Patient-Specific Vascular Flow Phantom for MRI- and Doppler Ultrasound Imaging

OBJECTIVE

Intraoperative Doppler ultrasound imaging of human brain vasculature is an emerging neuro-imaging modality that offers vascular brain mapping with unprecedented spatiotemporal resolution. At present, however, access to the human brain using Doppler Ultrasound is only possible in this intraoperative context, posing a significant challenge for validation of imaging techniques. This challenge necessitates the development of realistic flow phantoms outside of the neurosurgical operating room as external platforms for testing hardware and software. An ideal ultrasound flow phantom should provide reference-like values in standardized topologies such as a slanted pipe, and allow for measurements in structures closely resembling vascular morphology of actual patients. Additionally, the phantom should be compatible with other clinical cerebrovascular imaging modalities. To meet these criteria, we developed and validated a versatile, multimodal MRI- and ultrasound Doppler phantom.

METHODS

Our approach incorporates the latest advancements in phantom research using tissue-mimicking material and 3D-printing with water-soluble resin to create wall-less patient-specific lumens, compatible for ultrasound and MRI.

RESULTS

We successfully produced three distinct phantoms: a slanted pipe, a y-shape phantom representing a bifurcating vessel and an arteriovenous malformation (AVM) derived from clinical Digital Subtraction Angiography (DSA)-data of the brain. We present 3D ultrafast power Doppler imaging results from these phantoms, demonstrating their ability to mimic complex flow patterns as observed in the human brain. Furthermore, we showcase the compatibility of our phantom with Magnetic Resonance Imaging (MRI).

CONCLUSION

We developed an MRI- and Doppler Ultrasound-compatible flow-phantom using customizable, water-soluble resin prints ranging from geometrical forms to patient-specific vasculature.

Impact of osteoporosis and Cement-Augmented fusion on adjacent spinal levels Post-Fusion Surgery: Patient-Specific finite element analysis

Cement-augmentation is a technique commonly used during posterior lumbar instrumented fusion (PLIF) to reinforce compromised osteoporotic vertebral bone, minimize the risk of loosening screws, enhance stability, and improve overall surgical outcomes. In this study, we introduce a novel segmented vertebral body regional modeling approach to investigate the effects of osteoporosis and cement-augmented lumbar fusion on disc biomechanics at spinal levels adjacent to the fused vertebrae. Using our previously validated personalized-poroelastic-osteoligamentous FE model of the spine, fusion was simulated at L4-L5, and the biomechanics of adjacent levels were studied for 30 patients (non-osteoporotic patients (N = 15), osteoporotic patients (N = 15)). PLIF models, with and without cement-augmentation, were developed and compared after an 8 h-rest period (200 N), following a 16 h-cyclic compressive loading of 500-1000 N (40 and 20 min, respectively). Movement in different directions (flexion/ extension/ lateral bending/ axial rotation) was simulated using 10Nm moment before and after cyclic loading. The material mapping algorithm was validated by comparing the results of voxel-based and parametric models. The FE cement-augmented models, subject to daily activity loading, demonstrated significant differences in disc height loss and fluid loss as compared to non-cemented models. The calculated axial stress and fiber strain values were also significantly higher for these models. This work demonstrates that although osteoporosis does not significantly alter the time-dependent characteristics of adjacent IVDs post-surgery, cement-augmentation increases the risk of adjacent segment disease (ASD) incidence. A holistic understanding of the trade-offs and long-term complex interplay between structural reinforcement modalities, including cement augmentation, and altered biomechanics warrants further investigation.

Brain network classification based on dynamic graph attention information bottleneck

BACKGROUND AND OBJECTIVES

Graph neural networks (GNN) have demonstrated remarkable encoding capabilities in the context of brain network classification tasks. They excel at uncovering hidden static connections between brain states. However, brain network signals can be influenced by physiological traits and external variables during clinical detection, resulting in noisy brain graphs. Additionally, many existing algorithms for brain networks primarily focus on static topologies determined by threshold-based criteria, thereby overlooking the real-time variability in brain channel connectivity. These sources of noise and the persistence of static structures inevitably hinder the effective exchange of information during brain network computations.

METHODS

To address these challenges, we propose a novel framework called the dynamic graph attention information bottleneck (DGAIB). This framework is designed to dynamically enhance the input raw brain graph structure from the perspective of information theory and graph theory. First, we employ the Spearman function to construct a raw graph. Then, we use a graph information bottleneck (GIB) to optimize the internal graph connections by selectively masking redundant feature embeddings. Finally, we enhance the feature aggregation of each brain state by utilizing a graph attention network (GAT), which promotes improved information exchange among distinct brain regions within the model. These processed representations serve as input for subsequent classification tasks.

EXPERIMENT AND RESULTS

We systematically evaluated the robustness and generalizability of our proposed framework through a series of experiments. This evaluation included patient-specific experiments using the electroencephalography (EEG)-based CHB-MIT dataset and cross-patient experiments leveraging the functional magnetic resonance imaging (fMRI)-based ABIDE-I dataset from multiple perspectives.

Midfoot Tarsectomy in Cavovarus: Why PSI Makes a Difference?

The cavovarus foot is a complex deformity that can be treated using multiple surgical procedures, ranging from soft tissue surgery to triple arthrodesis. Among these options, anterior midfoot tarsectomy is a three-dimensional closed-wedge osteotomy, traditionally performed slowly and progressively in a blind fashion, and remaining a challenge for unexperimented surgeons with variable outcomes. As such, we investigated and discussed the use of patient-specific cutting guides (PSCGs) in computer-assisted anterior midfoot tarsectomy in terms of accuracy, reproducibility, and safety.

Design considerations for patient-specific bone fixation plates: a literature review

In orthopedic surgery, patient-specific bone plates are used for fixation when conventional bone plates do not fit the specific anatomy of a patient. However, plate failure can occur due to a lack of properly established design parameters that support optimal biomechanical properties of the plate.This review provides an overview of design parameters and biomechanical properties of patient-specific bone plates, which can assist in the design of the optimal plate.A literature search was conducted through PubMed and Embase, resulting in the inclusion of 78 studies, comprising clinical studies using patient-specific bone plates for fracture fixation or experimental studies that evaluated biomechanical properties or design parameters of bone plates. Biomechanical properties of the plates, including elastic stiffness, yield strength, tensile strength, and Poisson's ratio are influenced by various factors, such as material properties, geometry, interface distance, fixation mechanism, screw pattern, working length and manufacturing techniques.Although variations within studies challenge direct translation of experimental results into clinical practice, this review serves as a useful reference guide to determine which parameters must be carefully considered during the design and manufacturing process to achieve the desired biomechanical properties of a plate for fixation of a specific type of fracture.

Satisfaction after total knee arthroplasty: a prospective matched-pair analysis of patients with customised individually made and off-the-shelf implants

PURPOSE

Customised individually made (CIM) total knee arthroplasty (TKA) was introduced to potentially improve patient satisfaction and other patient-reported outcome measures (PROMs). The purpose of this study was to compare PROMs, especially patient satisfaction, of patients with CIM and OTS TKA in a matched-pair analysis with a 2-year follow-up.

METHODS

This is a prospective cohort study with a propensity score matching of 85 CIM and 85 off-the-shelf (OTS) TKA. Follow-up was at 4 months, 1 year and 2 years. The primary outcome was patient satisfaction. Secondary outcomes were as follows: overall improvement, willingness to undergo the surgery again, Knee injury and Osteoarthritis Outcome Score (KOOS), Forgotten Joint Score (FJS-12), High-Activity Arthroplasty Score (HAAS), EQ-5D-3L, EQ-VAS, Knee Society Score (KSS) and surgeon satisfaction.

RESULTS

Patient satisfaction ranged from 86 to 90% and did not differ between CIM and OTS TKA. The EQ-VAS after 4 months and the HAAS after 1 year and 2 years were higher for CIM TKA. KOOS, FJS-12 and EQ-5D-3L were not different at follow-up. The changes in KOOS symptoms, pain and daily living were higher for OTS TKA. The KSS was higher for patients with CIM TKA. Surgeon satisfaction was high throughout both groups. Patients who were satisfied after 2 years did not differ preoperatively from those who were not satisfied. Postoperatively, all PROMs were better for satisfied patients. Patient satisfaction was not correlated with patient characteristics, implant or preoperative PROMs, and medium to strongly correlated with postoperative PROMs.

CONCLUSION

Patient satisfaction was high with no differences between patients with CIM and OTS TKA. Both implant systems improved function, pain and health-related quality of life. Patients with CIM TKA showed superior results in demanding activities as measured by the HAAS.

LEVEL OF EVIDENCE

II, prospective cohort study.

Laser-cutting: A novel alternative approach for point-of-care manufacturing of bespoke tablets

A novel subtractive manufacturing method to produce bespoke tablets with immediate and extended drug release is presented. This is the first report on applying fusion laser cutting to produce bespoke furosemide solid dosage forms based on pharmaceutical-grade polymeric carriers. Cylindric tablets of different sizes were produced by controlling the two-dimensional design of circles of the corresponding diameter. Immediate and extended drug release patterns were achieved by modifying the composition of the polymeric matrix. Thermal analysis and XRD indicated that furosemide was present in an amorphous form. The laser-cut tablets demonstrated no significant drug degradation (<2%) nor the formation of impurities were identified. Multi-linear regression was used to quantify the influences of laser-cutting process parameters (laser energy levels, scan speeds, and the number of laser applications) on the depth of the laser cut. The utility of this approach was exemplified by manufacturing tablets of accurate doses of furosemide. Unlike additive or formative manufacturing, the reported approach of subtractive manufacturing avoids the modification of the structure, e.g., the physical form of the drug or matrix density of the tablet during the production process. Hence, fusion laser cutting is less likely to modify critical quality attributes such as release patterns or drug contents. In a point-of-care manufacturing scenario, laser cutting offers a significant advantage of simplifying quality control and a real-time release of laser-cut products such as solid dosage forms and implants.

