New comprehensive procedure for custom-made total ankle replacements: Medical imaging, joint modeling, prosthesis design, and 3D printing

Ankle and Foot Arthroplasty and Prosthesis: A Review on the Current and Upcoming State of Designs and Manufacturing

The foot and ankle serve vital roles in weight bearing, balance, and flexibility but are susceptible to many diverse ailments, making treatment difficult. More commonly, Total Ankle Arthroplasty (TAA) and Total Talus Replacement (TTR) are used for patients with ankle degeneration and avascular necrosis of the talus, respectively. Ankle prosthesis and orthosis are also indicated for use with lower limb extremity amputations or locomotor disability, leading to the development of powered exoskeletons. However, patient outcomes remain suboptimal, commonly due to the misfitting of implants to the patient-specific anatomy. Additive manufacturing (AM) is being used to create customized, patient-specific implants and porous implant cages that provide structural support while allowing for increased bony ingrowth and to develop customized, lightweight exoskeletons with multifunctional actuators. AM implants and devices have shown success in preserving stability and mobility of the joint and achieving fast recovery, as well as significant improvements in gait rehabilitation, gait assistance, and strength for patients. This review of the literature highlights various devices and technologies currently used for foot and ankle prosthesis and orthosis with deep insight into improvements from historical technologies, manufacturing methods, and future developments in the biomedical space.

Database of segmentations and surface models of bones of the entire lower body created from cadaver CT scans

The range of applications of digital surface models of the bones in science and industry is wide. Three-dimensional reconstructions of bones are used in biomechanics, biomedical engineering, medical image processing, orthopedics, traumatology, radiology, patient education, anatomy, anthropometry, forensic anthropology, ergonomics, usability and human factors engineering, or accident and injury analysis and prevention. No open access database or repository of skeletal surface models of the full lower extremities exists. Therefore, the objective of this publication was to provide access to consistent complete bone models of the pelvis and lower limbs of multiple subjects, including biometric data. Segmentations and surface models of the bones of the lower extremities of more than twenty subjects were created from open access postmortem whole-body computed tomography scans. The database provides a broad range of applications by giving access to the data of the complete process chain, from the raw medical imaging data through the segmentations to the surface models.

An overview of 3D printed metal implants in orthopedic applications: Present and future perspectives

With the ability to produce components with complex and precise structures, additive manufacturing or 3D printing techniques are now widely applied in both industry and consumer markets. The emergence of tissue engineering has facilitated the application of 3D printing in the field of biomedical implants. 3D printed implants with proper structural design can not only eliminate the stress shielding effect but also improve in vivo biocompatibility and functionality. By combining medical images derived from technologies such as X-ray scanning, CT, MRI, or ultrasonic scanning, 3D printing can be used to create patient-specific implants with almost the same anatomical structures as the injured tissues. Numerous clinical trials have already been conducted with customized implants. However, the limited availability of raw materials for printing and a lack of guidance from related regulations or laws may impede the development of 3D printing in medical implants. This review provides information on the current state of 3D printing techniques in orthopedic implant applications. The current challenges and future perspectives are also included.

Definitions and Measurements of Hindfoot Alignment and Their Biomechanical and Clinical Implications

This article presents a critical review of the past and the current state of the art in defining and measuring hindfoot, ankle, and subtalar alignment. It describes the transition occurring at present from two-dimensional to three-dimensional (3D) alignment measurements, which accompany the emergence of new, functional, high-resolution imaging modalities such as the weight-bearing cone-beam computerized tomography (CT) imaging. To ease and enhance the transition and acceptability of 3D alignment measurements, new acceptable standards for different clinical application are highly desirable.

