Search Results (9)

Currently, in countries with warm climatic conditions, the average height of corn stalks during silage harvesting reaches 2.5 m. However, trailed forage harvesters are designed for mowing stalks not more than 1.5 m. That is why there is a demand to develop a compact forage harvester that can mow and shred tall stalks. This research proposes a two-level mowing method for tall stalks. According to the obtained analytical expressions, the technological distance between the vertical axes of the mowing rotors is determined to be 700 mm. A forage harvester is developed, equipped with a device that orientates itself by the length of stalks at the entrance to the shredding chamber and two mowing rotors designed for mowing tall stalks. Analytical expressions are obtained, which determine the required power for the mass transportation processes by the screw working device and the mass supply by the orienting drum into the chamber of the radial-knife blade shredding rotor. The required powers of the screw conveyor and the orienting drum are determined based on the obtained expressions; they are, respectively, equal to 0.42 kW and 0.11 kW. As a result of the conducted laboratory field tests, the required powers for mowing and for the general processes of mowing, shredding, and transporting the mass through the deflector are determined. The power balance of the harvester units is compiled. It is established that 75% of the consumed power is used for effective work, while 25% is for used for idling the harvester. During the mowing and shredding of corn stalks with a height of 2.9 m, the harvester’s productivity reaches 16.3 tons per hour, with a required power of 12.5 kW. During the tests, the harvester functioned without losses and without any violation of the technological process. The test proves the performance of the design and technological scheme and the accuracy of the obtained analytical expression determining the technological distance between the vertical axes of mowing rotors. Full article

Background and Objectives: Robotic-assisted surgery (RS) has progressively emerged as a promising technology in modern thoracolumbar spinal surgery, offering the potential to enhance accuracy and improve clinical outcomes. To date, the benefits of robot-assisted techniques in thoracolumbar spinal surgery remain controversial. The objective of this study was to assess the efficacy and safety of RS compared to fluoroscopy-assisted surgery (FS) in spinal fusion procedures. Materials and Methods: In accordance with the PRISMA guidelines, a systematic review and meta-analysis was conducted, using REVMAN V5.3 software. The review protocol was registered in the Prospective Register of Systematic Reviews (PROSPERO) website with the following registration number: CRD42024567193. Results: Eighteen studies were included in the meta-analysis with a total of 1566 patients examined. The results demonstrated a worse accuracy in FS in cases with major violations of the peduncular cortex (D–E grades, according to Gertzbein’s classification) [(odds ratio (OR) 0.47, 95%-CI 0.28 to 0.80, I² 0%]. In addition, a lower complication rate was shown in the RS group compared to the FS group, specifically regarding the need for surgical revision due to screw mispositioning (OR 0.28-CI 0.17 to 0.48, I² 98%). Conclusions: Advantages of robot-assisted techniques were demonstrated in terms of postoperative complications, revision surgery rates, and the accuracy of screw placement. While RS represents a valuable and promising technological advancement in thoracolumbar spinal surgery, future studies are needed to further explore its advantages in thoracolumbar spinal surgery and to identify which spinal surgical approach has greater advantages when using the robot. Full article

Background and Objectives: Recent advances in intraoperative navigation systems have improved the accuracy of pedicle screw placement in spine surgery. However, many hospitals have limited access to these advanced technologies due to resource constraints. In such settings, postoperative computed tomography (CT) evaluation remains crucial for assessing screw placement and related potential complications. Metal artifacts in CT scans often compromise the diagnostic accuracy. This study aimed to develop and validate three-dimensional (3-D) reconstruction software to enhance screw localization accuracy and facilitate its practical clinical application. Materials and Methods: This study included two phases: 3-D software development utilizing specific threshold values of Hounsfield units for titanium screws followed by internal validation. For validation, fifty pedicle screws were inserted into porcine lumbar vertebrae with random violation (superior, inferior, medial, or lateral). Three fellowship-trained surgeons evaluated screw positions using both conventional CT bone window settings and the developed software. Additional clinical validation involving 386 pedicle screws from cervical to lumbar spine was performed by two surgeons. Results: The software demonstrated significantly higher specificity (83% vs. 63%) and positive predictive value (96% vs. 91%) compared to conventional CT bone window settings, while maintaining 100% sensitivity and negative predictive value. Interobserver reliability was excellent for both methods (0.961 for bone window vs. 0.990 for software). In clinical validation, the software showed superior intraobserver (0.83 vs. 0.74) and interobserver reliability (0.855 vs. 0.513) compared to picture archiving and communication system (PACS) workstation evaluation. Conclusions: The developed software provides improved accuracy and reliability in pedicle screw position evaluation through distinct screw outline visualization and metal artifact reduction. Its equipment-independent nature and cost-effectiveness make it particularly valuable for clinical implementation. Full article

