Skull Implants Research Articles

Thickness and design features of clinical cranial implants-what should automated methods strive to replicate?

New deep learning and statistical shape modelling approaches aim to automate the design process for patient-specific cranial implants, as highlighted by the MICCAI AutoImplant Challenges. To ensure applicability, it is important to determine if the training data used in developing these algorithms represent the geometry of implants designed for clinical use. Calavera Surgical Design provided a dataset of 206 post-craniectomy skull geometries and their clinically used implants. The MUG500+ dataset includes 29 post-craniectomy skull geometries and implants designed for automating design. For both implant and skull shapes, the inner and outer cortical surfaces were segmented, and the thickness between them was measured. For the implants, a 'rim' was defined that transitions from the repaired defect to the surrounding skull. For unilateral defect cases, skull implants were mirrored to the contra-lateral side and thickness differences were quantified. The average thickness of the clinically used implants was 6.0 ± 0.5mm, which approximates the thickness on the contra-lateral side of the skull (relative difference of -0.3 ± 1.4mm). The average thickness of the MUG500+ implants was 2.9 ± 1.0mm, significantly thinner than the intact skull thickness (relative difference of 2.9 ± 1.2mm). Rim transitions in the clinical implants (average width of 8.3 ± 3.4mm) were used to cap and create a smooth boundary with the skull. For implant modelers or manufacturers, this shape analysis quantified differences of cranial implants (thickness, rim width, surface area, and volume) to help guide future automated design algorithms. After skull completion, a thicker implant can be more versatile for cases involving muscle hollowing or thin skulls, and wider rims can smooth over the defect margins to provide more stability. For clinicians, the differing measurements and implant designs can help inform the options available for their patient specific treatment.

Inverse design of skull osteoinductive implants with multi-level pore structures through machine learning.

How to accurately design a personalized matching implant that can induce skull regeneration is the focus of current research. However, the design space for the porous structure of implants is extensive, and the mapping relationships between these structures and their mechanical and osteogenic properties are complex. At present, the forward design of skull implants mainly relies on expert experience, leading to high cost and a lengthy process, while the existing inverse design approaches face challenges due to data dependence and manufacturing process errors. This study presents an efficient inverse design method for personalized multilevel structures of skull implants using a machine learning pipeline composed of a finite element method, topological optimization, and neural networks. Based on the mechanical response of the human body falls, this method can tailor multi-level structures for implants in various defect positions. The results show that the proposed method establishes a bidirectional relationship between topological parameters and mechanical properties, enabling the customization of mechanical behavior at low computational cost while accounting for manufacturing errors in the 3D printing process. Additionally, the design results are also mutually consistent with analytical relationships between lattice parameters and the elastic modulus obtained from experiments and finite element simulations. Thus, this study provides a general and practical approach to rapidly design skull osteoinductive implants.

A computational analysis of transcranial magnetic stimulation in patients with cranial defects and skull plate implants

We utilized computational analysis to investigate the impact of skull defects and skull implants on the TMS-induced EF. Our findings revealed a noteworthy alteration in the induced EF when acute skull defects were present. When high-conductivity titanium plates were used, we observed a pronounced increase in the peak EF, accompanied by a shift in the induced EF from the center towards both ends of the implant. These findings underscore the importance of carefully considering skull defects and implant materials during TMS.

Development of 3D printed patient-specific skull implants based on 3d surface scans

Sometimes cranioplasty is necessary to reconstruct skull bone defects after a neurosurgical operation. If an autologous bone is unavailable, alloplastic materials are used. The standard technical approach for the fabrication of cranial implants is based on 3D imaging by computed tomography using the defect and the contralateral site. A new approach uses 3D surface scans, which accurately replicate the curvature of the removed bone flap. For this purpose, the removed bone flap is scanned intraoperatively and digitized accordingly. When using a design procedure developed for this purpose creating a patient-specific implant for each bone flap shape in short time is possible. The designed skull implants have complex free-form surfaces analogous to the curvature of the skull, which is why additive manufacturing is the ideal manufacturing technology here. In this study, we will describe the intraoperative procedure for the acquisition of scanned data and its further processing up to the creation of the implant.