Articular geometry can affect joint kinematics, contact mechanics, and implant-bone micromotion in total ankle arthroplasty

Implant loosening and bearing surface wear remain the most common failure problems of total ankle arthroplasty (TAA). One of the main factors leading to these problems is the nonphysiologic design of articular surfaces. The goals of this study were to reveal the effects of the anatomical medial-lateral borders height differences, coronal and sagittal radii on the joint kinematics, contact mechanics, and implant-bone micromotion in TAA. A previously developed and validated musculoskeletal (MSK) multibody dynamics (MBD) modeling method of TAA based on AnyBody generic MSK MBD model (five simulations for each implant) was used by combining with a finite element analysis. Five ankle implant models with different articular surface morphologies were created according to the anatomic characteristics of Chinese measurement data, marked as Implant A to E. The total ankle forces and motions during walking simulation were predicted by MSK MBD models and the contact mechanics of the bearing surface and the micromotion of the implant-bone interface of TAA were predicted by FE models. Compared with Implant A, the internal-external rotation in Implant E increased by 12.14%, the maximum of anterior-posterior translation in Implant E increased by 5.62%, the maximum reduction of tibial micromotion in Implant E was 59.98%, and for talar, micromotion was 15.36%. The ankle implant with similar anatomic articular surface has the potential to allow patients to recover better motions and reduce the risk of early loosening. This study would provide design guidance for the development of new ankle implants and further advance the development of TAA. Clinical Significance: This study promoted the improvement of ankle implant design and made contributions to improve the service life of ankle implant and patient satisfaction.

Custom-Made Implants in Ankle Bone Loss: A Retrospective Assessment of Reconstruction/Arthrodesis in Sequelae of Septic Non-Union of the Tibial Pilon

Background and Objectives: Treating segmental tibial and ankle bone loss after radical surgery for chronic osteomyelitis is one of the most challenging problems encountered by orthopaedic surgeons. Open tibia and ankle fractures occur with an incidence of 3.4 per 100,000 and 1.6 per 100,000, respectively, and there is a high propensity of developing fracture-related infection with associated chronic osteomyelitis in patients. Segmental tibial and ankle bone loss have recently received new and improved treatments. Materials and Methods: Above all, 3D printing allows for the customization of implants based on the anatomy of each patient, using a personalized process through the layer-by-layer deposition of materials. Results: This article presents different cases from the authors' experience. Specifically, four patients suffered tibia and ankle fractures and after radical surgery for chronic osteomyelitis combined with high-performance antibiotic therapy underwent ankle reconstruction/arthrodesis with custom-made tibial spacers. Conclusions: Thanks to 3D-printed patient-specific devices, it is possible to perform surgical procedures that, for anatomical reasons, would have been impossible otherwise. Moreover, an improvement in overall functionality and an important reduction in pain were shown in the last follow-up in all patients.

Improved Pain and Function After TTC Fusion With a Custom Cage

BACKGROUND

Three-dimensional custom cages can be used to treat complex ankle and hindfoot pathology and bone loss with potentially better patient satisfaction and higher fusion rates than tibiotalocalcaneal (TTC) fusion alone or in combination with bulk femoral head allograft. Yet there is limited literature to support this procedure. The purpose of this study is to objectively quantify the clinical and radiologic outcomes of patients undergoing patient-specific 3D-printed custom cage implantation to fill large defects around the ankle joint region as part of a limb-salvaging TTC fusion.

METHODS

This is a retrospective review of 21 patients (mean age 59.3 years) who underwent custom cage implantation with a TTC retrograde fusion nail by a single surgeon for massive bone loss of the ankle and hindfoot. Patient charts were reviewed for pain and functional outcomes, complications, and various demographics, including number of previous surgeries to the ipsilateral ankle. Mean follow-up was 32 months. All 21 patients had preoperative and postoperative pain and function scores available for analysis.

RESULTS

A total of 20 (95.2%) of the 21 patients had their cage in situ at final follow-up. Overall, with the numbers available, visual analog scale (VAS) for pain, Foot and Ankle Ability Measure (FAAM) activities of daily living subscale, and the 12-Item Short Form Health Survey (SF-12) mental and physical health scores significantly improved from preoperative to final follow-up. However, when compared to the overall US population of age-matched 55- to 64-year-old individuals, patients still remained relatively disabled. There were 2 failures, one of which required amputation and the other was treated nonoperatively with bracing.

