How does pelvic rotation or tilt affect radiographic measurement of acetabular component inclination angle during THA?


R Mellano, C.; Spitzer, A.I.

Journal of Orthopaedics 12(4): 222-227

2015


It is unclear how radiographic measurements of cup position are sensitive to deviations from a perfect AP pelvis image. To quantify changes in radiographic measurements of cup abduction angle due to pelvic tilt or obliquity. Part A, a retrospective comparison of radiographic cup abduction angle measurements from intraoperative and post-operative radiographs of 23 patients undergoing THA. Part B, a pelvic sawbones model was used to quantify changes in radiographic measurement of cup abduction angle due to known changes in pelvic tilt or obliquity. Part A, a perfect AP pelvis was obtained in just 30% of intraoperative radiographs. The mean intraoperative cup angle measurement was underestimated by 3.4° compared to post-operative standard radiographs. In Part B, pelvic tilt caused cup abduction angle measurement to decrease on inlet view and increase on outlet view. Pelvic obliquity caused cup abduction angle measurement to decrease on obturator oblique view and increase on iliac oblique view. A trend exists toward slight underestimation of cup abduction angle measurement using intraoperative radiographs. Pelvic tilt or obliquity alters the measured cup abduction angle in known directions.

JOURNAL
OF
ORTHOPAEDICS
12
(2015) 222-227
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JOURNAL
of
ORTHO
ICS
'T
'
1
ENIER
Original
Article
How
does
pelvic
rotation
or
tilt
affect
radiographic
measurement
of
acetabular
component
inclination
angle
during
THA?
01)
CrossMark
Chris
R.
Mellano
,
Andrew
I.
Spitzer
a
Beach
Cities
Orthopedics
400
S.
Sepulveda
Blvd.
Suite
200
Manhattan
Beach,
CA
90266,
USA
b
Cedar-Sinai
Orthopaedic
Center,
Mark
Goodson
Building,
444
S.
San
Vicente
Blvd.,
Suite
603,
Los
Angeles,
CA
90048,
USA
ARTICLE
INFO
ABSTRACT
Article
history:
Received
15
April
2015
Accepted
24
May
2015
Available
online
23
June
2015
Background:
It
is
unclear
how
radiographic
measurements
of
cup
position
are
sensitive
to
deviations
from
a
perfect
AP
pelvis
image.
Purpose:
To
quantify
changes
in
radiographic
measurements
of
cup
abduction
angle
due
to
pelvic
tilt
or
obliquity.
Methods:
Part
A,
a
retrospective
comparison
of
radiographic
cup
abduction
angle
mea-
surements
from
intraoperative
and
post-operative
radiographs
of
23
patients
undergoing
THA.
Part
B,
a
pelvic
sawbones
model
was
used
to
quantify
changes
in
radiographic
measurement
of
cup
abduction
angle
due
to
known
changes
in
pelvic
tilt
or
obliquity.
Results:
Part
A,
a
perfect
AP
pelvis
was
obtained
in
just
30%
of
intraoperative
radiographs.
The
mean
intraoperative
cup
angle
measurement
was
underestimated
by
3.4°
compared
to
post-operative
standard
radiographs.
In
Part
B,
pelvic
tilt
caused
cup
abduction
angle
measurement
to
decrease
on
inlet
view
and
increase
on
outlet
view.
Pelvic
obliquity
caused
cup
abduction
angle
measurement
to
decrease
on
obturator
oblique
view
and
increase
on
iliac
oblique
view.
Conclusions:
A
trend
exists
toward
slight
underestimation
of
cup
abduction
angle
mea-
surement
using
intraoperative
radiographs.
Pelvic
tilt
or
obliquity
alters
the
measured
cup
abduction
angle
in
known
directions.
Copyright
©
2015,
Professor
P
K
Surendran
Memorial
Education
Foundation.
Publishing
Services
by
Reed
Elsevier
India
Pvt.
Ltd.
All
rights
reserved.
Keywords:
Total
hip
arthroplasty
Component
malposition
Intraoperative
radiograph
Acetabular
component
inclination
angle
1.
Introduction
Proper
acetabular
component
positioning
is
essential
to
a
successful
total
hip
arthroplasty.
A
poorly
positioned
acetabular
component
may
lead
to
unfavorable
hip
kine-
matics,
hip
instability,
and
bearing
surface
accelerated
wear
rates.
To
accurately
measure
acetabular
component
version
a
CT
scan
is
currently
the
gold
standard,
however
*
Corresponding
author.