3D-printed LEGO®-inspired titanium scaffolds for patient-specific regenerative medicine

Despite the recent advances in 3D-printing, it is often difficult to fabricate implants that optimally fit a defect size or shape. There are some approaches to resolve this issue, such as patient-specific implant/scaffold designs based on CT images of the patients, however, this process is labor-intensive and costly. Especially in developing countries, affordable treatment options are required, while still not excluding these patient groups from potential material and manufacturing advances. Here, a selective laser melting (SLM) 3D-printing strategy was used to fabricate a hierarchical, LEGO®-inspired Assemblable Titanium Scaffold (ATS) system, which can be manually assembled in any shape or size with ease. A surgeon can quickly create a scaffold that would fit to the defect right before the implantation during the surgery. Additionally, the direct inclusion of micro- and macroporous structures via 3D-printing, as well as a double acid-etched surface treatment (ST) in the ATS, ensure biocompatibility, sufficient nutrient flow, cell migration and enhanced osteogenesis. Three different structures were designed (non-porous:NP, semi-porous:SP, ultra-porous:UP), 3D-printed with the SLM technique and then surface treated for the ST groups. After analyzing characteristics of the ATS such as printing quality, surface roughness and interconnected porosity, mechanical testing and finite element analysis (FEA) demonstrated that individual and stacked ATS have sufficient mechanical properties to withstand loading in a physiological system. All ATS showed high cell viability, and the SP and UP groups demonstrated enhanced cell proliferation rates compared to the NP group. Furthermore, we also verified that cells were well-attached and spread on the porous structures and successful cell migration between the ATS units was seen in the case of assemblies. The UP and SP groups exhibited higher calcium deposition and RT-qPCR proved higher osteogenic gene expression compared to NP group. Finally, we demonstrate a number of possible medical applications that reveal the potential of the ATS through assembly.

3D-printed patient specific surgical guides: Balancing accuracy with practicality

Introduction

Three-dimensional (3D) printing technology has been used in orthopaedic surgery in recent years to manufacture customized surgical cutting jigs. However, there is scarcity of literature and information regarding the optimal parameters of an ideal jig. Our study aims to determine the optimum parameters to design surgical jigs that can produce accurate cuts, and remain practical for use, to serve as a guide for jig creation in future.

Methods and materials

A biomechanical lab study was designed to investigate whether the thickness of a jig and the height of its cutting slot can significantly affect cutting accuracy. Surgical jigs were 3D printed in medical grade, and an oscillating sawblade was used to mimic intraoperative surgical cuts through the cutting slots onto wooden blocks, which were then analysed to determine the accuracy of cuts.

Results

Statistical analysis was performed on a total of 72 cuts. The cutting accuracy increased when the thickness of the jig increased, at all slot heights. The cutting accuracy also increased as the slot height decreased, at all jig thicknesses. Overall, the parameters for jig construction that yielded the most accurate cuts were a jig thickness of 15 mm, in combination with a slot height of 100 % of the width of the sawblade. Additionally, at a jig thickness of 15 mm, there was no statistically significant difference in cutting accuracy when increasing the slot height to 120 %.

Conclusion

This study is the first to propose tangible parameters that can be applied to surgical jig construction to obtain reproducible accurate cuts. Provided that a jig of 15 mm thickness can be accommodated by the size of the wound, the ideal surgical jig with a superior balance of accuracy and useability is 15 mm thick, with a cutting slot height of 120 % of the sawblade thickness.

Computer numerical control (CNC) carving as an on-demand point-of-care manufacturing of solid dosage form: A digital alternative method for 3D printing

Computer numerical control (CNC) carving is a widely used method of industrial subtractive manufacturing of wood, plastics, and metal products. However, there have been no previous reports of applying this approach to manufacture medicines. In this work, the novel method of tablet production using CNC carving is introduced for the first time. This report provides a proof-of-concept for applying subtractive manufacturing as an alternative to formative (powder compression) and additive (3D printing) manufacturing for the on-demand production of solid dosage forms. This exemplar manufacturing approach was employed to produce patient-specific hydrocortisone (HC) tablets for the treatment of children with congenital adrenal hyperplasia. A specially made drug-polymer cast based on polyethene glycol (PEG 6,000) and hydroxypropyl cellulose was produced using thermal casting. The cast was used as a workpiece and digitally carved using a small-scale 3-dimensional (3D) CNC carving. To establish the ability of this new approach to provide an accurate dose of HC, four different sizes of CNC carved tablet were manufactured to achieve HC doses of 2.5, 5, 7.5 and 10 mg with a relative standard deviation of the tablet weight in the range of 3.69-4.79%. In addition, batches of 2.5 and 5 mg HC tablets met the British Pharmacopeia standards for weight uniformity. Thermal analysis and X-ray powder diffraction indicated that the model drug was in amorphous form. In addition, HPLC analysis indicated a level of purity of 96.5 ± 1.1% of HC. In addition, the process yielded mechanically strong cylindrical tablets with tensile strength ranging from 0.49 to 1.6 MPa and friability values of <1%, whilst maintaining an aesthetic look. In vitro, HC release from the CNC-carved tablets was slower with larger tablet sizes and higher binder contents. This is the first report on applying CNC carving in the pharmaceutical context of producing solid dosage forms. The work showed the potential of this technology as an alternative method for the on-demand manufacturing of patient-specific dosage forms.

Computational Assessment of Unsteady Flow Effects on Magnetic Nanoparticle Targeting Efficiency in a Magnetic Stented Carotid Bifurcation Artery

PURPOSE

Worldwide, cardiovascular disease is the leading cause of hospitalization and death. Recently, the use of magnetizable nanoparticles for medical drug delivery has received much attention for potential treatment of both cancer and cardiovascular disease. However, proper understanding of the interacting magnetic field forces and the hydrodynamics of blood flow is needed for effective implementation. This paper presents the computational results of simulated implant assisted medical drug targeting (IA-MDT) via induced magnetism intended for administering patient specific doses of therapeutic agents to specific sites in the cardiovascular system. The drug delivery scheme presented in this paper functions via placement of a faintly magnetizable stent at a diseased location in the carotid artery, followed by delivery of magnetically susceptible drug carriers guided by the local magnetic field. Using this method, the magnetic stent can apply high localized magnetic field gradients within the diseased artery, while only exposing the neighboring tissues, arteries, and organs to a modest magnetic field. The localized field gradients also produce the forces needed to attract and hold drug-containing magnetic nanoparticles at the implant site for delivering therapeutic agents to treat in-stent restenosis.

METHODS

The multi-physics computational model used in this work is from our previous work and has been slightly modified for the case scenario presented in this paper. The computational model is used to analyze pulsatile blood flow, particle motion, and particle capture efficiency in a magnetic stented region using the magnetic properties of magnetite (Fe3O4) and equations describing the magnetic forces acting on particles produced by an external cylindrical electromagnetic coil. The electromagnetic coil produces a uniform magnetic field in the computational arterial flow model domain, while both the particles and the implanted stent are paramagnetic. A Eulerian-Lagrangian technique is adopted to resolve the hemodynamic flow and the motion of particles under the influence of a range of magnetic field strengths (Br = 2T, 4T, 6T, and 8T). Particle diameter sizes of 10 nm-4 µm in diameter were evaluated. Two dimensionless numbers were evaluated in this work to characterize relative effects of Brownian motion (BM), magnetic force induced particle motion, and convective blood flow on particle motion.

RESULTS

The computational simulations demonstrate that the greatest particle capture efficiency results for particle diameters within the micron range of 0.7-4 µm, specifically in regions where flow separation and vortices are at a minimum. Similar to our previous work (which did not involve the use of a magnetic stent), it was also observed that the capture efficiency of particles decreases substantially with particle diameter, especially in the superparamagnetic regime. Contrary to our previous work, using a magnetic stent tripled the capture efficiency of superparamagnetic particles. The highest capture efficiency observed for superparamagnetic particles was 78% with an 8 T magnetic field strength and 65% with a 2 T magnetic field strength when analyzing 100 nm particles. For 10 nm particles and an 8 T magnetic field strength, the particle capture efficiency was 55% and for a 2 T magnetic field strength the particle capture efficiency was observed to be 43%. Furthermore, it was found that larger magnetic field strengths, large particle diameter sizes (1 µm and above), and slower blood flow velocity improves the particle capture efficiency. The distribution of captured particles on the vessel wall along the axial and azimuthal directions is also discussed. Results for captured particles on the vessel wall along the axial flow direction showed that the particle density decreased along the axial direction, especially after the stented region. For the entrance section of the stented region, the captured particle density distribution along the axial direction is large, corresponding to the center-symmetrical distribution of the magnetic force in that section.

CONCLUSION

The simulation results presented in this work have shown to yield favorable capture efficiencies for micron range particles and superparamagnetic particles using magnetized implants such as the stent discussed in this work. The results presented in this work justify further investigation of MDT as a treatment technique for cardiovascular disease.

Editorial by Reza Mehrazin and Shirin Razdan on p. 388-389 of this issue: Can preoperative planning using IRIS™ three-dimensional anatomical virtual models predict operative findings during robot-assisted partial nephrectomy?

Objective

To evaluate the predictive validity of IRIS™ (Intuitive Surgical®, Sunnyvale, CA, USA) as a planning tool for robot-assisted partial nephrectomy (RAPN) by assessing the degree of overlap with intraoperative execution.

Methods

Thirty-one patients scheduled for RAPN by four experienced urologists were enrolled in a prospective study. Prior to surgery, urologists reviewed the IRIS™ three-dimensional model on an iphone Operating System (iOS) app and completed a questionnaire outlining their surgical plan including surgical approach, and ischemia technique as well as confidence in executing this plan. Postoperatively, questionnaires assessing the procedural approach, clinical utility, efficiency, and effectiveness of IRIS™ were completed. The degree of overlap between the preoperative and intraoperative questionnaires and between the planned approach and actual execution of the procedure was analyzed. Questionnaires were answered on a 5-point Likert scale and scores of 4 or greater were considered positive.

