Least Amount Of Motion Research Articles

Reducing VR Sickness by Directing User Gaze to Motion Singularity Point/Region as Effective Rest Frame

Simulation sickness is one major obstacle in proliferation of virtual reality. The sensory mismatch between the visual and vestibular senses about user motion is attributed as the main cause. One effective method has been the use of the rest frame, which refers to the reference object that remains fixed in position with respect to the user. A popular choice of the rest frame is the virtual nose, but it can direct one’s attention away from the main part of the navigation content. We propose to instead use the area within the screen space that represents the least amount of motion in the navigation content, called the Motion Singularity Point/Region (MSP/R) as such a rest frame. Viewing such a region is thus expected to reduce the sensory conflict and ensuing sickness. Such a region can be found by analyzing the content with respect to motion and estimating the region(s) of the image space with the least relative amount of the total optical flow. We experimentally validated the VR sickness reduction effect of looking at the MSP/R compared to that of the virtual nose. In addition, we confirmed that the content agnostic MSP/R to be much coinciding with the user’s natural viewing direction, making it less distracting from the main content. This makes the MSP/R a more practical and viable rest frame object for sickness reduction than e.g. the virtual nose.

Pelvic stability during simulated total hip arthroplasty motions: Comparing different hip positioners

IntroductionTotal hip arthroplasty (THA) requires forceful maneuvers that can cause the pelvis to shift from its original position. Various methods for stabilizing the pelvis in the lateral decubitus position exist, but there is limited data quantifying the relative stability of each hip positioner. We sought to quantify the pelvic movement that occurred in four commercially available hip positioners during surgeon induced motion of the hip. MethodsAn infrared marker was attached to the ilium of a cadaver secured in the lateral decubitus position. Four commercially available hip positioners were used for positioning: Beanbag, Pegboard, Stulberg, and ExactFit. Rotation and translation was captured using an infrared marker and camera system while the hip was moved through six motions (Flexion, Extension, Internal Rotation, External Rotation, Push, and Pull). ResultsThe Beanbag had the greatest amount of rotation and translation of the pelvis, with maximum hip rotation of 41.5°. The Stulberg and Pegboard positioners showed intermediate stability, with a maximum rotation of 7.8° and 17.1°, respectively. The ExactFit hip positioner resulted in the least amount of motion of the pelvis, with a maximum rotation of the pelvis of up to 3.2°. Of the simulated motions performed, internal rotation and flexion of the hip led to the greatest changes in pelvic rotation and translation. ConclusionThe ExactFit positioner was associated with the smallest amount of pelvic motion during simulated motions of hip arthroplasty, followed by the Stulberg, Pegboard, and Beanbag positioners. Further studies are required to correlate this information with clinical outcomes following total hip arthroplasty.

Investigating How Smartphone Movement is Affected by Lying Down Body Posture

In this paper, we investigated how "lying down'' body postures affected the use of the smartphone user interface (UI) design. Extending previous research that studied body postures, handgrips, and the movement of the smartphone. We have done this in three steps; (1) An online survey that examined what type of lying down postures, participants, utilized when operating a smartphone; (2) We broke down these lying down postures in terms of body angle (i.e., users facing down, facing up, and on their side) and body support; (3) We conducted an experiment questioning the effects that these body angles and body supports had on the participants' handgrips. What we found was that the smartphone moves the most (is the most unstable) in the "facing up (with support)'' condition. Additionally, we discovered that the participants preferred body posture was those that produced the least amount of motion (more stability) with their smartphones.

Computational modelling of motion at the bone–implant interface after total knee arthroplasty: The role of implant design and surgical fit

