Dislocation Force Research Articles

In-situ compression tests and analysis of strength-ductility synergy in heterogeneous structured copper-tin composite joint

Copper-tin (Cu–Sn) serves as a prevalent alloy system in electronic packaging, envisioned for future high-power device applications. However, interdiffusion in Cu–Sn yields rigid and brittle Cu6Sn5 and Cu3Sn phases, causing joint hardening and embrittlement. This paper introduces a novel, non-homogeneous Cu–Sn composite employing heterostructure design. Through room temperature in-situ compression tests and molecular dynamics (MD) simulations, we investigate mechanical property degradation origins and Cu–Sn composite strength-ductility mechanisms. Our findings reveal hierarchical heterostructures in joints stimulate dynamic stress distribution at interfaces, generating a high density of geometrically necessary dislocations (GNDs). This enhances the material's work-hardening rate and imparts robust strain-hardening capabilities. This unique structural feature has altered the interaction between dislocations and interfaces, thereby effectively promoting the formation and driving force of dislocations. The combined effects of strain inhomogeneity induced by soft and hard phases, along with a hybrid mechanism involving stacking faults (SFs), Lomer-Cottrell (L-C) locking, and dislocation bypassing and shearing, realize exceptional strength-ductility synergies in Cu–Sn composite joints. This study presents a promising paradigm for designing microstructures in high-strength, deformable, and high-temperature-resistant soldered composites.

Does glenoid inclination affect the anterior stability of reverse total shoulder arthroplasty? A biomechanical study

PurposeThe anterior stability of reverse total shoulder arthroplasty is affected by multiple factors. However, the effect of glenosphere inclination on stability has rarely been investigated, which is what this study aims to look into.MethodsReverse shoulder arthroplasty was performed on 15 cadaveric human shoulders. The anterior dislocation forces and range of motion in internal rotation in the glenohumeral joint (primary measured parameters) were tested in a shoulder simulator in different arm positions and implant configurations, as well as with a custom-made 10° inferiorly inclined glenosphere. The inclination and retroversion of the baseplate as well as the distance between the glenoid and coracoid tip in two planes (secondary measured parameters) were evaluated on CT scans.ResultsIn biomechanical testing, the custom-made inclined glenosphere showed no significant influence on anterior stability other than glenoid lateralisation over all arm positions as well as the neck-shaft angle in two arm positions. The 6 mm lateralised glenosphere reduced internal rotation at 30° and 60° of glenohumeral abduction. In 30° of glenohumeral abduction, joint stability was increased using the 155° epiphysis compared with the 145° epiphysis. The mean inclination was 16.1°. The inclination was positively, and the distance between the glenoid and coracoid tip in the anterior-to-posterior direction was negatively correlated with anterior dislocation forces.ConclusionsThe custom-made inferiorly inclined glenosphere did not influence anterior stability, but baseplate inclination itself had a significant effect on stability.

Influence of Sutureless Scleral Fixation Techniques With 3-Piece Intraocular Lenses on Dislocation Force

PurposeTo compare four different secondary IOL fixation techniques regarding the least required force to dislocate a scleral fixated 3-piece IOL in human corneoscleral donor tissue (CST). DesignExperimental Laboratory investigation MethodsThe least required dislocation force (LRDF) of four different secondary IOL fixation techniques, namely the techniques using transscleral tunnels (TT, as described by Scharioth), glued haptics (GH, Argawa), flanged haptics (FH, Yamane) and bent haptic ends (BH, Behera/Bolz) were investigated using 40 three-piece IOLs (Sensar AR40) fixated to human scleral tissue. The main outcome of the study, dislocation force between different techniques, was measured with a tensiometer. ResultsThe dislocation force needed to dislocate the haptics was highest with the FH technique and was significantly higher than with all the other techniques (GH vs FH: -1.02±0.02 N, p<0.001; TT vs FH: -1.08±0.21 N, p<0.001; BH vs FH: -1.00±0.25 N, p=0.044). There was no significant difference regarding the dislocation force between the other techniques (GH vs TT (-0.06±0.100 N, p=0.988), GH vs BH (-0.02±0.03 N, p=0.60), TT vs BH (-0.08±0.04 N, p=1.000). ConclusionsThe flange haptic technique as described by Yamane proved to be the strongest form of secondary IOL fixation regarding dislocation force in this in vitro study. The other fixation techniques showed significantly less resistance to axial traction.