CONCLUSION

In conclusion, in this relatively small, single-surgeon series, we found that 3D-printed custom cage technology offered a viable option for complex TTC fusion procedures performed in the presence of significant bone loss, with good fusion rates, however relatively modest improvement in functional outcomes.

LEVEL OF EVIDENCE

Level IV, retrospective case series.

Comparison of Bone Segmentation Software over Different Anatomical Parts

Three-dimensional bone shape reconstruction is a fundamental step for any subject-specific musculo-skeletal model. Typically, medical images are processed to reconstruct bone surfaces via slice-by-slice contour identification. Freeware software packages are available, but commercial ones must be used for the necessary certification in clinics. The commercial software packages also imply expensive hardware and demanding training, but offer valuable tools. The aim of the present work is to report the performance of five commercial software packages (Mimics®, AmiraTM, D2PTM, SimplewareTM, and Segment 3D PrintTM), particularly the time to import and to create the model, the number of triangles of the mesh, and the STL file size. DICOM files of three different computed tomography scans from five different human anatomical areas were utilized for bone shape reconstruction by using each of these packages. The same operator and the same hosting hardware were used for these analyses. The computational time was found to be different between the packages analyzed, probably because of the pre-processing implied in this operation. The longer “time-to-import” observed in one software is likely due to the volume rendering during uploading. A similar number of triangles per megabyte (approximately 20 thousand) was observed for the five commercial packages. The present work showed the good performance of these software packages, with the main features being better than those analyzed previously in freeware packages.

Foot Orthosis and Sensorized House Slipper by 3D Printing

BACKGROUND

In clinical practice, specific customization is needed to address foot pathology, which must be disease and patient-specific. To date, the traditional methods for manufacturing custom functional Foot Orthoses (FO) are based on plaster casting and manual manufacturing, hence orthotic therapy depends entirely on the skills and expertise of individual practitioners. This makes the procedures difficult to standardize and replicate, as well as expensive, time-consuming and material-wasting, as well as difficult to standardize and replicate. 3D printing offers new perspectives in the development of patient-specific orthoses, as it permits addressing all the limitations of currently available technologies, but has been so far scarcely explored for the podiatric field, so many aspects remain unmet, especially for what regards customization, which requires the definition of a protocol that entails all stages from patient scanning to manufacturing.

METHODS

A feasibility study was carried out involving interdisciplinary cooperation between industrial engineers and podiatrists. To that end: (i) For patient-specific data acquisition, 3D scanning of the foot is compared to traditional casting. (ii) a modelling GD workflow is first created to design a process permitting easy creations of customized shapes, enabling the end user (the podiatrist) to interactively customize the orthoses. Then, (iii) a comparison is made between different printing materials, in order to reproduce the same mechanical behavior shown by standard orthoses. To do this, the mechanical properties of standard materials (Polycarbonate sheets), cut and hand-shaped, are compared with four groups of 3D printed samples: poly(ethylene glycol) (PETG), poly(acrylonitrile-butadiene.styrene) (ABS), polycarbonate (PC) and poly(lactic acid) (PLA) obtained by Fused Filament Fabrication (FFF).

RESULTS

Differences found between the foot plaster model obtained with the plaster slipper cast in a neutral position and the model of the real foot obtained with 3D scanning in the same position can be ascribed to the non-stationarity of the patient during the acquisition process, and were limited by a locking system with which no substantial differences in the almost entire sole of the foot scan were observed.

CONCLUSIONS

Using the designed GD workflow, podiatrists with limited CAD skills can easily design and interactively customize foot orthoses to adapt them to the patients' clinical needs. 3D printing enables the complex shape of the orthoses to be reproduced easily and quickly. Compared to Polycarbonate sheets (gold standard), all the printed materials were less deformable and reached lower yield stress for comparable deformation. No modifications in any of the materials as a result of printing process were observed.

