Objectives

Preservation of both anterior and posterior cruciate ligaments in total knee arthroplasty (TKA) can lead to near-normal post-operative joint mechanics and improved knee function. We hypothesised that a patient-specific bicruciate-retaining prosthesis preserves near-normal kinematics better than standard off-the-shelf posterior cruciate-retaining and bicruciate-retaining prostheses in TKA.

Orbital floor (OF) fractures are commonly treated by implanting either bioinert titanium or polyethylene implants, or by autologous grafts. A personalized implant made of biodegradable and osteopromotive poly(trimethylene carbonate) loaded with hydroxyapatite (PTMC-HA) could be a suitable alternative for patients where a permanent implant could be detrimental. A workflow was developed from the implant production using stereolithography (SLA) based on patient CT scan to the implantation and assessment its performance (i.e. implant stability, orbit position, bone formation) compared to personalised titanium implants in a repair OF defect sheep model. Implants fabrication was done using SLA of photo-crosslinkable PTMC mixed with HA [1–3]. Preclinical study: (sheep n=12, ethic number 34_2016) was conducted by first scanning the OF bone of each sheep in order to design and to fabricate patient specific implants (PSI) made of PTMC-HA. The fabricated PSI was implanted after creating OF defect. Bone formation and defect healing was compared to manually shaped titanium mesh using time-laps X-ray analyses, histology (Giemsa-Eosin staining) and sequential fluorochrome staining over 3-months. Additionally, the osteoinductive property of the biomaterials was assessed by intramuscular implantation (IM). In this study, we showed that the composite PTMC-HA allowed for ectopic bone formation after IM implantation, without requiring any biotherapeutics. In addition, we could repair OF defect on sheep using SLA-fabricated PTMC-HA with a good shape fidelity (compared to the virtual implant) and a better bone integration compared to the titanium mesh. This study opens the field of patient-specific implants made of degradable and osteoinductive scaffolds fabricated using additive manufacturing to replace advantageously autologous bone and titanium implants

3D-printed orthopedic implants have been gaining popularity in recent years due to the control this manufacturing technique gives the designer over the different design aspects of the implant. This technique allows us to manufacture implants with material properties similar to bone, giving the implant designer the opportunity to address one of the main complications experienced after total hip arthroplasty (THA), i.e. aseptic loosening of the implant. To restore proper function after implant loosening, the implant needs to be replaced. During these revision surgeries, some extra bone is removed along with the implant, further increasing the already present defects, and making it harder to achieve proper mechanical stability with the revision implant. A possible way to limit the increasing loss of bone is the use of biodegradable orthopedic implants that optimize long-term implant stability. These implants need to both optimize the implant such that stress shielding is minimized, and tune the implant degradation rate such that newly formed bone is able to replace the degrading metal in order to maintain a proper bone-implant contact. The hope is that such (partly) degradable implants will lead to a reduction in the size of the bone defects over time, making possible future revisions less likely and less complex. We focused on improving the long-term implant stability of patient-specific acetabular implants for large bone defects and the modeling of their biodegradable behavior. To improve long-term implant stability we implemented a topology optimization approach. A patient-specific finite element model of the hip joint with and without implant was derived from CT-scans to evaluate the performance of the designs during the optimization routine. To evaluate the biodegradation behavior, a quantitative mathematical model was developed to assess the degradation rates of the biodegradable part of the implant. Currently, the biodegradation model has been implemented for magnesium (Mg) implants as a first proof of concept. For a first test case, an optimized implant was found with stress shielding levels below 20% in most regions. The highest stress shielding levels were found at the bone implant interface. The biodegradation model has been validated using experimental data, which includes immersion tests of simple scaffolds created from Commercial Pure Mg. The mass loss of the scaffold is about 0.8 mg/cm. 2. for the first day of immersion in simulated body fluid (SBF) solution. After the formation of a protective film on the surface of the simple scaffold, the degradation rate starts to slow down. Initial results presented serve as a proof of concept of the developed computational framework for the implant optimization and the implant biodegradation behavior. Currently, timing calibration, benchmarking and validation are taking place. Reducing implant-induced stress shielding, obtaining a better implant integration and reduction of bone defects, by allowing for bone to partially replace the implant over time, are crucial design factors for large bone defect implants. In this research, we have developed in-silico models to investigate these factors. Once validated and coupled, the models will serve as an important tool to find the appropriate biodegradable implant designs and biodegradable metal properties for THA applications, that improve current implant lifetime while ensuring proper mechanical functioning