Dislocation force of scleral flange-fixated intraocular lens haptics

PurposeTo measure the dislocation forces in relation to haptic material, flange size and needle used.SettingHanusch Hospital, Vienna, Austria.DesignLaboratory Investigation.Methods, main outcome measures30 G (gauge) thin wall and 27 G standard needles were used for a 2 mm tangential scleral tunnel in combination with different PVDF (polyvinylidene fluoride) and PMMA (polymethylmethacrylate haptics). Flanges were created by heating 1 mm of the haptic end, non-forceps assisted in PVDF and forceps assisted in PMMA haptics. The dislocation force was measured in non-preserved cadaver sclera using a tensiometer device.ResultsPVDF flanges achieved were of a mushroom-like shape and PMMA flanges were of a conic shape. For 30 G needle tunnels the dislocation forces for PVDF and PMMA haptic flanges were 1.58 ± 0.68 N (n = 10) and 0.70 ± 0.14 N (n = 9) (p = 0.003) respectively. For 27 G needle tunnels the dislocation forces for PVDF and PMMA haptic flanges were 0.31 ± 0.35 N (n = 3) and 0.0 N (n = 4), respectively. The flange size correlated with the occurring dislocation force in experiments with 30 G needle tunnels (r = 0.92), when flanges were bigger than 384 micrometres.ConclusionsThe highest dislocation forces were found for PVDF haptic flanges and their characteristic mushroom-like shape for 30 G thin wall needle scleral tunnels. Forceps assisted flange creation in PMMA haptics did not compensate the disadvantage of PMMA haptics with their characteristic conic shape flange.

Varus-valgus alignment of humeral short stem in reverse total shoulder arthroplasty: does it really matter?

BackgroundThe utilization of short humeral stems in reverse total shoulder arthroplasty (RTSA) has gained attention in recent times. However, concerns regarding the risk of misalignment during implant insertion are associated with their use. MethodsEight fresh-frozen cadaveric shoulders were prepared for dissection and biomechanical testing. A bespoke humeral implant was fabricated to facilitate assessment of neutral, varus, and valgus alignments using a single stem, and 10° was established as the maximum permissible angle for misalignments. Shift in humerus position and changes in deltoid length attributable to misalignments relative to the neutral position were evaluated using a Microscribe 3DLx system. The impingement-free range of motion (IFROM), encompassing abduction, adduction, internal rotation (IR), and external rotation (ER), was gauged using a digital goniometer. The capacity for abduction was evaluated at maximal abduction angles under successive loading on the middle deltoid. A specialized traction system coupled with a force transducer was employed to measure anterior dislocation forces. ResultsRelative to the neutral alignment, valgus alignment resulted in a more distal (10.5 ± 2.4 mm) and medial (8.3 ± 2.2 mm) translation of the humeral component, whereas the varus alignment resulted in the humerus shifting more superiorly (11.2 ± 1.3 mm) and laterally (9.9 ± 0.9 mm) at 0° abduction. The valgus alignment exhibited the highest abduction angle than neutral alignment (86.2°, P<0.001). Conversely, the varus alignment demonstrated significantly higher adduction (18.4±7.4°, P<0.001), IR (68.9±15.0°, P=0.014), and ER (45.2±10.5°, P=0.002) at 0° abduction compared to the neutral alignments. Anterior dislocation forces were considerably lower (23.8N) in the varus group compared to the neutral group at 0°ER (P=0.047). Additionally, abduction capability was markedly higher in varus alignment at low deltoid loads than the neutral alignment (5N, P=0.009; 7.5N, P=0.007). ConclusionsThe varus position enhances rotational ROM but increases instability, while the valgus position does not significantly impact ROM or instability compared to the neutral position.

Biomechanical Evaluation of Posterior Shoulder Instability With a Clinically Relevant Posterior Glenoid Bone Loss Model

