Rotational Components Research Articles

Comparison of Femoral Component Rotation between Robotic-Assisted vs. Soft-Tissue Tensor Total Knee Arthroplasty with Anatomic Implants.

Background and Objectives: Total knee arthroplasty (TKA) is the most effective treatment method for end-stage osteoarthritis. One of the most important aspects of this surgery is adequate implant positioning, as it guarantees the desired outcome of restoring limb biomechanics. Surgical technique is being continuously improved along with hardware development. There are two novel devices designed to help establish proper femoral component rotation: soft-tissue tensor and robotic-assisted TKA (RATKA). This study compared the femoral component rotation achieved with the use of three methods: RATKA, soft tissue tensioner and the conventional measured-resection technique, all of them utilizing anatomical design prosthesis components. Materials and Methods: A total of 139 patients diagnosed with end-stage osteoarthritis underwent total knee arthroplasty between December 2020 and June 2021. After the surgery, they were divided into three groups depending on procedure technique and implant type: Persona (Zimmer Biomet) + Fuzion Balancer, RATKA + Journey II BCS or conventional TKA + Persona/Journey. Postoperatively, a computed tomography examination was performed in order to measure femoral component rotation. All three groups were compared independently during statistical analysis. Fisher's exact, Kruskal-Wallis and Dwass-Steel-Crichtlow-Fligner tests were used for particular calculations. Results: Statistically significant differences in femoral component rotation between groups were noticed. However, in terms of values other than 0° in external rotation, no significant variance was revealed. Conclusions: Additional total knee arthroplasty instruments seem to improve the outcomes of the surgery, providing better component positioning than in the conventional measured-resection technique based only on bone landmarks.

Coupled model biases and extended‐range prediction skill during the onset phase of the Indian summer monsoon with different initializations related to land surface and number of observations

AbstractIn this study, we have analyzed the role of the initialization in the forecast of the monsoon onset phase beyond 10 days lead time (i.e., in the extended range) to understand the impact of displacement or shift in initial conditions in the extended‐range forecast. Two displacement errors are considered: (a) the initial error arising due to a change in land surface initial conditions and (b) the initial error arising due to a change in the number of observations. For the first part (a), we have analyzed and compared the difference in prediction skills in the United Kingdom Met Office (UKMO) GloSea5 forecasts run with two different land surface initial conditions (IC) configurations. In one configuration, the IC is prepared using a monthly land surface climatology; in the other configuration, it is based on daily land surface reanalysis. In the other part (b), we used the Indian Institute of Tropical Meteorology's Climate Forecast System (IITM_CFS) model with two different ICs (NCEP and NCMRWF differing in the number of observations over the Indian land region). Both runs indicate a shift in the initial condition, which manifests as displacement error. UKMO and IITM_CFS runs have the same land surface model when the corresponding twin experiments are compared in (a) and (b). Analysis of the initial displacement errors from these runs indicates that improving the realism in the land surface initial conditions can effectively modulate or change the surface meteorological fields in the prediction model during the onset phase. The result shows that the rotational and divergence components of the surface winds differ in the two sets of runs. Results also indicate that the difference in surface initialization manifests as differences in rotational and divergent kinetic energy. This could lead to a difference in the forecast of monsoon onset rain. Further analysis also suggests that the local land surface initial condition error, in addition to an error in large‐scale teleconnections, affects the monsoon onset forecast and its prediction skill in the extended‐range time‐scale.

What influences on their professional development do general practice trainees report from their hospital placements? A qualitative study

BackgroundThe clinical learning environment is important in GP specialty training and impacts professional development. Uniquely for GP trainees, about half of their training periods occur in a hospital environment, which is not their final workplace. There is still little understanding of how hospital-based training influences GP's professional development.ObjectivesTo seek the views of GP trainees on how their hospital experience contributes to their professional development as a GP.MethodsThis international and qualitative study seeks the views of GP trainees from Belgium, Ireland, Lithuania, and Slovenia. Semi-structured interviews were performed in the original languages. A joint thematic analysis in the English language resulted in key categories and themes.ResultsFrom the four themes identified, GP trainees were found to experience additional challenges on top of the service provision/education tensions, which are common to all hospital trainees. Despite these, the hospital rotation component of GP training is valued by trainees. A strong finding of our study is the need to ensure that learning from the hospital placements is placed firmly in the context of general practice, e.g. GP placements prior or parallel with the hospital placements, educational activities resourced by GPs during their hospital experience, encouraging hospital teachers to have greater awareness of the educational needs of GPs, including an awareness of their training curriculum.ConclusionThis novel study highlights how hospital placements for GP trainees could be enhanced. Further study could be broadened to recently qualified GPs, which may uncover new areas of interest.