BackgroundAseptic loosening, osteolysis, and infection are the most commonly reported reasons for revision total knee arthroplasty (TKA). This study examined the role of implant design features (e.g. condylar box, pegs) and stems in resisting loosening, and also explored the sensitivity of the implants to a loose surgical fit due to saw blade oscillation. MethodsFinite element models of the distal femur implanted with four different implant types: cruciate retaining (CR), posterior stabilising (PS), total stabilising (TS) with short stem (12mm×50mm), and a total stabilising (TS) with long stem (19mm×150mm) were developed and analysed in this study. Two different fit conditions were considered: a normal fit, where the resections on the bone exactly match the internal profile of the implant, and a loose fit due to saw blade oscillation, characterised by removal of one millimetre of bone from the anterior and posterior surfaces of the distal femur. Frictional interfaces were employed at the bone–implant interfaces to allow relative motions to be recorded. ResultsThe results showed that interface motions increased with increasing flexion angle and loose fit. Implant design features were found to greatly influence the surface area under increased motion, while only slightly influencing the values of peak motion. Short uncemented stems behaved similarly to PS implants, while long canal filling stems exhibited the least amount of motion at the interface under any fit condition. ConclusionIn conclusion, long stemmed prostheses appeared less susceptible to surgical cut errors than short stemmed and stemless implants.

Does Lumbopelvic Fixation Add Stability? A Cadaveric Biomechanical Analysis of an Unstable Pelvic Fracture Model.

We sought to determine the role of lumbopelvic fixation (LPF) in the treatment of zone II sacral fractures with varying levels of sacral comminution combined with anterior pelvic ring (PR) instability. We also sought to determine the proximal extent of LPF necessary for adequate stabilization and the role of LPF in complex sacral fractures when only 1 transiliac-transsacral (TI-TS) screw is feasible. Fifteen L4 to pelvis fresh-frozen cadaveric specimens were tested intact in flexion-extension (FE) and axial rotation (AR) in a bilateral stance gliding hip model. Two comminution severities were simulated through the sacral foramen using an oscillating saw, with either a single vertical fracture (small gap, 1 mm) or 2 vertical fractures 10 mm apart with the intermediary bone removed (large gap). We assessed sacral fracture zone (SZ), PR, and total lumbopelvic (TL) stability during FE and AR. The following variables were tested: (1) presence of transverse cross-connector, (2) presence of anterior plate, (3) extent of LPF (L4 vs. L5), (4) fracture gap size (small vs. large), (5) number of TI-TS screws (1 vs. 2). The transverse cross-connector and anterior plate significantly increased PR stability during AR (P = 0.02 and P = 0.01, respectively). Increased sacral comminution significantly affected SZ stability during FE (P = 0.01). Two versus 1 TI-TS screw in a large-gap model significantly affected TL stability (P = 0.04) and trended toward increased SZ stabilization during FE (P = 0.08). Addition of LPF (L4 and L5) significantly improved SZ and TL stability during AR and FE (P < 0.05). LPF in combination with TI-TS screws resulted in the least amount of motion across all 3 zones (SZ, PR, and TL) compared with all other constructs in both small-gap and large-gap models. The role of LPF in the treatment of complex sacral fractures is supported, especially in the setting of sacral comminution. LPF with proximal fixation at L4 in a hybrid approach might be needed in highly comminuted cases and when only 1 TI-TS screw is feasible to obtain maximum biomechanical support across the fracture zone.

New method for determining apparent axial center of rotation of lumbar and thoracic spine segments

One main question in spinal kinematics is the determination of the spine's apparent axial center of rotation. Previous research on this topic has yielded contradictory results. The objective of this study was to determine the apparent axial center of rotation for seven lumbar and six thoracic spinal segments by developing and validating a new method. A custom six-degree-of-freedom device, allowing full range of motion, was used with motion recording and analysis software. This system tracked a grid of markers on a specimen when rotational torque was applied in both clockwise and counterclock wise directions at 3.53 Nm, 7.05 Nm, 10.58 Nm, and 14.10 Nm. The area encompassing the apparent axial center of rotation was determined by identifying the five markers with the least amount of motion. The marker angular displacement was calculated as the angle between a virtual line drawn between two points in the initial and final torque conditions. Rotation in both directions was averaged. The lumbar and thoracic spinal segments averaged an apparent axial center of rotation at the posterior border of the vertebral endplates and the anterior border of the spinal canal, with average clockwise to counterclockwise angular displacement ratios of 0.87 and 0.97, respectively.

