Custom 3D-printed porous titanium augments for Paprosky type III acetabular defects: a case series combining biomechanical rationale with early clinical outcomes

Abstract

Background

Severe acetabular bone defects (Paprosky type III) pose significant challenges for reconstruction and stable implant fixation. This study aimed to analyze the biomechanical properties and clinical safety of personalized 3D-printed porous titanium alloy reinforcement augments and evaluate their therapeutic efficacy in reconstructing these complex defects.

Methods

We reviewed three cases of Paprosky type III acetabular defects reconstructed using personalized 3D-printed porous titanium alloy augments. Finite element analysis (FEA) simulated the defects, utilizing a commercial augment as a control. Stress distribution within the augments, fixation screws, acetabular cups, and surrounding bone was analyzed under simulated single-leg standing (1 × body weight), walking (4 × BW), and jogging (6 × BW) loading conditions, with comparisons made to the control.

Results

Under all loading conditions, the peak stresses observed on the augment screws and acetabular cups in all three cases were lower than the buckling strength of titanium alloy and were consistently lower than those recorded in the control group. This indicates that the personalized augments provided stable support for acetabular cup fixation, aiding in the restoration of the hip rotation center and lower limb length.

Conclusions

Personalized 3D-printed porous titanium alloy augments demonstrate favorable biomechanical safety and clinical efficacy based on FEA and initial case review. For severe acetabular bone defects, these custom augments offer good initial stability, promoting bone integration for long-term fixation, and potentially reducing risks associated with cup loosening, dislocation, and periprosthetic fracture.

Introduction

Acetabular defects present significant challenges for surgeons performing primary or revision total hip replacements. The fundamental principles of acetabular bone defect reconstruction emphasize restoring the hip center of rotation (HCOR) and preserving as much native bone as possible. Following reconstruction, the acetabular prosthesis should achieve solid initial stability, progressively establishing long-term stability over time [1, 2]. Currently treatment options of acetabular bone defects include metal augments, Jumbo cups, structural bone grafts, reinforcement rings, customized acetabular prosthesis, and the cup-cage technique [3–5]. However, each method has limitations. Commercial metal augments and Jumbo cups are often inadequate for addressing Paprosky IIC or Type III acetabular defects, structural bone grafting carries a high complication rate, and the reinforcement ring and cup-cage techniques have high failure rates [6].

Recent studies have supported using a trabecular cup combined with metal trabecular augment to reconstruct complex acetabular bone defect [7, 8], However, commercial augments often fail to conform precisely to the bone defect, resulting in complications such as prosthetic loosening, which impedes their broader clinical applicability.

3D printing technology has seen extensive use in joint surgery, enabling the construction of custom modules for implantation by additive manufacturing based on 3D CAD model data to meet reconstruction requirements [9]. While several studies have explored personalized 3D printing in hip revision, the predominant approach remains the 3D-printed mortar cup [10–12]. Although effective for treating acetabular defects, this method has limitations, including complex configuration, prolonged prosthesis printing time, poor intraoperative fit with host bone, and high surgical difficulty. To address these issues, we propose combining an argument with 3D printing technology to create a custom-fit argument based on the host bone structure, which can effectively repair severe acetabular defects and enhance clinical operability.

In this study, we reviewed three cases of primary or revision hip replacement involving severe acetabular bone defect reconstruction with personalized 3D printed porous titanium alloy augments. Data from these patients were used to develop a finite element model simulating acetabular defect reconstruction with personalized 3D printed porous titanium augments, with a control model created using a commercial augment. The stress distribution and biomechanical properties of the augment, screw, mortar cup, and pelvis were simulated using varying loading intensities. All patients were followed for five years post-surgery to collect imaging data and assess recovery status. The biomechanical performance, design rationality, and clinical utility of the personalized 3D-printed porous titanium augments, screws, mortar cups, and bone were evaluated to explore the therapeutic effectiveness of these custom augments for acetabular defect reconstruction.