Results

Mean age was 65.1 years with a mean tumor size of 27.7 mm (interquartile range 17.5-44.0 mm). Hilar tumors consisted of 32.3%; 48.4% of patients had R.E.N.A.L. nephrometry scores of 7-9. On preoperative questionnaires, the surgeons reported that in 67.7% cases they were confident that they can perform the procedure successfully, and on intraoperative questionnaires, the surgeons reported that in 96.8% cases IRIS™ helped achieve good spatial sensation of the anatomy. There was a high degree of overlap between preoperative and intraoperative questionnaires for the surgical approach, interpreting anatomical details and clinical utility. When comparing plans for selective or off-clamp, the preoperative plan was executed in 90.0% of cases intraoperatively.

Conclusion

A high degree of overlap between the preoperative surgical approach and intraoperative RAPN execution was found using IRIS™. This is the first study to evaluate the predictive accuracy of IRIS™ during RAPN by comparing preoperative plan and intraoperative execution.

Patient-Specific Quantitative In-Vivo Assessment of Human Mitral Valve Leaflet Strain Before and After MitraClip Repair

PURPOSE

Mitral regurgitation (MR) is a highly prevalent and deadly cardiac disease characterized by improper mitral valve (MV) leaflet coaptation. Among the plethora of available treatment strategies, the MitraClip is an especially safe option, but optimizing its long-term efficacy remains an urgent challenge.

METHODS

We applied our noninvasive image-based strain computation pipeline [1] to intraoperative transesophageal echocardiography datasets taken from ten patients undergoing MitraClip repair, spanning a range of MR etiologies and MitraClip configurations. We then analyzed MV leaflet strains before and after MitraClip implementation to develop a better understanding of (1) the pre-operative state of human regurgitant MV, and (2) the MitraClip's impact on the MV leaflet deformations.

RESULTS

The MV pre-operative strain fields were highly variable, underscoring both the heterogeneity of the MR in the patient population and the need for patient-specific treatment approaches. Similarly, there were no consistent overall post-operative strain patterns, although the average A2 segment radial strain difference between pre- and post-operative states was consistently positive. In contrast, the post-operative strain fields were better correlated to their respective pre-operative strain fields than to the inter-patient post-operative strain fields. This quantitative result implies that the patient specific pre-operative state of the MV guides its post-operative deformation, which suggests that the post-operative state can be predicted using pre-operative data-derived modelling alone.

CONCLUSIONS

The pre-operative MV leaflet strain patterns varied considerably across the range of MR disease states and after MitraClip repair. Despite large inter-patient heterogeneity, the post-operative deformation appears principally dictated by the pre-operative deformation state. This novel finding suggests that though the variation in MR functional state and MitraClip-induced deformation were substantial, the post-operative state can be predicted from the pre-operative data alone. This study suggests that, with use of larger patient cohort and corresponding long-term outcomes, quantitative predictive factors of MitraClip durability can be identified.

Custom-made implants for massive acetabular bone loss: accuracy with CT assessment

BACKGROUND

Custom-made implants are a valid option in revision total hip arthroplasty to address massive acetabular bone loss. The aim of this study was to assess the accuracy of custom-made acetabular implants between preoperative planning and postoperative positioning using CT scans.

METHODS

In a retrospective analysis, three patients who underwent an acetabular custom-made prosthesis were identified. The custom-made designs were planned through 3D CT analysis considering surgical points of attention. The accuracy of intended implants positioning was assessed by comparing pre- and postoperative CT analyzing the center of rotation (CoR), anteversion, inclination, screws, and implant surface in contact with the bone.

RESULTS

The three cases presented satisfactory accuracy in positioning. A malpositioning in the third case was observed due to the posterization of the CoR of the implant of more than 10 mm. The other CoR vectors considered in the third patient and all vectors in the other two cases fall within 10 mm. All the cases were positioned with a difference of less than 10° of anteversion and inclination with respect to the planning.

CONCLUSIONS

The current case series revealed promising accuracy in the positioning of custom-made acetabular prosthesis comparing the planned implant in preoperative CT with postoperative CT.

Online prediction for respiratory movement compensation: a patient-specific gating control for MRI-guided radiotherapy

BACKGROUND

This study aims to validate the effectiveness of linear regression for motion prediction of internal organs or tumors on 2D cine-MR and to present an online gating signal prediction scheme that can improve the accuracy of MR-guided radiotherapy for liver and lung cancer.

MATERIALS AND METHODS

We collected 2D cine-MR sequences of 21 liver cancer patients and 10 lung cancer patients to develop a binary gating signal prediction algorithm that forecasts the crossing-time of tumor motion traces relative to the target threshold. Both 0.4 s and 0.6 s prediction windows were tested using three linear predictors and three recurrent neural networks (RNNs), given the system delay of 0.5 s. Furthermore, an adaptive linear regression model was evaluated using only the first 30 s as the burn-in period, during which the model parameters were adapted during the online prediction process. The accuracy of the predicted traces was measured using amplitude metrics (MAE, RMSE, and R2), and in addition, we proposed three temporal metrics, namely crossing error, gating error, and gating accuracy, which are more relevant to the nature of the gating signals.

RESULTS

In both 0.6 s and 0.4 s prediction cases, linear regression outperformed other methods, demonstrating significantly smaller amplitude errors compared to the RNNs (P < 0.05). The proposed algorithm with adaptive linear regression had the best performance with an average gating accuracy of 98.3% and 98.0%, a gating error of 44 ms and 45 ms, for liver cancer and lung cancer patients, respectively.

CONCLUSION

A functional online gating control scheme was developed with an adaptive linear regression that is both more cost-efficient and accurate than sophisticated RNN based methods in all studied metrics.

Modeling the biomechanics of laser corneal refractive surgery

We present a finite element model of the human cornea used to simulate corneal refractive surgery according to the three most diffused laser procedures, i. e., photo-refractive keratectomy (PRK), laser in-situ keratomileusis (LASIK) and small incision lenticule extraction (SMILE). The geometry used for the model is patient-specific in terms of anterior and posterior surfaces of the cornea and intrastromal surfaces originated by the planned intervention. The customization of the solid model prior to finite element discretization avoids the struggling difficulties associated with the geometrical modification induced by cutting, incision and thinning. Important features of the model include the identification of the stress-free geometry and an adaptive compliant limbus to account for the surrounding tissues. By the way of simplification, we adopt a Hooke material model extended to the finite kinematics, and consider only the preoperative and short-term postoperative conditions, disregarding the remodeling and material evolution aspects typical of biological tissues. Albeit simple and incomplete, the approach demonstrates that the post-operative biomechanical state of the cornea, after the creation of a flap or the removal of a small lenticule, is strongly modified with respect to the preoperative state and characterized by displacement irregularities and stress localizations.

A new three-dimensional patient-specific cutting guide for opening wedge high tibial osteotomy based on ct scan: preliminary in vitro results

PURPOSE

The aim of this study was to evaluate the accuracy of a patient-specific cutting guide on both coronal and sagittal alignment compared to the pre-operative planning in OWHTO.

METHODS

Twelve OWHTO on 6 cadaveric specimens were performed by 3 experienced knee surgeons using patient-specific cutting guides based on 3D pre-operative planning. Since the specimens had no major deformities, a fixed correction of 6° on the left and 10° on the right legs were carried out to simulate different scenarios. A pre-operative and post-OWHTO 3D CT scans were performed, and images were superimposed using the dedicated 3D planning software to align their reference axes. A pre-operative planning was performed considering both Medial Proximal Tibial Angle (MPTA) and Posterior Tibial Slope (PTS), and a patient-specific cutting guide was produced. Planned and post-OWHTO MPTA and PTS were evaluated (mean and standard deviation), and Pearson's correlation coefficient was calculated to assess precision and accuracy of the whole treatment.

RESULTS

A mean correction of 6,1° (SD 1,9°) and 1,2° (SD 1°) was obtained respectively in the coronal plane (MPTA) and in the sagittal plane (PTS). The average difference between planned and post-OWHTO MPTA and PTS was respectively 1,2° (SD 0,6°) and 1,2° (SD 1°) in the sagittal plane (PTS). Pearson's correlation coefficient demonstrated a good accuracy of the treatment in both coronal and sagittal plane (respectively r=0,95 and r=0,86). No lateral hinge fractures were detected at the post-operative CT scan.

CONCLUSION

OWTHO performed with the help of 3D patient specific cutting guide on cadaveric specimens demonstrated good accuracy and reliability in obtaining the planned correction. In vivo studies are necessary to confirm these results and evaluate cost-effectiveness of this system.

LEVEL OF EVIDENCE

Level IV cadaveric study.

The Influence of Minor Aortic Branches in Patient-Specific Flow Simulations of Type-B Aortic Dissection

Type-B aortic dissection (TBAD) is a disease in which a tear develops in the intimal layer of the descending aorta forming a true lumen and false lumen (FL). Because disease outcomes are thought to be influenced by haemodynamic quantities such as pressure and wall shear stress (WSS), their analysis via numerical simulations may provide valuable clinical insights. Major aortic branches are routinely included in simulations but minor branches are virtually always neglected, despite being implicated in TBAD progression and the development of complications. As minor branches are estimated to carry about 7-21% of cardiac output, neglecting them may affect simulation accuracy. We present the first simulation of TBAD with all pairs of intercostal, subcostal and lumbar arteries, using 4D-flow MRI (4DMR) to inform patient-specific boundary conditions. Compared to an equivalent case without minor branches, their inclusion improved agreement with 4DMR velocities, reduced time-averaged WSS (TAWSS) and transmural pressure and elevated oscillatory shear in regions where FL dilatation and calcification were observed in vivo. Minor branch inclusion resulted in differences of 60-75% in these metrics of potential clinical relevance, indicating a need to account for minor branch flow loss if simulation accuracy is sought.