A novel methodology for exact targeting of human and non-human primate brain structures and skull implants using atlas-based 3D reconstruction

BackgroundAccurate targeting of brain areas for stimulation and/or electrophysiological recording is key in many therapeutic applications and basic neuroscience research. Nevertheless, there are currently no end-to-end packages that accommodate all steps required for exact localization, visualization, and targeting regions of interest (ROIs) using standard atlases and for designing skull implants. New MethodWe have implemented a new processing pipeline that addresses this issue in macaques and humans including various preprocessing, registration, warping procedures, and 3D reconstructions, and provide a noncommercial open-source graphical software which we refer to as the MATLAB-based reconstruction for recording and stimulation (MATres). ResultsThe results of skull stripping were shown to work seamlessly in humans and monkeys. Linear and nonlinear warping of the standard atlas to the native space outperformed state-of-the-art using AFNI with improvements being more prominent in humans which had a more complex gyration geometry. The skull surface extracted by MATres using MRI images had more than 90% match with CT ground truth and could be used to design skull implants that conformed well to the skull’s local curvature. Comparison with Existing Method(s)The accuracy of the various steps including skull stripping, standard atlas registration, and skull reconstruction in MATres was compared with and shown to outperform the AFNI. The localization accuracy of the recording chambers designed with MATres and implanted in two macaque monkeys was further confirmed using MRI imaging. ConclusionsPrecise localization of ROIs offered by MATres can be used to plan electrode penetrations for recording and shallow or deep brain stimulation (DBS).

Additively manufactured polyether ether ketone (PEEK) skull implant as an alternative to titanium mesh in cranioplasty.

173Cranioplasty is used for skull defects, involving lifting the scalp and restoring the contour of the skull with the original skull piece, titanium mesh, or solid biomaterial. Additive manufacturing (AM) technology, known as three-dimensional (3D) printing, is now utilized by medical professionals to develop customized replicas of tissues, organs and bones, offering a valid option with perfect anatomic fitting in the individual and skeletal reconstruction. Here, we report a case that underwent titanium mesh cranioplasty 15 years ago. The poor appearance of the titanium mesh weakened the left eyebrow arch and resulted in the formation of a sinus tract. Cranioplasty was performed using an additively manufactured polyether ether ketone (PEEK) skull implant. PEEK skull implants have been successfully implanted without any complications. To our knowledge, this is the first reported case of direct use of fused filament fabrication (FFF)-fabricated PEEK implant for cranial repair. The FFF-printed PEEK customized skull implant could possess simultaneously with adjustable material thickness and more complex structure, tunable mechanical properties, and low processing costs compared with traditional manufacturing processes. While meeting clinical needs, this production method is an appropriate alternative for promoting the use of PEEK materials in cranioplasty.

Research on three-dimensional skull repair by combining residual and informer attention

Cranial defects may result from clinical brain tumor surgery or accidental trauma. The defect skulls require hand-designed skull implants to repair. The edge of the skull implant needs to be accurately matched to the boundary of the skull wound with various defects. For the manual design of cranial implants, it is time-consuming and technically demanding, and the accuracy is low. Therefore, an informer residual attention U-Net (IRA-Unet) for the automatic design of three-dimensional (3D) skull implants was proposed in this paper. Informer was applied from the field of natural language processing to the field of computer vision for attention extraction. Informer attention can extract attention and make the model focus more on the location of the skull defect. Informer attention can also reduce the computation and parameter count from N 2 to log( N). Furthermore,the informer residual attention is constructed. The informer attention and the residual are combined and placed in the position of the model close to the output layer. Thus, the model can select and synthesize the global receptive field and local information to improve the model accuracy and speed up the model convergence. In this paper, the open data set of the AutoImplant 2020 was used for training and testing, and the effects of direct and indirect acquisition of skull implants on the results were compared and analyzed in the experimental part. The experimental results show that the performance of the model is robust on the test set of 110 cases fromAutoImplant 2020. The Dice coefficient and Hausdorff distance are 0.940 4 and 3.686 6, respectively. The proposed model reduces the resources required to run the model while maintaining the accuracy of the cranial implant shape, and effectively assists the surgeon in automating the design of efficient cranial repair, thereby improving the quality of the patient's postoperative recovery.