Summary Statement. In this study, excellent positioning of custom-made glenoid components was achieved using patient-specific guides. Achieving the preoperatively planned orientation of the component improved significantly and more screws were located inside the scapular bone compared to implantations without such guide. Introduction. Today's techniques for total or reverse shoulder arthroplasty are limited when dealing with severe glenoid defects. The available procedures, for instance the use of bone allografts in combination with available standard implants, are technically difficult and tend to give uncertain outcomes (Hill et al. 2001; Elhassan et al. 2008; Sears et al. 2012). A durable fixation between bone and implant with optimal fit and implant positioning needs to be achieved. Custom-made defect-filling glenoid components are a new treatment option for severe glenoid defects. Despite that the patient-specific implants are uniquely designed to fit the patient's bone, it can be difficult to achieve the preoperatively planned position of the component, resulting in less optimal screw fixation. We hypothesised that the use of a patient-specific guide would improve implant and screw positioning. The aim of this study was to evaluate the added value of a newly developed patient-specific guide for implant and screw positioning, by comparing glenoid implantations with and without such guide. Patients & Methods. Large glenoid defects, representative for the defects encountered in clinical practice, were created in ten cadaveric shoulders. A CT scan of each cadaver was taken to evaluate the defects and to generate three-dimensional models of the scapular bones. Based on these models, custom glenoid components were designed. Furthermore, a newly developed custom guide was designed for five randomly selected shoulders. New CT scans were taken after implantation to generate 3D models of the bone and the implanted component and screws. This enabled to compare the experimentally achieved and preoperatively planned reconstruction. The location and orientation of the glenoid component and screw positioning were determined and differences with the optimal preoperative planning were calculated. Results. An excellent component positioning (difference in location: 1.4±0, 7mm; difference in orientation: 2, 5±1, 2°) was achieved when using the guide compared to implantations without guidance (respectively 1, 7±0, 5mm; 5, 1±2, 3°). The guide improved component orientation significantly (P<0.1). After using the guide, all screws were positioned inside the scapular bone whereas 25% of the screws placed without guidance were positioned outside the scapular bone. Discussion/Conclusion. In this study, excellent positioning of custom-made glenoid components was achieved using patient-specific guides. Achieving the preoperatively planned orientation of the component improved significantly and more screws were located inside the scapular bone compared to implantations without such guide

Summary. This work proposes a novel, automatic method to obtain an anatomical reconstruction for 3D segmented bones with large acetabular defects. The method works through the fitting of a Statistical Shape Model to the non-defect parts of the bone. Introduction. Patient-specific implants can be used to treat patients with large acetabular bone defects (IIa-c, IIIb, Paprosky 1994). These implants require a full 3D preoperative planning that includes segmentation of volumetric images (CT or MRI), extraction of the 3D shape, reconstruction of the bone defect into its anatomic (non-defect) state, design of an implant with a perfect fit and optimal placement of the screws. The anatomic reconstruction of the bone defect will play a key role in diagnosing the amount of bone loss and in the design of the implant. Previous reconstruction methods rely on a healthy contralateral (Gelaude 2007); however this is not always available (e.g. partial scan or implant present). Statistical shape models (SSM) of healthy bones can help to increase the accuracy and usability of the reconstruction and will decrease the manual labor and user dependency. Skadlubowicz (2009) illustrated the use of an SSM to reconstruct pelvic bones with tumor defects; however tumors generally affect a smaller region of the bone so that the reconstruction will be easier than in large acetabular bone defects. Also, the tumor reconstruction method uses 80 manually indicated landmarks, while the proposed method only uses 14. Patients & Methods. CT-scans from subjects with a healthy hemi-pelvis (15 male, 33 female, mean age: 69±20) were used to generate an SSM. The CT-scans were segmented using Mimics (Materialise NV, Belgium) to create a triangulated mesh. Preprocessing of the meshes ensured that the triangulation was smooth and uniform to help solve the corresponding point problem. An algorithm based on Redert (1999) was used to morph the template hemi-pelvis onto each dataset entity, creating a dataset with corresponding points. From this dataset the SSM was calculated using principal component analysis, so that the principal components serve as parameters for the mathematical model of the hemi-pelvis. To fit the SSM to a new defect hemi-pelvis, a matching algorithm was used. The algorithm varies the Principal Components independently optimizing the distance of the non-defect parts of the defect hemi-pelvis to the SSM sample. To validate the reconstruction method, 6 healthy bone meshes were used to generate a synthetic defect in the acetabular region. The original mesh was used as ‘golden standard’ to measure the reconstruction error. To illustrate the clinical use of the reconstruction method, one hemi-pelvis with a substantial defect was reconstructed. Results. The correspondence error for the morphing algorithm was 4.68±0.78 mm. The leave-one-out error for the SSM was 1.30±0.96 mm. The reconstruction error for the non-defect part was 1.44±1.13mm and for the reconstructed part 2.15±1.53mm. Discussion/Conclusion. The proposed method performs comparable to the contralateral method and the tumor reconstruction method, without the need of a healthy contralateral geometry. Consequently, the validation and the clinical illustration show that the proposed method is promising for automatic reconstruction of large acetabular defects

Objectives

Meniscal injuries are often associated with an active lifestyle. The damage of meniscal tissue puts young patients at higher risk of undergoing meniscal surgery and, therefore, at higher risk of osteoarthritis. In this study, we undertook proof-of-concept research to develop a cellularized human meniscus by using 3D bioprinting technology.