Tibial Insert Micromotion of Various Total Knee Arthroplasty Devices

The objective of this study was to develop a novel method to quantify rotational micromotion of modular tibial components that incorporates physiologic loading conditions, a physiologic test environment, and constraint characteristics of the articulating surface. The methodology is reviewed and data are presented on four total knee designs. Results showed the design with a rotational stabilizing island to demonstrate the most capability in resisting rotational micromotion for a given reacted torque, followed by a full peripheral capture device, then a partial peripheral capture device, and then a full peripheral capture device with a posterior lipped edge. Under walking and stair-climbing loads, the full peripheral capture device imparts more torque to the insert than the other designs due to the higher constraint of its articulating surface and thus experiences the most micromotion. The rotational stabilizing island device reveals the least amount of motion, due to a combination of its locking mechanism and a less constrained articular surface.

Axial and torsional stability of supracondylar femur osteotomies: biomechanical comparison of the stability of five different plate and osteotomy configurations

Little is known regarding the biomechanical stability and stiffness of implants and techniques used in supracondylar femur osteotomies (SCO). Therefore, fixation stability and stiffness of implants to bone was investigated under simulated physiological loading conditions using a composite femur model and a 3D motion-analysis system. Five osteotomy configurations were investigated: (1) oblique medial closing-wedge fixated with an angle-stable implant; (2) oblique and (3) perpendicular medial closing-wedge, both fixated with an angled blade plate; and lateral opening-wedge fixated with (4) a spacer plate and (5) an angle-stable lateral implant. The motion measured at the osteotomy was used to calculate the stiffness and stability of the constructs. The least amount of motion and highest stiffness was measured in the medial oblique closing-wedge osteotomy fixated with the angled blade plate. The lateral opening-wedge techniques were less stable and had a lower stiffness compared with the medial; the oblique saw cuts were more stable and had a higher stiffness than the perpendicular. This experimental study presents baseline data on the differences in the primary stability of bone-implant constructs used in SCO. The data in this study can be used as reference for future testing of SCO techniques. Furthermore, it is recommended that based on the differences found, the early postoperative rehabilitation protocol is tailored to the stability and stiffness of the fixation method used.

Respiratory phase-correlated micro-CT imaging of free-breathing rodents

We provide a dedicated phase-correlated imaging procedure for respiratory gating in micro-CT imaging with automatic detection of the optimal data window providing the least amount of motion blurring. A rawdata-based motion function (kymogram) was used for synchronization purposes and for identification of the optimal data window used for phase-correlated image reconstruction. Measurements were performed on a dual-source micro-CT scanner. Projection data were acquired over ten rotations for multi-segment phase-correlated reconstruction. Visual assessment was performed on datasets of ten free-breathing subjects. The kymogram approach provided a reliable synchronization signal for phase-correlated image reconstruction. Also, it allowed for the identification of phase intervals of increased and decreased motion and the corresponding detection of the optimal reconstruction phase. Phase-correlated images showed a strong improvement with respect to motion blurring compared to standard image reconstruction. A reconstruction for the calculated optimal data window provided the least amount of motion blurring and even allowed for the assessment of small structures in the lung. The dedicated retrospective phase-correlated image reconstruction procedure for respiratory gating is a feasible approach for motion-free imaging. A subject-specific optimal reconstruction phase can minimize motion blurring and further improve image quality.

Quantification of head motion in children during various fMRI language tasks

Head motion during functional MRI scanning can lead to signal artifact, a problem often more severe with children. However, the documentation for the characteristics of head motion in children during various language functional tasks is very limited in the current literature. This report characterizes head motion in children during fMRI as a function of age, sex, and task. Head motion during four different fMRI language tasks was investigated in a group of 323 healthy children between the age of 5 and 18 years. A repeated measures ANOVA analysis was used to study the impact of age, sex, task, and the interaction of these factors on the motion. Pediatric subjects demonstrated significantly different amounts of head motion during fMRI when different language tasks were used. Word-Picture Matching, the only task that involved visual engagement, suffered the least amount of motion, which was significantly less than in any of the other three tasks; the latter were not significantly different from each other. Further examination revealed that the main effect of language task on motion was significantly affected by age, sex, and their interaction. Our results suggest that age, sex, and task are all associated with the degree of head motion in children during fMRI experiments. Investigators working with pediatric patients may increase their success by using task components associated with less motion (e.g., visual stimuli), or by using this large scale dataset to estimate the effects of sex and age on motion for planning purposes.