Changes in femoral rollback and rotation with increasing coupling in knee arthroplasty—a biomechanical in-vitro study

BackgroundAfter total knee arthroplasty, 10–30% of patients still complain about knee pain, even after exact positioning of the components. Altered knee kinematics are crucial in this regard.The aim of our study was to experimentally determine the influence of different degrees of component coupling of knee prostheses on joint kinematics during muscle-loaded knee flexion in-vitro.MethodsFemoral rollback and femoral rotation of a standard cruciate retaining (GCR), a posterior stabilized (GPS), a rotational hinge (RSL) and a total hinge (SSL) design of the same series of knee replacement implants (SL-series) of one single manufacturer (Waldemar Link GmbH, Hamburg, Germany) were analyzed and set in relation to the motion of the corresponding native knee in a paired study design. All different coupling degrees were analyzed in the same human knees. To simulate muscle loaded knee flexion, a knee simulator was used. Kinematics were measured with an ultrasonic motion capture system and integrated in a calculated coordinate system via CT-imaging.ResultsThe largest posterior motion on the lateral side was found for the native knee (8.7 ± 7.0 mm), followed by the GPS (3.2 ± 5.1 mm) and GCR (2.8 ± 7.3 mm) implants, while no motion was found for the RSL (0.1 ± 3.0 mm) and the SSL (-0.6 ± 2.7 mm) implants. In contrast, on the medial side, only the native knee showed a posterior motion (2.1 ± 3.2 mm). Regarding femoral external rotation, the only implant where the observed difference did not reach statistical significance when compared to the native knee was the GCR (p = 0.007).ConclusionThe GCR and GPS kinematics closely imitate those of the native joint. Medial femoral rollback is reduced, however, with the joint pivoting around a rotational center located in the medial plateau. Without additional rotational forces, the coupled RSL and SSL prostheses closely resemble each other with no femoral rollback or relevant rotational component. The femoral axis, however, shifts ventrally in both models when compared with their primary counterparts. The positioning of the coupling mechanism in the femoral and tibial component thus can already lead to altered joint kinematics even in prostheses with an identical surface geometry.

Observability-Aware Online Multi-Lidar Extrinsic Calibration

Accurate and robust extrinsic calibration is necessary for deploying autonomous systems which need multiple sensors for perception. In this paper, we present a robust system for real-time extrinsic calibration of multiple lidars in vehicle base frame without the need for any fiducial markers or features. We base our approach on matching absolute GNSS (Global Navigation Satellite System) and estimated lidar poses in real-time. Comparing rotation components allows us to improve the robustness of the solution than traditional least-square approach comparing translation components only. Additionally, instead of comparing all corresponding poses, we select poses comprising maximum mutual information based on our novel observability criteria. This allows us to identify a subset of the poses helpful for real-time calibration. We also provide stopping criteria for ensuring calibration completion. To validate our approach extensive tests were carried out on data collected using Scania test vehicles (7 sequences for a total of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\approx$</tex-math></inline-formula> 6.5 Km). The results presented in this paper show that our approach is able to accurately determine the extrinsic calibration for various combinations of sensor setups.

Propagation dynamics of hybrid-order Poincaré beams in thermal nonlocal media

We study the propagation dynamics of hybrid-order Poincaré (HOP) beams, consisting of two coaxially propagating, orthogonal circularly polarized beams with different topological charges, in a nonlocal medium with thermal nonlinearity. By numerically observing the evolution of beamwidth, isosurface and light intensity with propagation distance, we verify that a HOP soliton with a certain beamwidth ratio can exist only at a proper power ratio. At a fixed propagation distance, the rotation of polarization component of the HOP breather can be controlled linearly by the input power. The polarization of HOP beams is observed as a function of the propagation distance, and the evolution regularity of the polarized rotation angle and ellipticity angle of HOP soliton and HOP breather is summarized.