23600
Telo
Ave
Suite
180,
Torrance,
CA
90505,
USA.
Tel.:
+1
310
257
1500;
fax:
+1
310
257
1508.
E-mail
address:
(C.
R.
Mellano).
http://dx.dotorg/10.1016/j.jor.2015.05.009
0972-978X/Copyright
©
2015,
Professor
P
K
Surendran
Memorial
Education
Foundation.
Publishing
Services
by
Reed
Elsevier
India
Pvt.
Ltd.
All
rights
reserved.
JOURNAL
OF
ORTHOPAEDICS
12 (2015) 222-227
223
compared
to
post-operative
standard
supine
images?
Second,
are
acetabular
component
abduction
angle
measurements
as
measured
on
intraoperative
CR
images
consistent
with
mea-
surements
on
post-operative
standard
radiographs?
Finally,
to
what
degree
does
a
less
than
perfect
AP
pelvic
image
due
to
alterations
in
patient
positioning
change
the
radiographic
measurements
of
the
acetabular
component
abduction
angle?
Fig.
1—
An
example
of
an
AP
pelvis
image
without
rotation
or
tilt.
The
obturator
foramina
are
symmetric
and
the
distance
from
the
tip
of
the
coccyx
to
the
superior
aspect
of
the
symphysis
pubis
is
less
than
3
cm
without
overlap.
standard
radiographs
have
been
validated
as
an
accurate
tool
to
measure
acetabular
component
abduction
angle
when
compared
to
CT.
6
Intraoperative
standard
portable
radiog-
raphy
is
one
technique
to
assess
component
positioning.
Recently,
intraoperative
computed
radiography
(CR)
has
been
utilized
as
a
time-efficient
alternative
to
assess
compo-
nent
positioning.'
For
both
standardized
portable
X-ray
and
CR
it
is
assumed
that
accurate
measurement
of
component
positioning
requires
perfect
AP
pelvis
imaging
without
pelvic
obliquity
or
tilt.
We
are
unaware
of
any
reports
in
the
English
language
literature
that
report
the
accuracy
of
intraoperative
imaging
to
obtain
a
perfect
AP
pelvic
image.
Furthermore,
to
our
knowl-
edge
no
study
has
determined
how
radiographic
measure-
ments
of
acetabular
component
positioning
are
sensitive
to
deviations
from
an
ideal
AP
pelvic
image
on
either
computed
radiography
or
standard
radiographs.
This
two-part
study
aims
to
determine
the
following:
First,
what
is
the
accuracy
of
intraoperative
CR
imaging
in
the
lateral
decubitus
position
to
obtain
a
perfect
AP
image
2.
Materials
and
methods
This
two-part
study
utilizes
radiographs
of
both
in-vivo
acetabular
components
and
radiographs
of
an
acetabular
component
in
a
pelvic
model
to
determine
how
measure-
ments
of
acetabular
component
abduction
angles
are
affected
by
changes
in
pelvic
positioning
or
incident
beam
trajectory.
For
both
parts
of
this
study
a
"perfect"
AP
pelvic
image
was
defined
by
a
significant
lack
of
pelvic
obliquity
or
tilt
(Fig.
1).
Pelvic
obliquity
was
considered
"perfect"
if
the
obturator
foramina
were
symmetric
and
imperfect
if
the
obturator
foramina
were
asymmetric.
Likewise,
tilt
was
considered
"perfect"
if
the
distance
from
the
tip
of
the
coccyx
to
the
su-
perior
aspect
of
the
symphysis
pubis
was
less
than
3
cm
and
imperfect
if
the
coccyx
overlapped
the
symphysis
pubis
or
the
distance
was
larger
than
3
cm.
9
2.1.
Part
A
After
IRB
approval
was
obtained,
a
retrospective
analysis
was
performed
utilizing
radiographic
measurements
of
acetabular
component
abduction
angles
from
twenty-three
consecutive
primary
THAs
in
23
patients
for
a
diagnosis
of
primary
oste-
oarthritis.
Pelvic
radiographs
of
intraoperative,
immediate
post-operative,
and
3-month
office
visit
were
reviewed
for
each
patient.
Low
anteroposterior
pelvis
digital
images were
obtained
during
surgery
using
portable
computed
radiography
(CR)
technology
(RadLink
Redondo
Beach,
CA)
with
the
patient
in
the
lateral
decubitus
position.
Immediately
post-operative
standard
radiographs
were
obtained
with
the
patient
supine
1
Fig.
