Finite element analysis of patient-specific additive-manufactured implants.

Introduction: Bone tumors, characterized by diverse locations and shapes, often necessitate surgical excision followed by custom implant placement to facilitate targeted bone reconstruction. Leveraging additive manufacturing, patient-specific implants can be precisely tailored with complex geometries and desired stiffness, enhancing their suitability for bone ingrowth. Methods: In this work, a finite element model is employed to assess patient-specific lattice implants in femur bones. Our model is validated using experimental data obtained from an animal study (n = 9). Results: The results demonstrate the accuracy of the proposed finite element model in predicting the implant mechanical behavior. The model was used to investigate the influence of reducing the elastic modulus of a solid Ti6Al4V implant by tenfold, revealing that such a reduction had no significant impact on bone behavior under maximum compression and torsion loading. This finding suggests a potential avenue for reducing the endoprosthesis modulus without compromising bone integrity. Discussion: Our research suggests that employing fully lattice implants not only facilitates bone ingrowth but also has the potential to reduce overall implant stiffness. This reduction is crucial in preventing significant bone remodeling associated with stress shielding, a challenge often associated with the high stiffness of fully solid implants. The study highlights the mechanical benefits of utilizing lattice structures in implant design for enhanced patient outcomes.

Image-Based Geometrical Characterization of Nodes in Additively Manufactured Lattice Structures.

Additive manufacturing (AM) enables the fabrication of lattice structures with optimal mechanical, fluid, and thermal properties. However, during the AM fabrication process, defects are produced in the strut and node elements, which comprise the lattice structure. This leads to discrepancies between the AM fabricated lattice and its idealized computer-aided design (CAD) model, negatively affecting the ability to predict the mechanical behavior of the fabricated lattice via numerical models. Current research is focused on quantification of geometric uncertainties in the strut elements of the lattice; as-manufactured node geometries remain relatively unexplored on an individual scale, despite their criticality to the mechanical response of the structure. Understanding the geometrical properties of as-manufactured nodes relative to CAD idealizations can be used to improve lattice designs and numerical models. In this research, X-ray microcomputed tomography (µCT) is used to analyze and quantify the as-manufactured nodal geometry, found in face-centered cubic and face-centered cubic with axial struts lattices fabricated via selective laser melting. A custom tool is developed that enables auto-isolation and classification of nodal joints from µCT-derived cross-sectional slices. Geometrical properties are extracted from the isolated nodal cross sections and compared with their idealized CAD model counterpart. Quantification of geometrical defects provides insight into how nodes within an AM lattice structure differ from each other and their idealized design. Overall, this research is an initial step toward developing accurate and efficient numerical models, as well as better node design for AM.

Specialized delivery room planning for fetuses with critical congenital heart disease.

Improvements in fetal echocardiography have increased recognition of fetuses with congenital heart disease (CHD) that require specialized delivery room (DR) care. In this study, care protocols for these low-volume and high-risk deliveries were created. Elements included (1) diagnosis-specific DR care plans and algorithms, (2) a multidisciplinary team with expertise, (3) simulation, (4) checklists, and (5) debriefing. The purpose of this study was to assess the accuracy of fetal echocardiography to predict the need for specialized DR care and determine the effectiveness of the care protocols for the treatment of patients with critical CHD. Fetal and postnatal medical records and echocardiograms of fetuses with CHD assigned to an advanced level of care were reviewed. Safety and outcome variables were analyzed to determine care plan and algorithm efficacy. Thirty-four fetuses were identified: 12 delivered at Children's National Medical Center and 22 at the adult hospital. Diagnoses included hypoplastic left heart syndrome, aortic stenosis, d-transposition of the great arteries, tetralogy of Fallot with absent pulmonary valve, complex pulmonary atresia, arrhythmias, ectopia cordis, and conjoined twins. Delivery at Children's National Medical Center was associated with a shorter time to specialty care or intervention. Measures of physiologic stability and survival were similar. Need for specialized care was predicted in 84% of deliveries. For hypoplastic left heart syndrome, intervention was predicted in 10 of 11 deliveries and for d-transposition of the great arteries in 10 of 12 deliveries. Care algorithms addressed most DR events. Of the unanticipated events, none were unrecoverable. DR survival was 100%, and survival to discharge was 83%. In conclusion, fetal echocardiography predicted the need for specialized DR care in fetuses with critical CHD. Algorithm-driven protocols enable planning such that maternal and infant risk is minimized and outcomes are good.

Feasibility of remote CT colonography at two rural Native American medical centers.

OBJECTIVE: Fort Defiance Indian Hospital and Tuba City Regional Health Care Center are two rural hospitals with limited availability of optical colonoscopy (OC) and other methods of colorectal cancer screening. Our goals were to determine whether adequate examinations could be obtained with remote supervision after brief onsite instruction and to share lessons learned in our experience with a remote CT colonography (CTC) screening program. MATERIALS AND METHODS: After brief onsite instruction, including performing a CTC examination on a volunteer to train the CT technologists, both sites began performing CTC using standard bowel preparation, fecal tagging, automatic insufflation, and low-dose technique. Studies were transferred to the University of Arizona Hospital for image quality assessment of stool, residual fluid, distention, and interpretation, with reports returned via the teleradiology information system. Clinical follow-up was performed on those patients referred for polypectomy or biopsy. RESULTS: Three hundred twenty-one subjects underwent CTC, including 280 individuals referred for screening examinations (87%). Ninety-two percent of subjects (295/321) had acceptable amounts of residual stool, 91% (293/321) had acceptable levels of fluid, and 92% (294/321) had acceptable distention. Fourteen percent (44/321) of CTC patients had polyps 6 mm or larger in size, with a positive predictive value of 41% for those who subsequently underwent colonoscopy-polypectomy (11/27). CONCLUSIONS: CTC can be introduced to rural underserved communities, performed locally, and interpreted remotely with satisfactory performance, thereby increasing colorectal cancer screening capacity. Important aspects of implementation should include technologist training, referring physician education, careful attention to image transmission, and clearly defined methods of communication with patients and referring providers.