The modification of bone cut angle and joint line obliquity did not change the tibiofemoral kinematics and stability of knee joint after total knee arthroplasty.

Previous reports using cadaveric knees and musculoskeletal computer simulation have shown that kinematically aligned (KA) total knee arthroplasty (TKA) provides more natural and physiological tibiofemoral kinematic patterns than mechanically aligned (MA) TKA. These reports suggested that the modification of joint line obliquity improve the knee kinematics. This study aimed to determine whether joint line obliquity change the intraoperative tibiofemoral kinematics in TKA candidates with knee osteoarthritis. Thirty consecutive knees with varus osteoarthritis that underwent TKA using a navigation system were evaluated. Two types of trial components were prepared: (1) MA TKA model: component trial in which articulating surface was parallel to the bone cut surface (2) KA TKA model: the femoral component trial, which mimicked the KA TKA method of Dossett et al. was designed 3° valgus and 3° internal rotation to the femoral bone cut surface, and the tibial component trial was designed 3° varus to the tibial bone cut surface. These two trials were set on the same knees during the operation, and the tibiofemoral rotational kinematics and varus-valgus laxity were measured from 0° to 120° of knee flexion using a navigation system. The joint gap was 20 ± 2mm and 3° ± 1° varus in extension and 20 ± 2mm and 3° ± 1°varus in flexion. The differences in femoral component rotation between KA TKA and MA TKA were not statistically significant for any knee flexion angle. The differences in varus-valgus laxity between KA TKA and MA TKA were also not statistically significant for any knee flexion angle. Although the degree of joint line obliquity varies widely in various KA TKA methods, this study, which mimicked the method of Dossett et al. showed that the modification of joint line obliquity did not change the tibiofemoral kinematics and stability of the knee joint in TKA candidates with knee osteoarthritis.

The contribution of perennial fodder crops to the nitrogen balance of agroecosystems in Western Siberia

The article presents the results of experiments obtained in stationary experiments on the basis of grain-fallow and grain-grass crop rotations on meadow-chernozem soil in the Omsk region. The influence of spring wheat precursors (alfalfa of the 3rd year of life and fallow) on individual elements of soil fertility and crop yield has been established. It was revealed that when cultivating spring wheat by fallow in the grain-fallow crop rotation, the nitrogen balance (-28 kg/ha) is negative with an intensity of 66 %. When sowing wheat in grain-grass crop rotation on a layer of perennial grasses, the nitrogen balance is positive (+21.0 kg/ha) and the intensity is 119 %. The favorable effect of the legume component in the crop rotation on the nitrogen regime of the soil significantly increased the yield of spring wheat by 0.5 t/ha in comparison with wheat cultivated in the field crop rotation by bare fallow. Under similar conditions, studies were carried out on irrigated meadowchernozem soil in an eight-field stationary grain-grass crop rotation. The removal of nitrogen by the yield of various perennial grasses, as well as the responsiveness of alfalfa, bromus and sweet clover with productivity parameters to the level of nitrogenphosphorus nutrition, were studied. The current mobilization of nitrogen under these conditions under the vegetative brome without fertilizers was 76 kg/ha. When optimizing the phosphate regime of the soil, this indicator increased to 99 kg/ha. The removal of nitrogen by alfalfa on similar agricultural backgrounds increases due to symbiotically fixed nitrogen, by 89 and 193 kg/ha, respectively, or 2.2 and 2.9 times. Alfalfa and sweet clover responded positively to the improvement of mineral fertilizing conditions (P60N60-160). In alfalfa of the 1-5 year of life the collection of green mass and fodder units increased to 40.56 and 7.00 t/ha, respectively, or by 86 and 54 % relative to the control without fertilizers, with 82.76 GJ of exchange energy per hectare. The productivity of sweet clover of the 2nd year of life increased up to 30.85 t/ha of green mass and 2.83 t/ha of fodder units or by 37 and 17 % relative to the control.