Additive Manufacturing in Orthopedics: A Review

Additive manufacturing is an advanced manufacturing manner that seems like the industrial revolution. It has the inborn benefit of producing complex formations, which are distinct from traditional machining technology. Its manufacturing strategy is flexible, including a wide range of materials, and its manufacturing cycle is short. Additive manufacturing techniques are progressively used in bone research and orthopedic operation as more innovative materials are developed. This Review lists the recent research results, analyzes the strengths and weaknesses of diverse three-dimensional printing strategies in orthopedics, and sums up the use of varying 3D printing strategies in surgical guides, surgical implants, surgical predictive models, and bone tissue engineering. Moreover, various postprocessing methods for additive manufacturing for orthopedics are described.

Design and analysis of three-dimensional printing of a porous titanium scaffold

Objective

Mechanic strength, pore morphology and size are key factors for the three-dimensional (3D) printing of porous titanium scaffolds, therefore, developing optimal structure for the 3D printed titanium scaffold to fill bone defects in knee joints is instructive and important.

Methods

Structural models of titanium scaffolds with fifteen different pore unit were designed with 3D printing computer software; five different scaffold shapes were designed: imitation diamond-60°, imitation diamond-90°, imitation diamond-120°, regular tetrahedron and regular hexahedron. Each structural shape was evaluated with three pore sizes (400, 600 and 800 μm), and fifteen types of cylindrical models (size: 20 mm; height: 20 mm). Autodesk Inventor software was used to determine the strength and safety of the models by simulating simple strength acting on the knee joints. We analyzed the data and found suitable models for the design of 3D printing of porous titanium scaffolds.

Results

Fifteen different types of pore unit structural models were evaluated under positive pressure and lateral pressure; the compressive strength reduced when the pore size increased. Under torsional pressure, the strengths of the imitation diamond structure were similar when the pore size increased, and the strengths of the regular tetrahedron and regular hexahedron structures reduced when the pore size increased. In each case, the compressive strength of the regular hexahedron structure was highest, that of the regular tetrahedron was second highest, and that of the imitation diamond structure was relatively low. Fifteen types of cylindrical models under a set force were evaluated, and the sequence of comprehensive compressive strength, from strong to weak was: regular hexahedron > regular tetrahedron > imitation diamond-120° > imitation diamond-90° > imitation diamond-60°. The compressive strength of cylinder models was higher when the pore size was smaller.

Conclusion

The pore size and pore morphology were important factors influencing the compressive strength. The strength of each structure reduced when the pore size (400, 600 and 800 μm) increased. The models of regular hexahedron, regular tetrahedron and imitation diamond-120°appeared to meet the conditions of large pore sizes and high compressive strength.

Clinical Use of Talar Prostheses

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The blood supply to the talus is vulnerable to damage, making the talus susceptible to osteonecrosis, with limited treatment options.

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Talar bone replacement has been investigated as a treatment option to preserve ankle function and maintain limb length.

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Successful talar bone replacements have been performed for the past >35 years, with variations in design, methods of fixation, materials, and manufacturing techniques.

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The designs of talar prostheses range from custom-made partial (talar body) or total prostheses to prefabricated universal (non-custom-made) prostheses.

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Total talar prostheses have been demonstrated to function better than partial talar prostheses; however, there is a need for long-term studies regarding custom-made total talar prostheses and prefabricated universal talar prostheses in order to determine their long-term effectiveness.

A new ligament-compatible patient-specific 3D-printed implant and instrumentation for total ankle arthroplasty: from biomechanical studies to clinical cases

Background

Computer navigation and patient-specific instrumentation for total ankle arthroplasty have still to demonstrate their theoretical ability to improve implant positioning and functional outcomes. The purpose of this paper is to present a new and complete total ankle arthroplasty customization process for severe posttraumatic ankle joint arthritis, consisting of patient-specific 3D-printed implant and instrumentation, starting from a ligament-compatible design.

