ABSTRACT:
We herein present a smartphone-assisted technique for acetabular cup placement during
revision total hip arthroplasty (rTHA). Four patients were operated on: three were
submitted to second-stage rTHA after infection, and one underwent surgery due to aseptic
loosening. The technique entails three main steps: evaluation of the amount of lateral
pelvic tilt (either clinically or radiographically); setting a supracetabular rod
using the smartphone app as a reference for inclination adjustment; and acetabulum
preparation and final cup placement using the smartphone to guide the inclination
angle after considering the amount of pelvic tilt. Cup anteversion was adjusted according
to the transverse acetabulum ligament. All 4 cases underwent a follow-up that ranged
from 17 to 24 months. None of the patients required further revision, and no complications
(intraoperative, early, or late postoperative) were observed. All cups were within
the Lewinnek safe zone for inclination (42°, 43°, 47°, and 41°). The functional outcome
per the Harris Hip Score was excellent for all patients. Smartphones are cheap tools
that can assist physicians in the adjustment of acetabular cup inclination during
rTHA; however, assessing the possible lateral pelvic tilt and considering it while
placing the cup are crucial.
Keywords: acetabulum; arthroplasty; replacement; hip; smartphone.
RESUMO:
Apresentamos Uma Técnica Assistida Por Smartphone Para A Colocação De Cúpula Acetabular Durante A Revisão De Artroplastia Total De
Quadril (Ratq). Quatro Pacientes Foram Submetidos À Cirurgia; Três à rATQ de segundo
estágio após infecção e um devido a afrouxamento asséptico. A técnica tem três etapas
principais: avaliação (clínica ou radiográfica) da inclinação pélvica lateral; colocação
de uma haste supra-acetabular usando o aplicativo do smartphone como referência para o ajuste da inclinação; e preparação do acetábulo e colocação
final da cúpula utilizando o smartphone para a orientação do ângulo de inclinação após considerar a inclinação pélvica. A
anteversão da cúpula foi ajustada de acordo com o ligamento acetabular transverso.
Todos os quatro casos foram acompanhados por 17 a 24 meses; nenhum paciente precisou
de outra cirurgia de revisão ou apresentou complicações (intraoperatórias pós-operatórias
precoces ou tardias). Todas as cúpulas estavam dentro da zona segura de Lewinnek de
inclinação (42° 43° 47° e 41°). O resultado funcional de acordo com o Harris Hip Score
foi excelente em todos os pacientes. Os smartphones são ferramentas baratas que podem auxiliar os médicos no ajuste da inclinação da
cúpula acetabular durante a rATQ; no entanto é crucial avaliar a possível inclinação
pélvica lateral e considerá-la ao posicionar a cúpula.
Palavras-chave: acetábulo; artroplastia do quadril; smartphone.
FIGURES
| Citation: Khalifa AA, Adam MF, Mahran MA. Adjustment of Acetabular Cup Inclination Assisted by Smartphone during Revision Total Hip Arthroplasty: Surgical Technique and Report of Four Cases. 60(01):. doi:10.1055/s-0045-1804490 |
| Note: Work developed at the Department of Orthopedic Surgery and Traumatology, Faculty of Medicine, Assiut University, Assiut, Egypt. |
| Financial Support The authors declare that they did not receive financial support from agencies in the public, private, or non-profit sectors to conduct the present study. |
|
Conflict of Interests The authors have no conflict of interests to declare. |
| Received: September 03 2024; Accepted: December 14 2024 |
INTRODUCTION
Proper implant positioning during primary total hip arthroplasty (THA) is one crucial factor for shortand 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.6-8
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
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 decubitusposition(asdescribedin theliterature;9,10 Figs. 3B and 4C); and computer tomography (CT) scans to assess the amount of bone defect, if suspected (►Fig. 1C). The same surgeon operated on all cases (patient details are described in ►Table 1 and in ►Figs. 1-4) 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).
| 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 | þ3 |
| 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 graftingusing 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°;8-10 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,8as well as in an invitro andcadaveric 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 smartphoneassisted 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. They3 also reported that using an inclinometer increased the operative time by 2to 7 minutes compared withother 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-assistedacetabularcupplacementto 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 ¼ 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.
ACKNOWLEDGMENTS
The authors would like to thank Dr. Amr A. Fadle for his assistance in obtaining the Ethics Committee approval and Prof. Ahmed M. Abdelaal for his support and insight.