2
Acetabular
component
abduction
angle
was
measured
by
determining
the
angle
between
the
face
of
the
acetabular
component
and
the
intra-ischial
line.
224
JOURNAL
OF
ORTHOPAEDICS
12
(2015) 222-227
then
made.
This
exercise
was
performed
for
three
different
starting
cup
abduction
angles
as
measured
on
the
initial
per-
fect
AP
image
in
order
to
replicate
a
neutral
cup
position
(42°),
a
more
horizontal
cup
position
(29°),
and
a
more
vertical
cup
position
(60°).
The
anteversion
of
15°
was
unchanged
for
each
of
these
starting
cup
angles.
3.
Results
3.1.
Part
A
Fig.
3
Sawbones
pelvic
cup
model
with
cup
abduction
angle
initially
measured
to
be
42°
on
a
perfect
AP
image.
While
maintaining
the
incident
beam
trajectory
stationary,
the
pelvic
model
was
rotated
20°
to
create
a
20°
iliac
oblique
image
(Fig.
3).
The
cup
angle
was
re-measured
to
be
4636°.
in
the
post-anesthesia
care
unit
(PACU),
and
again
in
the
su-
pine
position
in
the
office
at
a
3-month
postoperative
visit.
First,
all
films
were
reviewed
to
determine
the
percentage
of
films
that
were
truly
"perfect
AP
pelvis"
images
as
defined
above.
If
the
images
were
not
perfect
AP
pelvis
images
then
the
image
was
categorized
based
on
the
direction
of
tilt
or
obliquity
(inlet
view,
obturator
view,
iliac
oblique,
obturator
oblique).
The
rates
of
perfect
AP
pelvis
images
obtained
were
compared
for
both
intraoperative
images
and
post-operative
images.
Secondly,
acetabular
component
abduction
angles
were
measured
on
all
films
by
determining
the
angle
between
the
face
of
the
acetabular
component
and
the
intra-ischial
line
(Fig.
2).
For
each
patient
the
trends
in
cup
abduction
angle
were
statistically
compared
over
time
using
a
one-way
repeated
measures
analysis
of
variance
(RMANOVA)
with
Time
(3
levels)
as
the
within-subjects
factor.
Contrasts
were
used
to
compare
the
mean
angle
at
various
times.
Statistical
software:
SAS
version
9.2
(Cary,
North
Carolina).
2.2.
Part
B
A
saw-bones
pelvic
model
was
reamed
and
fitted
for
a
press-
fit
acetabular
component
(Zimmer,
Warsaw
IN).
The
compo-
nent
was
placed
in
15
of
anteversion
and
abducted.
A
perfect
AP
image
of
the
pelvic
model
was
obtained
and
the
acetabular
component
abduction
angle
was
measured
on
the
image
using
the
same
technique
as
in
phase
1.
Subsequent
images
were
taken
after
the
pelvic
model
was
repositioned
in
multi-
ple
known
degrees
of
deviation
away
from
the
perfect
AP
position,
including-
10°
and
20°
inlet,
10°
and
20°
outlet,
10°
and
20°
obturator
oblique,
and
10°
and
20°
iliac
oblique.
Acetabular
component
abduction
angles
were
measured,
as
in
phase
1,
for
each
change
in
position
(Fig.
3).
Correlations
be-
tween
cup
angle
measurements
and
pelvic
orientation
were
All
intraoperative,
immediate
post-op
PACU,
and
3
months
office
visit
images
were
reviewed
to
quantify
the
percentage
of
images
deemed
as
perfect
AP
pelvis
images.
Imperfect
pelvic
X-rays
were
more
commonly
seen
on
intraoperative
CR
im-
ages
than
in
portable
X-rays
obtained
in
the
PACU
or
at
3-
month
office
visit
images.
For
the
intraoperative
CR
images
the
most
common
images
was
an
inlet
view
43%
(10/23),
fol-
lowed
by
a
perfect
AP
image
obtained
in
30%
(7/23),
and
an
outlet
view
was
seen
in
22%
(5/23),
while
just
1
image
was
deemed
to
have
pelvic
obliquity
4%
(1/23).
In
comparison,
perfect
AP
pelvic
X-rays
were
more
commonly
attained
in
the
PACU
and
3-month
office
visit
X-rays.
A
perfect
AP
pelvis
was
obtained
in
56%
(13/23)
of
PACU
images
and
87%
(20/23)
of
3-
month
office
visit
images
(Table
1).
Acetabular
component
abduction
angles
were
then
measured
on
all
films
and
compared.