Quantitative identification of pulse-like ground motions based on intrinsic time-scale decomposition technique

Pulse-like earthquake ground motions may cause great seismic demands in engineering structures, and identifying these ground motions is significant in earthquake engineering. The intrinsic time-scale decomposition (ITD) is a self-adaptive time-frequency decompaction method that decomposes signals into proper rotation components. The instantaneous frequency and amplitude of the components are well defined, and the temporal information of frequency and amplitude has the exact resolution with the time-scale of extreme of the original signal. ITD was introduced in this study to decompose the non-stationary earthquake ground motion signals. A procedure for filtering and extracting the low-frequency pulses was constructed, and a quantitative criterion for classifying the pulse-like ground motions was proposed. The proposed method was tested on many ground motions and compared with the existing classification methods. The proposed method was demonstrated as an effective way to identify the pulse-like ground motion records, which can be readily implemented in earthquake engineering practices.

Gap Pattern in Valgus Knee: An Assessment with TKA Navigation

Background: Valgus knee is a challenge of ligament balance in total knee arthroplasty (TKA). A lateral release is often recommended to achieve symmetric extension gaps in valgus deformity, due to the traditional requirements of tight lateral gap. However, the gap pattern valgus osteoarthritis knee has not been studied. Materials and Methods: The present study was a retrospective study on navigated TKA with 89 valgus osteoarthritis knees. The gap measurement, bone cut, and component rotation values were collected from navigation and the data were analyzed. Results: Only 6.70% of valgus knees in the present series had a narrower lateral flexion gap than medial flexion gap and 7.90% had narrower lateral extension gap than medial extension gap. Conversely, most of valgus cases were seen in bigger lateral flexion gaps than medial flexion gaps at 76.4%. This was consistent with the extension gap patterns of 80.9%. The degree of valgus deformity positively correlated with all gaps, except for flexion lateral gap. The present study demonstrated a mean external rotation of 2.25±2.09° in the femoral component rotation and the degree of valgus deformity had no significant correlation with femoral rotation. Conclusion: The lateral distal femoral condyle hypoplasia might have more important role in the extension gap than the ligament tension. The lateral ligament might influence the lateral flexion gap more than the lateral femoral condyle deficiency. Lateral structural release for correction of valgus deformity during extension could lead to instability in flexion especially for gap patterns with a lateral flexion gap that is wider than the medial flexion gap. Keywords: Valgus knee; Navigated TKA; Gap pattern

Bubble-Based Microrobots with Rapid Circular Motions for Epithelial Pinning and Drug Delivery.

Remotely powered microrobots are proposed as next-generation vehicles for drug delivery. However, most microrobots swim with linear trajectories and lack the capacity to robustly adhere to soft tissues. This limits their ability to navigate complex biological environments and sustainably release drugs at target sites. In this work, bubble-based microrobots with complex geometries are shown to efficiently swim with non-linear trajectories in a mouse bladder, robustly pin to the epithelium, and slowly release therapeutic drugs. The asymmetric fins on the exterior bodies of the microrobots induce a rapid rotational component to their swimming motions of up to ≈150 body lengths per second. Due to their fast speeds and sharp fins, the microrobots can mechanically pin themselves to the bladder epithelium and endure shear stresses commensurate with urination. Dexamethasone, a small molecule drug used for inflammatory diseases, is encapsulated within the polymeric bodies of the microrobots. The sustained release of the drug is shown to temper inflammation in a manner that surpasses the performance of free drug controls. This system provides a potential strategy to use microrobots to efficiently navigate large volumes, pin at soft tissue boundaries, and release drugs over several days for a range of diseases.

Setting the Tibial Component Rotation Based on Femoral Landmarks Allows Congruent Knee Kinematics in Robotic-Assisted Medial Unicompartmental Knee Replacement.