Fiber Organization has Little Effect on Electrical Activation Patterns during Focal Arrhythmias in the Left Atrium

Over the past two decades there has been a steady trend towards the development of realistic models of cardiac conduction with increasing levels of detail. However, making models more realistic complicates their personalization and use in clinical practice due to limited availability of tissue and cellular scale data. One such limitation is obtaining information about myocardial fiber organization in the clinical setting. In this study, we investigated a chimeric model of the left atrium utilizing clinically derived patient-specific atrial geometry and a realistic, yet foreign for a given patient fiber organization. We discovered that even significant variability of fiber organization had a relatively small effect on the spatio-temporal activation pattern during regular pacing. For a given pacing site, the activation maps were very similar across all fiber organizations tested.

A novel three-dimensional-printed patient-specific sacral implant for spinopelvic reconstruction in sacral giant cell tumour

PURPOSE

Spinopelvic reconstruction after sacral tumour resection is one of the most demanding procedures in sacral tumour surgery. The aims of this study were to evaluate the feasibility of spinopelvic reconstruction with 3D-printed prostheses in sacral giant cell tumours and the clinical outcomes and complications at follow-up.

METHODS

We retrospectively analyzed ten consecutive patients with giant cell tumors of the sacrum who underwent intralesional nerve-sparing resection with curative intent and custom implant reconstruction between 2016 and 2021. There were four males and six females with a mean age of 40.2 years (range, 25-62 years) at surgery. A computer-aided-design implant was prepared using 3D printing technology that was both matched to the bone defect and biomechanically evaluated. A 3D-printed surgical guide was used to replicate the resection procedure as planned. We analyzed operational outcomes, oncological outcomes, functional outcomes, complications, and prosthetic outcomes. Pain at rest was assessed according to a 10-cm VAS score. The results of functional improvement were evaluated using the MSTS-93 score at the final follow-up.

RESULTS

All patients were observed for 26 to 61 months, with an average follow-up of 43.8 months. No deep infection or prosthetic structural failure occurred in this study. A total of 80% of patients had good neurological function and normal urinary, bowel, and ambulatory functions. The mean MSTS score was 24.1 (range, 22-26). The mean VAS score was 2 (range 0 to 2). Delayed wound healing occurred in three patients, and the wounds healed after debridement. One case had local recurrence and survived tumour-free after resection of the recurrent lesion. An aseptic loosening was found in a patient that did not require secondary surgery. By radiographical assessments, we found that 90% of implants were well osseointegrated at the final follow-up examination.

CONCLUSIONS

The 3D-printed sacral implants might provide a promising strategy for spinopelvic reconstruction in sacral giant cell tumours undergoing intralesional nerve-sparing surgery with satisfactory clinical outcomes, osseointegration, and excellent durability.

Mechanistic-mathematical modeling of intracranial pressure (ICP) profiles over a single heart cycle. The fundament of the ICP curve form

The intracranial pressure (ICP) curve with its different peaks has been comprehensively studied, but the exact physiological mechanisms behind its morphology has not been revealed. If the pathophysiology behind deviations from the normal ICP curve form could be identified, it could be vital information to diagnose and treat each single patient. A mathematical model of the hydrodynamics in the intracranial cavity over single heart cycles was developed. A Windkessel model approach was generalized but the unsteady Bernoulli equation was utilized for blood flow and CSF flow. This is a modification of earlier models using the extended and simplified classical Windkessel analogies to a model that is based on mechanisms rooted in the laws of physics. The improved model was calibrated with patient data for cerebral arterial inflow, venous outflow, cerebrospinal fluid (CSF), and ICP over one heart cycle from 10 neuro-intensive care unit patients. A priori model parameter values were obtained by considering patient data and values taken from earlier studies. These values were used as an initial guess for an iterated constrained-ODE (ordinary differential equation) optimization problem with cerebral arterial inflow data as input into the system of ODEs. The optimization routine found patient-specific model parameter values that produced model ICP curves that showed excellent agreement with clinical measurements while model venous and CSF flow were within a physiologically acceptable range. The improved model and the automated optimization routine gave better model calibration results compared to previous studies. Moreover, patient-specific values of physiologically important parameters like intracranial compliance, arterial and venous elastance, and venous outflow resistance were determined. The model was used to simulate intracranial hydrodynamics and to explain the underlying mechanisms of the ICP curve morphology. Sensitivity analysis showed that the order of the three main peaks of the ICP curve was affected by a decrease in arterial elastance, a large increase in resistance to arteriovenous flow, an increase in venous elastance, or a decrease in resistance to CSF flow in the foramen magnum; and the frequency of oscillations were notably affected by intracranial elastance. In particular, certain pathological peak patterns were caused by these changes in physiological parameters. To the best of our knowledge, there are no other mechanism-based models associating the pathological peak patterns to variation of the physiological parameters.

Strategic Application of Epigenetic Regulators for Efficient Neuronal Reprogramming of Human Fibroblasts

Background and Objectives

Cellular reprogramming in regenerative medicine holds great promise for treating patients with neurological disorders. In this regard, small molecule-mediated cellular conversion has attracted special attention because of its ease of reproducibility, applicability, and fewer safety concerns. However, currently available protocols for the direct conversion of somatic cells to neurons are limited in clinical application due of their complex nature, lengthy process, and low conversion efficiency.

Methods and Results

Here, we report a new protocol involving chemical-based direct conversion of human fibroblasts (HF) to matured neuron-like cells with a short duration and high conversion efficiency using temporal and strategic dual epigenetic regulation. In this protocol, epigenetic modulation by inhibition of histone deacetylase and bromodomain enabled to overcome "recalcitrant" nature of adult fibroblasts and shorten the duration of neuronal reprogramming. We further observed that an extended epigenetic regulation is necessary to maintain the induced neuronal program to generate a homogenous population of neuron-like cells.

Conclusions

Therefore, our study provides a new protocol to produce neurons-like cells and highlights the need of proper epigenetic resetting to establish and maintain neuronal program in HF.

Electromagnetic Navigation Assisted Patient-Personalized Femoral Osteotomy for Acute Correction of Posttraumatic Residual Multiplanar Femoral Deformity with Shortening

Improper healing of a femoral shaft fracture can result in posttraumatic residual multiplanar femoral deformity and limb shortening, which can be restored with a corrective osteotomy. Predominantly in complex posttraumatic circumstances, the use of computer assistance in orthopaedic surgery may facilitate meticulous preoperative planning, and further improve the accuracy and safety of such procedures, potentially resulting in better clinical outcomes. Herein, we present a unique case of electromagnetic navigation assisted patient-personalized femoral osteotomy for acute correction of posttraumatic residual multiplanar femoral deformity with shortening.

Custom total knee arthroplasty combined with personalised alignment grants 94% patient satisfaction at minimum follow-up of 2 years

PURPOSE

The purpose was to report detailed patient-reported outcome measures (PROMs) and satisfaction rates for computed tomography (CT)-based custom TKA at minimum follow-up of 2 years. The hypothesis was that custom TKA combined with 'personalised alignment' would yield equivalent or better PROMs compared to values reported in systematic reviews and meta-analyses on off-the-shelf (OTS) TKA.

METHODS

Of an initial cohort of 150 custom TKAs, four died (unrelated to surgery), one required a revision, and five refused participation, leaving 140 patients for analysis. Patients completed pre- and post-operative PROMs (Oxford Knee Score (OKS), Forgotten Joint Score (FJS), Knee injury and Osteoarthritis Outcome Score (KOOS), Western Ontario and McMaster osteoarthritis index (WOMAC)) as well as overall level of satisfaction. Proportions that attained a patient acceptable symptom state (PASS) were calculated for OKS and FJS. Clinical findings were compared to the average scores reported for PROMs in recent systematic reviews and/or meta-analyses on OTS TKA. Descriptive statistics were used to summarise the clinical findings as means, standard deviations (SD) and ranges, or numbers and percentages.

RESULTS

At mean follow-up 33.5 ± 4.5 months, 94% (135/143) were either satisfied or very satisfied. Proportions that achieved PASS were 89% for OKS (120/135), and 85% for FJS (118/139). Median OKS, WOMAC and KOOS Symptoms and Pain scores were all within the 4th quartile of medians reported in systematic reviews and/or meta-analyses.

CONCLUSIONS

At a minimum follow-up of two years following custom TKA combined with 'personalised alignment', 94% of patients were either satisfied or very satisfied, and the PASS criteria were achieved in 89% for OKS and 85% for FJS, all of which compare favourably to published outcomes of OTS TKA. Direct comparisons to the literature may not be appropriate, however, considering the heterogeneity of patient demographics and alignment techniques. Randomised controlled trials with sufficient statistical power are needed to corroborate these findings and generalise them to unselected TKA patients.

LEVEL OF EVIDENCE

IV, retrospective cohort study.

Patient-specific finite element modeling of scoliotic curve progression using region-specific stress-modulated vertebral growth

PURPOSE

This study describes the creation of patient-specific (PS) osteo-ligamentous finite element (FE) models of the spine, ribcage, and pelvis, simulation of up to three years of region-specific, stress-modulated growth, and validation of simulated curve progression with patient clinical angle measurements.

RESEARCH QUESTION

Does the inclusion of region-specific, stress-modulated vertebral growth, in addition to scaling based on age, weight, skeletal maturity, and spine flexibility allow for clinically accurate scoliotic curve progression prediction in patient-specific FE models of the spine, ribcage, and pelvis?

METHODS

Frontal, lateral, and lateral bending X-Rays of five AIS patients were obtained for approximately three-year timespans. PS-FE models were generated by morphing a normative template FE model with landmark points obtained from patient X-rays at the initial X-ray timepoint. Vertebral growth behavior and response to stress, as well as model material properties were made patient-specific based on several prognostic factors. Spine curvature angles from the PS-FE models were compared to the corresponding X-ray measurements.

RESULTS

Average FE model errors were 6.3 ± 4.6°, 12.2 ± 6.6°, 8.9 ± 7.7°, and 5.3 ± 3.4° for thoracic Cobb, lumbar Cobb, kyphosis, and lordosis angles, respectively. Average error in prediction of vertebral wedging at the apex and adjacent levels was 3.2 ± 2.2°. Vertebral column stress ranged from 0.11 MPa in tension to 0.79 MPa in compression.

