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PubMed2000

The relevance of the moment arm of shoulder muscles with respect to axial rotation of the glenohumeral joint in four positions.

OBJECTIVE: This study was undertaken to determine the efficiency of the shoulder girdle muscles during axial humeral rotation based on measurements of the moment arms. DESIGN: The instantaneous muscle moment arms of 10 shoulder muscles, including the three portions of the deltoid, the rotator cuff muscles, teres major, and the thoracohumeral muscle group, were measured during four specified glenohumeral rotations. BACKGROUND: Axial humeral rotation is a commonly performed movement during activities of daily living and is a targeted motion of shoulder rehabilitation, particularly in those protocols emphasizing rotator cuff strengthening. An understanding of the function of the movers and stabilizers of the shoulder requires such basic information of muscle moment arms. METHODS: The instantaneous moment arm values of the muscles were derived from the slope of the plot of tendon excursion versus glenohumeral joint rotation angle. Motion studied included axial rotation with the humerus elevated 90 degrees in the coronal, scapular, and sagittal planes, as well as in the neutral position with the arm at the side. RESULTS: Based on the findings, with the humerus in both neutral and elevated positions, the infraspinatus is potentially the most powerful external rotator, followed by teres minor and posterior deltoid. Subscapularis and possibly pectoralis major are the most effective internal rotators in this position. CONCLUSIONS: The moment arm in providing axial humeral rotation of 10 shoulder muscles in four planes were obtained. In general, the teres minor and infraspinatus had the largest moment arms in external rotation, and the subscapularis had the largest moment arm in internal rotation. The muscle function for axial humeral rotation was found to be modified by the plane of arm elevation. RELEVANCE: The data could be used for developing exercise programs in physical therapy.

Adult↗
PubMed2003

Economics versus alleles: balancing integrated pest management and insect resistance management for rotation-resistant western corn rootworm (Coleoptera: Chrysomelidae).

Western corn rootworm, Diabrotica virgifera virgifera LeConte, has overcome crop rotation in several areas of the central United States. We expanded a simple model of adult behavior and population genetics to explain how rotation resistance may have developed and to study ways to manage the western corn rootworm in a landscape of corn, soybean, and winter wheat where evolution of resistance may occur. We modeled six alternative management strategies over a 15-yr time horizon, as well as a strategy involving a 2-yr rotation of corn and soybean in 85% of the landscape, to investigate their effectiveness from both a biological and economic perspective. Generally, resistance to crop rotation evolves in fewer than 15 yr, and the rate of evolution increases as the level of rotated landscape (selection pressure) increases. When resistance is recessive, all six alternative strategies were effective at preventing evolution of rotation resistance. The two most successful strategies were the use of transgenic rotated corn in a 2-yr rotation and a 3-yr rotation of corn, soybean, and wheat with unattractive wheat (for oviposition) preceding corn. Results were most sensitive to increases in the initial allele frequency and modifications of the density-dependent survival function. Economically, three alternative strategies were robust solutions to the problem, if technology fees were not too high. Repellant soybean, attractive rotated corn, and transgenic rotated corn, all in 2-yr rotations, were economically valuable approaches. However, even the currently common 2-yr rotation was economical when resistance was recessive and the actual costs of resistance would not be paid until far in the future.

Agriculture↗
PubMed2004

Atlantoaxial rotatory fixation: Part 1--Biomechanics of normal rotation at the atlantoaxial joint in children.

