Abstract
BACKGROUND:
Increases in the numbers of surgical procedures for primary total hip arthroplasty (THA) inevitably lead to increases in the requirements for revision THA. The achievement of long-term stability is difficult or impossible by conventional implants in patients with severe destruction of the acetabulum.
OBJECTIVE:
This case report presents a successful treatment using a specific three-dimensional (3D)-printed porous titanium acetabular composite component without a flange in the management of Paprosky type IIIB acetabular defects.
METHOD:
A 65-year-old female diagnosed with right hip prosthetic loosening with a huge acetabular defect presented to our hospital. We designed the 3D model of the pelvis and created an individualized 3D-printed porous titanium acetabular composite component for revision THA. The procedure was performed through a posterolateral approach, and the component was implanted in the defect and fixed with cup screws using the drill guides.
RESULTS:
At the last follow-up at 2 years, the patient had a satisfactory hip joint function and no signs of loosening or other complications were found.
CONCLUSIONS:
The 3D-printed porous titanium acetabular composite component without a flange is showing promising clinical and radiological outcomes in the management of Paprosky type III acetabular defects.
Keywords
Introduction
The demand for primary total hip arthroplasty (THA) is expected to increase as the population ages [1]. In consequence, the requirements for revision THA will also increase over the next several decades. A common indication for revision THA is mechanical loosening of acetabular components with subsequent bone defects of the acetabulum [2]. Surgical management of acetabular defects represents one of the greatest challenges in revision THA, especially in patients with Paprosky type III acetabular defects [3].
The general principles for reconstruction of acetabular defects include reconstruction of the hip center of rotation (COR) and stable restoration of the continuity [4]. Previous studies have described several alternative methods of reconstruction, such as jumbo cups, structural allografts, cup-cage constructs, reinforcement rings, metal augments, and custom-made acetabular components (CMACs) [5, 6, 7, 8], however, a real consensus is far from being reached [9]. As a result, the use of three-dimensional (3D)-printed CMACs has gained popularity in recent years and has become part of surgical practice for the production of precise and CMACs [10]. We present a new application of 3D-printed technology in the setting of Paprosky type IIIB acetabular defects and discuss the advantages and disadvantages. In this case, a porous titanium composite CMAC without a flange was created to be used for revision THA.
Case presentation
The case and design objectives
A 65-year-old female with a body mass index of 20.5 kg/m
Pelvis AP (A) and 3D pelvis (B) demonstrating the acetabular cup protruded into the pelvis.
Preoperative planning for revision surgery was conducted including laboratory evaluation which found her to be free of infection. Radiographic analysis, including a computed tomography (CT) scan, demonstrated that the cup protruded into the pelvis, with a small mouth and a large bottom (Fig. 1). Due to the severe acetabular defect of Paprosky type IIIB [3], which was difficult to reconstruct with the conventional components, therefore, we decided to use a 3D-printed CMAC to complete the revision surgery. The trial was approved by the institutional review board of The Third Hospital of Mianyang (2019-4). Informed consent was obtained from the patient included in the study.
The design procedures of the acetabular composite component and screws were orderly. Firstly, the 3D model was built based on the CT scan to evaluate the bone defect and residual bone. Secondly, the cup was designed including the COR, orientation, and size. Thirdly, the augment was designed to reconstruct the supportive structure and restore bony contact while maintaining the cup location. Lastly, the screw placement, trajectory, and length were designed to enhance primary mechanical stability. Briefly, a preoperative 3D CT scan was performed throughout the complete pelvis in the supine position with a slice thickness of 1.5 mm. The data were saved in standard Digital Imaging and Communications in Medicine (DICOM) format and were then imported into Mimics 19.0 software (Materialise Corp., Leuven, Belgium). According to the characteristics of bone defect, the 3D model of the pelvis was designed to restore the COR and compensate the missing bone volume. To evaluate the precision of COR reconstruction, we mirrored the anatomic COR of the normal contralateral hip to the revised side as a reference landmark. Utilizing the software, individualized screw placement, trajectory, and length were also exactly planned through the cup top to the host bones of the ilium, ischium, and pubis. Meanwhile, the three-point fixation involving the inner upper margin, outer upper margin, and inferior margin of the acetabulum was achieved (Fig. 2).
3D pelvis demonstrating placement of composite acetabular component with individualized screw trajectory (A, B, and C). The red boxes represent three-point fixation involving the inner upper margin, outer upper margin, and inferior margin of the acetabulum. 