Methods

Study design and materials

Pelvic CT scan DICOM data from the three cases were collected for the experimental group, while one case of severe acetabular bone defect reconstruction using a standard acetabular augment served as the control group. The instruments and software used to construct the three-dimensional finite element model of the pelvis included: Hardware—Intel(R) Xeon(R) Wmure 2223 CPU @ 3.60 GHz with 8 computing cores. Software—Mimics Research 20.0 (Materialise, Belgium) for image processing, UG 12.0 (Siemens PLM Software, Germany) for 3D modeling, HyperMesh 14.0 (Altair, USA) for meshing, and Abaqus 10.0 (Dassault SIMULIA, France) for finite element analysis.

Research methods

The CT image data were stored in DICOM format and processed with a 1-mm slice thickness. Using Mimics Research 20.0 and Imageware, 3D reconstructions of the patients'pelvises were created. The 3D reconstructed images were then imported into CAD software to design the 3D-printed porous Ti6Al4V augment for acetabular bone defects. The design data were saved in stereolithography (STL) format. The surface mesh STL file was subsequently imported into Geomagic Studio 12.0 for reverse engineering reconstruction. In this step, the porous Ti6Al4V augment and the pelvis model underwent a series of processing steps, including segmentation, smoothing, polishing, denoising, and surface patch distribution. The final surface mesh file was then materialized to produce a 3D graphic file in IGES format, enabling further finite element analysis and customization for surgical planning.

Solid model modeling

Based on the actual dimensions, defect shape, and area of acetabular defects in the three cases of the experimental group and one case of the control group, the sizes of the acetabular prostheses and augments were simulated. Using UG 12.0 software (NX), the system modeling and assembly of a total hip arthroplasty (THA) combined with the implantation of a 3D-printed porous Ti6Al4V augment were completed (Fig. 1). This approach allowed precise customization to each patient’s unique anatomical structure, ensuring an optimal fit of the augment and acetabular prosthesis in preparation for finite element analysis and clinical application.

Fig. 1.

Establishment of finite element model for the reconstruction of acetabular bone defect with 3D printed porous Ti6Al4V augment/commercial augment

Grid division

The solid model was imported into HyperMesh 14.0 for discretization, with tetrahedral elements selected for meshing. During meshing, the sensitivity of the mesh to stresses was taken into account, and a mesh density convergence study was conducted to confirm optimal accuracy. Specifically, 1 mm and 1.5 mm mesh sizes were applied to the same model, and the computational results from different mesh densities were compared. The results between the two mesh size iterations differed by less than 5%, which was considered within acceptable limit for accuracy. The final mesh characteristics of each model are summarized in Table 1.

Table 1.

Elements and nodes for the 3 models that represented the three patients

	Node numbers	Element numbers
Case A	189428	878523
Case B	88400	387551
Case C	199124	915515
Control	103307	485933

The setting of material parameters and contact mode

The gridded finite element model was imported into Abaqus 6.13 for further processing. Material properties were assigned to the prosthesis and bone components, with attribute parameters set based on the specifics of this study. Contact relationships were established between each component to simulate post-surgical conditions, including the interactions between the pelvis and acetabular cup, the pelvis and augment, the acetabular cup and augment, the screw and augment, and the pelvis. Boundary conditions and loading stress calculations were applied accordingly, and Young’s modulus and Poisson's ratio values for each material component are provided in Table 2. To simplify the model, friction factors were omitted, and the roles of muscles and ligaments were not included in this simulation.

Table 2.

Property parameters of materials [13]

materials	Elastic modulus/MPa	Poisson's ratio
CT scan of the pelvic model	1600	0.3
Ti6Al4V	110000	0.3

Constraint and loading mode setting

To simulate a single-leg standing loading scenario, the iliac end of the pelvic model was constrained to prevent translation and rotation, ensuring stability in the model. and then a vertical upward force is applied to the lower end of the femoral prosthesis. Following the stress-testing methods reported in previous studies [14, 15], uniform pressure loads of 500 N, 2000 N, and 3000 N were applied to the inner surface of the acetabular cup, approximating forces exerted by body weight during different activities: standing on one foot, walking (4 times body weight), and jogging (6 times body weight), respectively. This approach facilitated an analysis of stress distribution in the augment and other components under varied load conditions, providing insights into their biomechanical performance.