Background: Existing biomechanical studies of posterior glenoid bone loss and labral pathology are limited by their use of anterior instability models, which differ in both orientation and morphology and have been performed in only a single, neutral arm position. Purpose: To evaluate the biomechanical effectiveness of a posterior labral repair in the setting of a clinically relevant posterior bone loss model in various at-risk arm positions. Study Design: Controlled laboratory study. Methods: Ten fresh-frozen cadaveric shoulders were tested in 7 consecutive states using a 6 degrees of freedom robotic arm: (1) native, (2) posterior labral tear (6-9 o’clock), (3) posterior labral repair, (4) mean posterior glenoid bone loss (7%) with labral tear, (5) mean posterior glenoid bone loss with labral repair, (6) large posterior glenoid bone loss (28%) with labral tear, and (7) large posterior glenoid bone loss with labral repair. Bone loss was created using 3-dimensional printed computed tomography model templates. Biomechanical testing consisted of 75 N of posterior-inferior force and 75 N of compression at 60° and 90° of flexion and scaption. Posterior-inferior translation, lateral translation, and peak dislocation force were measured for each condition. Results: Labral repair significantly increased dislocation force independent of bone loss state between 10.1 and 14.8 N depending on arm position. Dislocation force significantly decreased between no bone loss and small bone loss (11.9-13.5 N), small bone loss and large bone loss (9.4-14.3 N), and no bone loss and large bone loss (21.2-26.5 N). Labral repair significantly decreased posterior-inferior translation compared with labral tear states by a range of 1.0 to 2.3 mm. In the native state, the shoulder was most unstable in 60° of scaption, with 29.9 ± 6.1-mm posterior-inferior translation. Conclusion: Posterior labral repair improved stability of the glenohumeral joint, and even in smaller to medium amounts of posterior glenoid bone loss the glenohumeral stability was maintained with labral repair in this cadaveric model. However, a labral repair with large bone loss could not improve stability to the native state. Clinical Relevance: This study shows that larger amounts of posterior glenoid bone loss (>25%) may require bony augmentation for adequate stability.

Latissimus Dorsi and Teres major tendon transfer increases internal rotation torque following lateralized reverse shoulder arthroplasty with subscapularis insufficiency.

Limitation of active Internal Rotation (IR) following Reverse Shoulder Arthroplasty (RSA) in patients with massive Rotator Cuff Tears (mRCTs) with subscapularis insufficiency remains a challenge. Recently, RSA with Latissimus dorsi and Teres major (LDTM) transfer in patients with limited active IR has been demonstrated as a reliable treatment option. The purpose of this study was to biomechanically compare the IR torque following LDTM transfer with RSA in mRCT with subscapularis insufficiency to RSA without tendon transfer. Eight cadaveric shoulders were tested (mean age: 64.5 ± 1.9years) using a custom shoulder testing system that permits loading conditions of mRCT with subscapularis insufficiency. Two conditions were tested and compared. The first condition was RSA alone and the second condition was RSA with LDTM transfer. RSA with a medialized glenoid and lateralized humerus design was used for all specimens. The specimens were tested at 0°, 20° and 40° abduction at three different muscle loads: baseline, double, and triple, while the Teres minor and deltoid loads were kept constant. IR torque was measured with a torque wrench at 0°, 20°, and 40° abduction and 60° and 45° IR positions. Force required for anterior dislocation was measured at 20° abduction and 10° IR position. RSA with LDTM transfer had significantly higher IR torque at all abductions and muscle loading compared with RSA without transfer (average at all positions; RSA without transfer: 0.80 ± 0.02 Nm, LDTM transfer for all loads: 1.43 ± 0.10 Nm). RSA with LDTM transfer (91.4 ± 3.9 N) needed higher force for anterior dislocation compared to RSA alone (89.4 ± 4.1 N), but there was no significant difference. LDTM transfer with RSA increases IR torque compared to RSA without tendon transfer in a cadaveric model. LDTM transfer with RSA may be a reliable treatment option for patients with mRCT and subscapularis insufficiency who are expected to have limited active IR following RSA.

Should the vent hole of posterior implant crowns be placed on the lateral surface? An in vitro study of the hydrodynamic feature of cement extrusion and retention ability.

Although placing a vent hole on the occlusal surface of the implant crown can reduce cervical marginal cement extrusion, it has disadvantages. Transferring the hole to the buccal or lingual surface of the posterior implant crown could therefore be an alternative solution. This study investigated the effect of transferring the vent hole to the lateral side of the implant posterior crown on the hydrodynamics of excess cement extrusion and the crown’s retention ability. Specially fabricated posterior implant crowns were divided into five groups: crowns with an occlusal hole (OH), occlusal lateral hole (OLH), middle lateral hole (MLH), cervical lateral hole (CLH), and no hole (NH). Each set of implant analog-abutment-crown specimens was wrapped in a polymethylacrylate base. The base of the implant crown was divided into four 90-degree quadrants along the diagonal of the square base with a pen mark. Cement was used to bond the crowns and the abutments, and the weight of cement extrusions at the vent holes and the abutment cervical margins were calculated. The distribution of cement extrusion at the margin was photographed in each quadrant, and the areas of surface coverage of cement extrusion were compared with ImageJ software. Retentive strength was measured as the dislocation force using a universal testing machine. One-way analysis of variance was used for result analysis. The cervical marginal cement extrusions of crowns with lateral holes (OLH, MLH, and CLH) were significantly less than that of NH crowns (P<0.05), but more than that of OH crowns (P<0.05). Subgroup analysis among the lateral hole groups indicated that the higher the position of the lateral hole, the lower the weight of the cement extrusion, and the smaller the total distribution area of cement extrusion. The cement extrusion distribution area was larger in the quadrant with the hole than in those opposite and next to the hole. Retention strength comparison indicated no significant difference between crowns with NH, OH, or lateral holes. Transferring the vent hole of the posterior implant crown to the lateral side could reduce cement extrusion at the cervical margin while reducing retention strength deterioration and the esthetic drawbacks caused by occlusal hole opening.

