Can custom 3D printed implants successfully reconstruct massive acetabular defects? A 3D-CT assessment

Computational modeling of revision total hip arthroplasty involving acetabular defects: A systematic review

Revision total hip arthroplasty (rTHA) involving acetabular defects is a complex procedure associated with lower rates of success than primary THA. Computational modeling has played a key role in surgical planning and prediction of postoperative outcomes following primary THA, but modeling applications in rTHA for acetabular defects remain poorly understood. This study aimed to systematically review the use of computational modeling in acetabular defect classification, implant selection and placement, implant design, and postoperative joint functional performance evaluation following rTHA involving acetabular defects. The databases of Web of Science, Scopus, Medline, Embase, Global Health and Central were searched. Fifty-three relevant articles met the inclusion criteria, and their quality were evaluated using a modified Downs and Black evaluation criteria framework. Manual image segmentation from computed tomography scans, which is time consuming, remains the primary method used to generate 3D models of hip bone; however, statistical shape models, once developed, can be used to estimate pre-defect anatomy rapidly. Finite element modeling, which has been used to estimate bone stresses and strains, and implant micromotion postoperatively, has played a key role in custom and off-the-shelf implant design, mitigation of stress shielding, and prediction of bone remodeling and implant stability. However, model validation is challenging and requires rigorous evaluation and comparison with respect to mid- to long-term clinical outcomes. Development of fast, accurate methods to model acetabular defects, including statistical shape models and artificial neural networks, may ultimately improve uptake of and expand applications in modeling and simulation of rTHA for the research setting and clinic.

Virtual biomechanical assessment of porous tantalum and custom triflange components in the treatment of patients with acetabular defects and pelvic discontinuity

Aims

The aim of this study was to compare the biomechanical models of two frequently used techniques for reconstructing severe acetabular defects with pelvic discontinuity in revision total hip arthroplasty (THA) - the Trabecular Metal Acetabular Revision System (TMARS) and custom triflange acetabular components (CTACs) - using virtual modelling.

Methods

Pre- and postoperative CT scans from ten patients who underwent revision with the TMARS for a Paprosky IIIB acetabular defect with pelvic discontinuity were retrospectively collated. Computer models of a CTAC implant were designed from the preoperative CT scans of these patients. Computer models of the TMARS reconstruction were segmented from postoperative CT scans using a semi-automated method. The amount of bone removed, the implant-bone apposition that was achieved, and the restoration of the centre of rotation of the hip were compared between all the actual TMARS and the virtual CTAC implants.

Results

The median amount of bone removed for TMARS reconstructions was significantly greater than for CTAC implants (9.07 cm3 (interquartile range (IQR) 5.86 to 21.42) vs 1.16 cm3 (IQR 0.42 to 3.53) (p = 0.004). There was no significant difference between the median overall implant-bone apposition between TMARS reconstructions and CTAC implants (54.8 cm2 (IQR 28.2 to 82.3) vs 56.6 cm2 (IQR 40.6 to 69.7) (p = 0.683). However, there was significantly more implant-bone apposition within the residual acetabulum (45.2 cm2 (IQR 28.2 to 72.4) vs 25.5 cm2 (IQR 12.8 to 44.1) (p = 0.001) and conversely significantly less apposition with the outer cortex of the pelvis for TMARS implants compared with CTAC reconstructions (0 cm2 (IQR 0 to 13.1) vs 23.2 cm2 (IQR 16.4 to 30.6) (p = 0.009). The mean centre of rotation of the hip of TMARS reconstructions differed by a mean of 11.1 mm (3 to 28) compared with CTAC implants.

Conclusion

In using TMARS, more bone is removed, thus achieving more implant-bone apposition within the residual acetabular bone. In CTAC implants, the amount of bone removed is minimal, while the implant-bone apposition is more evenly distributed between the residual acetabulum and the outer cortex of the pelvis. The differences suggest that these implants used to treat pelvic discontinuity might achieve short- and long-term stability through different biomechanical mechanisms.

Is AI 3D-printed PSI an accurate option for patients with developmental dysplasia of the hip undergoing THA?

BACKGROUND

In traditional surgical procedures, significant discrepancies are often observed between the pre-planned templated implant sizes and the actual sizes used, particularly in patients with congenital hip dysplasia. These discrepancies arise not only in preoperative planning but also in the precision of implant placement, especially concerning the acetabular component. Our study aims to enhance the accuracy of implant placement during Total Hip Arthroplasty (THA) by integrating AI-enhanced preoperative planning with Patient-Specific Instrumentation (PSI). We also seek to assess the accuracy and clinical outcomes of the AI-PSI (AIPSI) group in comparison to a manual control group.

