A Fluoroscopic Grid in Supine Total
Improving Cup Position, Limb Length, and Hip Offset
Jeremy M. Gililland, MD, Lucas A. Anderson, MD, Shannon L. Boffeli, APRN,
Christopher E. Pelt, MD, Christopher L. Peters, MD, and Erik N. Kubiak, MD
Abstract: We hypothesized that use of a novel fluoroscopic grid would decrease operative time
and component positioning variability during anterior supine total hip arthroplasty (THA). We
reviewed 99 anterior supine THAs: 39 using a fluoroscopic grid, and 60 using fluoroscopy alone.
Goals were cup abduction of 40° ± 10° and limb length and hip offset within 10 mm of the
contralateral side. Surgical time was decreased in the study group (79 vs 94 minutes, P = .002). In
the study group, more components met the goal for cup abduction (97% vs 83%, P = .046), limb
length (100% vs 88%, P = .04), hip offset (85% vs 67%, P = .047), and all 3 combined (82% vs
52%, P = .002). We demonstrated decreased component positioning variability during anterior
supine THA with assistance of a fluoroscopic grid. Keywords: total hip arthroplasty, fluoroscopic
grid, limb length.
© 2012 Elsevier Inc. All rights reserved.
Current rates of total hip arthroplasty (THA) are on the
rise with demand expected to burgeon by 174% by 2030
. Efficient methods with which to improve compo-
nent positioning will become increasingly important to
maximize both productivity and patient outcomes for
the joint surgeon and the increasing number of general
orthopedists that will be required to meet this demand.
Patient satisfaction, survivorship, and stability are all
dependent on proper acetabular component positioning,
limb-length equalization, and restoration of hip offset.
Malpositioned acetabular components can result in
increased dislocation rate, impingement, limited range
of motion, increased osteolysis, increased polyethylene
wear, and increased acetabular component migration
[2-4]. Limb-length discrepancy after THA has been
associated with nerve palsy, low back pain, abnormal
gait, increased oxygen consumption and heart rate, and
litigation [5, 6]. Failure to restore femoral offset has been
tied to worsened gait and abductor function and
increased component wear rates [7-10].
Current methods for intraoperative evaluation of
component position, limb length, and offset include
imaging with plain radiographs and fluoroscopy, the use
of intraoperative mechanical devices, the use of ana-
tomical landmarks, and computer navigation [2,11-14].
The anterior supine approach greatly simplifies the use
of intraoperative fluoroscopy. However, although fluo-
roscopy is beneficial when compared with radiographs
in that it provides real-time imaging, the field of view is
too narrow to easily compare the operative hip with the
The purpose of our study was to evaluate an
intraoperative fluoroscopic technique involving the use
of a novel radiopaque grid in anterior supine THA. We
hypothesized that the use of the grid would decrease
component position variability including cup abduction,
limb-length equalization, and restoration of hip offset
when compared with the use of fluoroscopy alone. In
addition, we hypothesized that the use of the fluoro-
scopic grid would also decrease operative time when
compared with fluoroscopy alone.
Patients and Methods
We retrospectively reviewed 99 consecutive primary
THAs in 86 patients performed by a single surgeon (EK)
through an anterior supine approach on a fracture table
(PROfx; Mizuho OSI, Union City, Calif). All THAs were
From the University of Utah, Department of Orthopaedic Surgery, Salt
Lake City, Utah.
Submitted August 16, 2011; accepted March 15, 2012.
The Conflict of Interest statement associated with this article can be
found at doi:10.1016/j.arth.2012.03.027.
Reprint requests. Jeremy M. Gililland, MD, Department of
Orthopaedic Surgery, University of Utah School of Medicine, 590
Wakara Way Salt Lake City, Utah 84108.
© 2012 Elsevier Inc. All rights reserved.
The Journal of Arthroplasty Vol. 00 No. 0 2012
performed using cementless femoral and acetabular
components with the use of either a ceramic or metal-
on-polyethylene bearing. In the study group, 39 THAs
were performed in 35 patients between September 22,
2010, and August 5, 2011, with the use of fluoroscopy
and a novel radiopaque grid fixed to the operative table
made up of 1-cm squares and 40° abduction angles (Fig.
