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PubMedDate not supplied

Older adults use mental representations that reduce cognitive load: mental rotation utilizes holistic representations and processing.

Thirty-two participants (16 younger adults, mean age of 18, and 16 older adults, mean age of 70) were examined to determine whether older adults adopt mental representations and processes that are less taxing on the cognitive system. Specifically, they were asked to mentally rotate a variety of images with different levels of complexity to examine whether they mentally rotate stimuli holistically or piecemeal; that is, whether they rotate the image as a single undifferentiated unit or as a collection of segments that are connected together to form the image. Using analysis of variance (ANOVA) the authors observed that younger adults found the more complex images harder to rotate, whereas the older adults rotated the complex images with the same effort as the simple images. The data reflected that older adults used holistic representations and processing in visual mental rotation. This information-processing schema reduces the use of cognitive resources as its underpinning because it is less computationally intensive. Furthermore, such a schema is more robust because it is not dependant or affected by the complexity of the image. The younger adults used piecemeal representations and processing. In contrast to the holistic strategy, the piecemeal schema is more volatile because it entails that the demands on the cognitive system vary with different images.

Adolescent↗
PubMed1994

Recording orthopedic jaw movements. Part IV: The rotational component during mastication.

The recording and analysis of mastication provides information on neuromuscular engrams, and hence avoidance mechanisms. Avoidance mechanisms are pathologic movement patterns which are developed to avoid occlusal interferences during functional movements. Evaluation of hinge-axis rotation permits selective quantitative analysis of a complex movement pattern. The objective of this study was to determine the amount of hinge axis rotation in mastication using computerized axiography. Furthermore, the distance of the condyles from reference position (RP) at maximum rotation was evaluated and the chronological sequence of translation and rotation was investigated. The mean value for the rotational angle of the mandible (gamma) during mastication was 14.1 degrees in the volunteers and 13.44 degrees in the patients. The linear spatial distance from RP amounted to a mean of 6.57 mm on the right side and 6.21 mm on the left in the volunteers. In the patients, the measurements were 6.33 mm on the right side and 6.7 mm on the left. In most cases, maximum rotation did not correspond with maximum translation. The chronological sequence of maximum excursion was not constant.

Adolescent↗
PubMed2006

Tissue growth in a rotating bioreactor. Part I: mechanical stability.

We develop mathematical models to provide insights into the morphology of a tissue construct formed from a single-cell suspension in culture media, within a rotating bioreactor. The bioreactor consists of a cylindrical vessel of circular cross-section rotating about its longitudinal axis with constant angular speed. Experimental studies show that at rotation rates below a critical value, the cells 'self-assemble' to form smooth 'nodules' that are approximately cylindrical with elliptical cross-section; however, at rotation rates above a critical value, an amorphous construct forms with a highly irregular boundary. The construct is denser than the surrounding culture media and histological studies indicate that the interior of the construct, which is a mix of apoptotic cells and culture media, is surrounded by an outer rim of proliferating cells and collagen. The construct is modelled as a viscous fluid drop surrounded by an extensible membrane in a (less dense) immiscible viscous fluid within a rotating bioreactor. We consider both thin-disk and slender-pipe bioreactors for which the aspect ratio, L(*)/a(*) (where L(*) and a(*) are the bioreactor length and radius, respectively), is small and large, respectively, and obtain a series of spatially 2D problems (independent of the axial coordinate). We then examine the hypothesis that the construct morphology is a result of the mechanical forces that it experiences by considering the interfacial stability of an initially circular fluid-fluid interface to small-amplitude, oscillatory perturbations. The instability is driven by the density difference between the two fluids, and we investigate the effect of the rotation rate, the (time-dependent) gravitational field, and the material and geometrical properties of the system on the stability properties.

Algorithms↗
PubMed1986

Documentation of medial rotation accompanying shoulder flexion. A case report.

