Multi-joint Assessment of Proprioception Impairments Poststroke.

OBJECTIVES: To investigate shoulder, elbow and wrist proprioception impairment poststroke. DESIGN: Proprioceptive acuity in terms of the threshold detection to passive motion at the shoulder, elbow and wrist joints was evaluated using an exoskeleton robot to the individual joints slowly in either inward or outward direction. SETTING: A university research laboratory. PARTICIPANTS: Seventeen stroke survivors and 17 healthy controls (N=34). Inclusion criteria of stroke survivors were (1) a single stroke; (2) stroke duration <1 year; and (3) cognitive ability to follow simple instructions. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Threshold detection to passive motion and detection error at the shoulder, elbow and wrist. RESULTS: There was significant impairment of proprioceptive acuity in stroke survivors as compared to healthy group at all 3 joints and in both the inward (shoulder horizontal adduction, elbow and wrist flexion, P<.01) and outward (P<.01) motion. Furthermore, the distal wrist joint showed more severe impairment in proprioception than the proximal shoulder and elbow joints poststroke (P<.01) in inward motion. Stroke survivors showed significantly larger detection error in identifying the individual joint in motion (P<.01) and the movement direction (P<.01) as compared to the healthy group. There were significant correlations among the proprioception acuity across the shoulder, elbow and wrist joints and 2 movement directions poststroke. CONCLUSIONS: There were significant proprioceptive sensory impairments across the shoulder, elbow and wrist joints poststroke, especially at the distal wrist joint. Accurate evaluations of multi-joint proprioception deficit may help guide more focused rehabilitation.

Risk factors and incidence of oral tumors: Findings from a longitudinal population-based study.

OBJECTIVE: This study investigated risk factors contributed to benign and malignant oral tumors using longitudinal cohort big data. MATERIALS AND METHODS: We included individuals aged ≥40 years who participated in the National Health Examination in South Korea between 2003 and 2004. National Health Insurance claims data after 16 years were used to determine the incidence of oral tumors and the related risk factors. Hazard ratios were calculated using the Cox proportional hazard regression. RESULTS: A total of 5,992,671 participants were included. The incidence of oral cancer was significantly higher in men and increased with age, whereas that of benign tumors was unaffected by sex and decreased with age. Periodontal disease was associated with the incidence of oral cancer but not benign tumors. Soft tissue diseases were associated with both benign and malignant tumors. Various systemic diseases influence the development of oral tumors. Light alcohol consumption reduced the incidence of oral tumors, whereas heavy alcohol consumption increased the incidence of malignant tumors only. Smoking increased the incidence of benign but not malignant tumors. CONCLUSION: Recognized risk factors such as sex, age, comorbidities, and dental diseases were associated with oral tumors. Alcohol consumption and smoking were not significantly associated with malignant tumors.

Accuracy of 3-Dimensional Virtual Surgical Simulation Combined With Digital Teeth Alignment: A Pilot Study.

PURPOSE: To evaluate the accuracy of virtual surgical simulation combined with digital teeth alignment and the applicability of this technique to the diagnosis and establishment of a 3-dimensional (3D) visualized treatment objective for orthognathic surgery by comparing virtual simulation images with actual post-treatment images. MATERIALS AND METHODS: This retrospective study included patients who underwent computed tomography (CT) before and after treatment. The 3D digital images were constructed from the initial CT images and dental cast scan data, and virtual surgical simulation combined with digital teeth alignment was performed. Accuracy of the virtual simulation was analyzed by comparing the distances of skeletal and dental landmarks in the horizontal, sagittal, and coronal reference planes with those on post-treatment images using the Wilcoxon signed rank test. Intraclass correlation coefficients were calculated to evaluate the degree of concordance between the 2 images. RESULTS: The study sample included 11 patients (mean age, 18.8 yr). Most landmarks had differences smaller than 2 mm in the 3 reference planes between virtual simulation and post-treatment images; these differences were not statistically significant (P > .05). Most skeletal landmarks, except the A point, B point, and gonion, showed normal to high concordance between the virtual simulation and post-treatment images in the 3 reference planes (P < .05); dental landmarks exhibited a broad range of concordance. CONCLUSION: The 3D virtual surgical simulation combined with digital teeth alignment using pretreatment CT images yielded results sufficiently accurate to be used for the diagnosis and establishment of visualized treatment objectives for orthognathic surgery.

Pivoting neuromuscular control and proprioception in females and males.