1). This allows improved intraoperative assessment of
cup abduction, limb length, and hip offset. This group
consisted of 11 men (31%) and 23 women (69%). In the
control group, 60 THAs were performed in 51 patients
between July 1, 2009, and January 25, 2011, with the
use of fluoroscopy alone. This group consisted of 27 men
(53%) and 25 women (47%). The exclusion criteria for
this study were the following: revision THAs, THAs done
through any approach other than the anterior supine
approach, any anterior supine THAs done without the
use of fluoroscopy, and any patient without an adequate
postoperative anteroposterior pelvis film as defined
below. No patients were recalled specifically for this
study; all data were obtained from medical records. We
had approval of our institutional review board.
The study group consisted of more women than the
control group (69% vs 47%, P = .048). There was a
significant difference between the groups in terms of
weight (72 vs 85 kg, P = .004) and body mass index
(BMI) (26 vs 29 kg/m2, P = .01). There were no
differences between the 2 groups in terms of age or
height. There were no differences between the groups in
terms of presenting diagnosis (Table 1).
Our intraoperative fluoroscopy protocol with and
without the grid was similar. We first obtained an
anteroposterior pelvis image centered over the symphy-
sis and adjusted the rainbow and tilt until we had an
adequate image in which the coccyx was centered and
within 2 cm of the top of the pubic symphysis. We next
adjusted the contralateral extremity longitudinal boot
traction until the ischial tuberosities were parallel to the
grid coordinate system (this step was not performed
when the grid was not used.) We then saved our final
central image. Next, the fluoroscopy unit was telescoped
into position, and an anteroposterior image was saved of
the contralateral hip. This image was then transferred to
the opposing screen on the fluoroscopy unit and was
used for comparison when assessing the operative hip.
The fluoroscopy unit was then telescoped into position
over the operative hip. In this position, fluoroscopic
imaging was obtained while reaming and impacting the
acetabular component as well as when trialing with
various component combinations (Fig. 1).
Fig. 1. Fluoroscopic images with grid in place to aid in assessing limb length, hip offset, and acetabular component abduction.
Table 1. Patient Demographics and Presenting Diagnoses
Grid (n = 35) Nongrid (n = 51)
11 M (31%)
23 F (69%)
27 M (53%)
25 F (47%)
Data are presented as means with standard deviations in parentheses.
* These are binary variables and are thus presented as absolute
numbers with percentages in parentheses. Presenting diagnoses
percentages are calculated with respect to the total number of THAs
in each group (n = 39 in grid group, n = 60 in nongrid group).
2 The Journal of Arthroplasty Vol. 00 No. 0 Month 2012
Using an adequate postoperative anteroposterior plane
radiographs of the pelvis as defined by the legs
positioned in 15° of internal rotation and with the
coccyx centered within 2 cm of the pubic symphysis, 2
independent readers (JG and LA) blinded to patient
grouping measured the cup abduction, limb-length
inequality, and hip offset difference compared with the
contralateral limb. We measured limb length as the
perpendicular distance from the transteardrop line to the
apex of the lesser trochanter . We used the method
described by Dastane et al  to measure hip offset,
which is the femoral offset added to the horizontal
position of the center of rotation (COR) of the hip. We
decided to measure hip offset in lieu of femoral offset
because femoral offset does not represent the true
displacement of the femur from the pelvis because this
displacement is influenced by both femoral offset and
COR . Femoral offset was measured as the distance
perpendicular to the anatomical axis of the femur from
the center of the femoral head to the anatomical axis of
the femur (Fig. 2). The position of the COR was
measured as a distance parallel to the transteardrop
line from the teardrop to the center of the acetabulum or
acetabular component (Fig. 2). Interobserver differences
were noted and remeasured and reconciled by
10° (the safe zone). For limb length and hip offset, the
surgeon desired to be within 10 mm of the contralateral
side. For each THA being evaluated, the measurements
obtained were compared with each respective goal, and a
binary value of in or out of the desired zone was given for
abduction angle, limb-length inequality, and hip offset
difference. Ideally, a well-placed THA would be within all
3 of our goal zones, and we therefore performed 1 final
evaluation of the measurements and gave each hip a
binary value of in or out for all goals. We did not measure
component version because we do not feel that the grid
helps guide version.
Along with obtaining demographic information, re-
cords were reviewed for operative start time and end
time, allowing us to calculate elapsed surgical time for
Data were analyzed by an independent statistician
using commercially available software (STATA Version
11; StataCorp, College Station, Tex). Student t test was
used for comparing the continuous variables: elapsed
surgical time, age, height, weight, and BMI. The χ2test
was used to compare all binary variables if the expected
frequencies were all greater than 5. Fisher exact test was
used to compare those binary variables where the
expected frequencies were not adequate for the χ2test.
