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© 2013 Wichtig Editore - ISSN 1120-7000
Hip Int (2013 ;:6 ) 552- 55923
552
MRI evaluation of hip containment and congruency
after closed reduction in congenital hip dislocation
Claudia Druschel, Richard Placzek, Lina Selka, Tamara Seidl, Julia Funk
Centre for Musculoskeletal Surgery, Charité University Medicine Berlin, Berlin - Germany
ORIGINAL ARTICLE
DOI: 10.5301/hipint.5000070
INTRODUCTION
Developmental hip dysplasia (DDH) is the most common
congenital deformity of the musculoskeletal system with
an incidence of 2-4% (1). DDH describes an ossification
disorder of the cartilaginous acetabulum without dislo-
cation of the femoral head. In contrast, the incidence of
hip dislocation is significantly lower (0.4-0.7%). It is well
known that the early diagnosis and treatment of DDH
and hip dislocation are important for normal hip develop-
ment (2). The fundamental aim of the treatment remains
to obtain and maintain a concentrically reduced hip, with
minimal morbidity and subsequent normal acetabular and
proximal femoral development (3). Furthermore, the re-
quirements for secondary procedures later in childhood or
adolescence should be minimised (3). Early diagnosis and
prompt therapy is important as the highest growth poten-
tial of the acetabular roof lies within the first four months
of life (4). The duration and invasiveness of treatment are
closely related to the severity of the deformity but also to
the patient’s age at the beginning of therapy (4).
Before attempting open reduction, closed reduction and
spica casting for retention of the unstable hip or applica-
tion of a Pavlik harness are standard practice (5). Closed
reduction with casting is commonly performed under
ultrasonographic or fluoroscopic guidance with or without
additional arthrography (5). In young patients with unsta-
ble or dislocated hips closed reduction and retention can
Background: Developmental dysplasia of the hip is the most common congenital skeletal disease.
In its most severe form - dislocation - the treatment is directed at reducing the hip and establishing
normal congruency between the femoral head and the acetabulum. Closed reduction with casting is
a common primary treatment, where reduction is confirmed by magnetic resonance imaging (MRI).
Objective: This study analyses anatomical aspects depicted on MRI after closed reduction to identify
disparities in the growth behaviour of dislocated hips.
Materials and methods: In 38 patients MRI after closed reduction was available for analysis. After
exclusion of children with underlying diseases or syndromes, MRIs of 28 children were evaluated with
respect to head coverage index, acetabular head index and sphericity. The results were compared to
the stable opposite sides.
Results: Twenty-two stable and 27 initially unstable hips were available for further analysis. The head
coverage index as well as the acetabular head index of the unstable hips was significantly smaller than
that of the stable hips. The sphericity score of the dislocated femoral heads was significantly lower
than that of the stable ones.
Conclusion: Dislocated hips showed significantly lower values for all of the evaluated parameters
concerning congruency and containment. MRI is not only useful to confirm successful reduction
but may also help to predict outcome by evaluating following dislocation.
Keywords: Developmental hip dysplasia, Closed reduction, MRI, Containment, Congruency
Accepted: May 8, 2013
© 2013 Wichtig Editore - ISSN 1120-7000 553
Druschel et al
be achieved by these options in the vast majority of the
cases. Failed closed reduction in neonates occurs rarely
and has been reported in approximately 1-4% of all dislo-
cations (6, 7). Obstacles preventing reduction of the dis-
located hip include: inversion of the labrum, interposition
of the psoas tendon, narrowing of the capsular isthmus,
thickening of the round ligament (ligamentum teres) and of
the transverse ligament of the acetabulum, thickening of
the fibrofatty pulvinar tissue and hypertrophy of the carti-
lage of the acetabular roof (acetabular bulge) (6-8).