METHODS

This study included 60 patients diagnosed with congenital hip dysplasia, randomly assigned to either the AIPSI or manual group, with 30 patients in each. No significant demographic differences between were noted the two groups. A direct anterior surgical approach was employed. Postoperative assessments included X-rays and CT scans to measure parameters such as the acetabular cup anteversion angle, acetabular cup inclination angle, femoral stem anteversion angle, femoral offset, and leg length discrepancy. Functional scores were recorded at 3 days, 1 week, 4 weeks, and 12 weeks post-surgery. Data analysis was conducted using SPSS version 22.0, with the significance level was set at α = 0.05.

RESULTS AND CONCLUSION

The AIPSI group demonstrated greater prosthesis placement accuracy. With the aid of PSI, AI-planned THA surgery provides surgeons with enhanced precision in prosthesis positioning. This approach potentially offers greater insights and guidelines for managing more complex anatomical variations or cases.

High accuracy of positioning custom triflange acetabular components in tumour and total hip arthroplasty revision surgery

Aims

Custom triflange acetabular components (CTACs) play an important role in reconstructive orthopaedic surgery, particularly in revision total hip arthroplasty (rTHA) and pelvic tumour resection procedures. Accurate CTAC positioning is essential to successful surgical outcomes. While prior studies have explored CTAC positioning in rTHA, research focusing on tumour cases and implant flange positioning precision remains limited. Additionally, the impact of intraoperative navigation on positioning accuracy warrants further investigation. This study assesses CTAC positioning accuracy in tumour resection and rTHA cases, focusing on the differences between preoperative planning and postoperative implant positions.

Methods

A multicentre observational cohort study in Australia between February 2017 and March 2021 included consecutive patients undergoing acetabular reconstruction with CTACs in rTHA (Paprosky 3A/3B defects) or tumour resection (including Enneking P2 peri-acetabular area). Of 103 eligible patients (104 hips), 34 patients (35 hips) were analyzed.

Results

CTAC positioning was generally accurate, with minor deviations in cup inclination (mean 2.7°; SD 2.84°), anteversion (mean 3.6°; SD 5.04°), and rotation (mean 2.1°; SD 2.47°). Deviation of the hip centre of rotation (COR) showed a mean vector length of 5.9 mm (SD 7.24). Flange positions showed small deviations, with the ischial flange exhibiting the largest deviation (mean vector length of 7.0 mm; SD 8.65). Overall, 83% of the implants were accurately positioned, with 17% exceeding malpositioning thresholds. CTACs used in tumour resections exhibited higher positioning accuracy than rTHA cases, with significant differences in inclination (1.5° for tumour vs 3.4° for rTHA) and rotation (1.3° for tumour vs 2.4° for rTHA). The use of intraoperative navigation appeared to enhance positioning accuracy, but this did not reach statistical significance.

Conclusion

This study demonstrates favourable CTAC positioning accuracy, with potential for improved accuracy through intraoperative navigation. Further research is needed to understand the implications of positioning accuracy on implant performance and long-term survival.

Point-of-Care Orthopedic Oncology Device Development

BACKGROUND

The triad of 3D design, 3D printing, and xReality technologies is explored and exploited to collaboratively realize patient-specific products in a timely manner with an emphasis on designs with meta-(bio)materials.

METHODS

A case study on pelvic reconstruction after oncological resection (osteosarcoma) was selected and conducted to evaluate the applicability and performance of an inter-epistemic workflow and the feasibility and potential of 3D technologies for modeling, optimizing, and materializing individualized orthopedic devices at the point of care (PoC).

RESULTS

Image-based diagnosis and treatment at the PoC can be readily deployed to develop orthopedic devices for pre-operative planning, training, intra-operative navigation, and bone substitution.

CONCLUSIONS

Inter-epistemic symbiosis between orthopedic surgeons and (bio)mechanical engineers at the PoC, fostered by appropriate quality management systems and end-to-end workflows under suitable scientifically amalgamated synergies, could maximize the potential benefits. However, increased awareness is recommended to explore and exploit the full potential of 3D technologies at the PoC to deliver medical devices with greater customization, innovation in design, cost-effectiveness, and high quality.

Custom-made implants for massive acetabular bone loss: accuracy with CT assessment

BACKGROUND

Custom-made implants are a valid option in revision total hip arthroplasty to address massive acetabular bone loss. The aim of this study was to assess the accuracy of custom-made acetabular implants between preoperative planning and postoperative positioning using CT scans.