PURPOSE: Noncontact ACL injuries occur most commonly in pivoting sports and are much more frequent in females than in males. However, information on sex differences in proprioceptive acuity under weight-bearing and leg neuromuscular control in pivoting is scarce. The objective of this study was to investigate sex differences in pivoting neuromuscular control during strenuous stepping tasks and proprioceptive acuity under weight-bearing. METHODS: 21 male and 22 female subjects were recruited to evaluate pivoting proprioceptive acuity under weight-bearing, and pivoting neuromuscular control (in terms of leg pivoting instability, stiffness, maximum internal and external pivoting angles, and entropy of time-to-peak EMG in lower limb muscles) during strenuous stepping tasks performed on a novel offaxis elliptical trainer. RESULTS: Compared to males, females had significantly lower proprioceptive acuity under weight-bearing in both internal and external pivoting directions, higher pivoting instability, larger maximum internal pivoting angle, lower leg pivoting stiffness, and higher entropy of time-to-peak EMG in the gastrocnemius muscles during strenuous stepping tasks with internal and external pivoting perturbations. CONCLUSIONS: Results of this study may help us better understand factors contributing to ACL injuries in females and males, develop training strategies to improve pivoting neuromuscular control and proprioceptive acuity, and potentially reduce ACL and lower-limb musculoskeletal injuries.

Modification of planned postoperative occlusion in orthognathic surgery, based on computer-aided design/computer-aided manufacturing-engineered preoperative surgical simulation.

In orthognathic surgery, it is important to have a planned postoperative occlusion. A 3-dimensional preoperative simulation, based on 3-dimensional optically scanned occlusion data, can predict how the planned postoperative occlusion will affect the maxilla-mandibular relationship that results from orthognathic surgery. In this study we modified the planned postoperative occlusion, based on computer-aided design/computer-aided manufacturing-engineered preoperative surgical simulations. This modification made it possible to resolve the facial asymmetry of the patient successfully with a simple bilateral intraoral vertical ramus osteotomy and no additional maxillary or mandibular surgery.

Validation of mandibular genioplasty using a stereolithographic surgical guide: in vitro comparison with a manual measurement method based on preoperative surgical simulation.

PURPOSE: Stereolithographic guidance, increasingly used in orthognathic surgery, has not been completely verified for genioplasty. This study compared the accuracy of manual measurement with that of a stereolithographic guide in vitro. MATERIALS AND METHODS: Thirty rapid prototype (RP) mandibular models (15 pairs) were included in the experimental (stereolithographic) and control (manual) groups (15 each). Surgical simulation was performed in the 2 groups by advancing the chin 5 mm and then vertically reducing the chin 5 mm using Mimics software. In the stereolithographic group, genioplasty was performed on mandibular RP models using a 3-dimensionally printed surgical guide based on surgical simulation results. In the control group, it was performed using an osteotomy line drawn according to simulation measurements. For the 2 groups, anterior horizontal transverse error and anterior and posterior vertical errors were compared, as were data from the osteotomized chin segment and the preoperative surgical simulation. Positional difference error was calculated and the differences were evaluated with t tests. RESULTS: For advancement genioplasty, the absolute anterior transverse error value was 0.47 ± 0.35 (mean ± standard deviation) with the stereolithographic guide, less than with the manual method (0.77 ± 0.45; P = .001). For reduction genioplasty, the absolute anterior vertical error value was 0.27 ± 0.23 mm with the stereolithographic guide versus 0.58 ± 0.49 mm with the manual method (P < .001). CONCLUSION: Use of a stereolithographic surgical guide increased accuracy, but the difference in mean error values between methods was only approximately 0.3 mm. The superior accuracy may not be compelling in favor of stereolithographic surgical guides.

Construction and validation of the midsagittal reference plane based on the skull base symmetry for three-dimensional cephalometric craniofacial analysis.

OBJECTIVE: The objective of this study was to determine the reliable midsagittal (MS) reference plane in practical ways for the three-dimensional craniofacial analysis on three-dimensional computed tomography images. METHODS: Five normal human dry skulls and 20 normal subjects without any dysmorphoses or asymmetries were used. The accuracies and stability on repeated plane construction for almost every possible candidate MS plane based on the skull base structures were examined by comparing the discrepancies in distances and orientations from the reference points and planes of the skull base and facial bones on three-dimensional computed tomography images. RESULTS: The following reference points of these planes were stable, and their distribution was balanced: nasion and foramen cecum at the anterior part of the skull base, sella at the middle part, and basion and opisthion at the posterior part. CONCLUSIONS: The candidate reference planes constructed using the aforementioned reference points were thought to be reliable for use as an MS reference plane for the three-dimensional analysis of maxillofacial dysmorphosis.