We dissected a fresh cadaver to determine which glenohumeral structures causes medial rotation of the humerus during flexion in the sagittal plane. All structures associated with both shoulders were dissected thoroughly. Both elbows were disarticulated to expose the distal end of each humerus to be used as measurement landmarks. We used a universal goniometer for measurements of shoulder flexion. To determine which structures cause passive medial rotation, the associated shoulder muscles, ligaments, and the capsule were individually reflected from the humerus. Passive shoulder flexion to the point where medial rotation started was measured after each structure was resected. The end passive glenohumeral flexion without rotation was 60 degrees after reflection of all musculature and other periarticular shoulder structures. Our results support Steindler's conclusion that during flexion of the humerus beyond the horizontal there is forced rotation caused by ligamentous tension. We also found that the bony configuration of the glenohumeral joints also plays an important role in medial rotation accompanying shoulder flexion.

Biomechanical Phenomena↗
PubMed1994

Azimuth errors in pointing to remembered targets under extreme head rotations.

Errors in pointing to remembered target locations in 3-D space were studied when subjects were free to move their heads, and when they rotated their heads to the extreme right or left. Relative to pointing when the head was free to move, head rotations to the right shifted the final position of the responding arm to the left, whereas head rotations to the left shifted the final position of arm to the right. Horizontal rotation of the head had no systematic influence on elevation and radial distance errors. The influence of head rotations on pointing errors may be mediated by small shifts in the internal representation of external space, shifting the presentation of space in the opposite direction of the head rotation.

Adult↗
PubMed1997

Induction of periodic alternating nystagmus in intact goldfish by sinusoidal rotation.

During movement, the vestibulo-ocular reflex (VOR) normally maintains retinal image stability by making slow-phase eye rotations that counterbalance head rotations. These eye rotations are nystagmic when the on-going slow-phases are interrupted by fast-phase eye rotations that reset eye position. Periodic alternating nystagmus (PAN) is an eye-movement disorder characterized by uncontrollable nystagmus that alternates direction roughly sinusoidally (at about 0.005 Hz). PAN has been observed only in humans with cerebellar disorders and in monkeys with lesions to the cerebellar nodulus and uvula. We show experimentally in intact goldfish that prolonged rotation in darkness for 1 h at specific frequencies (0.05-0.1 Hz) induces PAN, upon which the normal VOR response is superimposed. We show computationally that rotation-induced PAN may result from decreased cerebellar inhibition of VOR brain stem neural pathways.

Animals↗
PubMed1996

Effect of rotation on periprosthetic bone mineral measurements in a hip phantom.

The effect of rotation on the measurement of periprosthetic bone mineral content and bone mineral density using dual energy xray absorptiometry was studied in 9 anatomic specimen femora implanted with noncemented titanium hip prostheses. An apparatus was constructed to permit accurate femoral rotation through an arc of 30 degrees internal to 30 degrees external rotation in 5 degrees increments. Two scans were obtained at each increment of rotation for a total of 26 scans for each implanted femur. Change in bone mineral content and bone mineral density was measured for each of 7 contiguous periimplant regions (Gruen zones). The precision of the paired bone mineral density measurements was 1.7%. In all Gruen zones, the means of bone mineral content and bone mineral density measurements varied within 5% between 15 degrees internal and 15 degrees external rotation. Variation in limb rotation, as might occur with temporal studies of periimplant bone remodeling, can be tolerated within easily controllable limits without excessive error in bone mineral measurements.

Absorptiometry, Photon↗
PubMed2000

Rotational malalignment of the femoral component in total knee arthroplasty.

Ligamentous balancing is a crucial part of total knee arthroplasty. To ensure proper kinematics, balance must be achieved in flexion and extension. Failure to do so may result in limited range of motion, premature polyethylene wear, or patellofemoral tracking problems. Balancing in extension is dependent on the type and extent of correctional ligamentous release. Flexion balance is dependent on proper femoral rotation. There are two methods to determine femoral rotation. In the classic method, the knee is tensed in flexion after ligamentous release in extension. The anteroposterior cut then is made parallel to the cut tibial surface. Alternatively, the anteroposterior cut can be based off fixed femoral landmarks. The purpose of the current study was to determine the variance between balancing the flexion gap with the classic method versus the technique of using fixed femoral landmarks to determine rotation. One hundred consecutive posterior stabilized knee arthroplasties were performed using the classic method. The resected posterior condyles in each case were measured. The actual difference between the resected condyles using the classic method was compared with the calculated difference of resected bone using bony landmarks to determine rotation. A variance analysis then was performed. Compared with classically balanced knees, rotational errors of at least 3 degrees occurred in 45 % of patients when rotation was determined from fixed bony landmarks. These patients had trapezoidal rather than rectangular flexion gaps. Such errors may have implications regarding polyethylene wear, range of motion, and long-term clinical results.