METHODS

In a retrospective analysis, three patients who underwent an acetabular custom-made prosthesis were identified. The custom-made designs were planned through 3D CT analysis considering surgical points of attention. The accuracy of intended implants positioning was assessed by comparing pre- and postoperative CT analyzing the center of rotation (CoR), anteversion, inclination, screws, and implant surface in contact with the bone.

RESULTS

The three cases presented satisfactory accuracy in positioning. A malpositioning in the third case was observed due to the posterization of the CoR of the implant of more than 10 mm. The other CoR vectors considered in the third patient and all vectors in the other two cases fall within 10 mm. All the cases were positioned with a difference of less than 10° of anteversion and inclination with respect to the planning.

CONCLUSIONS

The current case series revealed promising accuracy in the positioning of custom-made acetabular prosthesis comparing the planned implant in preoperative CT with postoperative CT.

3D printing metal implants in orthopedic surgery: Methods, applications and future prospects

Background

Currently, metal implants are widely used in orthopedic surgeries, including fracture fixation, spinal fusion, joint replacement, and bone tumor defect repair. However, conventional implants are difficult to be customized according to the recipient's skeletal anatomy and defect characteristics, leading to difficulties in meeting the individual needs of patients. Additive manufacturing (AM) or three-dimensional (3D) printing technology, an advanced digital fabrication technique capable of producing components with complex and precise structures, offers opportunities for personalization.

Methods

We systematically reviewed the literature on 3D printing orthopedic metal implants over the past 10 years. Relevant animal, cellular, and clinical studies were searched in PubMed and Web of Science. In this paper, we introduce the 3D printing method and the characteristics of biometals and summarize the properties of 3D printing metal implants and their clinical applications in orthopedic surgery. On this basis, we discuss potential possibilities for further generalization and improvement.

Results

3D printing technology has facilitated the use of metal implants in different orthopedic procedures. By combining medical images from techniques such as CT and MRI, 3D printing technology allows the precise fabrication of complex metal implants based on the anatomy of the injured tissue. Such patient-specific implants not only reduce excessive mechanical strength and eliminate stress-shielding effects, but also improve biocompatibility and functionality, increase cell and nutrient permeability, and promote angiogenesis and bone growth. In addition, 3D printing technology has the advantages of low cost, fast manufacturing cycles, and high reproducibility, which can shorten patients' surgery and hospitalization time. Many clinical trials have been conducted using customized implants. However, the use of modeling software, the operation of printing equipment, the high demand for metal implant materials, and the lack of guidance from relevant laws and regulations have limited its further application.

Conclusions

There are advantages of 3D printing metal implants in orthopedic applications such as personalization, promotion of osseointegration, short production cycle, and high material utilization. With the continuous learning of modeling software by surgeons, the improvement of 3D printing technology, the development of metal materials that better meet clinical needs, and the improvement of laws and regulations, 3D printing metal implants can be applied to more orthopedic surgeries.

The translational potential of this paper

Precision, intelligence, and personalization are the future direction of orthopedics. It is reasonable to believe that 3D printing technology will be more deeply integrated with artificial intelligence, 4D printing, and big data to play a greater role in orthopedic metal implants and eventually become an important part of the digital economy. We aim to summarize the latest developments in 3D printing metal implants for engineers and surgeons to design implants that more closely mimic the morphology and function of native bone.

Custom 3D-Printed Implants for Acetabular Reconstruction: Intermediate-Term Functional and Radiographic Results

The management of massive acetabular defects at the time of revision hip surgery is challenging. Severe pelvic bone loss and the heterogeneity and quality of the remaining bone stock can compromise the fixation and mechanical stability of the implant.

Methods

We reviewed a database of consecutive patients who had undergone acetabular reconstruction with the use of a custom 3D-printed implant with a dual-mobility bearing for the treatment of Paprosky type-3B defects between 2016 and 2019. Functional and radiological outcomes were assessed.

Results

A total of 26 patients (17 women and 9 men) with a minimum follow-up of 36 months (median, 53 months; range, 36 to 77 months) were identified. The median age at surgery was 69 years (range, 49 to 90 years), and 4 patients had pelvic discontinuity. The cumulative implant survivorship was 100%. The median Oxford Hip Score improved significantly from 8 (range, 2 to 21) preoperatively to 32 (range, 14 to 47) postoperatively (p = 0.0001). One patient had a transient sciatic nerve palsy, 1 hip dislocated 6 months postoperatively and was managed nonoperatively, and 1 infection recurred. No patient had a fracture. Radiographic evaluation showed bone ingrowth at the bone-implant interface in 24 patients (92%) at ≥12 months of follow-up and showed no evidence of implant loosening or migration at the latest follow-up (3 to 6 years).