CONCLUSION

Integration of region-specific stress-modulated growth, as well as adjustment of growth and material properties based on patient-specific data yielded clinically useful prediction accuracy while maintaining physiological stress magnitudes. This framework can be further developed for PS surgical simulation.

Toxicological applications of human induced pluripotent stem cell-derived hepatocyte-like cells: an updated review

Variability in supply, paucity of donors and cellular instability under in vitro conditions have limited the application of primary human hepatocytes (PHHs) to hepatotoxicity testing. Therefore, alternative sources have been sought for functional liver cells. Many of the earlier in vitro hepatotoxicity studies were carried out using hepatoma-derived cell lines. These cell lines have overcome some of the limitations of PHHs with regard to phenotypic stability and availability; however, they suffer from their own inherent limitations, such as the lack of drug-metabolizing functionality, which renders them inadequate for situations where toxic metabolite formation of the parent drug occurs. In the last decade we have witnessed a burgeoning interest of the research community in using hepatocyte-like cells (HLCs) derived from human induced pluripotent stem cells (iPSCs) as in vitro hepatotoxicity models. HLCs offer the perspective of a defined and renewable supply of functional hepatocytes; more importantly, HLCs maintain their original donor genotype and afford donor diversity, thus opening new avenues to patient-specific toxicity testing. In this review, we first introduce various in vitro hepatotoxicity models, then focus on HLCs and their application in hepatotoxicity studies, and finally offer some perspectives on future developments of the field.

Predicting mechanically ventilated patients future respiratory system elastance - A stochastic modelling approach

BACKGROUND AND OBJECTIVE

Respiratory mechanics of mechanically ventilated patients evolve significantly with time, disease state and mechanical ventilation (MV) treatment. Existing deterministic data prediction methods fail to comprehensively describe the multiple sources of heterogeneity of biological systems. This research presents two respiratory mechanics stochastic models with increased prediction accuracy and range, offering improved clinical utility in MV treatment.

METHODS

Two stochastic models (SM2 and SM3) were developed using retrospective patient respiratory elastance (E_rs) from two clinical cohorts which were averaged over time intervals of 10 and 30 min respectively. A stochastic model from a previous study (SM1) was used to benchmark performance. The stochastic models were clinically validated on an independent retrospective clinical cohort of 14 patients. Differences in predictive ability were evaluated using the difference in percentile lines and cumulative distribution density (CDD) curves.

RESULTS

Clinical validation shows all three models captured more than 98% (median) of future E_rs data within the 5th - 95th percentile range. Comparisons of stochastic model percentile lines reported a maximum mean absolute percentage difference of 5.2%. The absolute differences of CDD curves were less than 0.25 in the ranges of 5 < E_rs (cmH₂O/L) < 85, suggesting similar predictive capabilities within this clinically relevant E_rs range.

CONCLUSION

The new stochastic models significantly improve prediction, clinical utility, and thus feasibility for synchronisation with clinical interventions. Paired with other MV protocols, the stochastic models developed can potentially form part of decision support systems, providing guided, personalised, and safe MV treatment.

Virtual patient framework for the testing of mechanical ventilation airway pressure and flow settings protocol

BACKGROUND AND OBJECTIVE

Model-based and personalised decision support systems are emerging to guide mechanical ventilation (MV) treatment for respiratory failure patients. However, model-based treatments require resource-intensive clinical trials prior to implementation. This research presents a framework for generating virtual patients for testing model-based decision support, and direct use in MV treatment.

METHODS

The virtual MV patient framework consists of 3 stages: 1) Virtual patient generation, 2) Patient-level validation, and 3) Virtual clinical trials. The virtual patients are generated from retrospective MV patient data using a clinically validated respiratory mechanics model whose respiratory parameters (respiratory elastance and resistance) capture patient-specific pulmonary conditions and responses to MV care over time. Patient-level validation compares the predicted responses from the virtual patient to their retrospective results for clinically implemented MV settings and changes to care. Patient-level validated virtual patients create a platform to conduct virtual trials, where the safety of closed-loop model-based protocols can be evaluated.

RESULTS

This research creates and presents a virtual patient platform of 100 virtual patients generated from retrospective data. Patient-level validation reported median errors of 3.26% for volume-control and 6.80% for pressure-control ventilation mode. A virtual trial on a model-based protocol demonstrates the potential efficacy of using virtual patients for prospective evaluation and testing of the protocol.

CONCLUSION

The virtual patient framework shows the potential to safely and rapidly design, develop, and optimise new model-based MV decision support systems and protocols using clinically validated models and computer simulation, which could ultimately improve patient care and outcomes in MV.

Personalized 3D-printed forearm braces as an alternative for a traditional plaster cast or splint; A systematic review

Forearm fractures such as distal radius fractures are traditionally treated with a plaster or synthetic cast. Patients commonly report inconvenience of the cast, skin problems, and occasionally radial sensory nerve numbness. A known issue with casting is that the rate of secondary dislocation is high. As an alternative to casts, personalized 3D-printed braces are increasingly used. This review provides an inventory of current developments and experience with 3D-printed forearm braces. Main focus was on the design requirements, materials used, technical requirements, and preclinical and clinical results. Review of 12 studies showed that all printed braces used an open design. Fused Deposition Modelling is most commonly used 3D-printing technique (seven studies) and polylactic acid is the most commonly used material (five studies). Clinical evaluation was done in six studies, mainly involving distal radius fractures, and generally showed a low complication rate and high patient satisfaction with the printed brace. Whether or not the results obtained with 3D-printed braces are superior to results after casting requires further studies.

Time is Money! Influence on Operating Theater and Sterilization Times of Patient-specific Cutting Guides and Single-use Instrumentation for Total Knee Arthroplasty: A Full Factorial Design of 136 Patients

Background

Patient-specific cutting guides (PSGs) and single-use disposable instrumentation (SUI) have emerged as potential beneficial innovations for total knee arthroplasty. The aim of this study was to evaluate the impact of PSG and SUI for total knee arthroplasty on operating room (OR) and sterilization times.

Methods

A monocentric, prospective, interventional, full factorial design study, including 136 patients, compared patient-specific (PSG, n = 68) to conventional cutting guides (n = 68) and SUI (n = 68) to conventional instrumentation (CVI, n = 68). In the OR, we recorded the number of instrument trays, operating time, and room occupancy time. In the central sterile services department, the total sterilization duration was assessed. The primary outcome was operating time and sterilization duration. Secondary outcomes were difference in the number of trays, Oxford Knee Score, and postoperative mechanical axis.

Results

The median operating time was 80 minutes (Q1-Q3: 73-90) and was significantly increased for SUI compared to that for CVI (+5 minutes, P = .0072). The median sterilization duration was 1261 minutes (Q1-Q3: 934-1603). It was significantly in favor of SUI (936 minutes) over CVI (1565 minutes) (+629 minutes, P < .0001). The total number of instrument trays was 404 for 136 patients: 252 for CVI and 152 for SUI (P < .0001) and 189 for PSG and 215 for conventional cutting guides (P = .0006). There was no significant difference in OKS (P = .86) nor in the postoperative alignment which was between 177° and 183° (75% patients, P = .24).

Conclusions

SUI lowers the number of instrument trays and sterilization duration. PSG is not associated with significant OR or sterilization time reduction. The use of SUI could reduce the risk of noncompliance of instrument trays.

Enhanced 4D Flow MRI-Based CFD with Adaptive Mesh Refinement for Flow Dynamics Assessment in Coarctation of the Aorta

4D Flow MRI is a diagnostic tool that can visualize and quantify patient-specific hemodynamics and help interventionalists optimize treatment strategies for repairing coarctation of the aorta (COA). Despite recent developments in 4D Flow MRI, shortcomings include phase-offset errors, limited spatiotemporal resolution, aliasing, inaccuracies due to slow aneurysmal flows, and distortion of images due to metallic artifact from vascular stents. To address these limitations, we developed a framework utilizing Computational Fluid Dynamics (CFD) with Adaptive Mesh Refinement (AMR) that enhances 4D Flow MRI visualization/quantification. We applied this framework to five pediatric patients with COA, providing in-vivo and in-silico datasets, pre- and post-intervention. These two data sets were compared and showed that CFD flow rates were within 9.6% of 4D Flow MRI, which is within a clinically acceptable range. CFD simulated slow aneurysmal flow, which MRI failed to capture due to high relative velocity encoding (Venc). CFD successfully predicted in-stent blood flow, which was not visible in the in-vivo data due to susceptibility artifact. AMR improved spatial resolution by factors of 101 to 103 and temporal resolution four-fold. This computational framework has strong potential to optimize visualization/quantification of aneurysmal and in-stent flows, improve spatiotemporal resolution, and assess hemodynamic efficiency post-COA treatment.

Prediction of wall stress and oxygen flow in patient-specific abdominal aortic aneurysms: the role of intraluminal thrombus

In this study, the biomechanical role of intraluminal thrombus (ILT) in an abdominal aortic aneurysm (AAA) is investigated. The implications of ILT in AAA are controversial in literature. Previous studies have demonstrated that ILT provides a biomechanical advantage by decreasing wall stress, whereas other studies have associated ILT with inhibiting oxygen transport and inducing aortic wall weakening. Therefore, we sought to explore the connection between ILT, mechanical stresses, and oxygen flow in different geometries of patient-specific aneurysms with varying ILT morphologies. The objective is to investigate the extent to which ILT influences the prediction of aneurysmal wall stresses that are associated with rupture, as well as oxygen concentrations to measure tissue oxygen deprivation. Three patient-specific AAA geometries are considered, and two models, one with ILT and one without ILT, are created for each patient to assess the effect of ILT presence. A fluid-structure interaction approach is used to couple the blood flow, wall deformation, and oxygen mass transport. Results are presented for hemodynamics patterns, wall stress measures, and oxygen metrics within the arterial wall. While ILT is found to reduce wall stress, simulations confirm that ILT decreases oxygen transport within the tissue significantly, leading to wall hypoxia.