Case presentation

The new customization process was proposed in a 57-year-old male patient and involved image analysis, joint modeling, prosthesis design, patient-specific implant and instrumentation development, relevant prototyping, manufacturing, and implantation. Images obtained from a CT scan were processed for a 3D model of the ankle, and the BOX ankle prosthesis (MatOrtho, UK) geometries were customized to best fit the model. Virtual in silico, i.e., at the computer, implantation was performed to optimize positioning of these components. Corresponding patient-specific cutting guides for bone preparation were designed. The obtained models were printed in ABS by additive manufacturing for a final check. Once the planning procedure was approved, the models were sent to final state-of-the-art additive manufacturing (the metal components using cobalt-chromium-molybdenum powders, and the guides using polyamide). The custom-made prosthesis was then implanted using the cutting guides. The design, manufacturing, and implantation procedures were completed successfully and consistently, and final dimensions and location for the implant corresponded with the preoperative plan. Immediate post-op X-rays showed good implant positioning and alignment. After 4 months, clinical scores and functional abilities were excellent. Gait analysis showed satisfactory joint moment at the ankle complex and muscle activation timing within normality.

Conclusions

The complete customization process for total ankle arthroplasty provided accurate and reliable implant positioning, with satisfactory short-term clinical outcomes. However, further studies are needed to confirm the potential benefits of this complete customization process.

Level of evidence

5. Case report.

Predicting ground reaction and tibiotalar contact forces after total ankle arthroplasty during walking

The motion capture and force plates data are essential inputs for musculoskeletal multibody dynamics models to predict in vivo tibiotalar contact forces. However, it could be almost impossible to obtain valid force plates data in old patients undergoing total ankle arthroplasty under some circumstances, such as smaller gait strides and inconsistent walking speeds during gait analysis. To remove the dependence of force plates, this study has established a patient-specific musculoskeletal multibody dynamics model with total ankle arthroplasty by combining a foot-ground contact model based on elastic contact elements. And the established model could predict ground reaction forces, ground reaction moments and tibiotalar contact forces simultaneously. Three patients' motion capture and force plates data during their normal walking were used to establish the patient-specific musculoskeletal models and evaluate the predicted ground reaction forces and ground reaction moments. Reasonable accuracies were achieved for the predicted and measured ground reaction forces and ground reaction moments. The predicted tibiotalar contact forces for all patients using the foot-ground contact model had good consistency with those using force plates data. These findings suggested that the foot-ground contact model could take the place of the force plates data for predicting the tibiotalar contact forces in other total ankle arthroplasty patients, thus providing a simplified and valid platform for further study of the patient-specific prosthetic designs and clinical problems of total ankle arthroplasty in the absence of force plates data.

An Anatomical-Based Subject-Specific Model of In-Vivo Knee Joint 3D Kinematics From Medical Imaging

Biomechanical models of the knee joint allow the development of accurate procedures as well as novel devices to restore the joint natural motion. They are also used within musculoskeletal models to perform clinical gait analysis on patients. Among relevant knee models in the literature, the anatomy-based spatial parallel mechanisms represent the joint motion using rigid links for the ligaments’ isometric fibres and point contacts for the articular surfaces. To customize analyses, therapies and devices, there is the need to define subject-specific models, but relevant procedures and their accuracy are still questioned. A procedure is here proposed and validated to define a customized knee model based on a spatial parallel mechanism. Computed tomography, magnetic resonance and 3D-video-fluoroscopy were performed on a healthy volunteer to define the personalized model geometry. The model was then validated by comparing the measured and the replicated joint motion. The model showed mean absolute difference and standard deviations in translations and rotations, respectively of 0.98 ± 0.40 mm and 0.68 ± 0.29 ° for the tibia–femur motion, and of 0.77 ± 0.15 mm and 2.09 ± 0.69 ° for the patella–femur motion. These results show that accurate personalized spatial models of knee kinematics can be obtained from in-vivo imaging.