Conclusions

Excellent functional improvement, implant survivorship, and osseointegration were recorded in the patient cohort. Accurate preoperative planning and the adoption of custom 3D-printed implants showed promising results in complex revision hip surgery.

Level of Evidence

Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.

A systematic review of follow-up results of additively manufactured customized implants for the pelvic area

INTRODUCTION

While 3D printing of bone models for preoperative planning or customized surgical templating has been successfully implemented, the use of patient-specific additively manufactured (AM) implants is a newer application not yet well established. To fully evaluate the advantages and shortcomings of such implants, their follow-up results need to be evaluated.

AREA COVERED

This systematic review provides a survey of the reported follow-ups on AM implants used for oncologic reconstruction, total hip arthroplasty both primary and revision, acetabular fracture, and sacrum defects.

EXPERT OPINION

The review shows that Titanium alloy (Ti4AL6V) is the most common type of material system used due to its excellent biomechanical properties. Electron beam melting (EBM) is the predominant AM process for manufacturing implants. In almost all cases, porosity at the contact surface is implemented through the design of lattice or porous structures to enhance osseointegration. The follow-up evaluations show promising results, with only a small number of patients suffering from aseptic loosening, wear, or malalignment. The longest reported follow-up length was 120 months for acetabular cages and 96 months for acetabular cups. The AM implants have proven to serve as an excellent option to restore premorbid skeletal anatomy of the pelvis.

A new patient-specific overformed anatomical implant design method to reconstruct dysplastic femur trochlea

Patellar luxation with condylar defect is a challenging situation for reconstruction in humans. Patella reluxation, cartilage damage and pain are the most common complications. This study aims to present a new patient specific method of overformed implant design and clinical implantation that prevents luxation of patella without damaging the cartilage in a dog. Design processes are Computer Tomography, Computer Assisted Design, rapid prototyping of the bone replica, creation of the implant with surgeon's haptic knowledge on the bone replica, 3D printing of the implant and clinical application. The implant was fully seated on the bone. Patella reluxation or implant-related bone problem was not observed 80 days after the operation. However, before the implant application, there were soft tissue problems due to previous surgeries. Three-point bending test and finite element analysis were performed to determine the biomechanical safety of the implant. The stress acting on the implant was below the biomechanical limits of the implant. More cases with long-term follow-up are needed to confirm the success of this method in patellar luxation. Compared with trochlear sulcoplasty and total knee replacement, there was no cartilage damage done by surgeons with this method, and the implant keeps the patella functionally in sulcus. This is a promising multidisciplinary method that can be applied to any part of the bone and can solve some orthopaedic problems with surgeon's haptic knowledge.

Complex geometry and integrated macro-porosity: Clinical applications of electron beam melting to fabricate bespoke bone-anchored implants

The last decade has witnessed rapid advancements in manufacturing technologies for biomedical implants. Additive manufacturing (or 3D printing) has broken down major barriers in the way of producing complex 3D geometries. Electron beam melting (EBM) is one such 3D printing process applicable to metals and alloys. EBM offers build rates up to two orders of magnitude greater than comparable laser-based technologies and a high vacuum environment to prevent accumulation of trace elements. These features make EBM particularly advantageous for materials susceptible to spontaneous oxidation and nitrogen pick-up when exposed to air (e.g., titanium and titanium-based alloys). For skeletal reconstruction(s), anatomical mimickry and integrated macro-porous architecture to facilitate bone ingrowth are undoubtedly the key features of EBM manufactured implants. Using finite element modelling of physiological loading conditions, the design of a prosthesis may be further personalised. This review looks at the many unique clinical applications of EBM in skeletal repair and the ground-breaking innovations in prosthetic rehabilitation. From a simple acetabular cup to the fifth toe, from the hand-wrist complex to the shoulder, and from vertebral replacement to cranio-maxillofacial reconstruction, EBM has experienced it all. While sternocostal reconstructions might be rare, the repair of long bones using EBM manufactured implants is becoming exceedingly frequent. Despite the various merits, several challenges remain yet untackled. Nevertheless, with the capability to produce osseointegrating implants of any conceivable shape/size, and permissive of bone ingrowth and functional loading, EBM can pave the way for numerous fascinating and novel applications in skeletal repair, regeneration, and rehabilitation. STATEMENT OF SIGNIFICANCE: Electron beam melting (EBM) offers unparalleled possibilities in producing contaminant-free, complex and intricate geometries from alloys of biomedical interest, including Ti6Al4V and CoCr. We review the diverse range of clinical applications of EBM in skeletal repair, both as mass produced off-the-shelf implants and personalised, patient-specific prostheses. From replacing large volumes of disease-affected bone to complex, multi-material reconstructions, almost every part of the human skeleton has been replaced with an EBM manufactured analog to achieve macroscopic anatomical-mimickry. However, various questions regarding long-term performance of patient-specific implants remain unaddressed. Directions for further development include designing personalised implants and prostheses based on simulated loading conditions and accounting for trabecular bone microstructure with respect to physiological factors such as patient's age and disease status.