Different imaging techniques (ultrasound, arthrography,
MRI) are used to evaluate the obstacles preventing reduc-
tion and play a role in choosing the treatment strategy. Tré-
guier et al investigated irreducible DDHs with ultrasound
and demonstrated hypertrophy of the cartilage of the ace-
tabular roof (6). Ponseti reported this pathology for the first
time as result of autopsies in six cases and described it as
‘‘acetabular bulge’’ (8). Today post-reduction MRI is widely
used to confirm closed reduction (5, 9-12). However, use-
ful parameters to determine the growth restriction of the
dislocated hip are still missing.
The aims of this study were to describe the MRI parameters
for determination of containment and congruency between
the femoral head and acetabulum in infants as well as the
correlation of parameters with age and reduction success.
We hypothesised that hip dislocation leads to less congru-
ency confirmed by decreased acetabular head index, head
coverage index and sphericity as compared to the healthy
contralateral side.
MATERIALS AND METHODS
Patients
A retrospective cohort study of patients treated for develop-
mental hip dislocation with closed reduction and spica cast-
ing in our department between January 2005 and December
2010 was performed. Hips that underwent open reduction
were excluded. 47 congenital hip dislocations in 38 patients
(31 females) were identified. Patients with underlying diseas-
es or syndromes that are known to include the risk of terato-
logic or secondary neuromuscular dislocation were excluded
from the statistical analysis. Diagnosis was confirmed by ul-
trasound according to Graf as well as clinical investigation
(Ludloff sign, Galeazzi sign, abduction inhibition). Graf types
III and IV were treated according to our standard protocol.
Treatment protocol
Closed reduction with arthrography under fluoroscopic
guidance was performed under general anaesthesia in all
cases. A hip spica cast was applied with the hips in more
than 90° of flexion and 40° to 60° abduction, depending
on the position of maximal stability. MRI examination was
carried out under sedation within 24 hours after cast appli-
cation (Fig. 1). Whenever incomplete reduction was found
the cast was removed immediately and the procedure was
repeated within the next few days. In case of successful
reduction and retention the spica cast was left unchanged
for four weeks. After removal stability and hip type were
evaluated clinically and by ultrasound. If the situation was
stable, a Tuebingen flexion-abduction splint (13) was ap-
plied for further remodelling of the acetabulum according
to continuous ultrasound controls.
MRI assessment
In all cases a pelvic MRI depicting both hips was per-
formed. Affected and initially stable hips were evaluated
Fig. 1 - MRI presentation of the reduced left hip in: A) transversal
and B) coronal T2-weighted sequence.
© 2013 Wichtig Editore - ISSN 1120-7000
554
MRI evaluation after closed reduction in congenital hip dislocation
applying the same protocol. The patients were placed
in a supine position with the leg position limited by the
cast. Images were obtained using a General Electric Signa
System (GE Healthcare, Milwaukee, Wis, USA) with a field
strength of 1.5 Tesla. T2-weighted fast spin echo (FSE)
sequences in the transverse and coronal plane were used
for evaluation. The slice thickness was 2 mm (0.2sp). For
measuring areas and distances Centricity® (GE Health-
care) tools were applied.
Acetabular-head-index
The acetabular-head-index (AHI) described by Douira-
Khomsi et al (10) was applied after modification for the
cartilaginous infant hip. It is a description of the hip con-
tainment in the coronal plane. Hence, the MRI slice of the
coronal sequence with the largest femoral head area was
selected for each hip by two independent examiners. To
assess the lateral acetabular coverage of the femoral head
a vertical line was drawn from the internal cephalic carti-
laginous edge (Fig. 2). Perpendicular lines from this verti-
cal line were drawn to the lateral cartilaginous margin of
the acetabulum as well as the furthest lateral margin of
the cartilaginous femoral head. The modified cartilaginous
coronal AHI was expressed as relation of the acetabular
cover (DA
) to the largest extension of the femoral head (DH
)
in percent.
