Keywords
acetabulum - arthroplasty, replacement, hip - smartphone
Introduction
Proper implant positioning during primary total hip arthroplasty (THA) is one crucial
factor for short- and long-term outcomes and survival;[1]
[2] this becomes more demanding during revision THA (rTHA), especially if there are
bone defects or distorted anatomical landmarks.[2]
[3]
The economic burden of rTHA is increasing, and instability and aseptic loosening are
the leading causes of revision; therefore, various strategies have been employed to
reduce the risk of revision, including improving implant designs, bearing materials,
and newer technologies such as computer navigation and robotic-assisted surgeries;
however, most of these are expensive and unavailable at every institution.[1]
[4]
[5]
Smartphone-assisted acetabular cup placement has been investigated in primary THA
with promising results both in cadaveric and clinical settings, which showed acceptable
accuracy, ease of sue by young surgeons, and cheap application, especially in institutions
with economic constraints that limit the introduction of the aforementioned newer
technologies.[6]
[7]
[8]
We herein present a simple and economical technique entailing the use of smartphone
applications (apps) to adjust acetabular cup inclination in three steps during rTHA
and report the early results of the first four cases.
Surgical Technique and Description of the Cases
Surgical Technique and Description of the Cases
Approval was obtained from our local ethical committee (IRB No.:17300762), and written
informed consent was obtained from all patients before surgery.
The erioperative protocol for all patients was as follows: 1) detailed medical and
surgical history, 2) preoperative clinical evaluation; 3) laboratory investigations
as part of the regular preoperative assessment and to exclude infection (complete
blood count [CBC] with differential white blood cell [WBC] count, erythrocyte sedimentation
rate [ESR], and levels of C-reactive protein [CRP]); and 4) imaging studies: plain
preoperative radiographs of the pelvis in anteroposterior (AP) view (including both
hips; [Figs. 1A,B] and [2A,B]), of the affected hip in AP and lateral views ([Fig. 2A]), and of the pelvis in AP view while the patient was in the lateral decubitus position
(as described in the literature;[9]
[10]
[Figs. 3B] and [4C]); and computer tomography (CT) scans to assess the amount of bone defect, if suspected
([Fig. 1C]).
Fig. 1 Case 1. (A) A cementless bipolar hemiarthroplasty with dislocation and infection. (B) First -stage total hip arthroplasty (THA), with the application of a cement spacer
loaded with antibiotics (the stem was retained, as it was solidly ingrown). (C) Computed tomography (CT) scan to assess the amount of bone defect. (D) Intraoperative smartphone app-assisted adjustment of the supracetabular rod (white
arrow) as a reference for cup inclination (red arrow: smartphone in a sterile plastic
bag; red circle: the adjusted angle measured by the Spirit Level app; black arrow:
the supraacetabular Schanz screw; and yellow arrow: a clamp). (E) Acetabular reaming performed parallel to the supraacetabular rod. (F) Immediate postoperative anteroposterior (AP) radiograph of the pelvis showing cementless
dual mobility cup and an inclination angle of 41.9°. (G) The last follow-up visit (at 24 months), showing maintained cup position.
Fig. 2 Case 2. (A) A cemented bipolar hemiarthroplasty with infection after failure of the fixation
of a neck of the femur fracture. (B) First-stage THA with the application of an articulating cement spacer loaded with
antibiotics. (C) Intraoperative smartphone app-assisted adjustment of the supracetabular rod (white
arrow) as a reference for cup inclination (red arrow: smartphone in a sterile plastic
bag; red circle: the adjusted angle measured by the Spirit Level app; black arrow:
the supraacetabular Schanz screw; yellow arrow: a clamp; and blue arrow: transverse
acetabular ligament for anteversion adjustment). (D) Acetabular reaming performed parallel to the supraacetabular rod. (E) Green arrow showing the allografts used for impaction bone grafting to reconstruct
the bone defect. (F) Final acetabular cup insertion performed while the handle is parallel to the supracetabular
rod. (G) immediate postoperative AP radiographs of the pelvis showing cementless cup and
an inclination angle of 42.9°.
Fig. 3 Case 3. (A) A malpositioned cementless acetabular cup with aseptic loosening. (B) An AP radiograph of the pelvis with the patient in the lateral decubitus position
showing a lateral pelvic tilt (adduction) of -6°. (C) Intraoperative smartphone app-assisted adjustment of the supracetabular rod as a
reference for cup inclination (red arrow: smartphone in a sterile plastic bag; red
circle: the adjusted angle measured by the Spirit Level app). (D) Blue arrow showing the transverse acetabular ligament for anteversion adjustment.
(E) After acetabular reaming and insertion of a trial cup, the amount of acetabular
bone defect could be assessed (orange arrow). (F) Immediate postoperative AP radiograph of the pelvis view showing cemented dual mobility
cup with An inclination angle of 46.9°, and bone defect reconstruction using a metal
augment. (G) The last follow-up visit (at 17 months), showing maintained implant position.