The accurate positioning of the prosthetic components is essential for achieving successful results in medial unicompartmental knee arthroplasty (mUKA). The tibial component rotation in image-based robotic-assisted UKA is usually based on tibial bony landmarks matched to the pre-operative CT model. The study aimed to evaluate whether setting the tibial rotation on femoral CT-based landmarks allows congruent knee kinematics. We retrospectively analyzed data from 210 consecutive image-based robotic-assisted mUKA cases. In every case, we set the tibia rotation landmark parallel to the posterior condylar axis and centered it on the trochlea groove defined on the preoperative CT scan. The implant positioning was primarily set parallel to this rotation landmark and then adjusted based on tibial sizes avoiding component over- or under-hang. During surgery, we recorded the knee kinematics under valgus stress to reduce the arthritic deformity. A femoral-tibial contact point was recorded over the entire range of motion and displayed as a tracking profile on the tibia implant. The femoro-tibial tracking angle (FTTA) was then calculated based on a tangent line to the femoro-tibial tracking-points and the difference to the femur-based rotation landmark. In 48% of the cases, we could position the tibia component exactly to the femoral rotation landmark, whereas in 52% of cases, minimal adjustments were made to avoid component's under- or over-hang. The mean tibia component rotation (TRA) with reference to our femur-based landmark was +0.24° (SD ± 2.9°). The femur-based tibia rotation landmark showed a high correspondence to the FTTA with 60% of the cases having less than 1° of deviation. Mean FTTA was +0.7° (SD ± 2.2°). The mean difference between the absolute value of the TRA and the FTTA (|TRA| - |FTTA|) was -0.18° (SD ± 2°). Setting the tibial component rotation based on CT scan femoral landmarks and not on tibial anatomical landmarks is a reliable method to obtain congruent knee kinematics during image-based robotic-assisted medial UKA with less the 2° deviations on average.

Water-Structure-Specific Entropic Dominance in the Filling of Boron Nitride Nanotubes

The filling of nanometer and sub-nanometer channels/tubes with water governs applications ranging from desalination and filtration to nanoscale energy conversion. Here, we report the most nonintuitive entropy-dominated filling of mildly hydrophilic boron nitride nanotubes (BNNTs) with diameters ranging from 0.85 to 1.69 nm. For all the BNNT sizes, water inside the BNNT is more stable than water in the bulk. The factor dictating the favorable nature of the entropy depends on the specific-BNNT-diameter-dictated structure of the water molecules. For example, for the 0.85 nm BNNT, the rotational entropic component dominates due to the presence of a significant fraction of the dangling water OH bonds that do not participate in hydrogen bonding. The fraction of such dangling OH bonds (the average HBs per molecule) decreases (increases) with an increase in the BNNT diameter, leading to a progressively reduced contribution of the rotational entropy. For the 1 nm BNNT, the translational entropic component dominates due to the enhanced in-plane motion of the water molecules caused by the single-file nature of water molecules spanning a significant radial expanse inside the BNNT. For larger BNNTs, translational entropy decreases with an increase in the BNNT diameter, although it remains the dominant factor governing the entropy-driven filling of BNNTs. This favorable translational entropy for larger BNNTs can be associated with (1) the presence of chain-like regions formed by water in 1.13 nm BNNT and (2) the presence of a high specific water volume and reduced number of HBs per molecule (as compared with bulk water) in 1.27, 1.41, 1.55, and 1.69 nm BNNTs.

Identifying elastic wave polarization and bandgaps in periodic solid media

We present a new computational method to accurately identify the elastic wave propagation modes and polarizations in periodic solid structures and metamaterials. The method uses the eigenvectors associated with each propagating wave solution to calculate the contribution of each translational and rotational component of the total mass-in-motion. We use this information to identify the dominant wave propagation mode by defining a relative effective modal mass vector. Then, we associate each wave solution with its correct polarization by defining a polarization factor that quantifies the relative orientation between the wave propagation and lattice motion directions and provides a positive numerical value between 0 (pure S-wave) and 1 (pure P-wave). Further, we suggest a graphical representational scheme for easier visualization of the wave polarization within traditional dispersion plots. To validate the method, we compare our predictions against previously published results for various elastodynamic problems. Finally, we use the proposed method to analyze the effect of various lattice and structural parameter perturbations on the elastic wave propagation and polarized bandgap behavior of a square planar beam lattice. Our analysis reveals the emergence of previously unobserved dynamic characteristics, including various polarized bandgaps, fluid-like behavior, and ultralow-frequency SH- and SV-bandgaps that extend to 0 Hz. Our proposed method provides an alternative computational approach to the typically employed visual mode inspection technique and provides a robust method for analyzing the elastic wave response of periodic solid media.