Paediatric cranioplasty—Experience from a Singapore children’s hospital

Cranioplasty is a common neurosurgical procedure. Nonetheless, cranioplasty in the paediatric population pose a set of unique challenges owing to their developing craniums. We conducted a single institution, retrospective study of children that underwent cranioplasty; and corroborated our clinical outcomes with current literature. Data was statistically analysed to assess for factors associated with implant complications that required interval intervention. Thirty-two patients were recruited for the study from 01 January 2001 to 31 December 2021. Mean age was 7.9 years. For the cranial implants, there were 16 autologous (43.2%), 7 acrylic (18.9%), 5 titanium mesh (13.5%) and 4 PEEK (10.8%) grafts. Aetiologies for the skull defect include head injury (n = 22; 68.8%), neoplasm (n = 4; 12.5%), spontaneous intracranial haemorrhage (n = 3; 9.4%) and infection (n = 3; 9.4%). Eight patients (25%) required another surgery due to implant-related complications. Here, 3 patients had their implants removed due to infection (6.3%) and extrusion (3.1%); 4 had bone resorption of their autologous grafts (12.5%): and 1 patient (3.1%) had a postoperative acute extradural haematoma. A subgroup analysis was performed for patients (n = 16) with autologous skull implants. We observed that autologous bone cranioplasty at more than 6 weeks post-decompression was associated with higher rates of bone graft resorption (p = 0.008). The mean time for this group of patients to undergo a second surgery was 29.1 months. Overall, our results concur with the difficulties reported in previous publications and highlight the need for long-term followup to monitor for implant-related complications.

Treating mouse skull defects with 3D-printed fatty acid and tricalcium phosphate implants.

Skull surgery, also known as craniectomy, is done to treat trauma or brain diseases and may require the use of an implant to reestablish skull integrity. This study investigates the performance of 3D printed bone implants in a mouse model of craniectomy with the aim of making biodegradable porous implants that can ultimately be fitted to a patient's anatomy. A nonpolymeric thermoplastic bioink composed of fatty acids and β-tricalcium phosphate was used to 3D print the skull implants. Some of these were sintered to yield pure β-tricalcium phosphate implants. The performance of nonsintered and sintered implants was then compared in two semi-quantitative murine calvarial defect models using computed tomography, histology, and luciferase activity. Both types of implants were biocompatible, but only sintered implants promoted defect healing, with osseointegration to adjacent bone and the formation of new bone and bone marrow tissue in the implant pores. Luciferase scanning and histology showed that mesenchymal stem cells seeded onto the implants engraft and proliferate on the implants after implantation and contribute to forming bone. The experiments indicate that fatty acid-based 3D printing enables the creation of biocompatible and bone-forming β-tricalcium phosphate implants.

SLM 및 EBM 적층제조로 제작된 두개골 임플란트의 기계 물리적 특성 분석

Metal lamination manufacturing equipment and patient-specific implants that design and directly output implants suitable for patients by utilizing the medical image data of patients have been produced and used. The purpose of this study is to identify the mechanical characteristics of selective laser melting (SLM) and electron beam melting (EBM) 3D printer output methods of skull implants and to suggest a suitable output method for patient-specific skull implants. SLM and EBM samples were prepared in the hemispherical form with reference to commercial implants. Thereafter, the compressive strength and flange cantilever of the plates of the samples were examined; surface roughness and hardness were further evaluated. The EBM sample was found to have excellent strength and elasticity characteristics. As a result, it was judged that the sample prepared via EBM was suitable for skull implant preparation.

Aseptic bone-flap resorption after cranioplasty - incidence and risk factors.

ObjectiveOne of the common complications occurring after cranioplasty (CP) is aseptic bone-flap resorption (ABFR). Reoperation necessary because of the development of ABFR can lead to unfavorable complications during subsequent surgery using a synthetic skull implant, and also necessarily leads to higher costs. The aim of this study is to identify prognostic factors that may help to predict the development of ABFR.MethodsIn this study, 303 CP surgeries performed between 2002 and 2017 were examined retrospectively to identify factors predicting the occurrence of ABFR. A number of these factors (e.g., time lapse between decompressive craniectomy (DC) and CP, bone-flap size, specific laboratory signs, and the reason for the original DC) were analyzed as possibly influencing the risk of developing ABFR.ResultsABFR of an autologous bone flap that subsequently required a CP with synthetic skull implants occurred in 10 of 303 patients (3.0%). CP timing and patients' Karnofsky Performance Scores (KPS) (p = 0.008; p = 0.012) were identified as significant factors with an impact on the development of ABRF. Age did not reveal a significant value, but statistical analysis shows a clear trend. The younger the age, the more likely it was that an ABFR would develop.ConclusionThe risk of ABFR lessens the longer the period of time elapsed between DC and CP. Age does not reveal a significant value, but statistical analysis shows that there is a clear trend.