Fig. 2. Postoperative anteroposterior pelvis radiograph used to measure cup abduction (CA), limb-length (LL) difference, and hip
offset difference (COR + femoral offset [FO]).
A Fluoroscopic Grid in Supine Total Hip Arthroplasty ?
Gililland et al 3
Of the demographic data evaluated, potential con-
founders were identified as sex, height, weight, BMI, a
diagnosis of osteoarthritis, and a diagnosis of posttrau-
matic arthritis because the P values for these variables
were either significant or nonsignificant but less than
.25. A multivariable linear regression controlling for
these potential confounders was performed for the
continuous variable of elapsed surgical time.
There were significantly more acetabular components
within the safe zone of cup abduction (30°-50°) in the
study group (97% vs 83%, P = .046). With the use of the
grid, significantly more THAs had restoration of limb
length to within 10 mm of the contralateral extremity
(100% vs 88%, P = .04). Hip offset restoration to within
10 mm of the contralateral extremity was also signifi-
Finally, with the use of the grid, there were significantly
safe zone, limb-length restoration, and hip offset restora-
tion (82% vs 52%, P = .002) (Table 2).
Mean elapsed surgical time was statistically signifi-
cantly less (adjusted P = .002) in the grid group, with a
mean operative time of 79 minutes compared with 94
minutes in the control group and an adjusted elapsed
surgical time difference of 14 minutes when controlling
for potential confounders (Table 2).
Because patient satisfaction, survivorship, and stability
are all dependent on proper acetabular component
positioning, limb-length equalization, and restoration of
hip offset, efficient methods with which to improve
these factors are of paramount importance. In anterior
supine THA, fluoroscopy is commonly used as a tool for
intraoperative assessment of component positioning.
However, the fluoroscopic method frequently described
involves printing an image taken of the trial components
in position, and superimposing this image on a printed
image of the contralateral hip attempting to overlap the
radiographic landmarks of the pelvis and the femur to
compare length and offset . This technique has been
shown in a large series to yield excellent results in terms
of acetabular component positioning and limb-length
restoration . We desired to simplify this process and
developed the grid as a fluoroscopic adjunct to obtain
comparable results in component positioning with
We found that the use of the grid with intraoperative
fluoroscopy compared with the use of fluoroscopy alone
decreased component position variability in terms of cup
abduction, limb-length equalization, and restoration of
hip offset. In a recently published large registry series
evaluating cup positioning in THA and hip resurfacing
procedures, cup abduction was found to fall within the
safe zone in only 63% of cases. This study found that
lower surgeon volume, minimally invasive surgical
approaches, and patient obesity were independent pre-
dictors of cup malpositioning . However, Matta et al
 showed excellent radiographic results in component
positioning with the use of fluoroscopy in their experi-
ence of 494 anterior supine THAs; 96% of acetabular
components were found within the safe zone for cup
abduction, and limb lengths were within 11 mm of the
contralateral side in 99% of their hips. In this study,
Matta et al  also stated that unlike most minimally
invasive surgical approaches, the anterior supine ap-
proach could be done on any patient and did not require
selection of qualified patients based on body habitus. Our
results in the grid group compare favorably with the
results of Matta in that 97% of our acetabular compo-
nents were within the safe zone for abduction and 100%
of our THAs had limb lengths within 10 mm of the
contralateral side. In a recent study by Dastane et al, the
concept of hip offset was defined as the combination of
femoral offset and cup COR. They describe hip offset as a
more important measure than femoral offset because in
represents the displacement of the femur from the pelvis.
In this study, they were able to restore the hip offset to
within 6 mm of the contralateral side in 95% of 82 THAs
with the assistance of computer navigation . We had
similar results in that we were able to restore our hip
offset within 10 mm of the contralateral side in 85% of
our THAs with the use of the grid.
We found significantly shorter operative times in the
grid group compared with the use of fluoroscopy alone.
In aprospective randomizedclinical study by Kalteis et al
, acetabular component abduction was evaluated
Table 2. Goal Zone and Surgical Time Results
THAs Within Goals
Goal Grid (n = 39) Nongrid (n = 60)
Cup abduction goal
Limb-length goal (±10 mm) 39 (100%)
Hip offset goal (±10 mm)
Within all 3 goals
38 (97%)50 (83%) .046
(n = 39)
(n = 60)
79 (74-84) 94 (89-100)14 (6-23) .002
Data are presented as absolute numbers with percentages in
* Data presented as means with 95% confidence intervals in
† Adjusted for sex, height, weight, BMI, osteoarthritis, and posttrau-
adjusted mean difference from the linear regression model.