The
mean
intraoperative
cup
angle
of
38.2°
(R
29°-55°)
significantly
increased
(p
<
.0001)
to
41.7°
(R31°-55°)
in
the
PACU
and
to
41.6°
(R
30°-55°)
in
the
office.
The
mean
variance
between
intraoperative
CR
cup
abduction
angle
measurements
to
PACU
portable
X-rays
was
3.4°
(Range
—3°
to
+10°).
Three
angles
decreased,
3
remained
unchanged,
and
17
increased
between
intra-op
and
PACU
images.
The
mean
variance
of
cup
abduction
angle
between
intraoperative
CR
images
to
3
month
office
visit
portable
X-
rays
was
3.4°
degrees
(R
—3°
to
+9°).
Only
1
angle
decreased,
4
remained
unchanged,
and
18
increased
between
intra-op
and
3
months
post-op
images.
There
was
no
difference
in
measured
cup
abduction
angle
measured
on
portable
X-rays
Table
1—
Perfect
AP
pelvis
image
was
obtained
only
30%
of
the
time
intraoperatively
in
the
lateral
decubitus
position
compared
to
57%
and
87%
in
the
supine
position
immediate
post-op
and
at
3
month
visit.
Pelvic
Images
Obtained
100%
90%
80%
70%
60%
50%
40%
30%
20%
10%
0%
Perfect
AP
Inlet
Outlet
Obt
Obl.
Iliac
Obl.
Intraop
PACU
Office
3
mo
70
60
1
50
O
40
v30
.0
Table
3
Compared
to
a
perfect
AP
image,
the
inlet
views
tend
to
slightly
underestimate
cup
abduction
angle
whereas
outlet
views
tend
to
overestimated
cup
abduction
angles.
These
trends
were
consistent
for
both
regular
cup
position
(42°)
and
the
more
horizontal
cup
position
(29°).
The
more
vertical
cup
(60°)
actually
appeared
underestimated
with
both
inlet
and
outlet
views.
-4
Regular
Inlet-
Outlet
—M—Vertical
Inlet-
Outlet
—A—Horizontal
Inlet-Outlet
=20
U
10
0
20
10
AP
10
20
inlet
inlet
outlet outlet
X
-
ray
measurements.
Intraoperative
radiographs
during
total
hip
arthroplasty
can
provide
the
surgeon
with
important
information
regarding
component
positioning.
With
this
in-
formation
surgeons
can
confirm
proper
component
position,
or
when
necessary
make
adjustments
to
correct
component
mal-positioning
and
reduce
outliers.
The
two
most
popular
methods
of
obtaining
intraoperative
radiographs
are
standard
portable
radiographs
or
computed
radiography.
Standard
portable
radiographs
may
require
a
potentially
lengthy
pro-
cessing
time
that
can
delay
surgical
progression
and
prolong
anesthesia.
Intraoperative
computed
radiography
provides
Table
4
Compared
to
a
perfect
AP
image,
the
obturator
oblique
views
underestimated
cup
abduction
angle
measurements
whereas
iliac
oblique
images
overestimated
cup
abduction
angle
measurements.
These
trends
were
consisted
with
acetabular
components
in
regular
(42°),
horizontal
(29°),
or
vertical
(60°)
position.
Regular
Obt-
Iliac
Obl
Vetical
Obt-Iliac
Olb
Horizontal
Obt-
Iliac
Obl
20
obt
10
obt
AP
10
iliac
20
iliac
obl
obl obl
obl
70
60
t
50
o
40
-cs
30
lat.
20
10
0
JOURNAL
OF
ORTHOPAEDICS
12 (2015) 222-227
225
obtained
in
the
PACU
and
during
the
3-month
office
visit
(Table
2).
No
study
patient
reported
any
post
surgical
events
such
as
hip
or
pelvic
trauma
or
dislocation
event
that
could
have
been
responsible
for
changes
seen
in
acetabular
component
position
measurements.
3.2.
Part
B
Pelvic
model
cups
with
initial
abduction
angles
of
42.22°
(regular)
and
2957°
(horizontal)
on
standard
AP
images
were
measured
to
be
slightly
lower
when
the
pelvic
model
was
positioned
in
10°
and
20°
inlet
views
(-1.05°to
—0.72°and
0.24°
to
—0.06°,
respectively).
The
initial
more
vertical
orientated
cup
(60.14°)
on
standard
AP
was
measured
to
be
slightly
overestimated
on
10°,
20°
inlet
views
(+1.28°
to
+1.42°,
respectively).