Arthroplasty, Replacement, Knee↗
PubMed2001

Mobility and contact mechanics of a rotating platform total knee replacement.

Despite their increasing clinical use, mobile-bearing total knee replacements have not been well characterized biomechanically. An experimental and finite element analysis was done to assess the mobility and contact mechanics of a widely used rotating platform total knee replacement. Parameters that varied were axial load, condylar load allocation, flexion angle, and static versus dynamic loading. Similar results from the physical model and finite element model lend credence to the validity of the findings. The torque required to initiate rotation (static torque) was greater than that to sustain rotation (dynamic torque). At four times body weight axial load, peak resisting torque measured was 9.47+/-0.61 and 5.51+/-0.38 N-m, for static and dynamic torque, respectively. A 60-40 condylar load allocation produced slightly less resisting torque than the 50-50 load. For all practical purposes, the polyethylene insert rotated simultaneously with the femoral component, leading to maintenance of high contact area, desirable behavior clinically. Walking cycle simulations produced a total axial rotation range of motion of 6 degrees. The high frictional torques observed at the mobile interface may explain why a percentage of these mobile-bearings fail to rotate under routine functional load.

Biomechanical Phenomena↗
PubMed2002

Bone anatomy and rotational alignment in total knee arthroplasty.

The purpose of the current study was to investigate the bone anatomy in determining the rotational alignment in total knee arthroplasty using computed tomography. Axial images of 109 knees in 83 patients with varus osteoarthritis who had total knee arthroplasty were analyzed. On the images of the distal femur and the proximal tibia, a baseline for the anteroposterior axis of each component was drawn based on the epicondylar axis for the femur and the medial (1/3) of the tibial tuberosity for the tibia. The angle between these two lines was analyzed as the rotational mismatch between the components when they were aligned to the anatomic landmarks of each bone. Fifty-four knees (49.5%) had an angle of 5 degrees or greater and 13 knees (11.9%) had an angle of 10 degrees or greater. There was a tendency to align the tibial component in external rotation relative to the femoral component. The results indicated that the landmarks of each bone were the intrinsic cause of the rotational mismatch in knees with varus osteoarthritis. Surgeons doing total knee arthroplasties should be aware of this and check the rotational mismatch between the components. When it is present, the tibial component should be realigned to match the femoral component rotation to minimize problems caused by the mismatch.

Aged↗
PubMed2003

Anatomy of the posterior rotator interval: implications for cuff mobilization.

Release of the posterior rotator interval between the supraspinatus and infraspinatus tendons may be necessary to obtain appropriate mobilization for an anatomic rotator cuff repair. Ten cadaver shoulders were dissected to expose the region between the infraspinatus and supraspinatus from the spinoglenoid notch to the greater tuberosity. Measurements were made from the spinoglenoid notch to the glenoid rim, the glenoid rim to the confluence of the supraspinatus and infraspinatus musculotendinous junction, and from the confluence of the tendons to the insertion on the humerus. The histologic features of the posterior rotator interval were examined. The posterior rotator interval is a clear structure, consisting of the glenohumeral capsule medially, which fuses with the supraspinatus and infraspinatus tendons laterally. The average length of the posterior rotator interval was 77.8 mm which includes the distance from the spinoglenoid notch to the glenoid rim (25 mm; standard deviation, 2.89 mm; range, 21-28 mm), from the glenoid to the tendon confluence (25 mm; standard deviation, 1.95 mm; range, 21-28 mm), and from the tendon confluence to insertion (28 mm; standard deviation, 2.36 mm; range, 24-31 mm). Release of the posterior rotator interval can be important to realign the supraspinatus tendon if it is retracted and scarred at its posterior edge.

