In vitro experimental and numerical study on biomechanics and stability of a novel adjustable hemipelvic prosthesis

Exploring the optimal reconstruction strategy for Enneking III defects in pelvis bone tumors: a finite element analysis

BACKGROUND

Controversy exists regarding the reconstruction of bone defects in Enneking III. This study aimed to use the finite element analysis (FEA) method to clarify (1) the utility of reconstructing the pelvis Enneking III region and (2) the optimal approach for this reconstruction.

METHODS

FEA models were generated for three types of Enneking III defects in the pelvis, replacing all the defect areas in region III with a sizable solid box for topology optimization (TO). Based on the defect location and TO results, three reconstruction schemes were designed for each type of defect. We subsequently conducted simulations of static FEA under natural walking loads using ANSYS software (version 2022R1, Canonsburg, Pennsylvania, USA).

RESULTS

Compared with Scheme A, reconstruction of the Enneking III region (Schemes B and C) led to a more uniform stress distribution and lower peak stress in the pelvis. Moreover, prostheses and screws exhibit decreased peak stress and deformation, with complex reconstruction schemes (C) outperforming simpler ones (B).

CONCLUSIONS

The FEA results suggest that reconstructing Enneking Zone III defects improves stress distribution and reduces peak stress in the pelvis compared to non-reconstruction, potentially enhancing stability and reducing fracture risks. Complex reconstruction schemes involving more contralateral pelvis regions demonstrate superior biomechanical performance. However, clinical decisions should be individualized, integrating biomechanical insights with comprehensive patient-specific factors.

Pelvic-girdle reconstruction with three-dimensional-printed endoprostheses after limb-salvage surgery for pelvic sarcomas: current landscape

Resection of pelvic bone tumors and the subsequent reconstruction of the pelvic girdle pose challenges due to complex anatomy, load-bearing demands, and significant defects. 3D-printed implants have revolutionized pelvic girdle reconstruction by offering customized solutions, porous surface structures for precise resection with custom guides, and improved integration. Many tertiary medical centers have adopted 3Dprinted hemipelvic endoprostheses, leading to enhanced outcomes. However, most studies are limited to single centers, with a small number of cases and short follow-up periods. Additionally, the design of these implants often relies heavily on individual experience, resulting in a lack of uniformity and significant variation. To provide a comprehensive assessment of this technology, we conducted an analysis of existing literature, encompassing tumor resection classification, various types of prosthesis design, reconstruction concepts, and post-reconstruction functional outcomes.

Reconstruction with 3D-printed prostheses after type I + II + III internal hemipelvectomy: Finite element analysis and preliminary outcomes

Background: Prosthetic reconstruction after type I + II+ III internal hemipelvectomy remains challenging due to the lack of osseointegration and presence of giant shear force at the sacroiliac joint. The purpose of this study was to evaluate the biomechanical properties of the novel 3D-printed, custom-made prosthesis with pedicle screw-rod system and sacral tray using finite element analysis. Methods: Four models that included one intact pelvis were established for validation. Forces of 500 N and 2,000 N were applied, respectively, to simulate static bipedal standing and the most loaded condition during a gait cycle. Biomechanical analysis was performed, and the results were compared; the preliminary outcomes of four patients were recorded. Results: For the reconstructed hemipelvis, stress was mainly concentrated on the sacral screws, bone-prosthesis interface, and upper endplate of the L5 vertebra. The optimization of the design with the sacral tray structure could decrease the peak stress of the sacral screws by 18.6%, while the maximal stress of the prosthesis increased by 60.7%. The addition of the lumbosacral pedicle-rod system further alleviated stress of the sacral screws and prosthesis by 30.2% and 19.4%, respectively. The site of peak stress was contemporaneously transferred to the connecting rods within an elastic range. In the retrospective clinical study, four patients who had undergone prosthetic reconstruction were included. During a follow-up of 16.6 ± 7.5 months, the walking ability was found preserved in all patients who are still alive and no prosthesis-related complications had occurred except for one hip dislocation. The Musculoskeletal Tumor Society (MSTS) score was found to be 19.5 ± 2.9. Conclusion: The novel reconstructive system yielded favorable biomechanical characteristics and demonstrated promising preliminary outcomes. The method can be used as a reference for reconstruction after type I + II + III hemipelvectomy.

Finite element analysis of screw fixation durability under multiple boundary and loading conditions for a custom pelvic implant

Despite showing promising functional outcomes for pelvic reconstruction after sarcoma resection, custom-made pelvic implants continue to exhibit high complication rates due to fixation failures. Patient-specific finite element models have been utilized by researchers to evaluate implant durability. However, the effect of assumed boundary and loading conditions on failure analysis results of fixation screws remains unknown. In this study, the postoperative stress distributions in the fixation screws of a state-of-the-art custom-made pelvic implant were simulated, and the risk of failure was estimated under various combinations of two bone-implant interaction models (tied vs. frictional contact) and four load cases from level-ground walking and stair activities. The study found that the average weighted peak von Mises stress could increase by 22-fold when the bone-implant interactions were modeled with a frictional contact model instead of a tied model, and the likelihood of fatigue and pullout failure for each screw could change dramatically when different combinations of boundary and loading conditions were used. The inclusion of additional boundary and loading conditions led to a more reliable analysis of fixation durability. These findings demonstrated the importance of simulating multiple boundary conditions and load cases for comprehensive implant design evaluation using finite element analysis.