OBJECTIVE: Atlantoaxial rotatory fixation (AARF) remains a recondite entity loosely included under the panoply of cervical trauma. The difficulty in finding a precise definition and reliable diagnostic criteria for AARF has been chiefly because of a lack of normative biomechanical data for C1-C2 rotation. As Part 1 and foundation of a comprehensive undertaking to define the biomechanics, mechanism, diagnosis, classification, and management of AARF, the present study focuses on the dynamic behavior of C1 and C2 during normal voluntary head rotation in children. METHODS: Twenty-one normal children 3 to 11.5 years old underwent computed tomographic examinations from the lower clivus to the base of C3 in various head positions during axial rotation. The angles made by C1, C2, and the occiput with the vertical 0 degrees were recorded, and from these, the separation angles between C1 and C2 (C1-C2 degrees) were calculated for each head position (represented by the C1 angle) studied. In 18 children, the range of rotation was between 90 and -90 degrees, i.e., with the head making a full 180-degree turn from one side to the other. In 3 children, the head was first turned from 0 to 90 degrees and then back from 90 to 0 degrees, making only a half turn. All separation angles (C1-C2 degrees) were then plotted against the corresponding C1 angle to create a motion curve, which, in essence, describes the interaction between C1 and C2 through the full range of head positions. In the 18 children with full turns, both individual motion curves and a composite motion curve comprising all data were constructed. RESULTS: There is a high degree of concordance for rotational behavior of C1 and C2 in the 18 subjects undergoing full turn. C1 always crosses C2 at or near 0 degrees, the null point of full rotation. The predictable relationship between C1 and C2 is depicted by three distinct regions on the composite motion curve: when C1 rotates from 0 to 23 degrees, it moves alone, with C2 remaining stationary at approximately 0 degrees (the single-motion phase). When C1 rotates from 24 to 65 degrees, C1 and C2 move together, but C1 always moves at a faster rate (the double-motion phase), C2 being pulled by yoking ligaments. From 65 degrees onward, C1 and C2 move in exact unison (the unison-motion phase) with a fixed, maximum separation angle of approximately 43 degrees, head rotation being carried exclusively by the subaxial segments. In the 3 children with half turn, the forward rotation curve and the reverse rotation curve are almost superimposable, suggesting that the "yoking" between C1 and C2 is a result of more than just tensing and relaxing of ligaments but probably also to a mutual dragging by irregular bony surfaces between the two bones. CONCLUSION: C1 and C2 in children move in a predictable manner during axial head rotation, with a high degree of concordance among subjects and a relatively narrow variance from the mean. The composite motion curve can thus be used as a touchstone against which may be judged all manners of pathological interlock or "stickiness" between C1 and C2 in rotation that could be defined as AARF.

Algorithms↗
PubMed1990

Two-, three- and four-breed rotational crossbreeding of beef cattle: reproductive traits.

Reproductive data were collected on 4,596 cow exposures in a rotational crossbreeding study that spanned four generations (1970 through 1988). Angus (A), Brahman (B), Charolais (C) and Hereford (H) breeds were included in three two-breed (A-B, C-B and H-B), three three-breed (A-B-C, A-B-H and C-H-B) and one four-breed (A-B-C-H) rotational mating system. Contemporary straightbreds were produced each generation. Reproductive traits of interest were calving rate, calf survival, weaning rate, calf birth date and calving assistance. Overall means and standard errors for calving rate, calf survival, weaning rate, calf birth date and calving assistance were 82.1 +/- .6%, 92.8 +/- .4%, 76.2 +/- .6%, 50.4 +/- .3 d and 4.2 +/- .3%, respectively. Rotational mating systems had similar calving and calf survival rates that were greater (P less than .01) than those of straightbreds. Three- and four-breed rotation systems had similar weaning rates (81.5 +/- 1.1 and 80.8 +/- 2.0%) that were higher than those for two-breed rotations (77.1 +/- 1.2%). Two- and three-breed rotation systems had fewer assisted births (3.5 +/- .6 and 2.2 +/- .6%) than straightbreds (5.5 +/- .6%) and the four-breed rotation (5.4 +/- 1.0%). Three-breed rotation calves were born earlier in the calving season (46.8 +/- .6 d; P less than .05) than straightbred, two-breed or four-breed rotation calves (51.8 +/- .6, 52.1 +/- .6 and 51.1 +/- 1.0 d). Hereford-Brahman two-breed rotation cows had higher (P less than .05) calving and weaning rates than A-B or C-B two-breed rotation cows (87 +/- .4 vs 81.9 +/- 1.9 and 81.5 +/- 1.8%; 81.7 +/- 2.0 vs 76.4 +/- 2.1 and 74.1 +/- 2.0%). All three-breed rotation combinations had similar calving, calf survival and weaning rates, assistance at calving and calf birth dates. Rotational combinations tended to be more superior (P less than .05) to weighted purebred means for calving, calf survival and weaning rates than for calf birth date and calving assistance.