Arthroscopy↗
PubMedDate not supplied

Freedom of acetabular fragment rotation following three surgical techniques for correction of congenital deformities of the hip.

Femoral head coverage achieved with an acetabular osteotomy for hip dysplasia is achieved by acetabular rotation that can be restricted by osteotomy orientation and soft tissue attachments to the acetabular fragment. Procedures that allow excess rotation or motion in an undesirable direction (especially external rotation) may have undesirable consequences. Rotational aspects of these procedures have not been well described and are not well appreciated radiographically. This study examined the angular motion related to three operative techniques for redirectional acetabular osteotomies. The freedom of motion allowed for the Ganz periacetabular, Carlioz triple, and Tonnis triple osteotomies was quantified using three-dimensional motion measurement. The Ganz osteotomy allowed the greatest amount of motion. The Carlioz osteotomy allowed statistically less motion and depicted the "coupled motion" phenomenon in which a maximal angular rotation in one plane (abduction) is associated with a predicted angular change in another plane (external rotation). The Tonnis osteotomy allowed freedom of motion similar to the Ganz osteotomy without coupled motion.

Acetabulum↗
PubMedDate not supplied

Rotator cuff interval: evaluation with MR imaging and MR arthrography of the shoulder in 32 cadavers.

PURPOSE: The purpose of this work was to establish the optimal means of evaluation of the rotator cuff interval (RCI) and rotator interval capsule and demonstrate normal anatomy of the RCI using MR imaging and MR arthrography. METHOD: MR arthrography was performed in 32 cadaveric shoulders. In 20 cases, MR imaging was completed prior to arthrography. Pre- and postarthrography studies included standard imaging planes. Images were evaluated by the consensus of two musculoskeletal radiologists with attention to the RCI, rotator interval capsule (measurements on postarthrographic studies), and crossing structures. In five cases, specialized imaging planes were performed after arthrography. RESULTS: The RCI, rotator interval capsule, and crossing structures were best evaluated by MR arthrography. The anteroposterior dimension of the rotator interval capsule could be best depicted on postarthrogram images. CONCLUSION: MR arthrography, with both standard and specialized imaging planes, is a useful way to evaluate the RCI, the rotator interval capsule, and its crossing structures.

Aged↗
PubMed1991

Rotation of load during the prelift period.

Lifting is a major source of back injuries because of the mechanical effects on the spinal structures. A number of methods are known by which a lifter can reduce the load on the spine during lifting. This study explores an additional method: rotation of the load before it is actually lifted off the ground. The hypothesis tested is that when a lifter lifts a box, he or she rotates it before it leaves the floor. By the use of an optoelectronic system to study weight box rotation, it was established that rotation occurs in every lift before the actual lift occurs. Rotation time increased with increasing load, indicating that the rotation technique is more important when load reduction is most critical.

Adult↗
PubMed1992

Instantaneous axis of rotation as a function of the three columns of the spine.

A knowledge of the rotatory motion of the vertebral bodies is needed to understand the normal biomechanical behavior of the spine. The aims of this investigation were 1) to define the instantaneous axis of rotation of the lumbar spine in rotation; and 2) to study the effect of the loss of the anulus, facet joints, and ligamentous structures on the location of the instantaneous axis of rotation. The instantaneous axis of rotation was found in 10 human cadaver thoracolumbar spines by the method of Reuleaux from superimposed serial photographs. Long-segment specimens were tested to minimize the effect of the imposed axis of the testing device. The instantaneous axis of rotation was consistently posterior to the anulus in the intact spine. With isolated destruction of the columns of the spine, the instantaneous axis of rotation migrated to the remaining intact structures. Anterior releases enhance derotation by removing the primary rotatory stabilizer. Ultimate control of a rotatory deformity or instability lies in the recognition that the anterior structures have a mechanical advantage in resisting torsion.

Biomechanical Phenomena↗
PubMed1992

A comparative study of computed tomographic and plain radiographic methods to measure vertebral rotation in adolescent idiopathic scoliosis.