Paper 07: Biomechanical Evaluation of Posterior Shoulder Instability with a Clinically Relevant Posterior Bone Loss Model

Objectives: Though recognized as a risk factor, posterior glenoid bone loss has only recently been characterized and is distinctly different than anterior glenoid bone loss patterns. Existing biomechanical studies are limited by employment of anterior glenoid bone loss models which are different in both orientation and morphology than posterior glenoid bone loss, and testing in a single neutral arm position thus not fully accounting for the contribution of capsuloligamentous structures in various at-risk arm positions. The purpose of this study was to evaluate the biomechanical effectiveness of a posterior labral repair in the setting of a clinically relevant bone loss model using 3-dimensional computed tomography modeling of patients with recurrent posterior shoulder instability in various at-risk arm positions. Methods: Ten fresh-frozen cadaveric shoulders (mean age: 55.4 years, range: 39-65) were prepared by removing all tissue except the capsule and distal rotator cuff insertions. A joint coordinate frame was established, the specimens were potted, then mounted to a customized fixture on 6-degrees-of-freedom robotic arm. A posterior labral tear was created, then repaired with 3 horizontal mattress sutures and secured by drilling 6 transosseous holes along the peripheral glenoid face exiting the anterior glenoid neck. The sutures were secured for the labral repair states to the mounted fixture under maximal tension and released for the labral tear states and for creating the sequential bone loss models. Bone loss models were created based off a cohort of CT data on patients undergoing revision posterior labral repair surgery to develop 2 clinically relevant 3D models of glenoid bone loss: the first simulating the mean bone loss in this cohort and represented 7% or small bone loss; the second was the mean + 2SD representing 28% or large bone loss. The bone loss was created on each specimen with a 3mm round burr to match each respective 3D printed template (Figure 1). Each specimen was tested in 7 consecutive states: (1) native anatomy, (2) posterior labral tear (6-9 o’clock), (3) posterior labral repair, (4) mean posterior glenoid bone loss with labral tear, (5) mean posterior glenoid bone loss with labral repair, (6) large posterior glenoid bone loss with labral tear, and (7) large posterior glenoid bone loss with labral repair. Each state underwent 75N of posterior-inferior force and 75N of compression during the four tests at 60 and 90 degrees of flexion and 60 and 90 degrees of scaption. Posterior-inferior translation, lateral translation, and dislocation force were measured for each condition. Statistical analysis was performed using two-factor random-intercepts linear mixed-effects models. Results: Compared to the labral tear state, significant increases in dislocation forces occurred with labral repair independent of bone loss state or arm position with values as follows: 14.8N (60° scaption), 12.2N (90° scaption), 11.1N (60° flexion), and 10.1N (90° flexion) with mean 12.1 ± 2.0N across all arm positions (Figure 2). Dislocation force significantly decreased between no bone loss and small bone loss (mean 12.4 ± 0.7N) and between small bone loss and large bone loss (mean 11.8 ± 2.1N) regardless of labral state in all arm positions (table 1). Posterior-inferior translation significantly decreased with labral repair compared to labral tear states independent of bone loss state in all arm positions (Table 1). Lateral translation of the humeral head significant increased when the labrum was repaired independent of bone loss state in all arm positions except 90° scaption and decreased progressively in all bone loss states in all arm positions (table 1). In the native state, the shoulder significantly translated posterior-inferior in scaption at 60° and 90° elevation compared to flexion (p&lt;0.017) and was most unstable in 60° scaption with 29.9 ± 6.1mm posterior-inferior translation (Figure 3). Conclusions: This is the first study to biomechanically evaluate posterior glenoid bone loss using a clinical model in various at-risk arm positions on a 6 degree-of-freedom robot and through a precise linear effects model has established values for the increase in dislocation force posterior labral repair provides regardless of bone loss. The most significant finding of the study is that independent of bone loss, labral repair reduced posterior dislocation forces by 12.1 ± 2.0N and significantly decreased posterior-inferior translation. With a mean decrease in dislocation force of 12.4 ± 0.7N with small (7%) bone loss, labral repair alone may be enough to restore shoulder stability in most individuals. However, significant increases in posterior bone loss may require bony augmentation for adequate stability based on individual factors such as age and activity level. [Table: see text][Figure: see text][Figure: see text]