Analysis of Variance↗
PubMed2003

Complications of rotator cuff surgery in which bioabsorbable anchors are used.

OBJECTIVE: This study assessed the utility of MRI in patients with new or persistent pain after surgery with bioabsorbable rotator cuff anchors. SUBJECTS AND METHODS. Three musculoskeletal radiologists prospectively reviewed MRIs of 30 patients with pain after rotator cuff repair with fixation by rotator cuff anchors. Each radiologist described the location of the rotator cuff anchors and whether the supraspinatus tendon was intact or not. MRI findings were correlated with second-look arthroscopy. Consensus MRI interpretations by the three radiologists were obtained retrospectively. RESULTS: Of the 30 patients, nine had dislodgement of the rotator cuff anchors from the humeral head along with a full-thickness supraspinatus tendon retear. The dislodged rotator cuff anchor position could be determined on coronal and sagittal MRIs, providing the orthopedic surgeon a preoperative map for tendon reattachment and retrieval of the dislodged rotator cuff anchor. Four patients had loose rotator cuff anchors but intact supraspinatus tendons. Three patients had supraspinatus tendon retears, but the rotator cuff anchors were intact. In all 16 patients, arthroscopic findings confirmed MRI findings. Fourteen patients had intact rotator cuff anchors and intact supraspinatus tendons on MRI. Of these 14 patients, five had second-look arthroscopy confirming MRI findings. CONCLUSION: MRI is useful in the assessment of patients with persistent or new-onset pain after supraspinatus tendon repair with rotator cuff anchors. MRI provides a presurgical map for second-look arthroscopy to assess retear of the supraspinatus tendon and also aids in retrieval of dislodged rotator cuff anchors.

Absorbable Implants↗
PubMed1995

[Open surgical therapy of the rotator cuff].

Almost 100 years have passed since the first report of rotator cuff repair in 1898 by W. Müller. Even now new operative techniques are being developed. Various solutions for difficult extended forms of rotator cuff lesions are available besides the closed and semi-closed arthroscopic techniques. Anatomical reconstructive procedures such as local or distant tendon transfer compete with extra-anatomical procedures such as simple debridement, equatorial partial reconstruction or replacement with a delta flap. Hemiarthroplasty of the shoulder has proven to be more and more the treatment of choice in cases of inoperable rotator cuff defects with painful arthropathy. The euphoria caused by complicated reconstructive methods for massive tears has subsided due to an awareness that loss of function is inevitable in chronic degenerative tears with muscle atrophy. Reconstruction should be coordinated step by step with the operative procedure as well as adapted to the biological situation. It should definitely not be forced at any price using an algorithm for a rotator cuff tear operation, the best operative method must be selected by clinical, radiological and intraoperative criteria. The situation is completely different for an acute traumatic rotator cuff tear. Every effort should be made to perform early anatomic reconstruction in a young patient, as the function of the rotator cuff is of great importance in the working world. In contrast to degenerative changes of the rotator cuff tendon, large ruptures can be treated successfully if early immediate repair is performed. The long head of the biceps tendon plays a special role in combination with a rotator cuff tear. The concomitant lesions of the long head of biceps should not to be over-looked when repairing the rotator cuff tear. Until now, a special form of rotator cuff pathology has not received much attention--the so-called interval lesion. It is the forerunner of the rotator cuff tear. The interval lesion is a partial tear of the ligamentous structures between the supraspinatus and subscapularis tendon and leads to damage of the long head of the biceps. The interval lesion can only be diagnosed by arthroscopy or open exploration of the rotator interval.

Age Factors↗
PubMed1997

[Effect of the rotator cuff condition on the results of shoulder arthroplasty].