Accuracy assessment of image-based surface meshing for volumetric computed tomography images in the craniofacial region.

BACKGROUND: Three-dimensional printing and computer-assisted surgery demand a high-precision three-dimensional mesh model created from computed tomography (CT) imaging data using an image-based meshing algorithm. We aimed to evaluate the three-dimensional geometric accuracy of surface meshes produced from CT images with commercially available software packages. METHODS: The CT images were acquired for 3 human dry skulls and 10 manufactured plastic skulls. Four commercially available software packages were used to produce the surface meshes in stereolithography (STL) file format. These CT-based STL surface meshes were registered and compared with three-dimensional optical-scanned reference mesh surface for evaluating the accuracy of the STL mesh produced with each software package. RESULTS: The surface geometries produced by the CT-image-based meshing process were all relatively accurate; differences from the three-dimensional optical-scanned data were in the voxel or subvoxel range. However, when comparisons with the three-dimensional optical-scanned surface data were performed in individual anatomic regions, we found significantly different accuracies of the CT-based STL surface meshes produced by the different software packages. CONCLUSIONS: We found that all 4 software packages showed reasonably good meshing accuracies for clinical use. However, the range of errors inherent in the CT-image-based meshing process demands that caution should be taken in selecting and manipulating the software to avoid potential errors in specific clinical applications.

A distraction assembly system with fully-customized fixation plate unit and factory-manufactured distraction unit: Overview and accuracy validation for mandibular distraction osteogenesis.

A distraction assembly system (DAS), consisting of a distractor of fully individualized fixation plate unit and factory-engineered distraction unit, was recently developed to enhance the accuracy, stability, and workability of distraction osteogenesis (DO). We here wanted to evaluate the accuracy of DAS for mandibular DO, focusing on the consequences of the distractor design and manufacturing method. The bar-type distractor unit showed smaller discrepancies than did the cylinder-type one, both units showing far fewer discrepancies than those of a conventional distractor. And there were no significant differences in morphological accuracy between the plates produced by milling and 3D printing. These accuracies feature the promising application in clinical setting, and further work is anticipated to refine DAS for successful computer-aided DO.

Post-extraction bleeding in patients on direct oral anticoagulants.

Objectives: This study aimed to evaluate the association between use of direct oral anticoagulants (DOACs) and post-extraction bleeding and to quantify bleeding risk in patients receiving DOACs. Materials and Methods: The study included 293 patients who were taking DOACs and underwent tooth extraction (414 teeth). The patients were divided into those who had the extraction while taking DOACs and those who discontinued DOACs before the extraction. Bleeding complications were recorded and compared between the patient groups and types of DOACs. Results: Of the 293 patients, 12 patients (6.9%) had post-extraction bleeding. Post-extraction bleeding occurred in 12 of the 414 tooth extraction sites. Among the 246 patients who underwent dental extraction while continuing DOAC therapy, 12 patients (8.5%) had post-extraction bleeding. Among the 47 patients who underwent dental extraction after discontinuing the administration of DOACs, none reported post-extraction bleeding. There was no significant difference in the number of patients with post-extraction bleeding between the two groups (P=0.122). Conclusion: Continuing DOAC therapy during dental extraction does not increase post-extraction bleeding tendency. These results are consistent with those of previous studies.

Developing a device for simultaneously investigating pivoting neuromuscular control and muscle properties toward a multi-axis rehabilitation.

Understanding the pivoting neuromuscular control of the lower limb and its associated muscle properties is critical for developing diagnostic and rehabilitation tools. However, to the best of our knowledge, a device that can evaluate these factors simultaneously remains lacking. To address this gap, a device that can investigate pivoting neuromuscular control and associated muscle properties was developed in this study. The proposed device consisted of a pivoting mechanism and height-adjustable chair with a brace interface. The device can control a footplate at various speeds to facilitate pivoting stretching and quantify neuromuscular control. Time-synchronized ultrasonographic images can be acquired simultaneously to quantify muscle properties during both active and passive pivoting movements. The muscle displacement, fascicle length/displacement, pennation angle, pivoting stiffness, and pivoting instability were investigated using the proposed device. Further, the feasibility of the device was demonstrated through a cross-sectional study with healthy subjects. The proposed device successfully quantified changes in muscle displacement during passive and active pivoting movements, pivoting stiffness during passive movements, and neuromuscular control during active movements. Therefore, the proposed device is expected to be used as a research and therapeutic tool for improving pivoting neuromuscular control and muscle functions and investigating the underlying mechanisms associated between muscle properties and joint movement in the transverse plane.