Properties and Implementation of 3-Dimensionally Printed Models in Spine Surgery: A Mixed-Methods Review With Meta-Analysis

OBJECTIVE

Spine surgery addresses a wide range of spinal pathologies. Potential applications of 3-dimensional (3D) printed in spine surgery are broad, encompassing education, planning, and simulation. The objective of this study was to explore how 3D-printed spine models are implemented in spine surgery and their clinical applications.

METHODS

Methods were combined to create a scoping review with meta-analyses. PubMed, EMBASE, the Cochrane Library, and Scopus databases were searched from 2011 to 7 September 2021. Results were screened independently by 2 reviewers. Studies utilizing 3D-printed spine models in spine surgery were included. Articles describing drill guides, implants, or nonoriginal research were excluded. Data were extracted according to reporting guidelines in relation to study information, use of model, 3D printer and printing material, design features of the model, and clinical use/patient-related outcomes. Meta-analyses were performed using random-effects models.

RESULTS

Forty articles were included in the review, 3 of which were included in the meta-analysis. Primary use of the spine models included preoperative planning, education, and simulation. Six printing technologies were utilized. A range of substrates were used to recreate the spine and regional pathology. Models used for preoperative and intraoperative planning showed reductions in key surgical performance indicators. Generally, feedback for the tactility, utility, and education use of models was favorable.

CONCLUSIONS

Replicating realistic spine models for operative planning, education, and training is invaluable in a subspeciality where mistakes can have devastating repercussions. Future study should evaluate the cost-effectiveness and the impact spine models have of spine surgery outcomes.

The analysis of defects in custom 3D-printed acetabular cups: A comparative study of commercially available implants from six manufacturers

Three-dimensional (3D) printing is used to manufacture custom acetabular cups to treat patients with massive acetabular defects. There is a risk of defects occurring in these, often in the form of structural voids. Our aim was to investigate the presence of voids in commercially available cups. We examined 12, final-production titanium custom acetabular cups, that had been 3D-printed by six manufacturers. We measured their mass, then performed micro-computed tomography (micro-CT) imaging to determine their volume and density. The micro-CT data were examined for the presence of voids. In cups that had voids, we computed (1) the number of voids, (2) their volume and the cup volume fraction, (3) their sphericity, (4) size, and (5) their location. The cups had median mass, volume, and density of 208.5 g, 46,471 mm³ , and 4.42 g/cm³ , respectively. Five cups were found to contain a median (range) of 90 (58-101) structural voids. The median void volume and cup volume fractions of cups with voids were 5.17 (1.05-17.33) mm³ and 99.983 (99.972-99.998)%, respectively. The median void sphericity and size were 0.47 (0.19-0.65) and 0.64 (0.27-8.82) mm, respectively. Voids were predominantly located adjacent to screw holes, within flanges, and at the transition between design features; these were between 0.17 and 4.66 mm from the cup surfaces. This is the first study to examine defects within final-production 3D-printed custom cups, providing data for regulators, surgeons, and manufacturers about the variability in final print quality. The size, shape, and location of these voids are such that there may be an increased risk of crack initiation from them.

Morphometric analysis of patient-specific 3D-printed acetabular cups: a comparative study of commercially available implants from 6 manufacturers

Background

3D printed patient-specific titanium acetabular cups are used to treat patients with massive acetabular defects. These have highly porous surfaces, with the design intent of enhancing bony fixation. Our aim was to characterise these porous structures in commercially available designs.

Methods

We obtained 12 final-production, patient-specific 3D printed acetabular cups that had been produced by 6 manufacturers. High resolution micro-CT imaging was used to characterise morphometric features of their porous structures: (1) strut thickness, 2) the depth of the porous layer, (3) pore size and (4) the level of porosity. Additionally, we computed the surface area of each component to quantify how much titanium may be in contact with patient tissue. Statistical comparisons were made between the designs.

Results

We found a variability between designs in relation to the thickness of the struts (0.28 to 0.65 mm), how deep the porous layers are (0.57 to 11.51 mm), the pore size (0.74 to 1.87 mm) and the level of porosity (34 to 85%). One manufacturer printed structures with different porosities between the body and flange; another manufacturer had two differing porous regions within the body of the cups. The cups had a median (range) surface area of 756.5 mm² (348 – 1724).