PURPOSE OF THE STUDY: The purpose of this report was to study the repercussions of rotator cuff condition on unconstrained shoulder arthroplasty results. METHODS: Between 1986 and 1993, 40 unconstrained shoulder prostheses were performed (24 total and 16 hemiarthroplasties). At the time of the operation, rotator cuff condition was reported to be normal in 15 shoulders, atrophic in 10, scarred in 3, torn in 12. Clinical and radiographical results were analyzed and supplemented with a rotator cuff echography. Postoperative follow-up averaged 42.25 months (12 to 97 months). RESULTS: When the rotator cuff was intact at the time of operation, clinical results were the best at the time of review. Constant score, overall mobility, forward elevation, external rotation with the elbow along the side were better for intact than for atrophic, scarred or torn rotator cuffs (p < 0.01). Ruptures repaired by local tissue transfer or trapezo deltoidal flap substitution (3 cases) gave satisfactory results, whereas two dacron cuff prostheses failed. In the non repaired ruptures (7 cases), arthroplasty resulted in 3/4 fair or poor results. At the time of review, the total incidence of postoperative rotator cuff tears was high (12 cases), functional repercussions were variable. Among the 15 rotator cuff tears observed at the time of the review, the long head of the biceps was present and in place in 9 cases and ruptured in 6 cases. In these latter cases, Constant score (p < 0.01), the forward elevation (p < 0.01), external rotation with elbow along side (p < 0.05) and overall mobility (p < 0.05) were worse; moreover, humeral head superior migration was greater (p < 0.01). DISCUSSION: Our study confirms the superiority of clinical results when the cuff was intact at the time of the operation. The repair of rotator cuff tears seems to be justified. When the rupture has not been repaired, clinical results were fair or poor in 5 cases out of 7, the initial rupture spread to the other tendons in 3 cases out of 7. Secondary ruptures were frequent (12 cases). No predictive factor was identified, but an overlapping of the greater tuberosity appears to be detrimental. Among rotator cuff tears present at the time of review, long head of the biceps rupture jeopardized clinical results and was associated with a proximal migration of the humeral head which was significantly more severe than with an intact non displaced long head of the biceps. CONCLUSION: During unconstrained shoulder prosthesis implantation, it is therefore recommend to systematically repair any associated rotator cuff rupture, in order to avoid any greater tuberosity overlap relative to the prosthetic head and to preserve the long head of the biceps tendon which limits upward migration of the humeral head and improves prosthetic kinetics.

Adult↗
PubMed2002

Balance in a rotating artificial gravity environment.

When subjects stand at the center of a fully enclosed room that is rotating at constant velocity, their natural postural sway generates Coriolis forces that destabilize their center of mass and head. We quantitatively assessed how exposure to constant velocity rotation at 10 rpm affected postural control. Twelve subjects stood in a heel-to-toe stance in the rotating room. Each test session involved three phases: (1) pre-rotation, (2) per-rotation, and (3) post-rotation. In each phase, subjects were tested in both eyes open and eyes closed conditions. Four measures were used to characterize center of mass movement and head movement: mean sway amplitude, total power, mean power frequency, and frequency of maximum power. Each measure was computed for anterior-posterior and medial-lateral sway. Both anterior-posterior and medial-lateral head and center of mass sway during rotation had significantly greater mean sway amplitude and total power compared with pre- and post-rotation values. Mean power frequency and frequency of maximum power were little affected. Eyes open conditions were significantly more stable in all test phases than eyes-closed, but vision did not completely suppress the effects of rotation. The greatest effect of rotation was in the eyes-closed condition with mean sway amplitude and total power increasing more than twofold. Inverted pendulum sway was maintained in all phases of both test conditions. No aftereffects of rotation were present after the four 25-s exposures each subject received. We expect that with longer exposure periods and with active generation of body sway subjects would both adapt to rotation and exhibit post-rotary aftereffects.

Adult↗
PubMed2000

Oculomotor responses to on-axis rotational stepping in normal and adaptively altered podokinetic states.

