Additively manufactured versus conventionally pressed cranioplasty implants: An accuracy comparison

This article compared the accuracy of producing patient-specific cranioplasty implants using four different approaches. Benchmark geometry was designed to represent a cranium and a defect added simulating a craniectomy. An ‘ideal’ contour reconstruction was calculated and compared against reconstructions resulting from the four approaches –‘conventional’, ‘semi-digital’, ‘digital – non-automated’ and ‘digital – semi-automated’. The ‘conventional’ approach relied on hand carving a reconstruction, turning this into a press tool, and pressing titanium sheet. This approach is common in the UK National Health Service. The ‘semi-digital’ approach removed the hand-carving element. Both of the ‘digital’ approaches utilised additive manufacturing to produce the end-use implant. The geometries were designed using a non-specialised computer-aided design software and a semi-automated cranioplasty implant-specific computer-aided design software. It was found that all plates were clinically acceptable and that the digitally designed and additive manufacturing plates were as accurate as the conventional implants. There were no significant differences between the additive manufacturing plates designed using non-specialised computer-aided design software and those designed using the semi-automated tool. The semi-automated software and additive manufacturing production process were capable of producing cranioplasty implants of similar accuracy to multi-purpose software and additive manufacturing, and both were more accurate than handmade implants. The difference was not of clinical significance, demonstrating that the accuracy of additive manufacturing cranioplasty implants meets current best practice

Computer-aided methods for single stage fibrous dysplasia excision and reconstruction in the zygomatico-orbital complex

Computer Aided Design and Additive Manufacture (CAD/AM) technologies are sufficiently refined and meet the necessary regulatory requirements for routine incorporation into the medical field, with long-standing application in surgeries of the maxillofacial and craniofacial region. They have resulted in better medical care for patients, and faster, more accurate procedures. Despite ever-growing evidence about the advantages of computer aided planning, CAD and AM in surgery, detailed reporting on critical design decisions that enable methodological replication, and the development and establishment of guidelines to ensure safety, are limited. This paper presents a novel application of CAD and AM to a single stage resection and reconstruction of fibrous dysplasia in the zygoma and orbit. It is reported in sufficient fidelity to permit methods replication and design guideline developments in future cases, wherever they occur in the world. The collaborative approach included engineers, designers, surgeons and prosthetists to design patient-specific cutting guides and a custom implant. An iterative design process was used, until the desired shape and function were achieved, for both of the devices. The surgery followed the CAD plan precisely and without problems. Immediate post-operative subjective clinical judgements were of an excellent result. At 19 months post-op, a CT scan was undertaken to verify the clinical and technical outcomes. Dimensional analysis showed maximum deviation of 4.73 mm from the plan to the result, while CAD-Inspection showed that the deviations range between -0.1 and -0.8 mm, and that the majority of deviations are located around the –0.3 mm. Improvements are suggested and conclusions drawn regarding the design decisions considered critical to a successful outcome for this type of procedure in the future

A Glass Polyalkenoate Cement Carrier for Bone Morphogenetic Proteins

This work considers a glass polyalkenoate cement (GPC)-based carrier for the effective delivery of bone morphogenetic proteins (BMPs) at an implantation site. A 0.12 CaO–0.04 SrO–0.36 ZnO–0.48 SiO2 based glass and poly(acrylic acid) (PAA, Mw 213,000) were employed for the fabrication of the GPC. The media used for the water source in the GPC reaction was altered to produce a series of GPCs. The GPC liquid media was either 100 % distilled water with additions of albumin at 0, 2, 5 and 8 wt% of the glass content, 100 % formulation buffer (IFB), and 100 % BMP (150 µg rhBMP-2/ml IFB). Rheological properties, compressive strength, ion release profiles and BMP release were evaluated. Working times (Tw) of the formulated GPCs significantly increased with the addition of 2 % albumin and remained constant with further increases in albumin content or IFB solutions. Setting time (Ts) experienced an increase with 2 and 5 % albumin content, but a decrease with 8 % albumin. Changing the liquid source to IFB containing 5 % albumin had no significant effect on Ts compared to the 8 % albumin-containing BT101. Replacing the albumin with IFB/BMP-2 did not significantly affect Tw. However, Ts increased for the BT101_BMP-2 containing GPCs, compared to all other samples. The compressive strength evaluated 1 day post cement mixing was not affected significantly by the incorporation of BMPs, but the ion release did increase from the cements, particularly for Zn and Sr. The GPCs released BMP after the first day, which decreased in content during the following 6 days. This study has proven that BMPs can be immobilized into GPCs and may result in novel materials for clinical applications

Safety of 80% vs 30–35% fraction of inspired oxygen in patients undergoing surgery: a systematic review and meta-analysis