Augmentation genioplasty using discarded bone fragments following proximal segment osteotomy of the ramus in intraoral vertical ramus osteotomy (IVRO).

BACKGROUND: Based on a three-dimensional (3D) orthognathic simulation, this technical report introduces a method for augmentation genioplasty using a proximal bone fragment of the mandible, which is typically discarded in intraoral vertical ramus osteotomy (IVRO). RESULTS: A 43-year-old female patient diagnosed with Class III malocclusion, presenting with a protruding mandible and long facial height, underwent surgical treatment. The surgical plan involved mandibular setback position using IVRO and augmentation genioplasty. The 3D orthognathic surgery including augmentation genioplasty simulation was performed. An excessively elongated proximal segment was sectioned following IVRO. The inferior part of the sectioned proximal bone fragment of the mandible was positioned to align with the requirements of advancement genioplasty. After ensuring that the placement of the fragment matched that of the simulated surgery, each bone fragment was fixed. At 1.5 years post-surgery, the grafted bone on the augmentation genioplasty was well maintained, with slight bone resorption. CONCLUSIONS: Augmentation genioplasty using the proximal bone fragment of the mandible, which is typically discarded in IVRO, reduces the surgical complications associated with chin osteotomy. When a secondary genioplasty is required, genioplasty with osteotomy, movement of the cut bone fragments, partial bone-shaving osteotomy, and additional bone grafting are viable options.

Pediatric mandibular chronic nonbacterial osteomyelitis: A case report with 12 years of radiologic follow-up.

Chronic nonbacterial osteomyelitis (CNO) is histologically characterized by nonspecific osteitis. This inflammatory disorder, which lacks an infectious origin, typically presents with chronic pain and swelling at the affected site that can persist for months or even years. However, it is rare for CNO to affect the mandible. A 10-year-old girl presented with a primary complaint of pain in her left mandible. She had no significant medical or dental history. On examination, swelling was visible on the left buccal side, and imaging revealed radiolucent bone deterioration within the left mandible. This case report presents the radiological changes observed over a 12-year follow-up period. Variations in radiopacity, radiolucency, and periosteal reactions were noted periodically. This case highlights the radiological characteristics and findings that are crucial for the diagnosis of CNO, a condition for which no clear diagnostic criteria are currently available.

Transition of endochondral bone formation at the normal and botulinum-treated mandibular condyle of growing juvenile rat.

OBJECTIVE: The aim of this study was to understand the temporal and spatial distribution of canonical endochondral ossification (CEO) and non-canonical endochondral ossification (NCEO) of the normal growing rat condyle, and to evaluate their histomorphological changes following the simultaneous hypotrophy of the unilateral masticatory closing muscles with botulinum toxin (BTX). DESIGN: 46 rats at postnatal 4 weeks were used for the experiment and euthanized at postnatal 4, 8, and 16 weeks. The right masticatory muscles of rats in experimental group were injected with BTX, the left being injected with saline as a control. The samples were evaluated using 3D morphometric, histological, and immunohistochemical analysis with three-dimensional regional mapping of endochondral ossifications. RESULTS: The results showed that condylar endochondral ossification changed from CEO to NCEO at the main articulating surface during the experimental period and that the BTX-treated condyle presented a retroclined smaller condyle with an anteriorly-shifted narrower articulating surface. This articulating region showed a thinner layer of the endochondral cells, and a compact distribution of flattened cells. These were related to the load concentration, decreased cellular proliferation with thin cellular layers, reduced extracellular matrix, increased cellular differentiation toward the osteoblastic bone formation, and accelerated transition of the ossification types from CEO to NCEO. CONCLUSION: The results suggest that endochondral ossification under loading tended to show more NCEO, and that masticatory muscular hypofunction by BTX had deleterious effects on endochondral bone formation and changed the condylar growth vector, resulting in a retroclined, smaller, asymmetrical, and deformed condyle with thin cartilage.