Effect of the neck-shaft angle on stability in the onlay type of reverse shoulder arthroplasty: a cadaveric study

BackgroundAlthough reverse shoulder arthroplasty (RSA) has been indicated for treating patients suffering from cuff tear arthropathy, instability is a severe complication. The relationship between the humeral neck-shaft angle and joint stability in RSA as well as the clinical effect of subscapularis tendon repair on postoperative stability after RSA remain controversial. This study is primarily aimed to investigate the relationship between humeral neck-shaft angle and stability using the onlay type of RSA with preserved shoulder girdle muscles using fresh frozen cadavers. Moreover, we aimed to investigate the effect of subscapularis tendon repair after RSA placement. MethodsAn onlay type RSA of not-lateralized glenosphere in a massive rotator cuff tear model with preserved shoulder component muscles was placed on 7 fresh frozen cadavers, and traction tests were performed to dislocate by changing the neck-shaft angle of the stem to 135°, 145°, and 155°. The anterior dislocation force (DF) was evaluated in 6 patterns as follows: 2 patterns at 30° and 60° of abduction and 3 patterns at 30° of internal rotation, in neutral rotation, and 30° of external rotation. DF was recorded at neck-shaft angles of 135°, 145°, and 155° and with and without subscapularis tendon repair. ResultsAt 30° abduction, DF was significantly higher at a neck-shaft angle of 155° regardless of the rotational position (P < .05), and at abduction 60°, there was no difference in DF according to any rotational position and any neck-shaft angle. Regardless of the neck-shaft angle, the DF was significantly higher at 60° abduction than at 30° abduction (P < .05). Furthermore, the DF was significantly higher with subscapularis tendon repair (P < .01). ConclusionOur results showed some relationship between humeral neck-shaft angle and stability in the onlay type of RSA with preserved shoulder component muscles using fresh frozen cadavers. Moreover, a neck-shaft angle of 155° showed the highest anterior DF among neck-shaft angles of 135° and 145° at 30° abduction, and there was no difference at abduction 60° among any neck-shaft angle. Furthermore, subscapularis tendon repair also contributed to anterior stability.

Selection of 1-mm venting or 2.5-mm screw access holes on implant crowns based on cement extrusion and retention capacity

BackgroundThis in vitro study aimed to provide evidence regarding the selection of hole diameters of implant crowns to reduce excess cement extrusion at the abutment margin, and to examine the maintenance of their retention capacity in anterior and posterior cement-retained implant crowns.MethodsSix groups of implant crowns were prepared according to the position of the teeth and the size of their holes as follows: anterior crown without hole (ANH), anterior crown with 1-mm mini venting hole (AMH), anterior crown with 2.5-mm regular screw access hole (ARH), posterior crown without hole (PNH), posterior crown with 1-mm mini venting hole (PMH), and posterior crown with 2.5-mm regular screw access hole (PRH). Temporary cement was used to bond the crowns to the abutments. The mean amount of excess cement extrusion among the different groups at the abutment margin was calculated. Retentive strength under different hole designs was measured as the dislocation force of the crown using a universal testing machine. One-way ANOVA and Welch’s t-test were used to analyze the results.ResultsThe average amounts of extruded excess cement were 18.96 ± 0.64, 1.78 ± 0.41, and 1.30 ± 0.41 mg in the ANH, AMH, and ARH groups, respectively, and 14.87 ± 0.36, 1.51 ± 0.40, and 0.82 ± 0.22 mg in the PNH, PMH, and PRH groups, respectively. The hole opening in the crowns could significantly reduce residual cement regardless of its size (p < 0.001). The mean retentive strengths were 54.16 ± 6.00, 47.63 ± 13.54, and 31.99 ± 7.75 N in the ANH, AMH, and ARH groups, respectively, and 57.84 ± 10.19, 53.22 ± 6.98, and 39.48 ± 5.12 N in the PNH, PMH, and PRH groups, respectively. The retention capacity of the implant crown deteriorated rapidly as the holes on the crown surface enlarged.ConclusionsThe presence of a hole on the implant crown reduced the amount of excess cement. The retention ability of the implant crowns deteriorated as the size of the hole increased. Considering the esthetic effect of the crown and the possible influence on crown retention, an implant crown with a 1-mm mini venting hole is a better clinical choice than the one with a 2.5-mm regular screw access hole.

