Search Results (10)

Adjacent segment degeneration remains a major biomechanical concern after lumbar fusion, whereas fully dynamic topping-off constructs may provide an alternative strategy by preserving segmental motion and unloading degenerated discs. In this study, a three-dimensional nonlinear finite element model of the L1-L5 lumbar spine with L3-L5 double-segment degeneration was developed to compare transforaminal lumbar interbody fusion (TLIF)-based pedicle screw fixation systems (PSFS) and Bioflex-based pedicle screw dynamic stabilization systems (PSDSS). Three interspinous process spacers, namely DIAM, Wallis, and Coflex-F, were implanted at L3-L4, and three pedicle screw diameters of 6.5, 5.5, and 4.5 mm were evaluated under flexion and extension to quantify screw-rod parameter sensitivity. The results showed that both TLIF- and Bioflex-based topping-off constructs reduced intradiscal pressure (IDP) and restricted excessive range of motion (ROM) at the transition segment, especially during extension, with a maximum L3-L4 IDP reduction of 39.49% compared with the degenerated model. Compared with fusion-based constructs, Bioflex-based PSDSS provided greater surgical-segment unloading, reducing L4-L5 IDP by 55.07% in extension and 25.30% in flexion. However, this motion-preserving effect was accompanied by higher pedicle screw stress sensitivity; in the 4.5 mm Bioflex model, the average L4 screw stress reached 15.62 MPa in flexion, representing a 51.71% increase compared with the 6.5 mm screw. In contrast, PSFS constructs showed greater stress variation in the rigid connecting rods. Overall, under the present modeling assumptions, Bioflex-based fully dynamic topping-off constructs showed more favorable disc unloading and transition-segment motion regulation than fusion-based configurations, but their biomechanical benefit should be balanced against diameter-dependent pedicle screw stability. Full article

Study Design: This was a single-institution, retrospective cohort study. Objective: The objective of this study was to assess a surgical technique for spinal reconstruction after corpectomy, integrating an allograft/autograft within a vertebral body replacement cage linked to spinal rods via pedicle screws. This method aims to enhance biomechanical stability and promote long-term fusion without cage endcaps. Summary of Background data: Recent advancements in spinal surgery feature innovative constructs that improve healing and fusion rates. FDA-approved mesh cages provide enhanced stability and superior fusion with fewer complications. Our approach combines allografts/autografts with vertebral replacements, using a pedicle screw through the cage for significant biomechanical enhancement. Methods: Two patients undergoing cervical and lumbar spinal reconstructions due to different pathologies were selected. The surgical technique involved shaping the allograft/autograft to fit precisely within the cage, extending beyond its ends to facilitate fusion at both ends, and securing the construct to the spinal rods with pedicle screws for added stability. Patient outcomes were assessed based on post-operative stability, fusion rates, and the presence of any complications. Results: Both cases successfully utilized the technique, achieving stabilization and fusion. Improvements were noted in post-operative recovery. There were no instances of cage subsidence, or any significant complications directly related to the novel construct. Conclusions: Our case series highlights a post-corpectomy reconstruction technique involving a mesh cage construct integrated with an autograft/allograft and connected to posterior instrumentation for enhanced stability. This technique was applied successfully in two cases, demonstrating its feasibility, durability, and potential to promote biological integration. Further studies with larger cohorts and extended follow-up periods are necessary to refine the approach for wider clinical use. Full article

(1) Background: Pelvic fractures, and particularly instabilities of the dorsal pelvic ring, are becoming increasingly prevalent, particularly in orthogeriatric patients. Spino-pelvic triangular osteosynthesis is an effective approach to achieve sufficient stabilization in vertically unstable fractures. This study compares two types of osteosynthesis: the conventional one and a novel instrumentation where the iliosacral screw is placed through a fenestrated iliac screw. (2) Methods: Sixteen artificial osteoporotic L5+pelvis models with an unstable sacral fracture have been instrumented with either an iliac screw connected with a rod to a L5 pedicle screw and an iliosacral screw (TF) or a fenestrated ilium screw connected with a rod to a L5 pedicle screw and an iliosacral screw passing through the fenestra of the iliac screw (TFS). Biomechanical testing was performed using cyclic loading until failure. (3) Results: Both configurations yielded comparable results with regard to initial stiffness, implant loosening, and cycles to failure. The TFS exhibited markedly higher values for cycles to failure and markedly lower values for loosening. However, due to the characteristics of the artificial bone model, these findings were not significant. (4) Conclusions: The novel triangular fixation systems demonstrated comparable results to the standard triangular osteosynthesis configuration. Full article