Position-dependent, hyperexcitable patellar reflex dynamics in chronic stroke.

OBJECTIVES: To quantify tendon tap response (TTR) properties and their position dependence using multiple neuromechanical parameters, and to analyze correlations among neuromechanical and clinical measures. DESIGN: Hyperexcitable dynamics of TTR were investigated in a case-control manner. An instrumented hammer was used to induce the patellar deep tendon reflex (DTR), with reflex-mediated electromyography and torque responses measured across a range of knee flexion. SETTING: Research laboratory in a rehabilitation hospital. PARTICIPANTS: Chronic hemiplegic stroke survivors (n=9) and healthy subjects (n=13). INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Neuromechanical measures (system gain, contraction rate, half-relaxation rate, reflex loop delay, peak reflex torque, peak reflex electromyography, and reflex threshold in tapping force) were measured to characterize neuromuscular properties of patellar TTR. Clinical measurements were taken using the DTR scale and the Modified Ashworth Scale. RESULTS: The system gain, contraction rate, half-relaxation rate, and peak reflex-mediated torque in the stroke group were generally higher, whereas the reflex threshold in the stroke group was significantly lower than their counterparts in the control group across 45° to 90° of knee flexion (P<.05). The 4 parameters were significantly higher at 60° and 75° of flexion than at 15°, 30°, 45°, and 90°, and their correlations with the 2 clinical scales at 60°, 75°, and 90° of flexion were also significantly higher than those at 15°, 30°, and 45° (P<.05). CONCLUSIONS: The results showed hyperexcitability of TTR in stroke, quantified using a number of neuromechanical measures. Those measures peak around 60° to 75° of knee flexion and were correlated with clinical scales.

The validity of marker registration for an optimal integration method in mandibular navigation surgery.

PURPOSE: The aim of this study was to verify the accuracy of 2 registration methods (marker-based registration and marker-free registration) during mandibular navigation surgery. MATERIALS AND METHODS: Two point-to-point registration methods (marker-based registration and marker-free registration) were tested using software and navigation equipment: 1) 3 implanted orthodontic screws and 2) 3 anatomic points on the cusp tips of the teeth (central incisor and first molars bilaterally). RESULTS: For the navigation equipment, the 3-point matching method of screw references was more accurate for all anatomic areas except the coronoid process and second premolar alveolar area. The registration error was largest for the condyle area. Errors were larger than 2.0 mm in the condyle, condyle neck, sigmoid notch, coronoid process, posterior border, lingula, and angle areas. In the oblique ridge, mental foramen, and dentoalveolar areas, the registration error using screws was smaller than 1.5 mm. For the software, tooth cusp references were more accurate for anatomic areas such as the mental foramen and dentoalveolar areas, but not the molar area. In all cases, the registration error was smaller than 1.0 mm, and that for the first molar was similar between the tooth tip overlap and the screw overlap. CONCLUSIONS: Registration using screws generally was more accurate than registration using tooth cusps for mandibular navigation surgery. However, tooth tip references can be used for registration in dentoalveolar surgery.

The anterior deltoid's importance in reverse shoulder arthroplasty: a cadaveric biomechanical study.

BACKGROUND: Frequently, patients who are candidates for reverse shoulder arthroplasty have had prior surgery that may compromise the anterior deltoid muscle. There have been conflicting reports on the necessity of the anterior deltoid thus it is unclear whether a dysfunctional anterior deltoid muscle is a contraindication to reverse shoulder arthroplasty. The purpose of this study was to determine the 3-dimensional (3D) moment arms for all 6 deltoid segments, and determine the biomechanical significance of the anterior deltoid before and after reverse shoulder arthroplasty. METHODS: Eight cadaveric shoulders were evaluated with a 6-axis force/torque sensor to assess the direction of rotation and 3D moment arms for all 6 segments of the deltoid both before and after placement of a reverse shoulder prosthesis. The 2 segments of anterior deltoid were unloaded sequentially to determine their functional role. RESULTS: The 3D moment arms of the deltoid were significantly altered by placement of the reverse shoulder prosthesis. The anterior and middle deltoid abduction moment arms significantly increased after placement of the reverse prosthesis (P < .05). Furthermore, the loss of the anterior deltoid resulted in a significant decrease in both abduction and flexion moments (P < .05). CONCLUSION: The anterior deltoid is important biomechanically for balanced function after a reverse total shoulder arthroplasty. Losing 1 segment of the anterior deltoid may still allow abduction; however, losing both segments of the anterior deltoid may disrupt balanced abduction. Surgeons should be cautious about performing reverse shoulder arthroplasty in patients who do not have a functioning anterior deltoid muscle.