The Addition of Remplissage to Free Bone Block Restores Translation and Stiffness Compared to Bone Block Alone or Latarjet in a Bipolar Bone Loss Model

<h3>Purpose</h3> The purpose of this study was to compare glenohumeral stability following a Latarjet, a free bone block (FBB), and a FBB with remplissage for bipolar bone loss. <h3>Methods</h3> Nine matched pairs of fresh frozen cadavers were tested in a custom biomechanical apparatus with rotation and progressive translational loading. The free bone block group consisted of a distal tibial allograft with an all-suture tape construct. The Latarjet group was performed with the native coracoid and two partially threaded cannulated screws. A bipolar bone loss model was created with 20% glenoid bone loss and an off-track Hill-Sachs lesion. Testing conditions included the 1) native state, 2) bipolar bone loss model, 3) Latarjet, 4) FBB with distal tibial allograft secured with cerclage sutures, and 5) FBB with remplissage. Each condition was tested for translation, humeral head apex shift, stiffness, and dislocation force. <h3>Results</h3> There were no differences in translation, stiffness, or dislocation forced between the FBB alone and Latarjet groups. The FBB with remplissage group demonstrated the lowest anterior-inferior translation at 90° of ER, which was statistically significant compared to Latarjet 20N (<i>P</i> = .013) and compared to the FBB alone at 40N (<i>P</i> = .024) and 50N (<i>P</i> = .011). The FBB with remplissage group was significantly stiffer compared to FBB alone at 90° ER with approximately 60% change in stiffness (<i>P</i> = .028). The force required to dislocate the humeral head after treatment was highest in the FBB with remplissage group, which was statistically significant compared to the FBB alone (<i>P</i> = .003) and Latarjet groups (<i>P</i> = .018). <h3>Conclusion</h3> The addition of remplissage to a FBB restores translation and stiffness closer to the intact state compared to a FBB alone or Latarjet in a bipolar bone loss model with an off-track Hill-Sachs lesion. In this model, dislocation force significantly increased with the addition of remplissage to the FBB. <b>Clinical Relevance</b>: This biomechanical study provides evidence that Latarjet and FBB are both acceptable forms of treatment for bipolar bone loss, but stability can be enhanced with the addition of remplissage following glenoid reconstruction.

Prediction of hardening effect by irradiation-induced vacancy clusters with dislocation dynamics

Development of irradiation hardening models attracts extensive attention in designing nuclear materials. Dislocation dynamics (DD) method is a powerful tool in this field for its advantages of predicting mechanical response with microstructural changes such as dislocation evolution, and its extendibility by incorporating the hardening mechanisms, i.e., the dislocation motion impeded by irradiation-induced defects such as vacancy/interstitial clusters, dislocation loops, precipitates etc. Focusing on the hardening effect contributed by vacancy cluster (VC) that is of high number density even at low irradiation dose, this work develops a VC-dislocation interaction model based on Eshelby's equivalent inclusion method. Specifically, a VC is treated as an inclusion with a certain eigenstrain that gives zero stress inside the VC at the presence of dislocation. By adding the interaction force between VC and dislocation derived using the eigenstrain to dislocation force, we implement this model in open-source DD software ParaDiS. Further, we apply the model to investigate the hardening effect by VCs with varying size and number density. Simulation results show that the hardening by VCs of different sizes is all proportional to the 2/3 power of total number density. To further quantify the hardening effect of VCs, we propose a hardening model which modifies the previous Frediel-Kroupa-Hirsch (FKH) model by making the hardening coefficient in linear relation with VC diameter and introducing an effective diameter that account for size distribution of VCs. The MFKH (modified FKH) model with no free parameter shows good accuracy in predicting VC induced hardening in tungsten comparing with experiments.