Head coverage index
To determine the containment of the femoral head in the
acetabulum for each hip the MRI slice of the transverse
sequence with the largest area of the femoral head was
selected by two independent examiners for further evalu-
ation. The area (in mm2) of the femoral head (AH
) and the
acetabulum (AA
) were measured as well as the fraction
of the femoral head (AHP) enclosed in the acetabulum
(Fig. 3). The ratio AHP/AH was expressed as head cover-
age index (%). The percentage of the acetabulum filled
with femoral head was also evaluated as a marker for
congruency.
To evaluate the reliability of this measurement index the
intraclass correlation coefficient was determined for intra-
rater and inter-rater reliability. While the analysis of the
intra-rater reliability was based upon the results from the
measurements of the repeated blinded measurements of
the newly established parameters AH, AA and AHP by one of
the authors (CD) at two different time points, the inter-rater
reliability was determined on the base of an independent
Fig. 2 - Measurement of the modified acetabular-head-index in
a schematic drawing and in a coronal T2-weighted image after
closed reduction of the left hip. A = vertical line from the inter-
nal cephalic cartilaginous edge DA = Distance from vertical line to
the lateral cartilaginous margin of the acetabulum, DH = distance
from ver tical line to the lateral margin of the femoral head. AHI =
DA/DH x 100 (%).
Fig. 3 - A) Presentation of the femoral head area (AH
) evaluation in
a schematic drawing and in a transversal T2-weighted image after
closed reduction of the left hip. B) Visualisation of the acetabular
area (A A
) and the in the acetabulum included femoral head area (AHP
)
in schematic drawing and MRI image. The AHP of the reduced hip is
markedly smaller than that of the opposite side.
AHI
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Druschel et al
and blinded MRI analysis by two trained paediatric ortho-
paedic surgeons (CD, JF).
Sphericity
Any deformation of the femoral head was examined using
the modified method from Sankar et al (14). The spericity
was evaluated in the same images in which the AHI was
measured. The largest femoral head diameter was deter-
mined. From its midpoint, which also divided the diameter
into the largest femoral head radii three further radii at 45°,
90° and 135° were added in a clockwise direction. Dmax
was defined as the difference between the largest and the
smallest radius. The modified sphericity score was then cal-
culated according to the formula: sphericity score (SS) = 1 -
Dmax (Fig. 4). For a completely circular head Dmax - as
the maximum difference of the radii - would be 0 and the
sphericity score would be 1.
Reduction obstacles
Obstacles preventing reduction of the dislocated hip
were investigated by two independent observers. They
were classified as inverted labrum, psoas tendon inter-
position, pulvinar tissue or narrowing of the capsular isth-
mus. The shape of the labrum and the cartilaginous roof
was evaluated in both planes and described as normal or
deformed.
Statistical analysis
Data were analysed using PASW Statistics 18.0 (SPSS
Inc., Chicago, IL). A minimum sample size per group (two-
tailed hypothesis) of 22 was evaluated with an anticipated
effect size of 0.88 resulting from the assumption drawn
from preliminary measurements that AHI is at least 10%
lower in primarily centred than in reduced hips and that the
standard deviation of AHI is twice as high in reduced hips
as in primarily stable ones. After confirming normal distri-
bution of data significant differences between the groups
of reduced and primarily stable hips were evaluated apply-
ing the unpaired two-tailed Student t-test using the con-
ventional 95% level of confidence. To determine the age
dependency the Pearson correlation coefficient was used.
The inter- and intraobserver agreement was determined
by calculating the intraclass correlation coefficient (ICC).
The reliability was interpreted as poor (ICC = 0-0.2), fair
(ICC = 0.3-0.4), moderate (ICC = 0.5-0.6), strong (ICC =
0.7-0.8) or almost perfect (ICC>0.8) (15).
RESULTS
The mean age at reduction was 81 days, with a range of sev-
en to 334 days. Twelve patients underwent a pretreatment
“alio loco” with a Pavlik harness or Tuebingen splint before
being referred to our department. In six hips either longitu-
dinal or overhead traction was performed before reduction.
