (95% CI ⫺0.46, ⫺0.03 mm). This difference was slightly attenuated after adjustment for age and
BMI (adjusted difference ⫺0.19 mm [95% CI ⫺0.41,
0.02]). Figure 3 shows crude cumulative frequency
curves of cartilage thickness in those with and those
without a cam-type deformity, with a shift of the cumulative frequency curve to the left by ⬃0.20 mm in those
with a deformity.
Figure 3. Cumulative frequency curves for cartilage thickness in
subjects with and subjects without a cam-type deformity. The cumulative frequency curve for cartilage thickness in those with a cam-type
deformity was shifted to the left by ⬃0.20 mm. The P value was
calculated using the 2-sided Wald test.
In our population-based cross-sectional study of
244 asymptomatic young Swiss men, we found that
definite cam-type deformities were associated with
labral damage, impingement pits, and decreased anterosuperior cartilage thickness. These relationships persisted after adjusting for age and BMI as potential
confounding factors. Most of the cam-type deformities
and most of the signs of damage on MRI were located in
the anterosuperior position. As reported previously (12),
the frequency of cam-type deformities was high (adjusted prevalence 24%), as was the frequency of signs of
joint damage.
To our knowledge, this is the first populationbased MRI study to examine the role of cam-type
deformities of the hip as a potential biomechanical risk
factor for joint damage. It is currently believed that the
signs of joint damage used in the present study are
potential intermediate outcomes in the sequence from
normal to OA hips (29). The cross-sectional nature of
our study, which was designed to form an inception
cohort of asymptomatic young men, prevents us from
determining at this point whether this assumption is true
and whether the cam-type deformities and their association with joint damage will be associated with an
increased risk of developing symptomatic OA of the hip
with clinically relevant pain and disability. Only longer
term followup in this and other longitudinal studies will
clarify the clinical relevance of our findings. Considering
that cam-type deformities are predominantly seen in
symptomatic men in tertiary care settings, our study was
restricted to men only (8). Additional population-based
studies are therefore required in women.
Due to ethical considerations, we were unable to
perform MRI arthrography because of the invasiveness
of the intervention. The high-resolution protocol of the
1.5T MRI device used in our study was sophisticated,
and anatomic structures could be adequately evaluated
even in the absence of intraarticular contrast. As a result
of a lack of contrast, we were unable to separately
measure the thickness of femoral and acetabular cartilage, however, and reported only the overall thickness of
the cartilage in the anterosuperior position.
We found that a large number of subjects (67%)
exhibited labral abnormalities, even in the group without
cam-type deformities. We cannot exclude some extent of
overreading as an explanation of these findings. However, frequencies of labral signal alterations have previously been reported in asymptomatic individuals
(22,30,31). Abe et al (22) found abnormal MRI signal
intensities in 40 of 71 of volunteers (56%) with an age
range of 13 to 65 years. Cotten et al (30) studied 52 hips
in 46 asymptomatic volunteers ages 15–85 years. They
found intralabral regions of intermediate or high signal
intensity in 58% of the cases. Lecouvet et al (31)
evaluated high-resolution T1-weighted spin-echo coronal MRIs of 1 hip in each of 200 asymptomatic individuals ages 15–82 years. They reported signal alterations in
44%. All 3 of the studies described above included both
men and women, but no information was provided
regarding sex differences. In our own experience, labral
abnormalities are considerably less frequent in women
than in men. Therefore, our results in men are likely to
be compatible with those previously published for men
and women combined (22,30,31). All 3 studies reported
on variation in labral shape. Triangular shapes were
described in 66% (31) to 88% (30) of participants,
whereas other forms were reported in the remaining
12–34%. Lecouvet et al (31) found that a triangular
shape was less prevalent in older people compared to
younger people, and it is unclear whether deviations
from a triangular shape are mere physiologic variations
rather than pathologic changes.
Two previously published studies of conventional
anteroposterior radiographs of the pelvis determined
the association of pistol grip deformities with OA. In a
population-based cross-sectional study in Copenhagen,
Gosvig et al (32) reported an adjusted risk ratio of 2.2
(95% CI 1.7, 2.8) for the association between pistol
grip deformities and hip OA. Doherty et al (33)
published the results of a case–control study including
cases with symptomatic radiographic hip OA and
asymptomatic controls without radiographic OA. Based
on conventional anteroposterior radiographs of the
pelvis (33), they found an adjusted OR for the association of cam-type deformities with OA of 6.95 (95% CI
4.6, 10.4).
Although pistol grip deformities as observed on
conventional radiography largely correspond to the camtype deformities observed on MRI in our study, both of
the previous studies were subject to the same two
limitations. First, they used conventional anteroposterior radiographs of the pelvis to determine whether an
individual showed a cam-type deformity, which underestimates the prevalence (12). This view predominantly
depicts cam-type deformities at the superior position
(34,35), which corresponds to 11 o’clock and 1 o’clock in
our MRI study; the majority of deformities that were
found in the present study would therefore not have
been observed in those previous studies (12,36). This
misclassification is likely to result in an underestimation
of the association between cam-type deformities and
OA. The second limitation was that, as pointed out by
Doherty et al (33), both studies predominantly included
older individuals in whom it is difficult to distinguish
between genuine cam-type deformities already present
at a young age and secondary osseous alterations developing later in life with the progression of OA. This may
result in an overestimate of the true associations.
The biomechanical mechanism that could causally explain our findings is that the increased radius of
the femoral head associated with cam-type deformity
results in shear forces at the acetabular cartilage when
the anterosuperior region of the femoral head enters the
acetabulum during flexion and internal rotation. This
can lead to chronic damage of the joint cartilage through
abrasion and to accompanying alterations of labrum and
bone, which may occur earlier in the process than
initially assumed (13,37). The high frequency of MRI
signs in participants without anterolateral cam-type deformities, however, suggests that the etiology of these
intermediate signs is multifactorial and that other factors, such as far-reaching ranges of motion or extensive
shear forces at the hip, may contribute to the disease
process. Longitudinal studies are needed to determine
whether cam-type deformity is a risk factor for symptomatic hip OA in accordance with currently established
classification criteria (38).
All authors were involved in drafting the article or revising it
critically for important intellectual content, and all authors approved
the final version to be published. Dr. Reichenbach had full access to all
of the data in the study and takes responsibility for the integrity of the
data and the accuracy of the data analysis.
Study conception and design. Reichenbach, Leunig, Odermatt, Hofstetter, Ganz, Jüni.
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DOI 10.1002/art.33473
In the article by Meune et al in the September 2011 issue of Arthritis & Rheumatism (pages 2790–2796), an
error for the correcting factors applied to FVC and DLCO/alveolar volume was introduced. The third and fourth
sentences of the Statistical Analysis section (page 2791) should have read “To calculate RPS indicative of
higher risk, some measurements that decrease with advancing disease were corrected by subtracting the
observed value from the highest value measured in the sample. For example, FVC and DLCO/alveolar volume
were corrected to 150% of predicted ⫺ FVC and 100% of predicted ⫺ DLCO/alveolar volume, respectively.”
In addition, the last sentence of the Patients Included in the Derivation Sample section (page 2792) should
have read “We calculated the Cochin RPS score as follows: RPS ⫽ 0.0001107(age) ⫹ 0.0207818(150 ⫺ FVC)
⫹ 0.04905(100 ⫺ DLCO/alveolar volume).”
We regret the error.
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