Quantification of Malalignment and Corrective Osteotomies in Patients With Malunion After Elastic Stable Intramedullary Nailing of Pediatric Forearm Fractures

This study looked at postoperative malunion with restricted function after elastic stable intramedullary nailing (ESIN) in pediatric patients in their childhood or adolescence. The primary objective was to compare the magnitude of the osseous malposition to the healthy opposite side. Second, these individuals were treated with patient-specific surgical instrumentation, and functional outcomes were documented. Patients under the age of 18 at the time of a corrective osteotomy due to a forearm malunion after initial ESIN treatment were included in this study. The healthy contralateral side was used as a reference for preoperative analysis and planning of the osteotomy. Osteotomies were performed using patient-specific guides and the direction and extent of the malunion were compared to the change in range of motion (ROM) after the operation. Fifteen patients met the inclusion criteria at three years after initial ESIN placement, with the most pronounced malposition in the rotational axis. The postoperative function significantly improved by 12° (pre-op: 60°±17; post-op: 72°±10) of pronation and 33° (pre-op: 43°±26; post-op: 76°±13) of supination. There was no correlation between the amount and direction of malformation and the change in ROM. The most noticeable malunion after forearm fractures treated with the ESIN technique is in the rotational direction. Patient-specific corrective osteotomy of pediatric forearm malunion following forearm fracture fixation with ESIN achieves significant improvement in forearm range of motion. The findings are clinically relevant since forearm fractures are the most common pediatric fracture, affecting a large number of patients who can benefit from the findings of this study. It has the potential to raise awareness of the significance of the accurate rotational component of intraoperative bone alignment in the ESIN procedure.

Knee

The April 2023 Knee Roundup360 looks at: Does bariatric surgery reduce complications after total knee arthroplasty?; Mid-flexion stability in total knee arthroplasties implanted with kinematic alignment: posterior-stabilized versus medial-stabilized implants; Inflammatory response in robotic-arm-assisted versus conventional jig-based total knee arthroplasty; Journey II bicruciate stabilized (JII-BCS) and GENESIS II total knee arthroplasty: the CAPAbility, blinded, randomized controlled trial; Lifetime risk of revision and patient factors; Platelet-rich plasma use for hip and knee osteoarthritis in the USA; Where have the knee revisions gone?; Tibial component rotation in total knee arthroplasty: CT-based study of 1,351 tibiae.

Curve-on-curve technique does not improve tibial coverage in total knee arthroplasty in comparison to tibial tuberosity technique with use of anatomical implants: randomized controlled trial

IntroductionDuring the last years, main attention while performing total knee replacement was paid to femoral component alignment; however, there is still lack of studies concerning tibial baseplate rotational alignment, especially in terms of anatomical designs of knee prosthesis. Some recent studies proved that tibial baseplate malrotation might be a cause of knee pain and patients’ dissatisfaction. The aim of this study was to compare tibial component rotation and its coverage on the tibial plateau achieved with curve-on-curve and tibial tuberosity techniques (t-t technique) with use of anatomic knee designs with asymmetric tibial baseplate.Materials and methodsA total of 88 patients were randomly assigned in a 1:1 ratio to undergo total knee arthroplasty with use of the PERSONA PS (Zimmer Biomet) knee design with an asymmetric baseplate. The rotation of the tibial component was assessed and performed with two different techniques: curve-on-curve technique and tibial tuberosity technique. Tibial component rotation was measured on computed tomography (CT) scans using the method suggested by Benazzo et al. and designed for asymmetrical implants. For the measurement of the tibial bone coverage, the component surface area was outlined and measured on a proper CT section, then the tibial cut surface area was outlined and measured on a section just below the cement level. Pre- and post-operative range of motion was measured by another independent researcher 12 months post-operatively during follow-up visit.ResultsThere was a statistically significant difference between both groups in median value of tibial rotation angle: 7° (interquartile range (IQR) = 0–12) in curve-on-curve technique group vs 2° (IQR-1–7) in tibial tuberosity technique group, probability value (p) = 0.0041, with values above 0 meaning external rotation of the component. There was no statistically significant difference between both groups in terms of range of motion (ROM) with average values of 124.3° ± 13.0° for curve-on-curve technique and 125.6° ± 12.8° for t-t technique with p = 0.45. There was a statistically insignificant difference between both groups in terms of coverage percentage in slight favor for curve-on-curve technique (85.9 ± 4.2 vs 84.5 ± 4.8, p = 0.17).ConclusionIn this study, no difference between the groups in terms of tibial bone coverage and range of motion was proved, even though both techniques differed significantly with values of tibial rotation. Future studies should be focused on influence of specific values of tibial rotation on patient-reported outcomes and survivorship of anatomic knee implants.