Comparison of cartilage and bone morphological models of the ankle joint derived from different medical imaging technologies

Background

Accurate geometrical models of bones and cartilage are necessary in biomechanical modelling of human joints, and in planning and designing of joint replacements. Image-based subject-specific model development requires image segmentation, spatial filtering and 3-dimensional rendering. This is usually based on computed tomography (CT) for bone models, on magnetic resonance imaging (MRI) for cartilage models. This process has been reported extensively in the past, but no studies have ever compared the accuracy and quality of these models when obtained also by merging different imaging modalities. The scope of the present work is to provide this comparative analysis in order to identify optimal imaging modality and registration techniques for producing 3-dimensional bone and cartilage models of the ankle joint.

Methods

One cadaveric leg was instrumented with multimodal markers and scanned using five different imaging modalities: a standard, a dual-energy and a cone-beam CT (CBCT) device, and a 1.5 and 3.0 Tesla MRI devices. Bone, cartilage, and combined bone and cartilage models were produced from each of these imaging modalities, and registered in space according to matching model surfaces or to corresponding marker centres. To assess the quality in overall model reconstruction, distance map analyses were performed and the difference between model surfaces obtained from the different imaging modalities and registration techniques was measured.

Results

The registration between models worked better with model surface matching than corresponding marker positions, particularly with MRI. The best bone models were obtained with the CBCT. Models with cartilage were defined better with the 3.0 Tesla than the 1.5 Tesla. For the combined bone and cartilage models, the colour maps and the numerical results from distance map analysis (DMA) showed that the smallest distances and the largest homogeneity were obtained from the CBCT and the 3.0 T MRI via model surface registration.

Conclusions

These observations are important in producing accurate bone and cartilage models from medical imaging and relevant for applications such as designing of custom-made ankle replacements or, more in general, of implants for total as well as focal joint replacements.

Orthopedic Surgeons' Perspectives on the Decision-Making Process for the Use of Bioprinter Cartilage Grafts: Web-Based Survey

BACKGROUND

Traumatic and degenerative lesions in the cartilage are one of the most difficult and frustrating types of injuries for orthopedic surgeons and patients. Future developments in medical science, regenerative medicine, and materials science may allow the repair of human body parts using 3D bioprinting techniques and serve as a basis for new therapies for tissue and organ regeneration. One future possibility is the treatment of joint cartilage defects with in vivo 3D printing from biological/biocompatible materials to produce a suitable cell attachment and proliferation environment in the damaged site and employ the natural recovery potential of the body. This study focuses on the perspectives of orthopedic surgeons regarding the key factors/determinants and perceived clinical value of a new therapeutic option.

OBJECTIVE

This study aimed to determine the knowledge and expectations of orthopedic surgeons regarding the clinical use of bioprinted cartilage.

METHODS

The survey, conducted anonymously and self-managed, was sent to orthopedic surgeons from the Catalan Society of Orthopedic and Traumatology Surgery. In accordance with the method devised by Eysenbach, the Checklist for Reporting Results of Internet E-Surveys was used to analyze the results. The following factors were taken into consideration: the type and origin of the information received; its relevance; the level of acceptance of new technologies; and how the technology is related to age, years, and place of experience in the field.

RESULTS

Of the 86 orthopedic surgeons included, 36 believed the age of the patient was a restriction, 53 believed the size of the lesion should be between 1 and 2 cm to be considered for this type of technology, and 51 believed that the graft should last more than 5 years. Surgeons over 50 years of age (38/86, 44%) gave more importance to clinical evidence as compared to surgeons from the other age groups.

CONCLUSIONS

The perspective of orthopedic surgeons depends highly on the information they receive and whether it is specialized and consistent, as this will condition their acceptance and implementation of the bioprinted cartilage.