Outlet
views
of
10°,
20°
overestimated
the
abduction
angle
of
the
neutral
cup
by
+058°
to
+3.96°,
and
the
horizontal
cup
by
+0.12°
to
+2°,
and
the
vertical
cup
by
+2.73°
to
+5.58°
(Table
3).
Obturator
Oblique
views
of
10°,
20°
degrees
underestimated
the
abduction
angle
of
the
neutral
cup
by
1.63°
to
—5.01°,
the
horizontal cup
by
—1.75°
to
—2.29°,
and
the
vertical
cup
by
—0.74°
to
—3.31°.
Iliac
oblique
views
of
10°,
20°
changed
the
neutral
cup
measurement
by
+1.24°
to
+3.14°,
the
horizontal
cup
by
—0.52°
to
+0.68°,
and
the
vertical
cup
by
+
0.1°
to
+0.45°
(Table
4).
4.
Discussion
Consistently
accurate
acetabular
component
positioning
is
crucial
to
successful
THA.
A
surgeon's
ability
to
recognize
intraoperative
acetabular
component
malposition
may
not
be
as
accurate
as
once
believed.
In
a
study
of
fifty
consecutive
THAs
evaluating
a
surgeon's
ability
to
accurately
predict
the
acetabular
component
abduction
angle
using
intraoperative
alignment
guides
and
anatomic
landmarks
the
surgeon
was
outside
of
the
desired
zone
21/50
times
with
an
average
error
of
(range
0-20°)
when
compared
to
standard
postoperative
Table
2
Mean
abduction
angle
measurements
of
23
patients
including
intraoperative
lateral
decubitus,
immediate
post-operative
supine
and
3
month
office
supine
images
showed
a
trend
towards
intraoperative
underestimation
of
cup
abduction
angle
measurement
compared
to
post-operative
angle
measurements.
42
Mean
Abduction
Angle
Measurements
41
140
g
1
39
38
37
36
Intraop
PACU
Office
3
mo
Aids
Title
226
JOURNAL
OF
ORTHOPAEDICS
12
(2015) 222-227
rapid
image
processing
in
the
operating
room
that
avoids
surgical
delay.
Regardless
of
radiographic
imaging
method
used,
the
goal
is
to
obtain
a
perfect
AP
image
of
the
pelvis
to
accurately
measure
acetabular
component
position.
If
the
pelvis
imaged
has
obliquity
or
pelvic
tilt
due
to
either
patient
mal-positioning
or
improper
incident
beam
trajectory
then
radiographic
measurements
of
the
acetabular
component
abduction
angle
may
be
inaccurate
or
misleading.
Hayakawa
et
al
compared
acetabular
cup
abduction
angle
measurements
from
intraoperative
radiographs
in
lateral
decubitus
position
to
postoperative
supine
position
and
noted
a
mean
5.3°
dif-
ference
in
measurement
in
one
hundred
consecutive
total
hip
arthroplasties.
n
The
authors
postulated
that
the
difference
in
cup
abduction
measurement
was
due
to
difference
in
patient
positioning
while
obtaining
the
radiographs.
To
our
knowl-
edge
this
series
is
the
first
to
report
the
accuracy
of
intra-
operative
pelvic
images
to
obtain
a
perfect
AP
image
and
to
quantify
how
radiographic
measurements
of
acetabular
component
abduction
angle
are
sensitive
to
deviations
from
an
ideal
AP
pelvis
image.
The
clinical
results
from
Part
A
demonstrate
that
a
perfect
AP
pelvis
image
was
more
difficult
to
obtain
intraoperatively
with
the
patient
in
the
lateral
decubitus
position
than
compared
to
post-operative
supine
images
in
the
PACU
or
office
visit.
A
perfect
AP
image
was
obtained
in
just
30%
of
intraoperative
radiographs
compared
with
56%
of
PACU
films
and
87%
of
office
visit
films.
The
most
common
mal-
positioned
intraoperative
image
obtained
in
the
clinical
se-
ries
was
an
inlet
view
(43%)
followed
by
an
outlet
view
(22%).
Pelvic
obliquity
was
found
in
just
one
patient
(4%).
Overall
there
was
a
trend
of
underestimation
of
the
acetabular
component
abduction
angle
on
the
intraoperative
images
by
3.4°
compared
to
the
post-operative
images
however
the
range
varied
(-3
to
+9°).
Part
B
attempted
to
quantify
how
pelvic
obliquity
or
tilt
would
alter
radiographic
measurements
of
acetabular
component
abduction
angle.