The relationships between the results of pre- and intraoperative motor evoked potential recordings during neuromonitoring and whether idiopathic scoliosis (IS) surgical correction improves the spinal efferent transmission have not been specified in detail. This study aims to compare the results of surface-recorded electromyography (EMG), electroneurography (ENG, M, and F-waves), and especially motor evoked potential (MEP) recordings from tibialis anterior muscle (TA) bilaterally in 353 girls with right idiopathic scoliosis (types 1–3 according to Lenke classification). It has not yet been documented whether the results of MEP recordings induced by transcranial single magnetic stimulus (TMS, pre- and postoperatively) and trains of electrical stimuli (TES; intraoperatively in T0—before surgery, T1—after pedicle screws implantation, and T2—after scoliosis curvature distraction and derotation following two-rod implantation) can be compared for diagnostic verification of the improvement of spinal cord neural transmission. We attempted to determine whether the constant level of optimal anesthesia during certain surgical steps of scoliosis treatment affects the parameters of MEPs recorded during neuromonitoring procedures. No neurological deficits have been observed postoperatively. The values of amplitudes but not latencies in MEP recordings evoked with TMS in IS patients compared before and after surgery indicated a slight improvement in efferent neural transmission. The results of all neurophysiological studies in IS patients were significantly asymmetrical and recorded worse on the concave side, suggesting greater neurological motor deficits at p = 0.04. The surgeries brought significant improvement (p = 0.04) in the parameters of amplitudes of sEMG recordings; however, the consequences of abnormalities in the activity of TA motor units were still reflected. ENG study results showed the symptoms of the axonal-type injury in peroneal motor fibers improving only on the concave side at p = 0.04, in parallel with F-wave parameters, which suggests that derotation and distraction might result in restoring the proper relations of the lumbar ventral roots in the spinal central canal, resembling their decompression. There were no significant differences detected in the amplitudes or latencies of MEPs induced with TMS or TES when comparing the parameters recorded preoperatively and intraoperatively in T0. The amplitudes of TES-evoked MEPs increased gradually at p = 0.04 in the subsequent periods (T1 and T2) of observation. A reduction in MEP latency at p = 0.05 was observed only at the end of the IS surgery. Studies on the possible connections between the level of anesthesia fluctuations and the required TMS stimulus strength, as well as the MEP amplitude changes measured in T0–T2, revealed a lack of relationships. These might not be the factors influencing the efferent transmission in spinal pathways beside the surgical procedures. Pre- (TMS-evoked) and intraoperative (TES-evoked) recordings are reliable for evaluating the patient’s neurological status before and during surgical scoliosis correction procedures. An increase in MEP amplitude parameters recorded on both sides after scoliosis surgery proves the immediate improvement of the total efferent spinal cord transmission. Considering comparative pre- and postoperative sEMG and ENG recordings, it can be concluded that surgeries might directly result in additional lumbar ventral root decompression. We can conclude that MEP parameter changes are determined by the surgery procedures during neuromonitoring, not the anesthesia conditions if they are kept stable, which influences a decrease in the number of false-positive neuromonitoring warnings. Full article

Fretting fatigue is a well-known and dangerous damage mode that occurs on the mating surfaces of mechanical components, mainly promoted by a combination of stress distribution, contact pressure distribution, and relative sliding (micro)motion between the surfaces. However, predicting this mechanism is challenging, necessitating specific studies for each assembly due to variable influences. This article presents a methodology for evaluating fretting fatigue damage at the contact between a titanium connecting rod big end and the bearing, adopting the Ruiz parameter as a quantifying damage index. For this purpose, a thermal-structural finite element model is prepared. In particular, the machining and assembly of the split conrod big end are simulated, considering thermal effects. A full engine cycle is first simulated, and results are used for identifying critical instants to be considered for accurate yet computationally efficient calculations. The dependence of fretting fatigue on three factors is studied: bearing crush, bolts tightening torque, and friction coefficient between the big end and the bearing. In summary, the damage increases with a higher crush and friction, while tightening torque has marginal effects. Following a 20% increase in crush height, a corresponding 10% rise in the Ruiz parameter is observed. Conversely, reducing the crush height by 20% leads to an approximately 8% decrease in the Ruiz parameter. When the influence of the bolt preload is taken into account, only a marginal 1% increase of the Ruiz parameter is recorded despite a 30% rise in preload. Evaluating the impact of the friction coefficient on the Ruiz parameter reveals an almost linear relationship. These findings suggest that adjusting the screw preload can enhance the hydrodynamic behavior of the bearing without exacerbating fretting. Furthermore, exploiting the linear correlation between Ruiz and the friction coefficient allows for the generalization of results obtained with specific coefficient values. This methodology can, therefore, serve as a valuable reference for adjusting different variables during the initial design phases of a four-stroke internal combustion engine’s dismountable connecting rod. Full article

This article presents a new technology for forming automotive connecting rod forgings by means of die forging from cast performs from EN AB-71100 (EN AB-AlZn10Si8Mg) aluminum alloy. A premise was made that the production process would be carried out on forging presses. The process of forming connecting rod forgings was analyzed considering different deformation rates related to the type of machine used: a crank press and a screw press. The billet in the form of in-house designed, shaped preforms cast into sand molds with two variants of geometry was used in the process. The numerical analysis of the new process was carried out on the basis of the finite element method using Deform 3D, the simulation software for metal forming. The simulations were conducted in the spatial deformation conditions, considering the full thermomechanical analysis. Based on the simulations, certain important findings concerning the novel process were acquired, including the distribution of stress, deformation, temperatures, cracking criterion and energy parameters. The results of numerical tests confirmed the possibility of producing defect-free forgings of connecting rods from EN AB-71100 aluminum alloy on forging presses by means of the proposed technology. The proposed process of forging using crank and screw presses was verified in the course of tests conducted in industrial conditions. The properly formed connecting rod forgings were subjected to quality tests in terms of their structure and mechanical properties. Full article