Treatment results
Of the 38 treated patients 10 infants had underlying diseas-
es or syndromes that are known to coincide with either tera-
togenic or neurologic hip dislocations. These patients were
excluded from statistical analysis. The seven hips in six chil-
dren where closed reduction was impossible were excluded
from statistical analysis as well and described separately.
Fig. 4 - Imaging of the method to determine the sphericity (SS = 1 –
Dmax) presented in a schematic drawing and in a coronal T2-weight-
ed images after closed reduction of the left hip.
© 2013 Wichtig Editore - ISSN 1120-7000
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MRI evaluation after closed reduction in congenital hip dislocation
Since four of the six children with irreducible hips belonged
to patients who were excluded for underlying diseases
statistical analysis was performed for 49 hips (46 females)
of 26 patients with a mean age of 82 ± 51 days (median
75 days range 7–217 days) at time of closed reduction.
22 stable hips and 27 initially unstable hips with successful
closed reduction and stable retention were analysed.
MRI Assessment
MRI was found to be a satisfactory tool for assessing the
adequacy of reduction. The available sequences sufficed
for applying the modified scores and indices to evaluate
containment and congruency. Table I displays the means,
ranges and standard deviations of the described values
(Tab. I).
Acetabular-head-index
The AHI was 8% higher in primarily stable hips (AHI = 76.37 ±
5.78%) than in reduced hips (AHI = 69.85 ± 10.9%). This im-
plicates significantly less coverage of the femoral head (p =
0.015) in reduced hips than in stable hips. In irreducible hips
the AHI was smaller than that of the reduced hips (AHI =
38.0 ± 14.85%).
Head coverage index
The mean femoral head area of the reduced hips (AH =
202.08 ± 43.45 mm2) was significantly (p = 0.04) smaller than
that of the primarily stable hips (AH = 235.80 ± 62.53 mm2).
The mean acetabular area was also significantly (p = 0.003)
smaller in reduced hips (AA = 53.22 ± 16.71 mm2) as com-
pared to the stable hips (AA = 67.24 ± 13.34 mm2). Although
head as well as acetabulum area were smaller in the re-
duced hips, the femoral area that was enclosed in the ac-
etabulum was significantly (p<0.001) smaller in the reduced
hips (AHP = 27.94 ± 15.39 mm2) in comparison to the initially
stable hips (AHP = 48.54 ± 14.44 mm2). The head coverage
index as a description of femoroacetabular containment of
the reduced hips (AHP/AH x100 = 14.08 ± 6.72%) was 33%
smaller than that of the stable hips (AHP/AH x100 = 21.11 ±
5.48%) which illustrates a significant difference between
both groups concerning the containment (p<0.001). The
femoral head area of those hips where reduction had failed
averaged to AH = 173.7 ± 68.8 mm2 which is even smaller
than that of the reduced hips. The acetabular area of the ir-
reducible hips (AA = 30.4 ± 17.1 mm2) also was smaller than
that of the successfully reduced hips. The head coverage
index was not calculable for non-reduced hips, neither was
any area of the head enclosed in the acetabulum in these
cases. Furthermore, the area of the femoral head as well as
that of the acetabulum correlated significantly with age at
closed reduction (p<0.001) in all cases.
The reliability coefficients for these newly developed pa-
rameters concerning intra-rater and inter-rater agreement
are presented in Table II. They represent a strong to almost
perfect agreement concerning reliability of these variables.
The smallest coefficient is 0.78 (intra-rater reliability AA) and
the largest coefficient is 0.98 (inter-rater reliability AH).
Sphericity score
Regarding the shape of the femoral head reduced hips
(SS = 0.77 ± 0.13) showed a significant (p = 0.001) defor-
mation when compared to the initially stable hips (SS =
0.89 ± 0.08). The irreducible hips seemed to be even
more deformed with regard to the sphericity score (SS =
0.5 ± 0.14).