Conclusions

There is a wide variability between manufacturers in the porous titanium structures they 3D print. We do not currently know whether there is an optimal porosity and how this variability will impact clinically on the integrity of bony fixation; this will become clearer as post market surveillance data is generated.

Three dimensional printing as an aid for pre-operative planning in complex cases of total joint arthroplasty: A case series

Purpose

Digital templating is an essential aspect of pre-operative planning for total joint arthroplasty procedures. For complex cases of joint reconstruction, the standard templating software is insufficient to achieve the desired accuracy. 3D printing significantly aids the pre-operative planning in complicated cases of joint reconstruction and offers immense potential towards improving outcomes in these cases. The purpose of the present study is to present the various ways in which 3D printing has aided our department in facilitating complex cases of lower extremity reconstruction.

Methods

Data was retrospectively retrieved for all patients that underwent total hip arthroplasty (THA) and total knee arthroplasty (TKA) with the aid of 3D printing technology at our institution between January 2016-February 2021. Patient pain was determined before and after surgery using the visual analogue scale (VAS). Patient reported outcome measures (PROMs) were additionally analyzed using the hip disability and osteoarthritis outcome score (HOOS) and knee injury and osteoarthritis outcome score (KOOS).

Results

The final study population consisted of 39 patients that underwent TKA or THA procedures with the use of 3D printing. Twenty-four (61.5%) of the surgeries in the study were THA procedures, whereas 15 (38.5%) were TKA procedures. The average VAS for patients reduced from 8.4% before surgery to 5.4% after surgery (p < 0.001). The mean KOOS of patients that underwent TKA was 17.33 ± 9.33 (43%) and the mean HOOS of patients that underwent THA was 13.79 ± 6.6 (42%).

Conclusions

The following series demonstrates the ability by which 3D printing facilitates complex cases of hip and knee reconstruction. 3D printing offers an improvement in understanding of patient specific anatomy, enhancing patient outcomes. Departments should consider the use of 3D printing technology as an adjunct when performing complex cases of lower extremity reconstruction.

Defining the canal for ischial and pubic screws in cup revision surgery

Purpose

When revising acetabular cups, it is often necessary to provide additional stabilisation with screws. In extensive defect situations, the placement of screws caudally in the ischium and/or pubis is biomechanically advantageous. Especially after multiple revision operations, the surgeon is confronted with a reduced bone stock and unclear or altered anatomy. In addition, screw placement caudally is associated with greater risk. Therefore, the present study aims to identify and define safe zones for the placement of caudal acetabular screws.

Methods

Forty-three complete CT datasets were used for the evaluation. Sixty-three distinctive 3D points representing bone landmark of interests were defined. The coordinates of these points were then used to calculate all the parameters. For simplified visualisation and intra-operative reproducibility, an analogue clock was used, with 12 o’clock indicating cranial and 6 o’clock caudal.

Results

A consistent accumulation was found at around 4.5 ± 0.3 hours for the ischium and 7.9 ± 0.3 hours for the pubic bone.

Conclusions

The anatomy of the ischium and pubis is sufficiently constant to allow the positioning of screws in a standardised way. The interindividual variation is low — regardless of gender — so that the values determined can be used to position screws safely in the ischium and pubis. The values determined can provide the surgeon with additional orientation intra-operatively when placing caudal acetabular screws.

Custom Massive Allograft in a Case of Pelvic Bone Tumour: Simulation of Processing with Computerised Numerical Control vs. Robotic Machining

The use of massive bone allografts after the resection of bone tumours is still a challenging process. However, to overcome some issues related to the processing procedures and guarantee the best three-dimensional matching between donor and recipient, some tissue banks have developed a virtual tissue database based on the scanning of the available allografts for using their 3D shape during virtual surgical planning (VSP) procedures. To promote the use of future VSP bone-shaping protocols useful for machining applications within a cleanroom environment, in our work, we simulate a massive bone allograft machining with two different machines: a four-axes (computer numerical control, CNC) vs. a five-axes (robot) milling machine. The allograft design was based on a real case of allograft reconstruction after pelvic tumour resection and obtained with 3D Slicer and Rhinoceros software. Machining simulations were performed with RhinoCAM and graphically and mathematically analysed with CloudCompare and R, respectively. In this case, the geometrical differences of the allograft design are not clinically relevant; however, the mathematical analysis showed that the robot performed better than the four-axes machine. The proof-of-concept presented here paves the way towards massive bone allograft cleanroom machining. Nevertheless, further studies, such as the simulation of different types of allografts and real machining on massive bone allografts, are needed.