Reconstruction of Tumor-Induced Pelvic Defects With Customized, Three-Dimensional Printed Prostheses

Background

Reconstruction of pelvis girdle stability after tumor-induced hemipelvectomy remains challenging. We surgically treated 13 patients with custom-made, three-dimensional printed hemipelvic prostheses. We aim to identify the preliminary outcomes for patients who have been managed with more mixed regions of prosthetic pelvic reconstruction and the feasibility of two reconstructive systems.

Methods

Seven male patients and 6 female patients treated at our center between January 2019 and May 2021 were included. There were 11 primary sarcomas and 2 solitary bone metastases. After en bloc tumor resection, two types of personalized, three-dimensional printed prostheses were fixed to restore the stability and rebuild the load transfer. The position of the reconstructed hemipelvis was evaluated on an anteroposterior plain radiograph. The complications and outcomes were traced. One amputation specimen was discovered through histological analysis of the porous structure.

Results

The operative duration was 467 ± 144 min, and the blood loss was 3,119 ± 662 ml. During a follow-up of 22.4 ± 8.5 months, two patients had delayed wound healing and one had a second-stage flap transfer. One patient with osteosarcoma died of pulmonary metastasis 27 months after surgery. Two patients with marginal resection suffered from local recurrence and had extra surgeries. One patient had traumatic hip dislocation 2 months after surgery and manipulative reduction was performed. The acetabular inclination of the affected side was 42.2 ± 4.3°, compared with 42.1 ± 3.9° on the contralateral side. The horizontal distance between the center of the femoral head and the middle vertical line was 10.4 ± 0.6 cm, while the reconstructed side was 9.8 ± 0.8 cm. No significant difference in acetabular position after surgery was found (p > 0.05). The amputation specimen harvested from one patient with local recurrence demonstrated bone and soft tissue ingrowth within the three-dimensional printed trabecular structure. Walking ability was preserved in all patients who are still alive and no prosthesis-related complications occurred. The MSTS score was 22.0 ± 3.7.

Conclusions

Both types of custom-made, three-dimensional printed prostheses manifested excellent precision, mechanical stability, and promising functional rehabilitation. The porous structure exhibited favorable histocompatibility to facilitate the ingrowth of bone and soft tissue.

Computer-aided automatic planning and biomechanical analysis of a novel arc screw for pelvic fracture internal fixation

BACKGROUND AND OBJECTIVE

The sacroiliac joint screw is a common fixation method for pelvic posterior ring fractures. The complex anatomical structure around the pelvis makes it impossible to find a suitable fixed path, which increases the difficulty of surgical operation. In this paper, we propose an automatic planning algorithm based on a computer-aided internal arc fixation channel for pelvic fractures for the first time.

METHODS

A channel generation algorithm based on seed derived points was designed, and the optimal channel was selected by scoring rules based on 3D erode algorithm for the generated channel. The biomechanical properties of the internal arc fixation screw and traditional internal straight fixation screw in three postures were compared using biomechanical finite element analysis.

RESULTS

The proposed algorithm verified the existence of a more adaptable internal arc fixation channel and can quantitatively plan a relatively optimal constant-curvature internal arc fixation channel in pelvises of ten adults. Significantly high stresses concentrated around the interaction region between the screws and bone may increase the risk of bone fractures and screw loosening in the long term. The experimental results show that the internal arc fixation screw has better strain and deformation performance than the internal straight fixation screw.

CONCLUSIONS

A novel arc internal fixation method for pelvic fractures was proposed to improve the safety and stability of screw fixation of pelvic fracture. The nonparametric test proved that the sacroiliac dislocation model repaired by internal arc fixation screw was significantly different from that repaired by internal straight fixation screw. The computer-aided automatic planning algorithm provides the possibility of robot-assisted pelvic fracture fixation.

New adjustable modular hemipelvic prosthesis replacement with 3D-print osteotomy guide plate used in periacetabular malignant tumors: a retrospective case series

BACKGROUND

Periacetabular malignant tumor seriously endangers the life and health of patients. Hemipelvic replacement provides a good method for patients who want complete resection of the tumor while retaining or restoring the function of the affected limb.

OBJECTIVE

To investigate the performance and clinical application of the new adjustable modular hemipelvic prosthesis and to compare the effects of three kinds of hemipelvic prosthesis.

METHODS

In this study, 23 patients, with an average age of 44.6 years (21-75 years), were collected, who received hemipelvic replacement with new adjustable, modular, and screw-rod system hemipelvic prosthesis. Preoperative preparation was conducted on them, and operative complications were recorded. Postoperative functional follow-up was performed regularly.

RESULTS

The average operation time was 319 min (170-480 min), and the average blood loss was 2813 ml (1000 mL-8000 ml). The incidence of complications was 47.8%, and type A (wound-related complications) had the highest incidence (34.8%). Postoperative dislocation occurred in 3 cases (13.0%), and no dislocation occurred in the new adjustable modular hemipelvic prosthesis group. The average MSTS score of the patients was 18.6 (10-23), and the average Harris score was 73.7 (53-87).

CONCLUSIONS

The new adjustable modular hemipelvic prosthesis has the feasibility of reconstruction and good functional outcome, making it ideal for periacetabular tumors. Furthermore, preoperative tumor-feeding artery embolization and abdominal aortic balloon implantation may be an effective choice to reduce intraoperative blood loss and facilitate the operation of tumor resection.