Fig. 4 Case 4. (A) A cemented bipolar hemiarthroplasty with loosening and infection. (B) First-stage THA with a dislocated cement spacer loaded with antibiotics. (C) An AP radiograph of the pelvis with the patient in the lateral decubitus position
showing a lateral pelvic tilt (abduction) of 3°. (D) Intraoperative smartphone app-assisted adjustment of the supracetabular rod (white
arrow) as a reference for cup inclination (red arrow: smartphone in a sterile plastic
bag; red circle: the adjusted angle measured by the Spirit Level app; black arrow:
the supraacetabular Schanz screw; and yellow arrow: a clamp). (E,F) Acetabular reaming and final cup insertion performed parallel to the supraacetabular
rod. (G) Immediate postoperative AP radiograph of the pelvis showing cementless cup and an
inclination angle of 40.6°. (H) The last follow-up visit (at 19 months), showing maintained
cup position.
The same surgeon operated on all cases (patient details are described in [Table 1] and in [Figs. 1]
[2]
[3]
[4]) under spinal anesthesia, with the patient in the lateral decubitus position (after
ensuring that the table was parallel to the floor) through a modified direct lateral
approach (incorporating the previous surgical incision); after adequate exposure,
implant removal, and debridement, at least five tissue samples were obtained and sent
for bacterial culture and sensitivity assessment. We aimed at inserting the cup within
the Lewinnek safe zone (40° ± 10° for inclination and 15° ± 10° for anteversion).
Table 1
|
Case 1
([Fig. 1])
|
Case 2
([Fig. 2])
|
Case 3
([Fig. 3])
|
Case 4
([Fig. 4])
|
|
Age (years)
|
35
|
61
|
58
|
60
|
|
Gender
|
Female
|
Male
|
Male
|
Male
|
|
Side
|
Right
|
Left
|
Right
|
Left
|
|
Preoperative diagnosis
|
PJI requiring second-stage rTHA
|
PJI requiring second-stage rTHA
|
Malpositioned cup with aseptic loosening
|
PJI requiring second-stage rTHA
|
|
Number of previous surgeries
|
3
|
4
|
1
|
3
|
|
Follow-up (months)
|
24
|
23
|
17
|
19
|
|
Acetabular bone defect
|
Yes
|
Yes
|
Yes
|
Yes
|
|
Bone defect per the Paprosky classification
|
2A
|
2C
|
3A
|
2A
|
|
Preoperative lateral pelvic tilt (degrees)
|
0
|
0
|
-6
|
+3
|
|
Implants used
|
Cementless dual mobility cup, the femoral side was not revised
|
Cementless primary cup and cementless stem (Wagner)
|
Cemented dual mobility cup, the femoral side was not revised
|
Cementless primary cup and cementless stem (Wagner)
|
|
Bone defect reconstruction
|
Not required
|
Impaction bone grafting using allograft
|
Metal (tantalum) augment
|
Not required
|
|
Postoperative cup inclination (degrees)
|
41.9
|
42.9
|
46.9
|
40.6
|
|
Cup inclination at the last follow-up (degrees)
|
41.5
|
Not acquired
|
46.4
|
40.6
|
|
Complications
|
Mild, occasional pain and limping gait
|
Mild, occasional pain
|
None
|
None
|
|
Harris Hip Score (at the last follow-up)
|
95
|
Not acquired*
|
92
|
90
|
The three main steps of smartphone-assisted adjustment of acetabular cup inclination
during rTHA are as follows:
-
1) Radiological or clinical calculation of the possible lateral pelvic tilt; radiological:
in the pelvis AP radiograph with the patient in the lateral decubitus position, as
the angle between a transverse pelvis axis (interteardrop or interischial lines) and
the level of the radiology table ([Figs. 3B] and [4C]); if it cannot be obtained preoperatively, it can be obtained using fluoroscopy
after final positioning of the patient on the operative table. The pelvis could be
in a neutral position (0°) if the angle is of 90°, abducted (positive value) if the
angle is > 90°, and adducted (negative value) if the angle is < 90°;[8]
[9]
[10] clinical: as an angle between a line connecting marks placed on the anterosuperior
iliac spines (ASISs) bilaterally and the level of the operative table.[6]
[8]
-
2) Setting the intraoperative reference for cup inclination: we followed steps described
previously in the literature,[6]
[8] entailing the use of a sterile plastic bag as a protector for the smartphone after
turning on the Spirit Level app with a built-in compass on an iPhone XR smartphone
(Apple Inc., Cupertino, CA, United States), or other similar, free, and downloadable
apps (for Android platform-based smartphones). A supra-acetabular Schanz screw was
inserted from within the surgical approach to which a rod was connected using an adjustable
clamp. The rod acts as the reference to adjust the cup inclination after considering
the value of the pelvic tilt measured. For a target final inclination angle of 45°
and if the pelvic tilt is of -10°, for example, we adjust the rod at 35°, and vice
versa for pelvic abduction ([Figs. 1D, ]
[2C, ]
[3C], and [4D]).