A Biomechanical Study of Flanged Intrascleral Haptic Fixation of Three-Piece Intraocular Lenses

Flanged intrascleral haptic fixation (FISHF) is a useful method for securing intraocular lenses (IOLs) in eyes without capsular support. Biomechanical studies were conducted to support the use of this technique. Laboratory investigation. Haptics of 3-piece IOLs were passed through cadaveric human sclera using 30- and 27-gauge needles. Flanges were created by melting 1.0 mm from the haptic ends using cautery. The forces required to remove the flanged haptic from the sclera and disinsert the haptic from the optic were measured using a mechanical tester and a custom-fabricated mount. The mean FISHF dislocation force using 30-gauge needles was greatest with the CT Lucia 602 (2.04 ± 0.24 newtons [N]) compared to the LI61AO (0.93 ± 0.41 N; P=.001), ZA9003 (0.70 ± 0.34 N; P=<.001), and MA60AC (0.27 ± 0.19 N; P <.001). Using 27-gauge needles with the CT Lucia resulted in a lower dislocation force (0.56 ± 0.36 N; P <.001). The FISHF dislocation force was correlated with the flange-to-needle diameter ratio (r=0.975). The FISHF dislocation forces of the CT Lucia and LI61AO using 30-gauge needles were not significantly different from their haptic-optic disinsertion forces (P=.79 and .27, respectively). There were no differences in flange diameters between 1.0 mm and 2.0 mm haptic melt lengths across the IOLs (P=.15-.85). These data strongly support the biomechanical stability of FISHF with the polyvinylidene fluoride haptics of the CT Lucia using small diameter instruments for the creation of an intrascleral tunnel. 1.0 mm of haptic may be the optimal melt length.

Lattice-based J integral for a steadily moving dislocation

According to continuum theory and the conservation theorem, the J integral represents the net translational force acting on a defect and, specifically, it is equivalent to the Peach–Koehler force for dislocation. In this study, we newly derive the J integral to quantify driving force on a uniformly moving dislocation with considering its core-induced dynamic behaviors. Using both molecular dynamics simulation and lattice dynamics theory based on atomic chain model, we prove that radiation drag and self-stress asymmetry during the dislocation motion, which are generated by lattice discreteness, make the newly derived J integral depend on the distance from the dislocation core, which is lumped into resistance to the dislocation motion. Finally, we show that the J integral converges to the Peach–Koehler force as the resistance term disappears for a stationary dislocation.

Anti-plane problem of nanocrack with surface piezoelectricity—a finite-form solution

A solution in finite form for the screw dislocation interacting with the nanocrack incorporating surface piezoelectricity under anti-plane loads is developed. By the boundary integration and the Cauchy’s integral formula to convert the problem into a first-order differential equation, the finite-form solution in physical region is established via the mapping technique. At the crack tip, the results from the present solution indicate that the electric displacements and the stresses are finite and the singularities are removed when the surface piezoelectricity is incorporated, which is against those in the classic solution and also different from other reported solutions where the singularities are weakened but non-trivial. The numerical results shows that the stresses, the electric displacements and the dislocation forces are strongly size dependent and their magnitudes reduce with the decrease in crack length, and the results approach to those by the classic solution with an increasing in the crack length.

Factors Affecting Stability of the Reverse Total Shoulder Arthroplasty: A Cadaveric Biomechanical Study

Background: The overall objective of this study was to investigate whether a reverse shoulder arthroplasty could provide adequate stability to a shoulder even with extreme soft tissue loss. The specific objectives of this study were: to determine if just the deltoid, conjoined tendon, and triceps are sufficient soft tissues to allow a Reverse Shoulder Arthroplasty (RSA) to provide shoulder stability and to determine the influence of load direction, rotation, shoulder position, and polyethylene thickness on RSA stability in this soft-tissue deficient model. Methods: This study utilized six cadaveric shoulders that had all soft tissue removed, with the exception of the deltoid, conjoint tendon, and long head of triceps. A reverse shoulder arthroplasty was then performed (Delta III, DePuy Inc., Warsaw, IN) and an increasing dislocation force was applied perpendicular to the humeral socket centerline until dislocation occurred, or a maximum load of 100 N was reached. This was repeated to measure the effect of four factors: load direction, arm position, polyethylene thickness, and arm rotation on force to dislocation. Results: For load direction, there was an increase in force to dislocate an inferior load direction (p=0.01). There was a lower not dislocated percentage and lower survival for a posterior load direction (p=0.02). For arm position, there was a decrease in force for dislocation and lower survival for both abduction and extension arm positions. There was a higher not dislocated percentage for a flexion arm position (p=0.01). For arm rotation, there was a lower not dislocated percentage and lower survival for an external rotation arm position (p=0.03). There was no statistically significant influence of polyethylene thickness (p=0.26). Conclusion: The deltoid, conjoined tendon, and triceps are sufficient to stabilize an RSA. Load direction, arm position, and arm rotation were all shown to significantly affect stability. Finally, polyethylene thickness may not affect overall RSA stability in this soft-tissue deficient model. Level of Evidence: Basic science study, Biomechanical study.