Cases report

Case A

The patient, a 48-year-old male, initially underwent right total hip arthroplasty at an outside hospital for a chronic destructive lesion in the right hip joint. Over a year post-operation, he experienced worsening right hip pain, along with a sinus tract with purulent discharge from the incision. Based on multiple culture results and the MSIS PJI diagnostic criteria, a diagnosis of chronic multiple periprosthetic hip infections was confirmed. He underwent staged revision surgery, beginning with an antibiotic-laden bone cement spacer implanted during the first stage. Intraoperative cultures of joint fluid, periprosthetic tissue, and prosthetic ultrasonic lysate confirmed the presence of multiple infections. Postoperatively, intravenous vancomycin and imipenem were administered for two weeks, followed by four weeks of oral antibiotics. Six months later, with infection control achieved, the patient was readmitted to complete the second-stage revision surgery. The patient presented with a severe posterior column defect in the right acetabulum (Paprosky-type IIIA) (Fig. 2A). Following preoperative planning, a personalized 3D-printed porous titanium augment combined with a biotype sleeve cup was selected (Figs. 2B and C). Intraoperatively, no pus or necrotic tissue was observed in the right acetabulum, confirming successful infection control. The 3D-printed augment was secured to the sciatic and iliac bones with screws (Fig. 2D). A 52-mm biotype acetabular cup was chosen for the acetabular trial mold, bonded to the augment with bone cement to ensure stability. Given the lateral proximal femoral bone defect (Paprosky-type IIIA), a distally fixed femoral stem was selected, and hip stability was assessed across all planes after right hip resurfacing. After more than five years of regular follow-ups, the patient’s Harris Hip Score (HHS) improved from 32.8 preoperatively to 88.1, and the limb-length discrepancy (LLD) improved from 56 mm pre-surgery to 6 mm. The patient reported no hip pain, had a well-healed incision, and was able to walk unaided, regaining independence in self-care. CRP and ESR remained normal on multiple follow-ups, with no signs of infection recurrence. Radiographic evaluations of both hips and the right lateral hip showed excellent prosthesis positioning and bone scab growth (Fig. 2E, F).

Fig. 2.

Case A, 46-year-old male. A Six months post spacer implantation, infection control achieved; B, C Preoperative planning and design for the second stage of two-stage revision surgery; D Implantation of the 3D-printed porous Ti6Al4V augment, showing good fit with the host bone; E, F Follow-up X-rays post second-stage revision, demonstrating favorable prosthesis positioning and robust callus formation

Case B

The patient, a 70-year-old male, presented with pain and difficulty walking due to an old fracture of the left hip (Fig. 3A). CT 3D reconstruction revealed a severe posterior column defect of the acetabulum's posterior wall (Paprosky-type IIIB) caused by this prior fracture. Following preoperative planning, acetabular reconstruction was performed using a personalized 3D-printed porous titanium augment combined with a biotype socket cup (Fig. 3B). Intraoperative exploration found extensive granulation tissue filling the left acetabulum and significant bone loss at the superior and posterolateral acetabular regions. The 3D-printed porous titanium augment was securely fixed to the sciatic and iliac bones with screws. After confirming primary stability with a trial mold, a 54-mm biotype cup was selected and bonded to the augment using bone cement, with a biotype femoral stem prosthesis chosen. The patient’s Harris Hip Score (HHS) improved from 43.2 preoperatively to 87.6 at the last follow-up, and the limb-length discrepancy (LLD) improved from 72 mm pre-surgery to 5 mm. He reported no left hip pain, had a well-healed incision, and was able to walk unassisted, regaining independence in daily activities. The radiographs of the 5-year outpatient follow-up after surgery showed excellent prosthesis positioning and substantial bone scab growth (Fig. 3C, D).

Fig. 3.

Case B, 70-year-old male. A Preoperative X-ray showing an old fracture of the left acetabulum; B Preoperative planning and design for total hip arthroplasty; C Five-year follow-up anteroposterior X-ray of the left hip post-total hip arthroplasty, demonstrating satisfactory prosthesis positioning with no radiological signs of malfunction