-
3) Acetabulum reaming and final acetabular cup insertion: acetabulum reaming in a
progressed manner was performed by adjusting the reamer handle parallel to the supraacetabular
rod for inclination adjustment ([Figs. 1E, ]
[2D], and [4E]). For the anteversion, we rely mainly on the transverse acetabular ligament (TAL;
[Figs. 2C] and [3D]), a consistent anatomical landmark in nearly most revision cases.[11]
[12] After reaching a proper fit, a trial acetabular component is used to assess the
final cup size, the stability, and the need to reconstruct the present acetabular
defect ([Fig. 3E]). The final cup insertion (cemented or cementless) is performed while the inserter
handle is parallel to the supraacetabular rod ([Figs. 2F] and [4F]).
Postoperative Assessment and Follow-up
Postoperatively and at the last follow-up visit, AP radiographs of the pelvis were
obtained to evaluate the inclination (abduction) angle of the acetabular cup, measured
between the interteardrop or interischial lines and a line along the axis of the cup
eclipse formed by the superolateral edge and inferomedial edge as reference points
([Figs. 1F, ]
[2G, ]
[3F], and [4G]). The functional outcomes at the last follow-up visit were assessed according to
the Harris Hip Score (HHS), and complications at any point of the follow-up were reported.
The outcomes are shown in [Table 1].
Discussion
Most surgeons agree that optimum acetabular cup positioning is crucial for long-term
results and to reduce the incidence of instability after primary and revision THA.[2]
[5]
[11]
The use of computer navigation and robotics in rTHA showed satisfactory results regarding
the decrease in the risk of instability due to proper placement of the implants and
the reduction in dislocation rates after rTHA of up to 0%.[13] However, these technologies are expensive, unavailable in every institution, and
require specific training and preparation.[4]
[5]
To overcome these obstacles, we have applied smartphone apps that successfully assisted
acetabular cup adjustment in four rTHA surgeries. We believe that the technique is
simple and surgeon-friendly without the need for complex preparation or special preoperative
imaging studies apart from AP radiographs of the pelvis with the patient in the lateral
decubitus position to calculate the lateral pelvic tilt, and helped in achieving the
acetabular cup inclination angle within the safe zone; furthermore, no complications
or infections were reported in any of the cases.
The smartphone-assisted cup placement technique has described in primary THA, and
it showed promising results in terms of helping young, less experienced surgeons obtain
optimum acetabular cup placement comparable to their senior peers, with further improvement
in cup placement accuracy compared with visual methods; this was proven in clinical
studies,[8] as well as in an invitro and cadaveric models.[7]
In the current technique, we employed the same manual instruments used routinely during
THAs, without the need for a complex setup. The time spent using the smartphone app
and adjusting the angles was of approximately 5 minutes, without external assistance.
We admit that the smartphone-assisted technique cannot compete with the accuracy of
computer navigation or robotic-assisted cup placement; however, we believe it is more
economical and time-saving than these technologies.
In a systematic review on the role of an inclinometer (including smartphone apps)
in the adjustment of acetabular cup positioning during THA, van Duren et al.[3] reported that, in the inclinometer group, the cup inclination angle was significantly
more within the target zone compared with the freehand or mechanical guide-assisted
techniques. They[3] also reported that using an inclinometer increased the operative time by 2 to 7 minutes
compared with other techniques based on the results of 3 clinical studies.
The amount of lateral pelvic tilt was reported to reach ± 10° in the literature, with
up to 45% of the patients having an absolute tilt of 5°.[8]
[9]
[14] Therefore, one crucial preoperative step we recommend is to anticipate the amount
of lateral pelvic tilt, which could pass unnoticed by the surgeon and get obscured
after draping, especially in overweight patients or when there is a fixed hip joint
deformity.[9]
[10]
[14]
We obtained acetabular cup inclination within the safe zones in all patients, and
no instability was reported during the follow-up. Kurosaka et al.[7] compared the accuracy of iPhone-assisted acetabular cup placement to computer navigation
in five cadaveric hips in procedures performed by 7 surgeons (4 first-year residents
and 3 senior hip surgeons); they reported a mean difference between both techniques
of 2.1° ± 1.6° (range: 0°–6°), no significant difference between residents or senior
surgeons in inclination adjustment (p = 0.74), and that all acetabular cups placed using the iPhone technique were within
the Lewinnek safe zone.[7]
One limitation of the smartphone technique is the difficulty in assessing anteversion,
as reported in previous studies.[7] To overcome this obstacle, we relied on the TAL in all cases as a consistent patient-specific
anatomical landmark.[12]
Conclusion
Smartphones can assist young surgeons or those who do not have access to newer technologies
in the adjustment of acetabular cup inclination when placing the cup in rTHA; however,
assessing the possible lateral pelvic tilt and considering it while placing the cup
are crucial.
Bibliographical Record
Ahmed A. Khalifa, Mahmoud Faisal Adam, Mohamed A. Mahran. Ajuste de inclinação do
acetábulo assistido por smartphone durante revisão de artroplastia total de quadril: Técnica cirúrgica e relato de quatro
casos. Rev Bras Ortop (Sao Paulo) 2025; 60: s00451804490.
DOI: 10.1055/s-0045-1804490