UNSTABLE LUMBAR FRACTURE-DISLOCATION TREATED BY LONG SEGMENT POSTERIOR PEDICLE SCREW INSTRUMENTATION

Background: Among all the thoracolumbar fractures, 50-60% affects the thoracolumbar transitional zone, and 51% AO Type C Fractures has a neurological deficit. We experienced treating a case of unstable lumbar fracture-dislocation treated with long segment pedicle screw instrumentation.Case: A 26-year-old man came to the ER after his back hit by a canopy while working 2 hours before admission. The motoric function was diminished from the L2-S1 level and hypoesthesia at the T12 level. Plain X-Ray showed Fracture-Dislocation Lumbar Vertebral 1-2 Denis Classification Flexion Rotation (AO Type C) ASIA A. The patient underwent reduction, decompression, and long-segment posterior pedicle screw instrumentation.Discussion: The surgery’s primary purpose is to restore alignment and stability to improve the patient’s quality of life by enabling daily activity in a wheelchair without significant pain. Short segment or long segment pedicle screw instrumentation remains a debate. In this case report, we apply long segment pedicle screw instrumentation for lumbar vertebral fracture-dislocation.Conclusion: Thoracolumbar fracture and dislocation fixation aim to restore alignment and stability, to reduce kyphotic deformity, and to decompress the spinal canal. The long segment pedicle screw instrumentation can resist the deforming force of thoracolumbar fractures and dislocations that will inevitably collapse into further kyphosis, resulting in a better outcome.

Anatomic factors influencing the anterior stability of reverse total shoulder arthroplasty

Several factors affect the stability of the reverse shoulder arthroplasty. The influence of bony anatomy on anterior stability remains unclear. This study aimed to identify the correlations between bony anatomy and anterior dislocation forces. The differences in anterior dislocation force in reverse total shoulder arthroplasty reported in a previous biomechanical study were used to analyze the anatomic factors influencing anterior stability. The critical shoulder angle, glenocoracoid distance in 2 planes, and glenoid inclination were measured in the tested specimens using 3-dimensional computed tomographic scans and radiographs. Anatomic parameters were then correlated with the anterior dislocation forces. The critical shoulder angle had no correlation with anterior stability. The glenocoracoid distance in anteroposterior direction showed a negative correlation with the stability of a reverse shoulder arthroplasty with a 9-mm lateralized glenosphere and 155° humeral inclination in 30° and 60° glenohumeral abduction with the arm in 30° external rotation (r = -0.662, P = .004; r = -0.794, P = .011) and 30° glenohumeral abduction with neutral rotation (r = -0.614, P = .009). Using the same hardware configuration, the anterior stability had a negative correlation with the glenocoracoid distance in the mediolateral direction in 30° of glenohumeral abduction with the arm in 0° and 30° of external rotation (r = -0.542, P = .025; r = -0.497, P = .042). The distance between the coracoid tip and glenoid in 2 planes had a significant negative correlation with the anterior stability of the reverse shoulder arthroplasty with a lateralized glenosphere and 155° humeral inclination. The findings suggest that only glenoid lateralization is influenced by the bony anatomy.

Theoretical development of continuum dislocation dynamics for finite-deformation crystal plasticity at the mesoscale

The equations of dislocation transport at finite crystal deformation were developed, with a special emphasis on a vector density representation of dislocations. A companion thermodynamic analysis yielded a generalized expression for the driving force of dislocations that depend on Mandel (Cauchy) stress in the reference (spatial) configurations and the contribution of the dislocation core energy to the free energy of the crystal. Our formulation relied on several dislocation density tensor measures linked to the incompatibility of the plastic distortion in the crystal. While previous works develop such tensors starting from the multiplicative decomposition of the deformation gradient, we developed the tensor measures of the dislocation density and the dislocation flux from the additive decomposition of the displacement gradient and the crystal velocity fields. The two-point dislocation density measures defined by the referential curl of the plastic distortion and the spatial curl of the inverse elastic distortion and the associate dislocation currents were found to be more useful in deriving the referential and spatial forms of the transport equations for the vector density of dislocations. A few test problems showing the effect of finite deformation on the static dislocation fields are presented, with a particular attention to lattice rotation. The framework developed provides the theoretical basis for investigating crystal plasticity and dislocation patterning at the mesoscale, and it bears the potential for realistic comparison with experiments upon numerical solution.