Dynamic connectedness and network in the high moments of cryptocurrency, stock, and commodity markets.

This study examines the connectedness in high-order moments between cryptocurrency, major stock (U.S., U.K., Eurozone, and Japan), and commodity (gold and oil) markets. Using intraday data from 2020 to 2022 and the time and frequency connectedness models of Diebold and Yilmaz (Int J Forecast 28(1):57-66, 2012) and Baruník and Krehlík (J Financ Econom 16(2):271-296, 2018), we investigate spillovers among the markets in realized volatility, the jump component of realized volatility, realized skewness, and realized kurtosis. These higher-order moments allow us to identify the unique characteristics of financial returns, such as asymmetry and fat tails, thereby capturing various market risks such as downside risk and tail risk. Our results show that the cryptocurrency, stock, and commodity markets are highly connected in terms of volatility and in the jump component of volatility, while their connectedness in skewness and kurtosis is smaller. Moreover, jump and volatility connectedness are more persistent than that of skewness and kurtosis connectedness. Our rolling-window analysis of the connectedness models shows that connectedness varies over time across all moments, and tends to increase during periods of high uncertainty. Finally, we show the potential of gold and oil as hedging and safe-haven investments for other markets given that they are the least connected to other markets across all moments and investment horizons. Our findings provide useful information for designing effective portfolio management and cryptocurrency regulations.

Target registration errors in navigation-assisted mandibular surgery according to the tracking methods and the type of markers: experiments using human dry mandibular bone.

OBJECTIVES: This study was conducted to evaluate the accuracy of navigation process according to the type of tracking methods and registration markers. The target registration errors (TREs) were measured at seven anatomical landmarks of the mandible. METHODS: Four different experiments were performed to obtain the TREs using two tracking methods, the optical tracker (Polaris) and the electromagnetic (EM) tracker (Aurora), and two types of registration markers, invasive and noninvasive markers. All comparisons of TREs were statistically analyzed using SPSS and Python-based statistical package. RESULTS: The average TRE values obtained from the four experiments were as follows: (1) 0.85 mm (± 0.07) using invasive marker and Aurora, (2) 1.06 mm (± 0.12) using invasive marker and Polaris, (3) 1.43 mm (± 0.15) using noninvasive marker and Aurora, and (4) 1.57 mm (± 0.23) using noninvasive marker and Polaris. Comparisons between all the experimental results revealed statistically significant differences except for the type of tracking system. Although the comparison between the modality of the tracking system showed no significant differences, the EM-based approach consistently demonstrated better performances than the optical type in all comparisons. CONCLUSIONS: This study demonstrates that irrespective of the tracking modality, using invasive marker is a better choice in terms of accuracy. When using noninvasive marker, it is important to consider the increased TREs. In this study, the noninvasive marker caused a maximum increment of TREs of 0.81 mm compared with the invasive marker. Furthermore, using an EM-based tracker with invasive marker may result in the best accuracy for navigation.

Frequency spillovers between green bonds, global factors and stock market before and during COVID-19 crisis.

This paper examines frequency dynamic spillovers in return and volatility and the hedging ability of Green Bonds, gold, silver, oil, the US dollar index, and volatility index against downside US stock prices before and during the COVID-19 pandemic outbreak and for the short and long run. To do so, we use the Diebold and Yilmaz (2014), the TVP-VAR model, and the frequency spillover index by Baruník and Krehlík (2018). We show that the short-term volatility spillovers dominate their long-term counterparts. Green Bond is net transmitters of spillovers in the system at the short term and net receivers at the long term. S&P500 and silver (USDX and oil) are net transmitters (receivers) of short- and long-term spillovers. Gold and VIX are net receivers of short-term spillovers and net transmitters of long-term spillovers. COVID-19 crisis has more effects on the short-term spillover, which reaches its highest level early 2020. COVID-19 and time horizons lead the direction and the magnitude of spillovers. The Quantile-on-Quantile regression analysis shows significant nonlinear relationships between markets under study. More interestingly, we show that green bonds and gold are safe haven assets for US equity investors during COVID-19. On the other hand, a mixed portfolio offers higher diversification benefits. Finally, hedging effectiveness is dependent on COVID-19 and time horizon.