Case C

The patient, a 77-year-old female, was admitted due to two years of worsening pain following left hip arthroplasty for developmental hip dysplasia (Fig. 4A and B). She developed persistent, activity-related left hip pain that progressively worsened. Upon admission, she was diagnosed with aseptic loosening of the left hip prosthesis, wear of the polyethylene liner, and a severe medial acetabular wall defect (Paprosky-type IIIB). Following preoperative planning, acetabular reconstruction was performed using a personalized 3D-printed porous titanium augment combined with a biotype socket cup (Fig. 4C and D). Intraoperative findings included extensive metal debris within the hip cavity and marked osteolysis surrounding the prosthesis, confirming aseptic loosening. After assessing the acetabular trial mold for primary stability, a 52-mm biotype cup was selected and secured to the augment with bone cement. A polyethylene inner cup was implanted along with a biotype femoral stem. Following over five years of regular follow-up, the patient’s Harris Hip Score (HHS) improved from 46.2 preoperatively to 89.3, and her limb-length discrepancy (LLD) was corrected from 62 mm pre-surgery to 8 mm. She reported no left hip pain, had a well-healed incision, and regained mobility without crutches. Radiographs from outpatient follow-ups showed stable prosthesis positioning and solid bone scab growth (Fig. 4F and G). In the sixth postoperative year, the patient passed away due to liver cancer.

Fig. 4.

Patient C, 77-year-old female. A, B Pre-revision X-rays showing a loose prosthesis and significant acetabular bone defect; C, D Preoperative planning and design for revision surgery; E The 3D-printed porous Ti6Al4V augment demonstrates a good match with the host bone; F, G Two-year follow-up X-rays of the left hip showing satisfactory prosthesis positioning and no radiological signs of malfunction

Results

Comparison of stress distribution in personalized 3D-printed porous titanium alloy augment versus commercial augment

The stress distribution contours for the personalized 3D-printed porous titanium alloy augment and the commercial augment (control group) under a single body weight load (unipedal standing) for cases A, B, and C are shown in Fig. 5A, with maximum stress values noted. The maximum principal stress distribution is located at the junction of the dome at the contact between the augment and the bone. The principal maximum stresses recorded were 12 MPa, 52.48 MPa, 66.49 MPa, and 67.14 MPa for cases A, B, C, and the control group, respectively. Under four times body weight load (walking), the maximum principal stresses were 48.37 MPa, 195.7 MPa, 217.2 MPa, and 262.4 MPa (Fig. 5B). At six times body weight (jogging), the maximum principal stresses increased to 72.99 MPa, 299.5 MPa, 329.8 MPa, and 387.8 MPa (Fig. 5C).

Fig. 5.

The stress distribution program of 3D printed porous Ti6Al4V augment/commercial augment under 500 N(A)/2000N(B)/3000N(C) loading mode

Comparison of stress distribution in screws: personalized 3D-printed porous titanium augments versus commercial augments

The stress distribution contours for the screws fixed in personalized 3D-printed porous titanium augments and the commercial augment (control group) under a single body weight load (unipedal standing) for cases A, B, and C are shown in Fig. 6, with the maximum principal stress values indicated. The maximum stress distribution is located in the lower part of the screw. The maximum principal stresses of the screws in cases A, B, C, and the control group were 7.845 MPa, 44.32 MPa, 48.23 MPa, and 38.46 MPa, respectively (Fig. 6A). Under a four times body weight load (walking), the maximum principal stresses were 31.62 MPa, 181.5 MPa, 196.3 MPa, and 159.6 MPa, respectively (Fig. 6B). At six times body weight (jogging), the maximum principal stresses were 47.66 MPa, 276.6 MPa, 297.8 MPa, and 245.1 MPa, respectively (Fig. 6C).

Fig. 6.

The stress distribution program of screws used to fix 3D printed porous Ti6Al4V augment/commercial augment under 500 N(A)/2000N(B)/3000N(C) loading mode

Comparison of acetabular cup stress distribution: personalized 3D-printed porous titanium augments versus commercial augments

The stress distribution contours for the acetabular cups with personalized 3D-printed porous titanium augments and commercial augments under a single body weight load (unipedal standing) for cases A, B, and C are shown in Fig. 7, with maximum principal stress values indicated. The maximum stress distribution is located at the contact between the cup and bone. The maximum principal stresses for the acetabular cups in cases A, B, C, and the control group were 3.359 MPa, 14.97 MPa, 7.316 MPa, and 30.48 MPa, respectively (Fig. 7A). Under a four times body weight load (walking), the maximum principal stresses were 13.52 MPa, 59.78 MPa, 29.71 MPa, and 118.7 MPa, respectively (Fig. 7B). At six times body weight (jogging), the maximum principal stresses were 20.35 MPa, 89.58 MPa, 45.01 MPa, and 175.1 MPa, respectively (Fig. 7C).