A comparative analysis of two methods of measuring vertebral rotation in adolescent idiopathic scoliosis is reported in this article. Nash and Moe's pedicle shift method (using plain anteroposterior radiographs) is compared with a new method using computed tomographic scans. The computed tomographic scans of the whole length of the major curve and the scout films obtained from seventeen girls aged 12.5-14 years were measured for rotation of each vertebra of the curve (total number of vertebrae measured by two methods = 173). This study has three interesting new findings: 1) Those vertebrae with Nash & Moe grade 0 had up to 11 degrees of vertebral rotation when measured using the computed tomographic method. Therefore, Nash & Moe's grade '0' is not a neutrally rotated vertebra; 2) For Nash & Moe grade 1 and 2, the computed tomographic method revealed statistically significantly greater rotation for lumbar vertebrae than thoracic vertebrae. There was a similar pattern for Nash & Moe grade 0 but these differences were not statistically significant; and 3) Simple formulae are reported to convert Nash & Moe's grades into angle of vertebral rotation as obtained by CT method separately for thoracic and lumbar vertebrae.

Adolescent↗
PubMed1992

Changes in vertebral rotation after Harrington and Luque instrumentation for idiopathic scoliosis.

This study was carried out to analyze the three-dimensional and in particular the rotational correction obtained after spine instrumentation for idiopathic scoliosis. Preoperative and postoperative radiographs and computed tomographic scans with single axial cuts through each vertebral level were obtained for 14 patients: 4 Harrington, 7 Luque, and 3 Harrington-Luque. Rotation of vertebrae relative to the spinal axis and rotation between vertebrae (segmental rotation) were measured from computed tomographic scans of instrumented and uninstrumented segments. The derotation and changes occurring after surgery were calculated. Before operation, rotation was maximal at the apex, and close to 0 at the end vertebra; segmental rotation was greatest at the end of the curve, and minimal at the apex. After Harrington instrumentation the apical vertebrae showed a median derotation of 16%, after Luque instrumentation it was 12% and after Harrington-Luque instrumentation it was 13%. Segmental derotation did not uniformly occur. Major derotation was obtained at the end vertebrae and 39% of the total derotation occurred outside of the instrumented levels of the spine.

Adult↗
PubMed1996

Effects of posture and structure on three-dimensional coupled rotations in the lumbar spine. A biomechanical analysis.

STUDY DESIGN: A biomechanical lumbar spine model was constructed to simulate three-dimensional spinal kinematics under the application of pure moments. Parametric analysis of the model allowed for the estimation of how much of the coupled motions could be predicted by the lumbar lordosis and the intrinsic mechanical properties of the spine. OBJECTIVES: To evaluate the relative effects of lordosis and intrinsic mechanical spine properties on the magnitude and direction of coupled rotations. SUMMARY OF BACKGROUND DATA: Clinical evidence suggests that abnormal coupled motion in the lumbar spine may be an indicator of low back disorders. METHODS: The biomechanical lumbar spine model consisted of five vertebrae separated by intervertebral joints that provided three rotational degrees of freedom. In vitro experimental data, obtained from nine fresh-frozen (L1-S1) cadaveric specimens, were used to establish the mechanical properties of the intervertebral joints. Two different submodels were considered in simulating the three-dimensional intervertebral rotations in response to the applied moments. In the first, it was assumed that the coupled motions were generated solely as a result of the vertebral orientation caused by lordosis. In the second, additional intrinsic motion coupling was assumed. RESULTS: Intervertebral coupling was partially predicted by lumbar lordosis; however, the inclusion of intrinsic mechanical coupling dramatically improved the simulation of the intervertebral rotations (root mean square error < 1 degree). Comparison of the results from the two models demonstrated that the lumbar lordosis and intrinsic mechanical properties of the spine had about an equal effect in predicting the coupling between axial rotation and lateral bending. In contrast, coupled flexion, associated with lateral bending, was almost fully accounted for by the presence of lumbar lordosis. CONCLUSIONS: The lumbar lordosis and intrinsic mechanical properties of the spine were equally important in predicting the magnitude and direction of the coupled rotations.

Adult↗