After that, the gap between the pelvis and the acetabular cup, where the titanium metal augments were to be made later, was filled using the Geomagic Studio 2012 software (Geomagic Corp., USA), and converted into a digital 3D model in stereolithography (STL) format. Based on the three-point fixation principle, the satisfactory match between the augment and bone interface was obtained through repeated filling and compression. The data of the titanium metal augment in STL format was imported into Magics 22.0 software (Materialise Corp., Leuven, Belgium) to design the microporous structure, in which the pore size was set of 500
The design of the acetabulum-augment composite component (A, B, and C). 
The image of the 3D porous metal acetabular composite component (A, B, C, and D).
A life-sized sterilizable plastic 3D-printed model of the pelvis with the composite acetabular component (A, B, C, and D).
After the acetabular cup and the porous augment were combined, the data in STL format was imported into a 3D printer (ARCAM Q10, Sweden) to prepare the required acetabulum-augment composite component using titanium alloys (Ti6Al4V, ARCAM, Sweden) (Fig. 3). The custom nature of the component ensures that it will fit the patient bony anatomy precisely, with minimal bone resection and preservation of bone stock. The component was designed by our clinical team and fabricated by Chunli Co, Ltd. (Tongzhou, Beijing, China) (Fig. 4). Meanwhile, a life-sized sterilizable plastic 3D-printed model of the pelvis was created to aid the revision surgery (Fig. 5).
Surgical procedure
Through a posterolateral approach, the procedure was performed under general anesthesia in the lateral decubitus position. After dislocation and removal of the head, the femoral stem was determined to be stable, so we proceeded without stem removal. The loosened acetabular component was removed along with the polyethylene liner, screws, and osteolytic tissue to expose the acetabular defect. With the support of the 3D-printed model of the pelvis, the custom-made acetabulum-augment composite component was implanted in the defect at 45
Installation procedures of the 3D porous metal acetabular composite component. (A and B) Implantation of structural allograft in the top of the component. (C) Placement of the 3D porous metal acetabular composite component and individualized screws. (D and E) Placement of polyethylene liner. (F) Placement of the metal femoral head.
The patient got out of bed and walked with crutches one week after surgery. Range of motion exercises of the hip and full-weight-bearing were performed from postoperative week 2. The patient was followed up every month for the first 3 months, then every 6 months to date. At the latest follow-up at 2 years, the patient was doing well, pain-free, and walking unaided. The hip joint function was satisfactory and the Harris Hip Score was 81 (Fig. 7). Radiography indicated that the component fitted well with the acetabulum, the porous augment was well integrated with the acetabulum, and no signs of loosening or other complications were found (Fig. 8). No intra- or postoperative complications occurred.
The satisfactory function of right hip 2 years after 3D-printed prosthesis reconstruction (A, B, C, and D).
Pelvis AP (A) and CT scan (B) immediately after surgery vs. pelvis AP (C) and CT scan (D) at 2-year follow-up. The red boxes represent that the porous augment was well integrated with the acetabulum.
This case report presents a successful treatment using a 3D-printed porous titanium composite CMAC in the management of Paprosky type IIIB acetabular defects. Avoiding assembly difficulties and being easy to install are the vital advantages of the composite component compared with the assembled component [7]. The three-point fixation and internal screw fixation through the cup could obtain excellent primary stability and improved hip scores with the guidance of a 3D model [12], and the absence of a flange at the rim of the acetabular cup minimizes soft tissue release and reduces bleeding [8]. Furthermore, the porous titanium alloy design could fit perfectly with the remaining acetabular bone stock to maximize bony apposition and allow for direct load transmission. Meanwhile, the microporous structure of the 3D-printed titanium trabecular cup is conducive to promoting bone ingrowth and providing long-term stability [13].
Composite CMAC is the product of combing an artificial acetabular cup with metal augment, and the latter is used to fill the defect. Although previous research suggested that the utilization of metal augments showed a better biomechanical reconstruction of the hip including a more anatomically positioned COR, less head-cup difference, and the improved femoral offset [7]. It also causes problems when using metal augments such as difficulty in installation and needing an osteotomy. Both the augment and the acetabular cup need screw fixation and cement bonding between each other, resulting in reduced overall stability. In the current case, the composite CMAC was designed according to the pelvic data of the patient, the appearance highly accorded with the acetabulum bone defect and easy to install. Moreover, the excessive filling bone graft and screw fixation, as well as unnecessary osteotomy, were avoided, which provide more primary stability and operation safety guarantee.