Spinal decompression with patient-specific guides

BACKGROUND CONTEXT

Patient-specific instruments (PSI) have been well established in spine surgery for pedicle screw placement. However, its utility in spinal decompression surgery is yet to be investigated.

PURPOSE

The purpose of this study was to investigate the feasibility and utility of PSI in spinal decompression surgery compared with conventional freehand (FH) technique for both expert and novice surgeons.

STUDY DESIGN

Human cadaver study.

METHODS

Thirty-two midline decompressions were performed on 4 fresh-frozen human cadavers. An expert spine surgeon and an orthopedic resident (novice) each performed 8 FH and 8 PSI-guided decompressions. Surgical time for each decompression method was measured. Postoperative decompression area, cranial decompression extent in relation to the intervertebral disc, and lateral recess bony overhang were measured on postoperative CT-scans. In the PSI-group, the decompression area and osteotomy accuracy were evaluated.

RESULTS

The surgical time was similar in both techniques, with 07:25 min (PSI) versus 06:53 min (FH) for the expert surgeon and 12:36 min (PSI) vs. 11:54 (FH) for the novice surgeon. The postoperative cranial decompression extent and the lateral recess bony overhang did not differ between both techniques and surgeons. Further, the postoperative decompression area was significantly larger with the PSI than with the FH for the novice surgeon (477 vs. 305 mm²; p=.01), but no significant difference was found between both techniques for the expert surgeon. The execution of the decompression differed from the preoperative plan in the decompression area by 5%, and the osteotomy planes had an accuracy of 1-3 mm.

CONCLUSION

PSI-guided decompression is feasible and accurate with similar procedure time to the standard FH technique in a cadaver model, which warrants further investigation in vivo. In comparison to the FH technique, a more extensive decompression was achieved with PSI in the novice surgeon's hands in this study.

CLINICAL SIGNIFICANCE

The PSI-guided spinal decompression technique may be a useful alternative to FH decompression in certain situations. A special potential of the PSI technique could lie in the technical aid for novice surgeons and in situations with unconventional anatomy or pathologies such as deformity or tumor. This study serves as a starting point toward PSI-guided spinal decompression, but further in vivo investigations are necessary.

Patient-specific dosimetry adapted to variable number of SPECT/CT time-points per cycle for [Formula: see text]Lu-DOTATATE therapy

BACKGROUND

The number of SPECT/CT time-points is important for accurate patient dose estimation in peptide receptor radionuclide therapy. However, it may be limited by the patient's health and logistical reasons. Here,  an image-based dosimetric workflow adapted to the number of SPECT/CT acquisitions available throughout the treatment cycles was proposed, taking into account patient-specific pharmacokinetics and usable in clinic for all organs at risk.

METHODS

Thirteen patients with neuroendocrine tumors were treated with four injections of 7.4 GBq of [Formula: see text]Lu-DOTATATE. Three SPECT/CT images were acquired during the first cycle (1H, 24H and 96H or 144H post-injection) and a single acquisition (24H) for following cycles. Absorbed doses were estimated for kidneys (LK and RK), liver (L), spleen (S), and three surrogates of bone marrow (L2 to L4, L1 to L5 and T9 to L5) that were compared. 3D dose rate distributions were computed with Monte Carlo simulations. Voxel dose rates were averaged at the organ level. The obtained Time Dose-Rate Curves (TDRC) were fitted with a tri-exponential model and time-integrated. This method modeled patient-specific uptake and clearance phases observed at cycle 1. Obtained fitting parameters were reused for the following cycles, scaled to the measure organ dose rate at 24H. An alternative methodology was proposed when some acquisitions were missing based on population average TDRC (named STP-Inter). Seven other patients with three SPECT/CT acquisitions at cycles 1 and 4 were included to estimate the uncertainty of the proposed methods.

RESULTS

Absorbed doses (in Gy) per cycle available were: 3.1 ± 1.1 (LK), 3.4 ± 1.5 (RK), 4.5 ± 2.8 (L), 4.6 ± 1.8 (S), 0.3 ± 0.2 (bone marrow). There was a significant difference between bone marrow surrogates (L2 to L4 and L1 to L5, Wilcoxon's test: p value < 0.05), and while depicting very doses, all three surrogates were significantly different than dose in background (p value < 0.01). At cycle 1, if the acquisition at 24H is missing and approximated, medians of percentages of dose difference (PDD) compared to the initial tri-exponential function were inferior to 3.3% for all organs. For cycles with one acquisition, the median errors were smaller with a late time-point. For STP-Inter, medians of PDD were inferior to 7.7% for all volumes, but it was shown to depend on the homogeneity of TDRC.

CONCLUSION

The proposed workflow allows the estimation of organ doses, including bone marrow, from a variable number of time-points acquisitions for patients treated with [Formula: see text]Lu-DOTATATE.

A Computational Framework for Pre-Interventional Planning of Peripheral Arteriovenous Malformations

PURPOSE

Peripheral arteriovenous malformations (pAVMs) are congenital lesions characterised by abnormal high-flow, low-resistance vascular connections-the so-called nidus-between arteries and veins. The mainstay treatment typically involves the embolisation of the nidus, however the complexity of pAVMs often leads to uncertain outcomes. This study aims at developing a simple, yet effective computational framework to aid the clinical decision making around the treatment of pAVMs using routinely acquired clinical data.

METHODS

A computational model was developed to simulate the pre-, intra-, and post-intervention haemodynamics of a patient-specific pAVM. A porous medium of varying permeability was employed to simulate the sclerosant effect on the nidus haemodynamics. Results were compared against clinical data (digital subtraction angiography, DSA, images) and experimental flow-visualization results in a 3D-printed phantom of the same pAVM.

RESULTS

The computational model allowed the simulation of the pAVM haemodynamics and the sclerotherapy-induced changes at different interventional stages. The predicted inlet flow rates closely matched the DSA-derived data, although the post-intervention one was overestimated, probably due to vascular system adaptations not accounted for numerically. The nidus embolization was successfully captured by varying the nidus permeability and increasing its hydraulic resistance from 0.330 to 3970 mmHg s ml-1. The nidus flow rate decreased from 71% of the inlet flow rate pre-intervention to 1%: the flow completely bypassed the nidus post-intervention confirming the success of the procedure.

CONCLUSION

The study demonstrates that the haemodynamic effects of the embolisation procedure can be simulated from routinely acquired clinical data via a porous medium with varying permeability as evidenced by the good qualitative agreement between numerical predictions and both in vivo and in vitro data. It provides a fundamental building block towards a computational treatment-planning framework for AVM embolisation.

Experimental evaluation of the patient-specific haemodynamics of an aortic dissection model using particle image velocimetry

Aortic Dissection (AD) is a complex pathology that affects the aorta. Diagnosis, management and treatment remain a challenge as it is a highly patient-specific pathology and there is still a limited understanding of the fluid-mechanics phenomena underlying clinical outcomes. Although in vitro models can allow the accurate study of AD flow fields in physical phantoms, they are currently scarce and almost exclusively rely on over simplifying assumptions. In this work, we present the first experimental study of a patient-specific case of AD. An anatomically correct phantom was produced and combined with a state-of-the-art in vitro platform, informed by clinical data, employed to accurately reproduce personalised conditions. The complex AD haemodynamics reproduced by the platform was characterised by flow rate and pressure acquisitions as well as Particle Image Velocimetry (PIV) derived velocity fields. Clinically relevant haemodynamic indices, that can be correlated with AD prognosis - such as velocity, shear rate, turbulent kinetic energy distributions - were extracted in two regions of interest in the aortic domain. The acquired data highlighted the complex nature of the flow (e.g. recirculation regions, low shear rate in the false lumen) and was in very good agreement with the available clinical data and the CFD results of a study conducted alongside, demonstrating the accuracy of the findings. These results demonstrate that the described platform constitutes a powerful, unique tool to reproduce in vitro personalised haemodynamic conditions, which can be used to support the evaluation of surgical procedures, medical devices testing and to validate state-of-the-art numerical models.

Validity of a patient-specific percutaneous nephrolithotomy (PCNL) simulated surgical rehearsal platform: impact on patient and surgical outcomes

INTRODUCTION

Simulators provide a safe method for improving surgical skills without the associated patient risks. Advances in rapid prototyping technology have permitted the reconstruction of patient imaging into patient-specific surgical simulations that require advanced expertise, potentially continuing the learning curve.

OBJECTIVES

To evaluate the impact of preoperative high-fidelity patient-specific percutaneous nephrolithotomy hydrogel simulations on surgical and patient outcomes.

MATERIALS AND METHODS

Between 2016 and 2017, a fellowship-trained endourologist performed 20 consecutive percutaneous nephrolithotomy procedures at an academic referral center. For the first ten patients, only standard review of patient imaging was completed. For the next ten patients, patient imaging was utilized to fabricate patient-specific models including pelvicalyceal system, kidney, stone, and relevant adjacent structures from hydrogel. The models were tested to confirm anatomic accuracy and material properties similar to live tissue. Full procedural rehearsals were completed 24-48 h before the real case. Surgical metrics and patient outcomes from both groups (rehearsal vs. standard) were compared.

RESULTS

Significant improvements in mean fluoroscopy time, percutaneous needle access attempts, complications, and additional procedures were significantly lower in the rehearsal group (184.8 vs. 365.7 s, p < 0.001; 1.9 vs. 3.6 attempts, p < 0.001; 1 vs. 5, p < 0.001; and 1 vs. 5, p < 0.001, respectively). There were no differences in stone free rates, mean patient age, body mass index, or stone size between the two groups.

CONCLUSION

This study demonstrates that patient-specific procedural rehearsal is effective reducing the experience curve for a complex endourological procedure, resulting in improved surgical performance and patient outcomes.