Fig. 7.

The stress distribution program of the acetabular cup using 3D printed porous Ti6Al4V augment/commercial augment under 500N(A)/2000N(B)/3000N(C) loading mode

Comparison of stress distribution in the pelvis: personalized 3D-printed porous titanium augments versus commercial augments

The stress distribution contours for the pelvis in contact with the fixation screws of personalized and commercial augments under a single body weight load (unipedal standing) are shown in Fig. 8, with the maximum principal stress values indicated. The maximum stress distribution is located at the contact area between the edge of the augment and bone. The maximum principal stresses in the acetabular cups for cases A, B, C, and the control group were 7.3 MPa, 5.11 MPa, 8.96 MPa, and 23.17 MPa, respectively (Fig. 8A). Under a four times body weight load (walking), the maximum principal stresses were 15.33 MPa, 14.85 MPa, 19.3 MPa, and 47.57 MPa, respectively (Fig. 8B). At six times body weight (jogging), the maximum principal stresses were 45.46 MPa, 31.15 MPa, 47.41 MPa, and 72.46 MPa, respectively (Fig. 8C).

Fig. 8.

The stress distribution program of the pelvis using 3D printed porous Ti6Al4V augment/commercial augment under 500 N(A)/2000N(B)/3000N(C) loading mode

Using the same loading conditions described above, the stress distributions in other components, including the acetabular prosthesis, femoral prosthesis, ceramic liner, and ceramic femoral head, remained below the yield strength of their respective materials.

Discussion

This paper reviews three cases of Paprosky type III acetabular defects reconstructed using personalized 3D-printed porous titanium augments. Using 3D CT data from these cases, finite element models were created to simulate severe acetabular defect reconstructions with personalized 3D-printed metal augments. Additionally, finite element models with commercial metal augments were developed as a control group to analyze the advantages and clinical outcomes of personalized 3D-printed augments in treating Paprosky type III acetabular defects.

The results of the finite element analysis showed that the stress peaks of the cups in cases A, B, and C were smaller than those in the control group under three identical load patterns (500 N, 2000 N, and 3000 N), indicating that the application of the personalized 3D printed porous titanium augments may improve the initial fixation of the cups by better matching the implant to the patient's bone defect. Amirouche et al [16] analyzed the effect of acetabular bone defects on cup placement and showed that acetabular bone defects in the superior or inferior wall had little effect on cup fixation, whereas acetabular bone defects in the anterior and posterior columns increased cup. All three patients reported had posterior wall defects of the posterior column, and the stresses in the cup and contact pelvis were reduced with the application of personalized 3D printed porous titanium augments compared to commercial augments, suggesting that the posterior wall of the posterior column may be the best indication for personalized 3D printed porous titanium augments. The finite element analysis also showed that the peak stresses in the pelvis-implant contact region of cases A, B, and C were less than those in the control group under three identical load-bearing modes (500N, 2000 N, and 3000 N). This indicated that the use of a personalized 3D-printed porous titanium augment resulted in less stress on the bone at the contact surface of the socket cup and augment with the pelvis, reducing the incidence of postoperative complications such as bone compression, fracture, and prosthesis loosening.

In addition, in this study, both the augment and screw were made of porous titanium alloy, and the literature indicated that the engineering flexural strength of titanium alloy is 889–921 MPa [17]. The finite element results showed that the peak stresses of the personalized 3D-printed porous titanium alloy augment were less than their engineering flexural strength under three identical load patterns (500 N, 2000 N, and 3000 N). This indicated that the augments and screws may improve the initial fixation of the cups by better matching the implant to the patient's bone defect. Pure titanium and titanium alloys are widely used in orthopedic and dental surgery because of their good mechanical properties, chemical stability, and biocompatibility [18]. Various physical and chemical treatments of titanium surfaces can produce the most biocompatible titanium surfaces [19, 20]. Porous titanium alloys, as a porous structure, have an internal microstructure similar to cancellous bone and have good mechanical properties that facilitate tissue regeneration and can be used under load-bearing conditions [21]. The use of porous titanium alloys can be a useful tool for surface treatment of titanium alloys. The use of personalized 3D printed porous titanium restorations can better match (or even perfectly match) the morphology of defective bone, have better stress distribution, and promote bone integration.