Background and Objectives: Stable fixation is essential for successful healing after medial open wedge high tibial osteotomy (MOWHTO) to minimize the risk of non-union and correction loss. In Asians, potential complications such as D-hole screw osteotomy plane violation (D-hole violation) and inadequate plate fitting arise due to improper plate size. This study aimed to evaluate the risk factors for D-hole violation and compare the conventional anatomic (CA) plate with an individualized anatomic (IA) plate in MOWHTO procedures. Materials and Methods: A simulation study on D-hole violation using the CA plate was conducted, involving preoperative radiographs and CT scans of 64 lower extremities from 47 MOWHTO patients. Additionally, a randomized controlled study compared CA and IA plates in MOWHTO procedures with 34 patients (17 in the CA plate group; 18 in the IA plate group). Patient demographics, patient-reported outcome measures (PROMs), and radiological measures were analyzed. Results: In the simulation study, the rates of D-hole violation ranged from 20.3% to 59.4%, with an increase observed as the plate was distalized from 5 mm to 10 mm away from the joint line. Short stature was identified as an independent risk factor for D-hole violation (p < 0.001), with a cutoff value of 155.3 cm. In the randomized controlled study, no significant difference in PROMs and D-hole violation was observed between the CA plate and IA plate groups. However, the IA plate group showed better plate fitting compared to the CA plate group (p = 0.041). Conclusions: This study identified a high risk of D-hole screw osteotomy plane violations in MOWHTO procedures, particularly when the plate is positioned more distally and in individuals with a stature below 155.3 cm. It also revealed that individualized plates provide better tibial fitting compared to conventional anatomic plates, particularly in Asian populations where tibial morphology tends to be shorter than in Western populations. Therefore, evaluating patient stature and selecting tailored plates are essential to optimize plate positioning and minimize plate-related complications in MOWHTO procedures. Full article

Since the 1980s, constitutive modeling has steadily migrated from phenomenological descriptions toward approaches that are based on micromechanics considerations. Despite significant efforts, crystal plasticity remains an open field of research. Among the unresolved issues are the anomalous behavior of metals at low temperatures and the stress upturn at extreme dynamics. This work is focused on the low-temperature responses of body-centered-cubic (bcc) metals, among them, molybdenum (Mo). At these conditions, the plastic flow strength is governed by the motion of screw dislocations. The resultant non-planarity of core structures and slip causes the following: the shear stress includes non-glide components, the Schmid law is violated, there is a tension-compression asymmetry, and the yield surface and plastic potential are clearly decoupled. We find that the behavioral complexities can be explained by atomistically resolved friction coefficients in macroscopic yield and flow. The plastic flow mechanisms establish the departure point into the follow-up analysis of yield surfaces. For example, we know that while the von Mises stress is explained based on energy considerations, we will also show that the stress has a clear geometric interpretation. Moreover, the von Mises stress is just one case within a much broader class of equivalent stresses. Possible correlations among non-Schmid effects (as represented macroscopically by friction coefficients), volume change (i.e., residual elastic dilatation) from dislocation lines, and elastic anisotropy are investigated. Extensions to the shock regime are also established. Full article

Replacement with larger diameter screws is always used in pedicle screw loosening but carries a risk of pedicle wall violation. A pedicle screw with more preserved bone stock is the preferred primary fixation choice. The purpose of this study was to evaluate whether a newly designed proximal-conical dual-thread screw with less bone occupancy provides fixation strength comparable to that of a traditional screw. Six types of pedicle screws based on three different shapes (cylindrical, conical, and proximal-conical) and two thread profiles (single-thread and dual-thread) were grouped. Conical and proximal-conical screws differed mainly in the slope of the outer diameter from the hub to the tip. Conical screws had an outer diameter (6.5 mm) that differed from the hub and tapered by 30% to an outer diameter (4.5 mm) at the tip and proximal-conical screws had the same outer diameter from the hub and tapered by 30% (4.5 mm) at 20 mm from the hub and then maintained the outer diameter (45 mm) to the tip. A total of 36 L4 Sawbones^® vertebrae were used in the study and six trials for each screw group. The results of the imaging, screw volume in bone, insertion torque, and pullout force were analyzed. For screws with the same shape, insertion torque and pullout force were significantly higher for those in the dual-thread groups than for those in the single-thread groups (p < 0.05). For screws with the same thread profile, there was no significant difference in either biomechanical test between the different screw shapes (p > 0.05). Our results demonstrated that these proximal-conical dual-thread screws, with the property of relative bone stock preservation, display a comparable biomechanical performance to traditional dual-thread screws and a better performance than single-thread screws. This screw design could serve as the primary pedicle screw choice to reduce revision difficulty. Full article