TABLE I - SUMMARY OF THE MRI ASSESSMENT
parameter primarily stable
hips (n = 2 2)
reduced
hips (n = 27)
significance
by t-test
AH-Index (in %) 76.37 ± 5.78 69.85 ± 10.90 p = 0.015
Head coverage
index (AHP/AH in %)
21.11 ± 5.4 8 14.08 ± 6.72 p<0.0 01
Area head (AH in mm2) 235.80 ± 62.53 202.08 ± 43.45 p = 0.039
Area acetabulum
(AA in mm2)
67.24 ± 13.34 53.22 ± 16.71 p = 0.003
Area head in acetabu-
lum (AHP in mm2)
48.54 ± 14.44 27.94 ± 15.39 p<0.0 01
Percentage acetabu-
lum filled with head (%)
71.94 ± 14.55 51.66 ± 18.54 p<0.0 01
Sphericity 0.89 ± 0.08 0.77 ± 0.13 p = 0.001
TABLE II - INTRA- AND INTER-RATER RELIABILITY FOR
THE NEWLY ESTABLISHED PARAMETERS
parameter Intra-rater
reliability
Inter-rater
reliabilty
Area head (AH)0.96 0.98
Area acetabulum (AA)0 .78 0.8
Area head in acetabulum (AHP)0.89 0.9
© 2013 Wichtig Editore - ISSN 1120-7000 557
Druschel et al
Reduction obstacles
In the patients with irreducible hips no obstacles such as
inverted labrum, psoas interposition, pulvinar tissue or nar-
rowing of the capsular isthmus were found in the available
MRI sequences. On the other hand all pathologic hips – the
reduced ones as well as the irreducible ones – showed
signs of deformation of the labrum (“bulging”) whereas none
of the initially stable hips had deformed cartilaginous roofs.
DISCUSSION
Concentric reduction of dislocated hip joints is a mandatory
precondition for the development of a healthy congruent hip
without the risk for early degenerative changes (9). Specific
MRI parameters were evaluated in this study to retrospec-
tively determine containment and congruency of femoral
head and acetabulum in infants after closed reduction.
Although the retrospective study design is a limitation which
may influence the interpretability of the presented results
the evaluated number of patients is within the margins of
the sample size analysis implying satisfactory power of the
results. On the other hand the number is not large enough
to perform valuable subgroup analysis. Therefore, it was
not possible to statistically analyse differences between
irreducible hips and reducible or primarily stable hips.
However, according to the main subgroups of dislocated
and stable hips a homogeneous distribution concerning
number (27 to 22) and age (75 to 76 days) was present.
Previously published measurement methods (10, 14) were
modified to apply them to the MRI analysis of infant hips
instead of older patients groups. Significant differences be-
tween the configuration of stable and reduced hips were
observed with the respective methods.
After closed reduction, MR imaging is the golden stan-
dard to confirm stable reduced retention and to evalu-
ate soft tissue interposition (5, 9-12). The advantage of
magnetic resonance tomograms is the good depiction
of cartilage and soft tissues with an adequate imaging of
bone (9, 11). It is well known that the transverse plane
shows concentric reduction the best whereas the coronal
plane tends to produce false positive results with regard to
proper reduction (11). In addition to documenting adequate
reduction of the hip joint, MRI allows to determine the ex-
tent of abduction in the plaster cast (9). In this study MRIs
produced for assessing the adequacy of reduction were
further evaluated concerning joint congruency and femoral
head containment applying different indices and scores af-
ter modification for MRIs of infant hips. Due to the fact that
the sequences evaluated in this study were initially used to
control the result of closed reduction a limited number of
selected slices was available. This may have influenced the
outcome of this study but would have affected the dislo-
cated hips as well as the stable ones equally.
Despite the generally good results of closed reduction it
has been described to fail in approximately 1-4% of all dis-
locations (7, 9). With the application of MRI as the golden
standard for diagnosing the post-reduction state of the hip
this number has raised to 4% to 6% (11, 16). The relatively
high rate of failed closed reductions (16%, six children out
of 38) in our study population can be explained by the num-
ber of patients with underlying diseases (four of these six
patients) and hence teratogenic or neurogenic dislocations
which are known to have a higher failure rate concerning
closed reduction. One of the remaining two children was
older than three months at the time of reduction. This is
comparable to 7% in our patients (2/28 children without
syndromes, one of them older than three months).