Rotational head motion concurrent to rhythmical mandibular opening movements.

We have previously demonstrated the existence of a functional-rhythmical coupling between the head and the mandible using maxillary and mandibular incisal tracking points. However, that data did not provide information neither on the movement of the head as a whole nor on the location of its instantaneous centre of rotation. Thus, the objective of the present study was to determine whether the head undergoes a rotational motion during mouth opening and to locate its putative instantaneous centre of rotation. The same 6 d.f. (degree of freedom) measuring device employed in our previous studies was used again to analyse data from five male adults (age range: 26-29 years old) chosen as subjects. Concomitant head and mandibular movements were assessed in the sagittal plane by allocating several reference points in the head (upper incisor, cranial base, occipital and parietal points) and a mandibular incisor point during maximal mouth open-close movements. Then, the magnitude and inclination of the vectors of motion in each reference point during the opening phase were calculated. The instantaneous centre of rotation was defined as the point showing the least amount of motion in a determined area around each head reference point. The mandibular incisal point and the maxillary incisal point showed concomitant movements; that is, during opening the mandibular point moved downwards and the maxillary incisor point upwards. Making a large jaw opening movement caused an inferior-anterior displacement in the O point, a posterior-inferior displacement of the P point, and an anterior-superior displacement in the C point in all subjects. During jaw closing all points followed a trajectory opposite to that described above. In other words, during opening the head moved clockwise and counter-clockwise during closing, at least in the sagittal plane of the subjects' left side. These results suggest that the head undergoes a rotation-like sagittal movement during mouth opening whose rotation centre seems to be located above the cranial base point, which was set close to the centre of mass of the head. However, its location varies according to the magnitude of mouth opening.

Assessment of exercise-induced minor muscle lesions: the accuracy of Cyriax's diagnosis by selective tension paradigm.

The Cyriax selective tension assessment paradigm is commonly used by clinicians for the diagnosis of soft tissue lesions; however, studies have not demonstrated that it is a valid method. The purpose of this study was to examine the construct validity of the active motion, passive motion, resisted movement, and palpation components of the Cyriax selective tension diagnosis paradigm in subjects with an exercise-induced minor hamstring muscle lesion. Nine female subjects with a mean age of 23.6 years (SD = 4.7) and a mass of 57.3 kg (SD = 10.7) performed two sets of 20 maximal eccentric isokinetic knee flexor contractions designed to induce a minor muscle lesion of the hamstrings. Active range of motion, passive range of motion, knee extension end-feel pain relative to resistance sequence, knee flexor isometric strength, pain perception during knee flexor resisted movement testing, and palpation pain of the hamstrings were assessed at 0, 5, 2, 12, 24, 48, and 72 hours postexercise and compared with Cyriax's hypothesized selective tension paradigm results. Consistent with Cyriax's paradigm, passive range of motion remained unchanged, and perceived pain of the hamstrings increased with resistance testing at 12, 24, 48, and 72 hours postexercise when compared with baseline. In addition, palpation pain of the hamstrings was significantly elevated at 48 and 72 hours after exercise (p < 0.05). In contrast of Cyriax's paradigm, active range of motion was significantly reduced over time (p < 0.05), with the least amount of motion compared to baseline (85%) occurring at 48 hours postexercise. Further, resisted movement testing found significant knee flexor isometric strength reductions over time (p < 0.05), with the greatest reductions (33%) occurring at 48 hours postexercise. According to Cyriax, when a minor muscle lesion is tested, it should be strong and painful; however, none of the postexercise time frames exhibited results that were strong and painful. This study suggests that the validity of using Cyriax's selective tension testing for the diagnosis of exercise-induced minor muscle lesions is questionable.