In the current case, there was a gap between the component and the bone of the acetabulum, which can be seen in Fig. 8b. In fact, in the treatment of the defect with a small mouth and a large bottom, it is difficult for the component to fit 100% with host bones in the condition of avoiding further bone loss. Therefore, to achieve the primary stability, the three-point fixation involving the inner upper margin, outer upper margin, and inferior margin of the acetabulum was used, which was proved to be effective in the jumbo cup [12]. Meanwhile, exact individualized screw fixation through the cup top to the host bones of the ilium, ischium, and the pubis was also beneficial to provide primary stability.
Different from previous reports, the component in the current case was in the absence of a flange, whereas the triflanged CMAC is popular [14, 15]. Berasi et al. [15] applied triflanged CMAC to revise Paprosky type IIIB acetabular defects. A minimum of 2 years follow-up showed that all of the 28 components were noted to be well-fixed with no migration or loosening observed. However, the survivorship after acetabular revision with a triflanged CMAC is still unsatisfactory. The reported overall complication rate was 29%, and dislocation and infection were the most common complications observed with an incidence of 11% and 6.2% [14]. Therefore, optimization of the triflanged CMAC is ongoing due to its limitations. A comparative study between triflanged and monoflanged CMAC conducted by Walter et al. [8] reported that monoflanged CMAC demonstrated similar clinical outcomes and survival rates as triflanged CMAC but superior biomechanical features. However, even a monoflanged design may affect the COR reconstruction due to angulation and tilting of the flange. In contrast, our porous titanium composite CMAC without a flange in the current case could tilt less as there is no flange and metal augmentation of the cup counteracts COR shifting provoked by screw tightening. Furthermore, no flange design is helpful to reduce the incidence of dislocation by reducing exposition of the acetabular bone with less soft tissue release.
In general, the long-term stability of the acetabular cup after revision THA is greatly influenced by the bone ingrowth between components and bone interface [16]. To facilitate osseointegration, 3D-printed porous surfaces and unique bone-void filling designs are often applied to the acetabular portion of the component to maximize host-bone apposition and ingrowth [17]. In a cohort of 58 revision THA using trabecular titanium cups, De Meo et al. observed a survivorship of 94.8% with a mean follow-up of 4 years, and they demonstrated that these components can successfully be implanted in patients with Paprosky type III defects [18]. In the current study, the porous titanium alloy design was created to fill the gap between the pelvis and the acetabular cup, we found satisfactory bone ingrowth after 2 years of follow-up due to similar pore size, porosity, and elasticmodulus as normal cancellous bone [19]. This further confirmed that 3D-printed porous titanium alloy CMACs could represent a solid treatment solution for Paprosky type III defects [9].
We consider the customization of the 3D-printed porous titanium acetabular composite component without a flange as a valid choice for Paprosky type III acetabular defects. However, some aspects should still be examined for a complete evaluation of the technique. Firstly, the CMACs were always the result of a strict collaboration between engineers and surgeons, but the design and manufacturing process usually takes several weeks with possible worsening of the bony defect. In contrast, the current component was independently designed by surgeons with a professional background. On the one hand, it can improve the matching degree of the component and facilitate intraoperative installation, but on the other hand, it also required highly the engineering design ability of surgeons. Secondly, the manufacturing costs are high than the standard available solutions. To prepare enough money, the treatments of some patients are delayed, leading to further aggravation when the cost of treatment is affordable. Besides, it is difficult for our custom-made component to fit 100% with host bones in the condition of avoiding further bone loss, especially in the treatment of the defect with a small mouth and a large bottom in the current case. Finally, the 3D printing technique fails to assess the bone quality which will compromise the assessment of supporting ability of the remaining bone or the ability of the screws to engage the bone effectively. Combining the technique of bone mineral density measurement with the development of 3D model material may help to solve this problem [20].
Conclusion
We recommend the use of the individualized 3D-printed porous titanium acetabular composite component without a flange in the management of specific patients with Paprosky type III acetabular defects. However, the long-term outcomes with more samples associated with this technique in comparison to other options remain to be determined.
Footnotes
Acknowledgments
This study was supported by the Research Project of Sichuan Provincial Health Committee (Grant no. 19PJ217), the Research Project of Sichuan Provincial Medical Association (Grant no. 2019SAT15), and the General Incubation Project of The Third Hospital of Mianyang (Grant no. 201919).
Conflict of interest
None to report.