Three-dimensional-printed titanium implants for severe acetabular bone defects in revision hip arthroplasty: short- and mid-term results

PURPOSE

Severe acetabular bone defect is challenging in revision hip arthroplasty. In the present study, we aimed to present new treatment options with the 3D printing technique and analyze the clinical and radiographic outcomes of 3D-printed titanium implants for the treatment of severe acetabular bone defects in revision hip arthroplasty.

METHODS

A total of 35 patients with Paprosky type 3 bone defect and pelvic discontinuity (PD), who underwent hip revisions using 3D-printed titanium implants between 2016 and 2019 at our institution, were retrospectively reviewed. Patient-specific 3D-printed titanium augments and shells (strategy A) were used in 22 type 3A and two type 3B patients. Custom 3D-printed flanged components (strategy B) were used in 11 type 3B patients, including five PD. The clinical outcomes were evaluated with the Harris hip score (HHS). In addition, radiographic results were analyzed by the hip centre of rotation (V-COR and H-COR), implant failure, and survivorship.

RESULTS

The mean follow-up was 41.5 months (range, 16-62). The HHS was improved from 47.8 ± 8.2 pre-operatively to 78.1 ± 10.1 at one year follow-up and 86.4 ± 5.1 at the last follow-up (p < 0.01). Post-operative V-COR and H-COR of the operated side were 20.8 ± 2.0 mm and 30.2 ± 1.6 mm compared with 51.4 ± 4.1 mm and 33.9 ± 9.0 mm pre-operatively (p < 0.01). The complications included one dislocation and one partial palsy of the sciatic nerve. At the latest follow-up, no radiological component loosening or screw breakage was present.

CONCLUSIONS

3D-printed titanium implants showed satisfactory short- and mid-term clinical and radiographic outcomes. It was an effective therapeutic regimen with a low rate of complications, providing a patient-specific and reliable strategy for the severe acetabular bone defect in revision hip arthroplasty.

Mechanical and Microstructural Anisotropy of Laser Powder Bed Fusion 316L Stainless Steel

This paper aims at an in-depth and comprehensive analysis of mechanical and microstructural properties of AISI 316L austenitic stainless steel (W. Nr. 1.4404, CL20ES) produced by laser powder bed fusion (LPBF) additive manufacturing (AM) technology. The experiment in its first part includes an extensive study of the anisotropy of mechanical and microstructural properties in relation to the built orientation and the direction of loading, which showed significant differences in tensile properties among samples. The second part of the experiment is devoted to the influence of the process parameter focus level (FL) on mechanical properties, where a 48% increase in notched toughness was recorded when the level of laser focus was identical to the level of melting. The FL parameter is not normally considered a process parameter; however, it can be intentionally changed in the service settings of the machine or by incorrect machine repair and maintenance. Evaluation of mechanical and microstructural properties was performed using the tensile test, Charpy impact test, Brinell hardness measurement, microhardness matrix measurement, porosity analysis, scanning electron microscopy (SEM), and optical microscopy. Across the whole spectrum of samples, performed analysis confirmed the high quality of LPBF additive manufactured material, which can be compared with conventionally produced material. A very low level of porosity in the range of 0.036 to 0.103% was found. Microstructural investigation of solution annealed (1070 °C) tensile test samples showed an outstanding tendency to recrystallization, grain polygonization, annealing twins formation, and even distribution of carbides in solid solution.

3D Puzzle in Cube Pattern for Anisotropic/Isotropic Mechanical Control of Structure Fabricated by Metal Additive Manufacturing

Metal additive manufacturing is a powerful tool for providing the desired functional performance through a three-dimensional (3D) structural design. Among the material functions, anisotropic mechanical properties are indispensable for enabling the capabilities of structural materials for living tissues. For biomedical materials to replace bone function, it is necessary to provide an anisotropic mechanical property that mimics that of bones. For desired control of the mechanical performance of the materials, we propose a novel 3D puzzle structure with cube-shaped parts comprising 27 (3 × 3 × 3) unit compartments. We designed and fabricated a Co–Cr–Mo composite structure through spatial control of the positional arrangement of powder/solid parts using the laser powder bed fusion (L-PBF) method. The mechanical function of the fabricated structure can be predicted using the rule of mixtures based on the arrangement pattern of each part. The solid parts in the cubic structure were obtained by melting and solidifying the metal powder with a laser, while the powder parts were obtained through the remaining nonmelted powders inside the structure. This is the first report to achieve an innovative material design that can provide an anisotropic Young’s modulus by arranging the powder and solid parts using additive manufacturing technology.