Previous studies investigated adaptive properties of a podokinetic (PK) system that senses and controls angular movement of the trunk relative to the stance foot when walking around a curved trajectory or during rotational stepping on the spot. In particular, after adaptively modifying the PK system by prolonged stepping-in-place over the axis of a horizontally rotating platform, blind-folded subjects could no longer step in place on firm ground. When trying to do so they invariably rotated themselves relative to space without perceiving their rotation, a phenomenon termed podokinetic after-rotation (PKAR). It is well known that normal rotational stepping generates a specifically podokinetic component of compensatory nystagmus which is independent of the VOR. The present study investigated whether during PKAR this podokinetic component of oculomotor activity follows the somatosensory correlate of actually stepping around, or the cognitive intent or percept of 'no rotation'. Experiments were conducted in two phases on five normal human subjects. In the first phase, the normal passively induced VOR was compared with the combined VOR and PK oculomotor response induced by intentional rotational stepping on the spot. In both cases the angular stimulus was a 2-min rotation at 15 degrees/s. Subtraction of the decaying VOR from the actively induced combined response revealed a constant podokinetic nystagmus with slow-phase velocity gain of about 0.4 maintained throughout this period. The PK and VOR response components appeared to sum linearly. In the second phase, we measured oculomotor activity during PKAR, when the blindfolded subjects involuntarily rotated themselves at around 15 degrees/s while attempting to step-in-place after the podokinetic adaptation procedure noted above. The striking result of the second phase of experiments was that, although an apparently normal decaying VOR was present, the maintained PK component of response was consistently absent, despite an essentially normal physical pattern of rotational stepping. Thus, in the adapted state, non-vestibular oculomotor activity followed the cognitive intent or percept of 'no rotation', rather than the prevailing somatosensory-motor activity of the lower limbs. The finding points to an important cognitive element in this form of oculomotor control.

Adaptation, Physiological↗
PubMed1992

Factors in amphetamine-induced contralateral rotation in the unilateral 6-OHDA lesion rat model during the first-week postoperative: implications for neuropathology and neural grafting.

Amphetamine induced ipsilateral rotation in rats with chronic unilateral 6-hydroxydopamine (6-OHDA) lesions is a widely accepted line of evidence supportive of dopaminergic mediation of amphetamine effects on motoric behavior. However, there is literature indicating that amphetamine induces contralateral rotation, in the early postoperative phase of a unilateral 6-OHDA lesion. In an attempt to reconcile these opposite amphetamine effects on rotation in terms of dopaminergic mechanisms, a series of 4 experiments were conducted. These studies showed that amphetamine reliably elicits contralateral rotation for up to 7 days postoperative but only ipsilateral rotation thereafter. The amphetamine induced contralateral rotation differed behaviorally in several respects from subsequent ipsilateral rotation induced by amphetamine. It was comparatively more intense; and, while onset of peak rotation was dose dependent, rate of rotation was independent of dose level (0.5, 1.0 and 2.5 mg/kg). Dopamine and dopamine metabolite analyses by HPLC-EC after 3 postoperative intervals (days 3, 6, and 9) indicated a progressive and severe depletion of striatal dopamine in conjunction with elevated dopamine turnover. Importantly, after 6 days postoperative, dopamine was reduced to less than 0.06% after intact hemisphere but yet, amphetamine (1.0 mg/kg) elicited contralateral rotation. It was proposed that amphetamine could release a small amount of dopamine present in a sparse number of residual degenerating terminals and this dopamine, unrestricted by reuptake, could widely access supersensitive dopamine receptors to elicit contralateral rotation. This possibility calls into question amphetamine tests for neural graft efficacy in animal models which use amphetamine induced contralateral rotation as the criterion response.

Amphetamine↗
PubMed1986

The degree of coupling of nuclear rotation in binucleate 3T3 cells.

In order to test the existence of mechanical coupling between the rotational movements of two adjacent nuclei, we prepared binucleate 3T3 cells and observed their nuclear movements by near infrared microscopy and recorded them with time-lapse video techniques. We found that 49 out of 110 (44%) of the selected binucleate cells expressed nuclear rotation. Rotation could occur in just one of the nuclei while the second nucleus remained stationary (31/110) or in both nuclei simultaneously (18/110). In almost all cases where both nuclei rotated simultaneously (15/110) they did so at different speeds and in opposite directions. The nuclei were observed to rotate in the same direction in only three of the examples. The results are consistent with a weak mechanical interaction between a rotating nucleus and its neighbor. Consistent with our previous observations in mononucleate cells, we did not find a characteristic position of the centrosphere or a special distribution of the microtubules or the intermediate filaments in binucleate cells with rotating nuclei. There was an absence of long, well-formed microfilament bundles beneath the nuclei during rotation, even in the local region beneath the rotating nucleus in those cells with one rotating and one stationary nucleus. Also consistent with observations of mononucleate cells, nuclear rotation was inhibited by treatment with colcemid, although the ability of the nuclei to rotate was eventually restored when the colcemid-containing medium was replaced with normal medium.