The second aim of this paper was to study the efficacy of personalized 3D-printed porous titanium augments when used in clinical practice,we followed two of these patients for 5 years. At the final follow-up, all patients had good functional recovery of the hip joint, and radiographs showed good prosthesis position and good bone scab growth in all patients. During the follow-up period, three patients were able to walk with crutches at 10, 14, and 16 days postoperatively, and all patients were able to walk with crutches at more than 1 month postoperatively. The main objective of acetabular revision surgery is to restore the length of the lower limb and the center of rotation of the hip joint. In the three patients in this paper, the length of the lower limb was basically restored to equal length, and the center of rotation of the hip joint was restored to near normal range. In addition, compared with the commercial metal augments the personalized 3D-printed porous titanium augments were confirmed before being repeatedly modified. It was also confirmed intraoperatively that the placement of the augment fits well with the bone defect and the fossa cup, which helped to maintain the stability of the prosthesis and obtained better clinical results.

This study has several limitations that impact the interpretation of the findings and suggest directions for future research. One significant limitation is the lack of validation of the FEA model. Although this study provides insights into the stress distribution of the implants, the validity of these predictions remains uncertain without comparison to clinical outcomes or experimental results. In this study, the finite element simulations conducted were focused exclusively on Paprosky type IIIA acetabular defects as it is one of the most encountered defects in clinical practice. However, we acknowledge that limiting the study to this defect type restricts the generalizability of our findings. Further studies considering a range of acetabular defects will be necessary to validate these results for a broader clinical context. Furthermore, this study utilized a simplified loading model representing single-leg standing load to achieve consistent stress distribution analysis, it does not include the effect of implant rotation, which can significantly influence load transfer and stress distribution in both the implant and surrounding bone. Addressing this limitation in future research would involve incorporating more complex, multi-axial loading models that replicate the natural range of hip motion, offering a more accurate representation of real-world forces on the acetabular components. Although we performed two iterations of mesh refinement with a 50% reduction in mesh size between iterations, which may affect the precision of the stress results. This study used a simplified solid model for the porous augment, which may not fully capture the actual implant's performance, which could affect stress distribution and load-bearing capacity, leading to differences in biomechanical behavior. Additionally, the model assumes uniform material properties across the augment, whereas a porous structure would have variable properties, potentially causing discrepancies in estimated stress and strain, especially in areas where porous materials would absorb and dissipate forces differently. In addition, single-patient control group for comparative analysis and absence of long-term clinical data beyond stress simulation may limit the robustness of our comparative analysis. By addressing these limitations, future studies can enhance the depth, relevance, and clinical applicability of findings on personalized 3D-printed porous titanium augments for severe acetabular defect reconstruction.

In summary, this study successfully established a comprehensive finite element model for the reconstruction of severe acetabular bone defects with personalized 3D-printed porous titanium alloy augments and evaluated the stress distribution across components under various loading conditions. The findings suggest that personalized 3D-printed porous titanium alloy augments can provide provide better stress distribution, promoting subsequent osseointegration to ensure long-term stability. This approach may effectively reduce the risk of complications such as acetabular cup loosening, dislocation, and periprosthetic fractures. Therefore, we propose that personalized 3D-printed porous titanium augments hold promising clinical potential for managing severe acetabular defects, particularly Paprosky-type III defects.

Authors’ contributions

Tengbin Shi: Conceptualization, Methodology, Data Curation, Formal Analysis, Writing, and Original Draft Preparation; Wenming Zhang and Xinyu Fang: Project Administration Funding Acquisition, Supervision.

Funding

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Data availability

No datasets were generated or analysed during the current study.

Declarations

Ethics approval and consent to participate

The study received approval from the Medical Ethics Committee of The First Affiliated Hospital of Fujian Medical University (Approval No. MRCTA, ECFAH of FMU [2019] 296), and all procedures were performed in accordance with the relevant guidelines and regulations of the Declaration of Helsinki. Written consent was obtained from patients or from the next of kin for deceased patients to have the case details published.

Consent for publication

Not applicable.

Competing interests

The authors declare no competing interests.