How specific are patient-specific simulations? Analyzing the accuracy of 3D-printing and modeling to create patient-specific rehearsals for complex urological procedures

PURPOSE

In the field of urology, 3D printing and modeling are now regularly utilized to enhance pre-operative planning, surgical training, patient-specific rehearsals (PSR), and patient education and counseling. Widespread accessibility and affordability of such technologies necessitates development of quality control measures to confirm the anatomical accuracy of these tools. Herein, we present three methods utilized to evaluate the anatomical accuracy of hydrogel PSR, developed using 3D printing and molding for pre-operative surgical rehearsals, of robotic-assisted partial nephrectomy (RAPN) and percutaneous nephrolithotomy (PCNL).

METHODS

Virtual computer-aided designs (CADs) of patient anatomy were created through segmentation of patient CT scan images. Ten patient-specific RAPN and PCNL hydrogel models were CT scanned and segmented to create a corresponding model CAD. The part compare tool (3-matic, Materialize), point-to-point measurements, and Dice similarity coefficient (DSC) analyzed surface geometry, alignment, and volumetric overlap of each model component.

RESULTS

Geometries of the RAPN parenchyma, tumor, artery, vein, and pelvicalyceal system lay within an average deviation of 2.5 mm (DSC = 0.70) of the original patient geometry and 5 mm (DSC = 0.45) of the original patient alignment. Similarly, geometries of the PCNL pelvicalyceal system and stone lay within 2.5 mm (DSC = 0.6) and within 15 mm (16% deviation) in alignment. This process enabled the refinement of our modeling process to fabricate anatomically accurate RAPN and PCNL PSR.

CONCLUSION

As 3D printing and modeling continues to have a greater impact on patient care, confirming anatomical accuracy should be introduced as a quality control measure prior to use for patient care.

The cutting edge of customized surgery: 3D-printed models for patient-specific interventions in otology and auricular management-a systematic review

PURPOSE

3D-printing (three-dimensional printing) is an emerging technology with promising applications for patient-specific interventions. Nonetheless, knowledge on the clinical applicability of 3D-printing in otology and research on its use remains scattered. Understanding these new treatment options is a prerequisite for clinical implementation, which could improve patient outcomes. This review aims to explore current applications of 3D-printed patient-specific otologic interventions, including state of the evidence, strengths, limitations, and future possibilities.

METHODS

Following the PRISMA statement, relevant studies were identified through Pubmed, EMBASE, the Cochrane Library, and Web of Science. Data on the manufacturing process and interventions were extracted by two reviewers. Study quality was assessed using Joanna Briggs Institute's critical appraisal tools.

RESULTS

Screening yielded 590 studies; 63 were found eligible and included for analysis. 3D-printed models were used as guides, templates, implants, and devices. Outer ear interventions comprised 73% of the studies. Overall, optimistic sentiments on 3D-printed models were reported, including increased surgical precision/confidence, faster manufacturing/operation time, and reduced costs/complications. Nevertheless, study quality was low as most studies failed to use relevant objective outcomes, compare new interventions with conventional treatment, and sufficiently describe manufacturing.

CONCLUSION

Several clinical interventions using patient-specific 3D-printing in otology are considered promising. However, it remains unclear whether these interventions actually improve patient outcomes due to lack of comparison with conventional methods and low levels of evidence. Further, the reproducibility of the 3D-printed interventions is compromised by insufficient reporting. Future efforts should focus on objective, comparative outcomes evaluated in large-scale studies.

No difference in patient-reported satisfaction after 12 months between customised individually made and off-the-shelf total knee arthroplasty

PURPOSE

A subset of patients is usually not satisfied after a total knee arthroplasty (TKA). Customised individually made (CIM) TKA are deemed to overcome drawbacks of classical off-the-shelf (OTS) TKA, but evidence is still sparse. The aim of this study was to compare satisfaction of patients with CIM and OTS TKA.

METHODS

This prospective cohort study compared clinical and patient-reported outcome measures (PROM) between patients with CIM and OTS TKA. The primary outcome was patient satisfaction after 12 months. Secondary outcomes were the Knee Society Score (KSS), the Knee injury and Osteoarthritis Outcome Score (KOOS), the Forgotten Joint Score (FJS-12) and the EQ-5D-3L after 4 and 12 months.

RESULTS

Data were analysed from 74 CIM TKA and 169 OTS TKA between January 2017 and September 2020. Patients with CIM TKA were slightly younger, more often male, had a lower body mass index, a lower KSS and partially higher preoperative PROMs. Patient satisfaction after 12 months was high and comparable (CIM 87%, OTS 89%). All PROMs improved for both groups (p < 0.001) and did not differ after 12 months (p > 0.063). The majority of patients improved above the minimal important difference (range 65 to 89%) and reported a clear overall improvement (CIM 86%, OTS 87%). The postoperative KSS, notably regarding knee stability, was higher for CIM TKA (p < 0.001).

CONCLUSION

No difference was found in patient satisfaction between CIM and OTS TKA after 12 months. In both groups, patient satisfaction was high and PROMs improved considerably.

LEVEL OF EVIDENCE

II, prospective cohort study.

Evaluation and verification of patient-specific modelling of type B aortic dissection

Quantitative assessment of the complex hemodynamic environment in type B aortic dissection (TBAD) through computational fluid dynamics (CFD) simulations can provide detailed insights into the disease and its progression. As imaging and computational technologies have advanced, methodologies have been developed to increase the accuracy and physiological relevance of CFD simulations. This study presents a patient-specific workflow to simulate blood flow in TBAD, utilising the maximum amount of in vivo data available in the form of CT images, 4D-flow MRI and invasive Doppler-wire pressure measurements, to implement the recommended current best practice methodologies in terms of patient-specific geometry and boundary conditions. The study aimed to evaluate and verify this workflow through detailed qualitative and quantitative comparisons of the CFD and in vivo data. Based on data acquired from five TBAD patients, a range of essential model inputs was obtained, including inlet flow waveforms and 3-element Windkessel model parameters, which can be utilised in further studies where in vivo flow data is not available. Local and global analysis showed good consistency between CFD results and 4D-MRI data, with the maximum velocity in the primary entry tear differing by up to 0.3 m/s, and 80% of the analysed regions achieving moderate or strong correlations between the predicted and in vivo velocities. CFD predicted pressures were generally well matched to the Doppler-wire measurements, with some deviation in peak systolic values. Overall, this study presents a validated comprehensive workflow with extensive data for CFD simulation of TBAD.

Custom total knee arthroplasty facilitates restoration of constitutional coronal alignment

PURPOSE

To describe a strategy for coronal alignment using a computed tomography (CT) based custom total knee arthroplasty (TKA) system, and to evaluate the agreement between the planned and postoperative Hip-Knee-Ankle (HKA) angle, Femoral Mechanical Angle (FMA) and Tibial Mechanical Angle (TMA).

METHODS

From a consecutive series of 918 primary TKAs, 266 (29%) knees received CT-based posterior-stabilized cemented custom TKA. In addition to a preoperative CT-scan, pre- and post-operative radiographs of weight-bearing long leg, anterior-posterior and lateral views of the knee were obtained, on which the FMA, TMA and HKA angles were measured. CT-based three-dimensional (3D) models enabled to correct for cases with bony wear by referring to the non-worn areas and to estimate the native pre-arthritic angles. The alignment technique aimed to preserve or restore constitutional alignment (CA) within predetermined limits, by defining a 'target zone' based on three criteria: 1) a ± 3° (range 87°-93°) primary tolerance for the femoral and tibial resections; 2) a ± 2° secondary tolerance for component obliquity, extending the bounds for FMA and TMA (range 85°-95°); 3) a planned HKA angle range of 175°-183°. Agreement between preoperative, planned and postoperative measurements of FMA, TMA and HKA angle were calculated using intra-class correlation coefficients (ICC).

RESULTS

Preoperative radiograph and CT-scan measurements revealed that, respectively, 73 (28%) and 103 (40%) knees were in the 'target zone', whereas postoperative radiographs revealed that 217 (84%) TKAs were in the 'target zone'. Deviation from the planned angles were - 0.5° ± 1.8° for FMA, - 0.5° ± 1.8° for TMA, and - 1.1° ± 2.1° for HKA angle. Finally, the agreement between the planned and achieved targets, indicated by ICC, were good for FMA (0.701), fair for TMA (0.462) and fair for HKA angle (0.472).

CONCLUSION

Using this strategy for coronal alignment, 84% of custom TKAs were within the 'target zone' for FMA, TMA and HKA angles. These findings support the concepts of emerging personalized medicine technologies, and emphasise the importance of accurate strategies for preoperative planning, which are key to achieving satisfactory 'personalised alignment' that can further be improved by customisation of implant components.

LEVEL OF EVIDENCE

IV.

Validation and performance of a machine-learning derived prediction guide for total knee arthroplasty component sizing

INTRODUCTION

Anticipation of patient-specific component sizes prior to total knee arthroplasty (TKA) is essential to avoid excessive cost associated with additional surgical trays and morbidity associated with imperfect sizing. Current methods of size prediction, including templating, are inconsistent and time-consuming. Machine learning (ML) algorithms may allow for accurate TKA component size prediction with the ability to make predictions in real-time.

METHODS

Consecutive patients receiving primary TKA between 2012 and 2020 from two large tertiary academic and six community hospitals were identified. The primary outcomes were the final femoral and tibial component sizes extracted from automated inventory systems. Five ML algorithms were trained with routinely corrected demographic variables (age, height, weight, body mass index, and sex) using 80% of the study population and internally validated on an independent set of the remaining 20% of patients. Algorithm performance was evaluated through accuracy, mean absolute error (MAE), and root mean-squared error (RMSE).

RESULTS

A total of 17,283 patients that received one of 9 TKA implants from independent manufacturers were included. The SGB model accuracy for predicting ± 4-mm of the true femoral anteroposterior diameter was 83.6% and for ± 1 size of the true femoral component size was 95.0%. The SGB model accuracy for predicting ± 4-mm of the true tibial medial/lateral diameter was 83.0% and for ± 1 size of the true tibial component size was 97.8%. Patient sex was the most influential feature in terms of informing the SGB model predictions for both femoral and tibial component sizing. A TKA implant sizing application was subsequently created.