Postoperative Care in Facial Implants.

Facial augmentation is a growing field, secondary to the appreciation of the changes seen in the facial skeleton with aging and the growing acceptance/popularity of facial fat grafting and facial fillers. In addition, it plays a significant role in patients with congenital facial deficiencies as well as those interested in facial feminization/masculinization surgery. Several facial implants are discussed in this article including classic facial implants such as malar, submalar, chin, and prejowl implants as well as newer facial implants such as mandible, temporal, forehead, and skull implants. Special care is given to the postoperative care of these implants. Custom-made implants with three-dimensional computed tomography reconstruction are also discussed.

CT image segmentation of bone for medical additive manufacturing using a convolutional neural network

BackgroundThe most tedious and time-consuming task in medical additive manufacturing (AM) is image segmentation. The aim of the present study was to develop and train a convolutional neural network (CNN) for bone segmentation in computed tomography (CT) scans. MethodThe CNN was trained with CT scans acquired using six different scanners. Standard tessellation language (STL) models of 20 patients who had previously undergone craniotomy and cranioplasty using additively manufactured skull implants served as “gold standard” models during CNN training. The CNN segmented all patient CT scans using a leave-2-out scheme. All segmented CT scans were converted into STL models and geometrically compared with the gold standard STL models. ResultsThe CT scans segmented using the CNN demonstrated a large overlap with the gold standard segmentation and resulted in a mean Dice similarity coefficient of 0.92 ± 0.04. The CNN-based STL models demonstrated mean surface deviations ranging between −0.19 mm ± 0.86 mm and 1.22 mm ± 1.75 mm, when compared to the gold standard STL models. No major differences were observed between the mean deviations of the CNN-based STL models acquired using six different CT scanners. ConclusionsThe fully-automated CNN was able to accurately segment the skull. CNNs thus offer the opportunity of removing the current prohibitive barriers of time and effort during CT image segmentation, making patient-specific AM constructs more accesible.

The evaluation of bio-mechanical properties of four different skull implants by finite element methods

Cranioplasty helps to restore skull’s integrity, stability the state of the intracranial structure, also to improve the aesthetic immensely and reduce the concerns caused by weakened of brain protection with decompressive craniectomy. By using stress-strain analyzing of the finite element methods, to analyse the shock resistance, ability of absorbing concussion and the stability after the implanting of four different skull implants, in the end to select the implant with the one with the best biological-mechanical properties combined with CT data of 2D imaging and computer-aided design technology to establish four implants: a. conventional 3D blanket titanium mesh; b. conventional wedge-shaped PEEK mesh; c. 3D blanket triangular parabolic titanium mesh with hole button; d. half wedge-shaped triangular parabolic PEEK mesh with hole button. To second by importing ansys-workbench 17.0 software, loading adding a 500N static force at the center of the implants area of 3.982 cm2 which simulate four different scenarios of the implants suffering a real impact of heavy weight or vehicles. Comparing stress distribution, the maximum stress, the strain distribution and the maximum deflection of four different implants and the corresponding defective skulls. Under 500N load force, both four implants and defective skulls didn’t have breakdown or deformation, On the models a and c the stress concentrated at the temporal region of skull base. Pars orbitalis and the connecting areas by implants and defective skulls and the points of strength of the prosthesises. On the model b, the stress concentrated at the frontoparietal, the points of strength of the prosthesis, temporal region of skull base and titanium strip. The outcome of the model d is similar to the case b, but without obvious stress concentration of triangular parabolic mesh with hole button. The σ and ε of implants a-d are respectively: 243.800 mpa; 21.002 mpa; 386.200 mpa; 2.731 mpa and 0.1644 mm; 0.0825 mm, 0.2782 mm, 0.0828 mm. The σ of defective skulls c is 6.039 mpa, its ε is 0.0408 mm. The σ and ε of th defective skulls of d are accordingly 1.829 mpa and 0.0175 mm. The mechanical properties of PEEK are superior to the titanium implant. It can take the better role of brain protection. D of four prosthesis demonstrates the best ability in the biomechanics, followed by the b.

Structural and mechanical implications of PMMA implant shape and interface geometry in cranioplasty--A finite element study.