The head coverage index is a valid measure of hip con-
tainment in the transverse plane. Furthermore, this study
successfully applies the measurement of the hip contain-
ment in the coronal plane as described for older patients
by Douira-Khomsi et al (10) to infants. With both methods
it can be shown that uncoupled growth of dislocated hips
during early life resulted in significantly less containment
when compared to the primarily stable hips. The values of
the irreducible hips were even lower although not statisti-
cally tested due to the small number of cases. To dem-
onstrate the difference between the morphology of the
normal and dysplastic acetabula on MRI other modified
parameters have been applied before emphasising angles
and outcome of reduction but not the congruency and
containment of the hip joints (14).
The significantly smaller areas of head and acetabulum of
the reduced hips demonstrated in this study can be valued
as an early sign of biomechanical-biological interaction.
This mechanism was shown in a rat model where after leg
fixation of newborn rats in the position of hip extension and
adduction, the acetabulum was shallow and small com-
pared to the control group (17).
The deformation of the femoral heads and the lateral thirds
of the acetabula was described qualitatively by Ferguson
et al when seen during open reduction (4). The spericity as
© 2013 Wichtig Editore - ISSN 1120-7000
558
MRI evaluation after closed reduction in congenital hip dislocation
CONCLUSION
The combination of the results of all applied measurement
methods legitimises the assumption that very early patho-
morphological changes of the dislocated hip joint due to
uncoupled growth lead to a lack of congruency and con-
tainment which ultimately prevent closed reduction. As the
deformation is known to progress with age, diagnosis and
treatment should be enforced as early as possible to yield
the best results with the least invasive therapy. MRI evalua-
tion may be helpful initially for decision making with regard
to the most successful procedure as it optimally shows the
amount of incongruency and lack of containment as a re-
sult of deformation and uncoupled growth of the infantile
hip joint.
Financial Support: No funding was received for this work.
Conflict of Interest: There is no potential conflict of interest, real or
perceived, in: 1) study design; 2) the collection, analysis, and interpre-
tation of data; 3) the writing of the report; and 4) the decision to submit
the paper for publication.
Address for correspondence:
Claudia Druschel
Charité University Medicine Berlin
Centre for Musculoskeletal Surgery
Campus Virchow Clinic, Augustenburger Platz 1
Berlin 13353, Germany
claudia.druschel@charite.de
a sign of femoral head deformation can also be evaluated
without surgical intervention on coronal MRI by the modi-
fied method of Sankar et al (14). The evaluated spheric-
ity score revealed a significant deformation of the reduced
femoral heads in comparison to the primarily stable hips
immediately after closed reduction. This can be interpreted
as an early sign of incongruency. The images of the irre-
ducible hips showed even more deformation.
The obstacles preventing reduction of the dislocated hip
that have been described in the literature: inversion of
the labrum, interposition of the psoas, narrowing of the
capsular isthmus, thickening of the round ligament and of
the transverse ligament of the acetabulum, thickening
of the fibrofatty pulvinar tissue and hypertrophy of the
cartilage of the acetabular roof (6-8). Due to the optimal
soft-tissue imaging with magnetic resonance tomogra-
phy, reduction obstacles can be identified easier on MRI
sequences than on arthrograms (18-20). No soft tissue
reduction obstacles were seen in the available MRIs of
this study. Bulging of the acetabular roof was seen in all
pathologic hips – the reduced as well as the irreducible
ones – at least in one plane whereas none of the primarily
stable hips showed this feature. Although a limited num-
ber of MRI slices was available for evaluation, it may be
assumed that incongruency with malcontainment but not
soft tissue interposition was the main reason for failed re-
duction in this population.
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