Compaction and separation algorithms for non-convex polygons and their applications

Given a two-dimensional, non-overlapping layout of convex and non-convex polygons, compaction can be thought of as simulating the motion of the polygons resulting from applied ‘forces’. By moving many polygons simultaneously, compaction can improve the material utilization of even tightly packed layouts. Compaction is hard: finding the tightest layout that a valid motion can reach is PSPACE-hard, and even compacting to a local optimum can require an exponential number of moves. Our first compaction algorithm uses a new velocity-based optimization model based on existing physical simulation approaches. The performance of this algorithm illustrates that these approaches cannot quickly compact tightly packed layouts. We then present a new position-based optimization model. This model represents the forces as a linear objective function, and it permits direct calculation, via linear programming, of new non-overlapping polygon positions at a local minimum of the objective. The new model yields a translational compaction algorithm that runs two orders of magnitude faster than physical simulation methods. We also consider the problem of separating overlapping polygons using the least amount of motion, prove optimal separation to be NP-complete, and show that our position-based model also yields an efficient algorithm for finding a locally optimal separation. The compaction algorithm has improved cloth utilization of human-generated layouts of trousers and other garments. Given a database of human-generated markers and with an efficient technique for matching, the separation algorithm can automatically generate layouts that approach human performance.

Acetabular micromotion as a measure of initial implant stability in primary hip arthroplasty: An in vitro comparison of different methods of intial acetabular component fixation

Micromotion has been shown to affect bony ingrowth into cementless components. This study was designed both to quantitate initial micromotion at the prosthesis-periacetabular bony interface and to compare different methods of commonly employed acetabular component fixations, ie, a press-fit hemispherical titanium cup, a press-fit hemispherical titanium cup with one and two dome screws, a press-fit titanium hemispherical cup with three spikes, and a cemented chromium-cobalt cup. The press-fit component without screws demonstrated the greatest motion equaling 162 μm at the ilium, 97 μm at the pubis, and 54 μm at the ischium. With one and two screws placed into the dome, the mean ileal displacement decreased by 28 μm (17%) and 36 μm (22%), respectively. Dome screw placement demonstrated a minimal effect at the pubis and ischium. Compared to the press-fit component without augmentation, the tri-spike motion was less at the pubis and ischium. The cemented prosthesis provided the least amount of motion in all three areas tested. This experiment demonstrates that the ilium provides the least amount of support to immediate acetabular fixation, while the pubis (anterior column) and ischium (posterior column) provide more stability. One dome screw does not afect the stability of a hemispherical prosthetic cup significantly. A two dome screw fixation provides an added method of support at the ilium, but fails to decrease motion at the pubis or ischium significantly. The tri-spike fixation does not restrict motion at the ilium to the extent as the dome screws, but its effect at the ischium and pubis is much more pronounced. The obvious difference between initial motion seen with cemented versus uncemented components may suggest that before surgery, patients may need a period of protected weight bearing until ingrowth has occurred.

Characterization of “native” apomyoglobin by molecular dynamics simulation

We have used molecular dynamics simulation methods to study the structure and fluctuations of “native” apomyoglobin in aqueous solution for a period of greater than 0.5 nanosecond. This work was motivated by the recent attempts of Hughson et al. to characterize the structure and motion of both this molecule and the less compact, acid stabilized I state, using methods of pulsed H 2 H exchange. The study of these systems provides new insights into protein folding intermediates and our simulation has yielded a detailed model for structure and fluctuations in apomyoglobin which complements the experimental studies. We find that local (short-time) fluctuations agree well with fluctuations observed for the holoprotein in aqueous solution, as well as results from the crystallographic B-factors. In addition, the structural features we observe for native apomyoglobin are very similar to the holoprotein, in basic agreement with the findings of Hughson et al. By examining larger-scale motions, developing only over timescales in excess of a 100 picoseconds, we are able to identify conformationally “labile” and “non-labile” regions within native apomyoglobin. These regions correspond extremely well to those identified in the nuclear magnetic resonance experiments as unstable and stable “'folding subdomains” in the I state of apomyoglobin. Overall we find that helices A, B, E, G and H show the least amount of motion and helices C, D and F move substantially over the timescales examined. The major motions, and the primary difference between the holo and apo structures as we have observed them, are due to the shifting motion of helices C, D and F into the vacant heme cavity. We also find that motions at the interface of helical segments can be large, with one important exception being the chain segment connecting helices G and H. This segment of chain interacts with the conformationally “non-labile” helix A to form a relatively rigid subdomain composed of helices A, G and H. We believe that these findings provide direct support for the suggestion of Hughson et al. that helices A, G and H constitute a compact subdomain that remains in a native-like conformation as the protein begins to unfold in environments of decreasing pH.