Aiming at the low efficiency of manual measurement of threads and the lack of practicability in machine vision measurement before, online size measurement of threads at the end of sucker rods based on machine vision was studied. A robotic arm is used to carry an optical device to achieve high-quality image acquisition of threads. Based on the prior knowledge of the thread profile angle, the directional edge detection operator is customized to achieve the accurate detection of the left and right edges of the thread. Noise filtering, sorting, and left and right edge-matching algorithms based on connected domains are developed to eliminate the interference effects of electrostatic dust and oil pollution in online measurement, and the dimension of thread profile angles, pitches, major diameters, and minor diameters can be precisely calculated. The experimental results show that the screw thread parameter measurement time is about 0.13 s; the maximum and minimum average errors of the thread angles are 0.011° and 0.632°, respectively; and the total average deviation is less than 0.08°. For the screw thread pitch, major diameter, minor diameter, and pitch diameter parameter measurement, the deviation of the measurement results between the proposed method and the universal tool microscope (UTM) method is less than 10 μm. It fully proves the effectiveness and accuracy of the method in this paper and, at the same time, shows that the method has good real-time performance and high application significance, which lays a good foundation for the subsequent online thread measurement. Full article

Background and Objectives: Spine surgery using a percutaneous pedicle screw placement (PPSP) is widely implemented for spinal trauma. However, percutaneous systems have been reported to have weak screw–rod connections. In this study, conventional open and percutaneous systems were biomechanically evaluated and compared. Material and Methods: The experiments were performed in two stages: the first stage was a break test, whereas the second stage was a fatigue test. Four systems were used for the experiments. System 1 was intended for conventional open surgery (titanium rod with a 6.0 mm diameter, using a clamp connecting mechanism). System 2 was a percutaneous pedicle screw (PPS) system for trauma (titanium alloy rod with a 6.0 mm diameter, using ball ring connections). System 3 was a PPS system for trauma (cobalt–chromium alloy rod with a 6.0 mm diameter, using sagittal adjusting screw connections). System 4 was a general-purpose PPS system (titanium alloy rod with a 5.5 mm diameter, using a mechanism where the adapter in the head holds down the screw). Results: Stiffness values of 54.8 N/mm, 43.1 N/mm, 90.9 N/mm, and 39.3 N/mm were reported for systems 1, 2, 3, and 4, respectively. The average number of load cycles in the fatigue test was 134,393, 40,980, 1,550,389, and 147,724 for systems 1 to 4, respectively. At the end of the test, the displacements were 0.2 mm, 16.9 mm, 1.2 mm, and 8.6 mm, respectively. System 1, with a locking mechanism, showed the least displacement at the end of the test. Conclusion: A few PPS systems showed better results in terms on stiffness and life than the open system. The experiments showed that mechanical strength varies depending on the spinal implant. The experiments conducted are essential and significant to provide the mechanical strength required for surgical reconstruction. Full article

In this study, experimental tests were performed to evaluate the shear performance of encased steel truss (EST) composite girders that can resist loads at construction and composite stages. Four full-scale EST composite girders were fabricated, where the truss type (Pratt truss and Warren truss) and presence of stirrups were set as main test variables. The test results showed that in specimens applied with the Pratt truss, horizontal shear cracking occurring along the interface between concrete and steel was the dominant failure mode. Based on the crack pattern and failure plane observed from the test, the horizontal shear strengths of the Pratt truss specimens were calculated, which provided conservative results. On the other hand, in the specimens with the Warren truss inside, the strengths of the specimens were governed by the shear failure occurring in the screw rod connecting the truss elements prior to the yielding of the diagonal member. The shear strengths of the Warren truss specimens calculated based on the shear failure of the screw rod were similar to that obtained from the test. Full article

Bolted joints are highly loaded components and serious issues may arise from improper fastening and in particular from too high or too low preload. Friction at the underhead plays an important role, as it significantly affects the achievable preload for fixed and controlled tightening torque. In addition, multiple tightening is usually performed on connecting rod screws, which may be a further source of friction increment. This study investigates the effect of two surface treatments, shot-peening and deep-rolling, on the tribological properties upon bolt fastening. This topic was tackled experimentally and the campaign involved MJ9 X 1 4 g grade 13.9 36 NiCrMo connecting rod screws, in both lubricated and dry conditions. The results, processed by statistical tools, indicate that deep-rolling does not affect friction, whereas shot-peening yields significant benefits. As an effect of the generation of dimples and multiple contacts, it is able to lower (up to 25%) the bearing frictional coefficient in lubricated conditions, also making the friction level independent of the number of re-tightenings. For a dry surface, an even higher friction decrease (up to 30%) is achieved. Without lubrication, the friction coefficient keeps increasing for the incremented number of tightenings, but the increase rate is lowered with respect to the untreated surface. Full article