Background: Evidence-based guidelines from the World Health Organization (WHO) have recommended a high (80%) fraction of inspired oxygen (FiO2) to reduce surgical site infection in adult surgical patients undergoing general anaesthesia with tracheal intubation. However, there is ongoing debate over the safety of high FiO2. We performed a systematic review to define the relative risk of clinically relevant adverse events (AE) associated with high FiO2. Methods: We reviewed potentially relevant articles from the WHO review supporting the recommendation, including an updated (July 2018) search of EMBASE and PubMed for randomised and non-randomised controlled studies reporting AE in surgical patients receiving 80% FiO2 compared with 30–35% FiO2. We assessed study quality and performed meta-analyses of risk ratios (RR) comparing 80% FiO2 against 30–35% for major complications, mortality, and intensive care admission. Results: We included 17 moderate–good quality trials and two non-randomised studies with serious-critical risk of bias. No evidence of harm with high FiO2 was found for major AE in the meta-analysis of randomised trials: atelectasis RR 0.91 [95% confidence interval (CI) 0.59–1.42); cardiovascular events RR 0.90 (95% CI 0.32–2.54); intensive care admission RR 0.93 (95% CI 0.7–1.12); and death during the trial RR 0.49 (95% CI 0.17–1.37). One non-randomised study reported that high FiO2 was associated with major respiratory AE [RR 1.99 (95% CI 1.72–2.31)]. Conclusions: No definite signal of harm with 80% FiO2 in adult surgical patients undergoing general anaesthesia was demonstrated and there is little evidence on safety-related issues to discourage its use in this population

Evolution of design considerations in complex craniofacial reconstruction using patient-specific implants

Previously published evidence has established major clinical benefits from using Computer Aided Design (CAD), Computer Aided Manufacturing (CAM), and Additive Manufacturing (AM) to produce patient-specific devices. These include cutting guides, drilling guides, positioning guides, and implants. However, custom devices produced using these methods are still not in routine use – particularly by the UK National Health Service (NHS). Oft-cited reasons for this slow uptake include: a higher up-front cost than conventionally-fabricated devices, material-choice uncertainty, and a lack of long-term follow-up due to their relatively recent introduction. This paper identifies a further gap in current knowledge – that of design rules, or key specification considerations for complex CAD/CAM/AM devices. This research begins to address the gap by combining a detailed review of the literature with first-hand experience of interdisciplinary collaboration on five craniofacial patient case-studies. In each patient case, bony lesions in the orbito-temporal region were segmented, excised, and reconstructed in the virtual environment. Three cases translated these digital plans into theatre via polymer surgical guides. Four cases utilised AM to fabricate titanium implants. One implant was machined from PolyEther Ether Ketone (PEEK). From the literature, articles with relevant abstracts were analysed to extract design considerations. 19 frequently-recurring design considerations were extracted from previous publications. 9 new design considerations were extracted from the case studies – on the basis of subjective clinical evaluation. These were synthesised to produce a design considerations framework to assist clinicians with prescribing and design engineers with modelling. Promising avenues for further research are proposed

Additively manufactured maxillofacial implants and guides – achieving routine use

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Glass Polyalkenoate Cements Designed for Cranioplasty Applications: An Evaluation of Their Physical and Mechanical Properties

Glass polyalkenoate cements (GPCs) have potential for skeletal cementation. Unfortunately, commercial GPCs all contain, and subsequently release, aluminum ions, which have been implicated in degenerative brain disease. The purpose of this research was to create a series of aluminum-free GPCs constructed from silicate (SiO2), calcium (CaO), zinc (ZnO) and sodium (Na2O)-containing glasses mixed with poly-acrylic acid (PAA) and to evaluate the potential of these cements for cranioplasty applications. Three glasses were formulated based on the SiO2-CaO-ZnO-Na2O parent glass (KBT01) with 0.03 mol % (KBT02) and 0.06 mol % (KBT03) germanium (GeO2) substituted for ZnO. Each glass was then mixed with 50 wt % of a patented SiO2-CaO-ZnO-strontium (SrO) glass composition and the resultant mixtures were subsequently reacted with aqueous PAA (50 wt % addition) to produce three GPCs. The incorporation of Ge in the glass phase was found to result in decreased working (142 s to 112 s) and setting (807 s to 448 s) times for the cements manufactured from them, likely due to the increase in crosslink formation between the Ge-containing glasses and the PAA. Compressive (σc) and biaxial flexural (σf) strengths of the cements were examined at 1, 7 and 30 days post mixing and were found to increase with both maturation and Ge content. The bonding strength of a titanium cylinder (Ti) attached to bone by the cements increased from 0.2 MPa, when placed, to 0.6 MPa, after 14 days maturation. The results of this research indicate that Germano-Silicate based GPCs have suitable handling and mechanical properties for cranioplasty fixation