This computational study investigates the effect of shape (defect contour curvature) and bone-implant interface (osteotomy angle) on the stress distribution within PMMA skull implants. Using finite element methodology, 15 configurations--combinations of simplified synthetic geometric shapes (circular, square, triangular, irregular) and interface angulations--were simulated under 50N static loads. Furthermore, the implant fixation devices were modelled and analysed in detail. Negative osteotomy configurations demonstrated the largest stresses in the implant (275 MPa), fixation devices (1258 MPa) and bone strains (0.04). The circular implant with zero and positive osteotomy performed well with maximum observed magnitudes of--implant stress (1.2 MPa and 1.2 MPa), fixation device stress (11.2 MPa and 2.2 MPa), bone strain (0.218e-3 and 0.750e-4). The results suggest that the preparation of defect sites is a critical procedure. Of the greatest importance is the angle at which the edges of the defect are sawed. If under an external load, the implant has no support from the interface and the stresses are transferred to the fixation devices. This can endanger their material integrity and lead to unphysiological strains in the adjacent bone, potentially compromising the bone morphology required for anchoring. These factors can ultimately weaken the stability of the entire implant assembly.

Is This the Future of Medical Technology?

Is This the Future of Medical Technology?

Using three-dimensional multigrid-based snake and multiresolution image registration for reconstruction of cranial defect

In cranioplasty, neurosurgeons use bone grafts to repair skull defects. To ensure the protection of intracranial tissues and recover the original head shape for aesthetic purposes, a custom-made pre-fabricated prosthesis must match the cranial incision as closely as possible. In our previous study (Liao et al. in Med Biol Eng Comput 49:203-211, 2011), we proposed an algorithm consisting of the 2D snake and image registration using the patient's own diagnostic low-resolution and defective high-resolution computed tomography (CT) images to repair the impaired skull. In this study, we developed a 3D multigrid snake and employed multiresolution image registration to improve the computational efficiency. After extracting the defect portion images, we designed an image-trimming process to remove the bumped inner margin that can facilitate the placement of skull implants without manual trimming during surgery. To evaluate the performance of the proposed algorithm, a set of skull phantoms were manufactured to simulate six different conditions of cranial defects, namely, unilateral, bilateral, and cross-midline defects with 20 or 40% skull defects. The overall image processing time in reconstructing the defect portion images can be reduced from 3 h to 20 min, as compared with our previous method. Furthermore, the reconstruction accuracies using the 3D multigrid snake were superior to those using the 2D snake.

Effective Use of Electroconvulsive Therapy After Craniofacial Reconstructive Surgery

The present case report describes a 53-year-old male patient with long-standing, refractory major depressive disorder admitted for electroconvulsive therapy. The patient had a history of head trauma and was status-post craniofacial surgery with mesh and metallic implants. We describe the patient's history and the concerns associated with performing electroconvulsive therapy on a patient with metallic skull implants, and we conclude with an account of successful treatment.

Determination of Average Contour of Thais Skulls for Design of Implants

In this study, 100 dry skulls of Thais collected at the Srinagarind Hospital in Khon Kaen, Thailand were CT scanned and served for the investigation of the geometric average contour of Thais skulls. Moreover, measurements of distances between landmark points on skulls (cranial anthropometry) were made with this set of skulls for future standardization of skull implants. Thus the main purpose of this study was to determine the average contour of Thai skulls using techniques of medical image processing, Computer Aided Design (CAD) and reverse engineering software tools. After obtaining the average contour or the skull template we were able to select a region of interest and cut it for each proper standardized implant. These standardized implants will reduce the time for surgeons in implant preparation process. With their presence there is no longer necessity for CT scanning process and therefore treatment costs for a patient decrease considerably. Therefore, the result will be a good alternative for cranioplasty compared with conventional methods.

Effect of filler surface morphology on the impact behaviour of hydroxyapatite reinforced high density polyethylene composites

Instrumented falling weight impact tests have been carried out to characterize the impact behaviour of hydroxyapatite reinforced high-density polyethylene composite (HA-HDPE) in order to use this biomaterial in skull implants. The effects of HA filler surface morphology and volume fraction on the fracture toughness were studied, and fracture mechanism investigated. Impact resistance was found to be markedly improved by using a sintered grade HA filler with smooth particle surface instead of spray dried grade HA with rough surface. SEM examination of impacted fracture surfaces revealed that the improvement of impact resistance was due to the stronger interfacial bonding between smooth HA particles and HDPE polymer matrix compared with that between rough HA and HDPE, which results in more energy absorption during impact and hence better fracture resistance.