Clinical and radiological outcomes in three-dimensional printing assisted revision total hip and knee arthroplasty: a systematic review

BACKGROUND

This study investigates whether three-dimensional (3D) printing-assisted revision total hip/knee arthroplasty could improve its clinical and radiological outcomes and assess the depth and breadth of research conducted on 3D printing-assisted revision total hip and knee arthroplasty.

METHODS

A literature search was carried out on PubMed, Web of Science, EMBASE, and the Cochrane Library. Only studies that investigated 3D printing-assisted revision total hip and knee arthroplasty were included. The author, publication year, study design, number of patients, patients' age, the time of follow-up, surgery category, Coleman score, clinical outcomes measured, clinical outcomes conclusion, radiological outcomes measured, and radiological outcomes conclusion were extracted and analyzed.

RESULTS

Ten articles were included in our review. Three articles investigated the outcome of revision total knee arthroplasty, and seven investigated the outcome of revision total hip arthroplasty. Two papers compared a 3D printing group with a control group, and the other eight reported 3D printing treatment outcomes alone. Nine articles investigated the clinical outcomes of total hip/knee arthroplasty, and eight studied the radiological outcomes of total hip/knee arthroplasty.

CONCLUSION

3D printing is being introduced in revision total hip and knee arthroplasty. Current literature suggests satisfactory clinical and radiological outcomes could be obtained with the assistance of 3D printing. Further long-term follow-up studies are required, particularly focusing on cost-benefit analysis, resource availability, and, importantly, the durability and biomechanics of customized prostheses using 3D printing compared to traditional techniques.

Functional and radiological outcomes after treatment with custom-made acetabular components in patients with Paprosky type 3 acetabular defects: short-term results

Background

Severe acetabular defects require special treatment with either impaction bone grafting, metal augmented cups or cup-cage constructs. Even these options are often not adequate, especially in hips with Paprosky type 3 defects with loss of anterior and posterior columns. This study investigates the clinical and radiological outcomes of custom-made acetabular components (© Materialise NV, Leuven, Belgium) for Paprosky type 3 defects.

Methods

Sixteen patients were eligible for this trial, nine of whom agreed to be included. All of them completed one year of follow-up. The Harris hip score and the Oxford hip score were used to compare pre- and postoperative functional outcomes. Radiological follow-up comprised anteversion and inclination of the implanted cup and offset measurements in both hips (femoral, medial, ischial offset and center of rotation). Statistical analyses were performed with IBM SPSS Statistics.

Results

The mean follow-up time of the nine patients was 12.2 months (range: 10–18). The Oxford hip score and Harris hip score improved from 19.8 and 50.1 to 29.4 and 68.8, respectively (p = 0.009 and 0.01). There were complications in three cases (33.3%), which led to one re-revision (11.1%). Radiologic follow-up showed restoration of the height of the center of rotation and of the global offset. Significant difference was detected in the femoral offset.

Conclusions

The functional and radiological outcomes are promising. However, long-term outcomes still need to be examined.

Level of evidence

Therapeutic Level IV.

The effect of metal artefact on the design of custom 3D printed acetabular implants

BACKGROUND

3D Printed custom-made implants constitute a viable option in patients with acetabular Paprosky III defects. In these patients, needing complex hip revision surgery, the appreciation of the bony defect is crucial to assure stable fixation of the customised implant, often intended to replace a failed one. We aimed to understand the effect of metal artefact on the design of customised implants.

METHODS

26 patients with massive acetabular defects were referred, between May 2016 and September 2018, to our institution classified as "un-reconstructable" by other hospitals. They all received custom 3D-printed acetabular cups. A subset of them underwent two-stage revision surgery due to infection. We then extended the two-stage procedure to the cases where metal artefacts were significantly affecting the reading of the CT scans. CT scans of patients' pelvises were taken pre and post-implant removal. We assessed for changes in bony shape and volume of the pelvis using 3D imaging software and quantified the effect on implant design with CAD software.

RESULTS

Eight (out of 26) patients (31%) underwent two-stage revision surgery. The CT bony reconstructions between the two timepoints changed in all cases. The changes were mostly associated to the shape and distribution of the acetabular defects. Three of these cases (37.5%) showed a remarkable difference in the remaining bone that led to a change in implant design. So far, there has been no difference in the clinical outcome between the patients who underwent single (n = 18) and two-stage surgery (n = 8).

CONCLUSIONS

The shape of the acetabulum reconstructed from CT data is potentially altered by metal artefact and bone excised during removal of the failed component. For "end-of-road" acetabular reconstruction, we recommend surgeons consider the use of two-stage surgery to enable a reliable fitting of the complex shape of 3D-printed implants.