Pelvic
tilt,
including
inlet
and
outlet
views
affected
abduction
angle
measurements.
An
inlet
view
was
shown
to
slightly
underestimate
the
true
cup
abduction
angle
measurement
as
compared
with
a
true
AP
however
this
trend
was
not
uniform
for
all
starting
cup
angles.
When
beginning
with
a
neutral
cup
position
(42°)
or
a
more
horizontal
cup
position
(29°)
then
the
inlet
view
slightly
underestimated
(less
than
or
equal
to
1°)
the
true
abduction
angle,
however
when
beginning
with
a
more
vertical
cup
po-
sition
(60)
an
inlet
view
actually
slightly
overestimated
the
abduction
angle
(+1.42°).
A
pelvic
outlet
view
uniformly
overestimated
the
cup
abduction
angle.
This
overestimation
was
more
severe
(+5.58°)
with
a
more
vertically
placed
cup
(60°)
than
with
a
horizontally
(29°)
placed
cup
(+2°).
Similarly
pelvic
obliquity,
including
obturator
oblique
and
iliac
oblique
images
uniformly
affected
abduction
angle
measurements
regardless
of
starting
cup
position,
however
the
changes
were
most
dramatic
in
the
neutral
(42°)
starting
cup
position
compared
with
the
vertical
(60)
or
horizontal
(29)
starting
cups.
Obturator
oblique
images
underestimated
the
abduction
angle
of
the
neutral
cup
by
up
to
5°,
and
the
horizontal
and
vertical
cup
were
underestimated
by
2.3°
and
3.3°
respectively.
Iliac
oblique
images
uniformly
overestimated
the
abduction
angle,
more
severely
in
the
neutral
cup
(+3.3°)
compared
to
the
horizontal
(+0.68)
and
vertical
cup
positions
(+0.45).
Limitations
of
this
study
must
be
acknowledged.
First,
radiographic
measurements
of
abduction angles
are
subject
to
intra-observer
and
inter-observer
variability.
This
variability
may
be
solely
responsible
for
the
differences
in
abduction
angles
seen
for
each
change
in
pelvic
orientation.
During
this
study
the
same
investigator
made
all
radiographic
measure-
ments
of
abduction
angles.
Second,
the
saw-bones
model
analysis
did
not
include
evaluation
of
combined
pelvic
obliq-
uity
and
tilt.
For
example,
no
evaluation
was
performed
for
a
combined
10°
inlet
+10°
iliac
oblique
view.
Finally,
the
anal-
ysis
of
acetabular
component
positioning
was
isolated
to
changes
in
abduction
angle
measurements
and
did
not
include
changes
to
acetabular
component
anteversion.
Furthermore,
changes
in
acetabular
component
anteversion
were
not
evaluated
as
a
variable
that
may
affect
radiographic
measurement
of
abduction
angle.
Throughout
each
saw-
bones
pelvic
image
the
anteversion
was
unchanged
at
15°.
For
the
senior
author,
intraoperative
assessment
of
acetabular
component
anteversion
is
made
clinically
and
adjusted
based
on
hip
stability
and
not
routinely
assessed
radiographically.
In
this
study,
intraoperative
images
in
the
lateral
decubitus
position
commonly
resulted
in
a
less
than
perfect
AP
pelvic
image,
most
commonly
due
to
pelvic
tilt.
On
average,
abduction
angles
were
underestimated
on
intraoperative
images
obtained
in
lateral
decubitus
position
as
compared
to
immediate
post-op
and
3-month
post-op
supine
images.
Pelvic
model
analysis
verified
that
the
radiographic
measurement
of
an
acetabular
component
abduction
angle
is
sensitive
to
deviations
from
a
perfect
AP
pelvis
image.
The
knowledge
of
the
trends
presented
in
this
study,
along
with
an
acknowledgement
of
the
study
limitations,
may
allow
the
hip
arthroplasty
surgeon
to
make
a
more
educated
assessment
of
acetabular
component
position
when
evaluating
a
less
than
perfect
AP
pelvic
image.
Conflicts
of
interest
Chris
Mellano
has
no
conflicts
of
interest.
Andrew
Spitzer
has
the
following
conflicts
of
interest
to
disclose:
1
Royalties
from
Depuy
2
Speakers
Bureau/
Paid
Presentations
for
Genzyme
Sanofi
Biosurgical
3
Paid
consulant
for
Genzyme
Sanofi
Biosurgical
4
Research
Support
from:
1
Genzyme
Sanofi
2
Baxter
3
Depuy
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