The slide–roll ratio and entrainment velocity are critical parameters in ball screw mechanism tribology investigations and are often determined by Chin-Chung Wei’s approach. Their findings indicated that substantial sliding always occurs between the ball and the raceways, which appears to violate the ball drive principle. We validated Wei’s approach using the Harris method, which is widely used in rolling bearing research. When the helix angle is set to zero, significant differences occur: when the Harris method is utilized, the entrainment velocity at the inner contact points is essentially equal to that at the outer contact points, and the slide–roll ratio is zero for both; however, when Wei’s method is utilized, the entrainment velocity at the inner side is nearly three-times that of the outer side, and the slide–roll ratio at the outer side approaches two—the level of pure sliding—which is clearly incorrect. To overcome this issue, we present an accurate approach for obtaining the slide–roll ratio and entrainment velocity for ball screws by regarding the Frenet frame as a virtual cage, which is particularly applicable to those with a long lead and operating at high speeds. Moreover, we investigated the effect of structural factors on the slide–roll ratio and entrainment velocity utilizing this model. Full article

Objective: percutaneous pedicle screw (PPS) fixation has been widely used in minimally invasive spine stabilization. Triggered electromyogram (TrEMG) monitoring is performed to prevent PPS misplacement, but is not widely accepted. We have newly developed an insulating tap device to minimize the misplacement of PPS. Methods: TrEMG was measurable in insulation tap devices in 31 cases, and in non-insulating tap devices in 27 cases. Fluoroscopy was used to insert 194 PPS and 154 PPS, respectively. Based on the Rampersaud classification of postoperative computed tomography, we classified PPS insertion into four categories (Grade A as no violation, Grade D as more than 4 mm perforation). Results: Grade A was noted in 168 PPSs (86.6%) and Grade B to D in 26 PPSs in the insulation tap device group, and Grade A was noted in 129 PPSs (83.8%) and Grade B to D in 25 PPSs in the non-insulating tap device group, respectively. At a cutoff value of 11 mA, the sensitivity was 41.4% and the specificity was 98.2%. The sensitivity and specificity of the non-insulating tap device were 4.0% and 99.2%, respectively. Conclusions: The insulation treatment of the tap device has improved the sensitivity of TrEMG. TrEMG using the insulating tap device is one of the methods for safe PPS insertion. Full article

Transpedicular screw instrumentation systems have been increasingly utilized during the fusion of lumbar spine procedures. The superior segment facet joint violation of the pedicle screw is thought to have potential for accelerating symptomatic adjacent-segment pathology (ASP). The purpose of this study was to investigate the relationship between the superior segment facet joint violation by transpedicular screws and the development of ASP. Among all patients who underwent operations involving one- or two-level posterior lumbar arthrodesis at the Chonnam National University Hospital from 1992 to 2012, 87 patients were selected for this study. Fifty-six patients were included in the ASP group, and 31 were included in the non-ASP group. We used lumbar three-dimensional computed tomography (CT) to assess the violation of the superior facet joint by a transpedicular screw. The assessment is presented in scores ranging from zero to two, with zero indicating no violation (type I); one point indicating suspected violation (type II); and two points indicating definitely facet joint violation (type III). Facet violation was reported in 31 patients in the ASP group (n = 56), and in 13 patients in the non-ASP group (n = 31). The types of facet joint violation according to our scoring system were as follows: type I, 59 screws (52.7%); type II, 26 screws (23.2%); and type III, 27 screws (24.1%) in the ASP group; and type I, 43 screws (69.4%), type II, 14 screws (22.6 %); and type III, 5 screws (8.0%) in the non-ASP group. The score of facet joint violation in each patient according to our scoring system were as follows: 0 points, 25 patients (44.6%); 1 point, 8 patients (14.3%); 2 points, 4 patients (7.1%); 3 points, 11 patients (19.7%); 4 points, 8 patients (14.3%) in the ASP group; and 0 points, 18 patients (58.1%); 1 point, 4 patients (12.9%); 2 points, 7 patients (22.6%); 3 points, 2 patients (6.4%); 4 points, 0 patients (0%) in the non-ASP group. The mean scores were 1.4 points in the ASP group and 0.8 points in the non-ASP group (p < 0.05). We conclude that the position of the pedicle screw farther away from the facet joint surface can reduce the degeneration of the superior adjacent segment. Therefore, close attention to the screw position during surgery may reduce the rate of superior adjacent-segment pathologies. Full article