Mobile bearing orbit on the tibial component in Oxford unicompartmental knee arthroplasty

PurposeTo evaluate the bearing orbit of the tibial component during extension–flexion motion in Oxford unicompartmental knee arthroplasty. Materials and methodsA total of 32 knees in 25 patients with medial osteoarthritis who underwent Oxford unicompartmental knee arthroplasty were evaluated. The distance between the vertical wall of the tibial component and the bearing (wall-bearing distance) and that between the anterior edge of the tibial component and the bearing (sagittal bearing position) were measured at 0°, 30°, 60°, 90° and 120° knee flexion with neutral tibial rotation (extension–flexion motion), and internal and external tibial rotation with 90° knee flexion (tibial rotation motion). A custom-made rounded trial bearing and caliper were used for this measurement. We calculated the wall-bearing distance, change in extension–flexion motion and tibial rotation motion. Wall-bearing distances and change in wall-bearing distance were compared using ANOVA or t-test. ResultsThe wall-bearing distance was smallest at 60° and increased 1.0 ± 1.1 mm in knee extension and 1.1 ± 1.5 mm in knee flexion. The bearing moved posteriorly with knee flexion, and the sagittal bearing position increased by 8.1 ± 3.4 mm during extension–flexion motion. Consequently, the bearing moved in a rough C-shaped orbit of the tibial component. ConclusionsThe mobile bearing moves in a rough C-shape and is mostly close to the vertical wall of the tibial component at 60°. The wall-bearing distance can change during extension–flexion motion and might be influenced by tibial component rotation. To avoid bearing separation from or contact with the vertical wall that may cause bearing dislocation, the wall-bearing distance should be evaluated before keel slot preparation.

Design and Modeling Framework for DexTeR: Dexterous Continuum Tensegrity Manipulator

AbstractThe field of tensegrity faces challenges in design to facilitate efficient fabrication, and modeling due to the antagonistic nature of tension and compression elements. The research presents design methodology, and modeling framework for a human-spine inspired Dexterous continuum Tensegrity manipulatoR (DexTeR). DexTeR is a continuum manipulator that comprises of an assembly of “vertebra” modules fabricated using two curved links and 12 strings, and actuated using motor-tendon actuators. The fabrication methodology involves the construction of the equivalent graph of the module and finding the Euler path that traverses every edge of the graph exactly once. The vertices and edges of the graph correspond to the holes and strings or links of the mechanism. Unlike traditional rigid manipulators, the design results in centralization of the majority of the weight of the actuators at the base with negligible effect on the manipulator dynamics. For the first time in literature, we fabricate a tensegrity manipulator that is assembled using ten modules to conceptually validate the time and cost efficiency of the approach. A dynamic model of a vertebra module is presented using the Euler–Newton approach with screw theory representation. Each rigid link is represented using a screw, a six-dimensional vector with components of angular rotation, and linear translation. The nonlinearity in the system arises from the discontinuous behavior of the strings and the “closed-chain” nature of the mechanism. The behavior of the strings is piece-wise continuous to model their slack, compliant, or tension states.

Grid-based state space exploration for molecular binding

Binding processes are difficult to sample with molecular dynamics (MD) simulations. In particular, the state space exploration is often incomplete. Evaluating the molecular interaction energy on a grid circumvents this problem but is heavily limited by state space dimensionality. Here, we make the first steps towards a low-dimensional grid-based model of molecular binding. We discretize the state space of relative positions and orientations of the two molecules under the rigid body assumption. The corresponding program is published as the Python package molgri. For the rotational component of the grids, we test algorithms based on Euler angles, polyhedra and quaternions, of which the polyhedra-based are the most uniform. The program outputs a sequence of molecular structures that can be easily processed by standard MD programs to calculate grid point energies. We demonstrate the grid-based approach on two molecular systems: a water dimer and a coiled-coil protein interacting with a chloride anion. For the second system we relax the rigid-body assumption and improve the accuracy of the grid point energies by an energy minimization. In both cases, oriented bonding patterns and energies confirm expectations from chemical intuition and MD simulations. We also demonstrate how analysis of energy contributions on a grid can be performed and demonstrate that electrostatically driven association is sufficiently resolved by point-energy calculations. Overall, grid-based models of molecular binding are potentially a powerful complement to molecular sampling approaches, and we see the potential to expand the method to quantum chemistry and flexible docking applications.