4 The Journal of Arthroplasty Vol. 00 No. 0 Month 2012
after freehand placement as compared with the assis-
tance of computed tomography (CT)–based and image-
less navigation systems. Navigation was found to
improve cup abduction from 45% in the safe zone
with freehand technique to 83% and 93% with
imageless navigation and CT-based navigation, respec-
tively. However, the operative time was increased by
8 minutes with imageless navigation and by 17 minutes
with CT-based navigation . We found similar
improvement in acetabular component abduction as
we improved from 83% in the safe zone with
fluoroscopy alone to 97% with the use of the grid.
However, unlike the Kalteis et al study, we did not find
increased operative time with the use of the grid
compared with fluoroscopy alone. Although it is difficult
to retrospectively assess the effect of the grid on
operative efficiency, we do believe that the grid has
the potential to improve efficiency over fluoroscopy
alone for several reasons. First, it allows for a simple
comparison of limb length and hip offset compared with
the contralateral side and requires less fluoroscopic
images to be obtained because the grid provides a static
frame of reference from image to image. In addition, it
can be used to evaluate the direction of reaming and the
cup abduction in real time while reaming and impacting
the cup, respectively. This allows for accurate placement
of the cup without having to go back and adjust for
malposition seen with trialing images. Of note, the use of
the fluoroscopic grid does require placing this device on
the fracture table preoperatively. Anecdotally, this only
adds approximately 1 minute to the preoperative setup
because the grid is quickly centered via the perineal
posthole and secured to the table with Velcro.
There are several limitations to our study. First, our
study was retrospective without any randomization.
Although there was some overlap in dates of surgery
between the groups, a greater percentage of the nongrid
THAs were performed during an earlier period in this
surgeon's experience with anterior supine THA. In-
creased surgeon experience may be a confounder when
evaluating accuracy of component positioning and
operative efficiency. However, we did not include the
first 20 anterior supine THA performed by the surgeon,
as a surgeon's first 10 anterior supine hips have been
shown to reflect the learning curve related to compli-
cations . In addition, we performed a separate
analysis comparing the last 5 patients from each group
to validate whether our exclusion of the first 20 cases
was effective in decreasing the potential bias from
increased surgeon experience. This analysis did not
yield any statistically significant differences between
these 2 subgroups, but this would be expected becauseof
the limited numbers of 5 patients per group. However,
the grid subgroup did have more hips meeting the goal
for abduction (100% vs 40%), limb-length restoration
(100% vs 80%), and all 3 goals combined (60% vs
20%), whereas the nongrid subgroup had more hips
meeting the goal for hip offset restoration (80% vs
60%). The mean elapsed surgical time was shorter in the
grid subgroup (75 vs 102 minutes). Other than hip
offset, the differences between these subgroups were
quite similar to those seen in Table 2 for the larger
groups, and we feel that these findings validate our
assumption that our cases beyond the first 20 were
outside of the learning curve.
A second limitation is that our study reflects 1
surgeon's experience at an academic center. Use of the
grid by additional surgeons will be necessary to prove
that these favorable results associated with use of the
grid are reproducible in the hands of surgeons with
varying levels of experience and THA volume.
Another limitation of our study was the asymmetric
demographics between the groups with more men with
higher BMIs in the nongrid group. We feel that the
difference in gender distribution is simply an anomaly,
and we are not aware of any potential confounding
effects that this may have had on our findings. The
difference in BMI is concerning for confounding as
Callanan et al  found obesity (compared with BMI's
in normal and overweight range) along with minimally
invasive surgical approaches and surgeons with low THA
volume to be independent risk factors for acetabular
component malpositioning. However, their study did
not include specifically break out the anterior supine
approach nor did it mention intraoperative fluoroscopy
as a real-time safe guard. In addition, Matta et al , in
their study of anterior THAs using intraoperative
fluoroscopy, reported consistent component positioning
regardless of body habitus.
In conclusion, we have demonstrated reduced vari-
ability in component positioning and reduced operative
times for anterior supine THA performed with intrao-
perative fluoroscopy coupled with a novel radiopaque
grid. Given the importance of accuracy in THA compo-
nent positioning, we recommend the use of this simple
and effective supplement to anterior supine THA.
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