CONCLUSION

Novel machine learning algorithms demonstrated good to excellent performance for predicting TKA component size. Patient sex appears to contribute an important role in predicting TKA size. A web-based real-time prediction application was created capable of integrating patient specific data to predict TKA size, which will require external validation prior to clinical use.

flexible fixation devices for the lumbar spine: A geometrically patient-specific poroelastic finite element study

BACKGROUND AND OBJECTIVE

Lumbar spinal stenosis (LSS), or the narrowing of the spinal canal, continues to be the leading preoperative diagnosis for adults older than 65 years who undergo spine surgery. Although the treatment of LSS depends on its severity, the optimal surgical technique towards decreasing the risk of adjacent segment disease (ASD) remains elusive. This study aimed to comparatively analyze spinal biomechanics with rigid and flexible fixation devices (i.e., rigid and dynamic posterolateral fusion (PLF) and interspinous process (ISP) devices) during daily activities.

METHODS

Using a validated parametric poroelastic finite element modeling approach, 8 subject-specific pre-operative models were developed, and their validity was evaluated. Parametric FE models of the lumbar spines were then regenerated based on post-operation images for (A) rigid PLF (B) dynamic PLF (C) rigid ISP device (Coflex) and (D) flexible ISP device (DIAM) at L4-L5 level. Biomechanical responses for instrumented and adjacent intervertebral discs (IVDs) were analyzed and compared subject to static and cyclic loading.

RESULTS

The preoperative models were well comparable with previous works in literature. The postoperative results for the PLF and Coflex rigid systems, demonstrated greater ROM; higher values of stress and strain in the AF region; and increased disc height and fluid loss at the adjacent levels, as compared with the pre-op models and the post-op results of the flexible systems (i.e., dynamic PLF and DIAM). The calculated forces on the facet joint were of smaller magnitude for the ISP devices as compared to the PLF, particularly during extension.

CONCLUSIONS

This study demonstrates that the dynamic PLF construct and DIAM implants could be effective to maintain the natural poroelastic characteristics of adjacent IVDs, which could be beneficial for enhancing long-term clinical outcomes. FEM provides clinicians with an invaluable patient-specific quantitative tool for informed surgical planning and discerning follow-up management.

Individual variability in animal-specific hemodynamic compensation following myocardial infarction

Ventricular enlargement and heart failure are common in patients who survive a myocardial infarction (MI). There is striking variability in the degree of post-infarction ventricular remodeling, however, and no one factor or set of factors have been identified that predicts heart failure risk well. Sympathetic activation directly and indirectly modulates hypertrophic stimuli by altering both neurohormonal milieu and ventricular loading. In a recent study, we developed a method to identify the balance of reflex compensatory mechanisms employed by individual animals following MI based on measured hemodynamics. Here, we conducted prospective studies of acute myocardial infarction in rats to test the degree of variability in reflex compensation as well as whether responses to pharmacologic agents targeted at those reflex mechanisms could be anticipated in individual animals. We found that individual animals use very different mixtures of reflex compensation in response to experimental coronary ligation. Some of these mechanisms were related - animals that compensated strongly with venoconstriction tended to exhibit a decrease in the contractility of the surviving myocardium and those that increased contractility tended to exhibit venodilation. Furthermore, some compensatory mechanisms - such as venoconstriction - increased the extent of predicted ventricular enlargement. Unfortunately, initial reflex responses to infarction were a poor predictor of subsequent responses to pharmacologic agents, suggesting that customizing pharmacologic therapy to individuals based on an initial response will be challenging.

No significant difference in early clinical outcomes of custom versus off-the-shelf total knee arthroplasty: a systematic review and meta-analysis

PURPOSE

The purpose of this systematic review and meta-analysis was to collect, synthesise and critically appraise findings of clinical studies that report outcomes of custom total knee arthroplasty (TKA). The hypothesis was that, compared to off-the-shelf (OTS) TKA, custom TKA would yield better surgical, clinical and radiographic outcomes.

METHODS

This systematic review and meta-analysis was performed in accordance with the guidelines of Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA). On 8 February 2021, two authors independently searched and screened articles using MEDLINE®, Embase® and the Cochrane Library without restriction on date of publication. Findings from eligible articles were narratively synthesised and tabulated, and when ≥ 3 comparative studies reported the same outcome, results were pooled and summarised in forest plots. Quality assessments of the studies were done according to the guidelines of the Joanna Briggs Institute (JBI) Checklists.

RESULTS

A total of 15 articles were eligible for data extraction, of which 9 were case-control studies reporting on 929 custom versus 998 OTS TKA, 5 were case series reporting on results of 587 custom TKA, and 1 was a cross-sectional study reporting on results of 44 custom versus 132 OTS TKA. Five studies that compared early revision rates found the overall effect in favour of OTS TKA (odds ratio (OR), 0.4; p = n.s.) but the result did not reach statistical significance. Four studies found no statistically significant difference in KSS knee (standardised mean difference (SMD), - 0.10; p = n.s.) and function (SMD, 0.03; p = n.s.), and five studies found no statistically significant difference in range of motion (SMD, 0.02; p = n.s.). One study that compared bone-implant fit between custom and three OTS tibial components found no overhang but revealed under-coverage of up to 18% in knees with custom tibial baseplates.

CONCLUSION

Custom TKA demonstrated no significant benefits compared to OTS TKA in terms of pooled clinical outcomes, but had considerably higher early revision rates. The findings of the present systematic review and meta-analysis suggest the need for studies with better comparable groups and standardisation of reporting outcomes amongst studies, that could increase the quality of evidence and enable pooling of results in future meta-analyses.

LEVEL OF EVIDENCE

Level IV.

Patient-specific microdosimetry: a proof of concept

Microscopic energy deposition distributions from ionizing radiation are used to predict the biological effects of an irradiation and vary depending on biological target size. Ionizing radiation is thought to kill cells or inhibit cell cycling mainly by damaging DNA in the cell nucleus. The size of cells and nuclei depends on tissue type, cell cycle, and malignancy, all of which vary between patients. The aim of this study was to develop methods to perform patient-specific microdosimetry, that being, determining microdosimetric quantities in volumes that correspond to the sizes of cells and nuclei observed in a patient's tissue. A histopathological sample extracted from a stage I lung adenocarcinoma patient was analyzed. A pouring simulation was used to generate a three-dimensional tissue model from cell and nucleus size information determined from the histopathological sample. Microdosimetric distributions including f(y) and d(y) were determined for Co-60,Ir-192,Yb-169 and I-125 in a patient-specific model containing a distribution of cell and nucleus sizes. Fixed radius models and a summation method (where f(y) from many fixed radii models are summed) were compared to the full patient-specific model to evaluate their suitability for fast determination of patient-specific microdosimetric parameters. Fixed radius models do not provide a close approximation of the full patient-specific model y ̅_f or y ̅_d for the lower energy sources investigated, Yb-169 and I-125. The higher energy sources investigated, Co-60 and Ir-192 are less sensitive to target size variation than Yb-169 and I-125. A summation method yields the most accurate approximation of the full model d(y) for all radioisotopes investigated. A summation method allows for the computation of patient-specific microdosimetric distributions with the computing power of a personal computer. With appropriate biological inputs the microdosimetric distributions computed using these methods can yield a patient-specific relative biological effectiveness as part of a multiscale treatment planning approach.

Exploration and Preparation of Patient-specific Ciprofloxacin Implants Drug Delivery System Via 3D Printing Technologies

A suitable drug-loaded implant delivery system that can effectively release antibacterial drug in the postoperative lesion area and help repair bone infection is very significant in the clinical treatment of bone defect. The work was aimed to investigate the feasibility of applying three-dimensional (3D) printing technology to prepare drug-loaded implants for bone repair. Semi-solid extrusion (SSE) and Fuse deposition modeling® (FDM) technologies were implemented and ciprofloxacin (CIP) was chosen as the model drug. All of the implants exhibited a smooth surface, good mechanical properties and satisfactory structural integrity as well as accurate dimensional size. In vitro drug release showed that the implants made by 3D printing technologies slowed down the initial drug burst effect and expressed a long-term sustained release behavior, compared with the implants prepared with traditional method. In addition, the patient-specific macrostructure implants, consisting of interconnected and different shapes pores, were created using unique lay down patterns. As a result, the weakest burst release effect and the sustained drug release were achieved in the patient-specific implants with linear pattern. These results clearly stated that 3D printing technology offers a viable approach to prepare control-releasing implants with patient-specific macro-porosity and presents novel strategies for treating bone infections.

Patient-specific high tibial osteotomy for varus malalignment: 3D-printed plating technique and review of the literature

PURPOSE

We report our experience with a 3D patient-specific instrument (PSI) in an opening-wedge tibial osteotomy for the correction of varus malalignment in a patient with prior anterior cruciate ligament reconstruction. Previous studies have not reported the use of 3D PSI in patients with prior knee surgeries.

METHODS

A pre-operative CT was used to create a 3D model of the lower extremity using Bodycad Imager. The pre-operative medial proximal tibial angle (MPTA), lateral distal femoral ankle, hip-knee-ankle (HKA), and tibial slope were calculated. The Bodycad Osteotomy software package was used to create a simulated osteotomy and correction. The resulting 3D patient-specific surgical guide and plate were used to conduct the high tibial osteotomy. Radiographic measurements and range of motion were evaluated at 6-week follow-up.

RESULTS

The arthroscopy and open portions of the procedure were performed in 65 min, with only three fluoroscopy shots taken intraoperatively. At 6-week follow-up, the patient had 125° of flexion and minimal pain. The angular correction of the bone was achieved within 1.9° (planned MPTA 91.9° vs. actual 90°); the HKA angle was achieved with an error of 0.7° (planned 2.4° vs. actual 1.7°); and there was no change in the posterior tibial slope (planned 13.5° vs 13.8° actual).

CONCLUSION

Three-dimensional PSI can be successfully used for the accurate and efficient correction of varus malalignment while accommodating pre-existing hardware, with good short-term clinical outcomes.