Actin Cytoskeleton↗
PubMed2006

Premolar and molar rotation in wild Japanese serow populations on Honshu Island, Japan.

The skulls of 1195 Japanese serow (Capricornis crispus) from six geographically distinct populations were examined for tooth rotation. Our objectives were to determine tooth rotation patterns in Japanese serows, investigate geographical variation in tooth rotation and examine whether space limitations in the jaw accounted for variations. We then sought to explain the origin of tooth rotation in the Japanese serow. Rotated teeth were found in 131 specimens (62 males, 57 females and 12 unknown gender), with no statistically significant difference between males and females (chi(2)=0.03, P=0.86, d.f.=1). Among the six populations, the frequency of tooth rotation varied from 3.7-32.1% (average 11.0%). Most tooth rotation occurred in the upper third and fourth premolars. The lingual cusp of anomalous teeth was rotated 30 degrees -90 degrees mesially or distally from the buccolingual tooth axis, and the rotation direction differed among populations. However, we found no difference in skull or tooth morphology between normal individuals and those with tooth rotation. Therefore, hereditary factors may be involved in Japanese serow tooth rotation. We concluded that genetic differentiation occurred in the past among local Japanese serow populations isolated in mountainous habitats. Gene frequencies were likely subject to random drift, especially during possible population bottlenecks, when genetic factors could most strongly affect the direction of rotation.

Animals↗
PubMed2005

Gender differences in pattern of hip and lumbopelvic rotation in people with low back pain.

BACKGROUND: Findings from previous studies suggest gender may affect the pattern of hip and lumbopelvic motion during a multi-segmental movement. To date, no studies have examined movement patterns and low back pain symptom behavior during hip lateral rotation. METHODS: Forty-six people (27 males and 19 females) with low back pain were examined. Three-dimensional kinematic data and low back pain symptoms were recorded during active hip lateral rotation. Percent of maximum lumbopelvic rotation was calculated for each 10% increment of maximum active hip lateral rotation. FINDINGS: Men exhibited a greater percent of maximum lumbopelvic rotation (mean 49.3, SD 13.3) during the first 60% of hip lateral rotation than women (mean 36.2, SD 16.4) (P < 0.01). Nineteen (70.4%) of the men and seven (36.8%) of the women had pain with the hip lateral rotation test (P = 0.02). INTERPRETATION: Men exhibited more lumbopelvic rotation in the early part of hip lateral rotation than women, and hip lateral rotation was more likely to be associated with symptoms in men than women. Greater lumbopelvic motion, earlier in hip lateral rotation, may make men more vulnerable to low back pain associated with hip lateral rotation. Factors that contribute to these gender differences should be investigated further.

Adult↗
PubMed1989

A model for bacterial flagellar motor: free energy transduction and self-organization of rotational motion.

A bacterial flagellar motor is an energy transducing molecular machine which shows some attractive characteristics. First, this motor is driven by a protonmotive force (PMF) across the membrane, two components of which, electric potential delta psi and chemical potential -(2.3RT/F)delta pH, are equivalently transduced to the mechanical work of the motor rotation. Second, a PMF threshold for rotation is observed. Third, this motor can rotate reversibly either counterclockwise (CCW) or clockwise (CW) at almost the same speed. To clarify the osmomechanical coupling of this motor, these characteristics must be explained consistently at the molecular level. In this paper, in order to allow quantitative analyses of the above characteristics, a theoretical model of a bacterial flagellar motor is constructed assuming that the torque generating sites are electrodes which can be charged by protons and that the electrostatic interaction between the electrodes generates the rotation torque. Electrode reaction reasonably derives the equivalence of delta psi and -(2.3RT/F)delta pH. In this model, rates of charging and discharging of protons are influenced by the motor rotation rate, so that the torque generating sites co-operatively work through the motor rotation. We named this kind of co-operativity among them "dynamic co-operativity" in torque generation. This co-operativity causes autocatalytic generation of motor torque and the existence of the rotation threshold. In this model, the appearance of the stable rotational states can be described by phase transition caused by the dynamic co-operativity among torque generating sites. According to this model, the flagellar motor has two stable rotational states corresponding to CCW and CW, which show the same torques. The motor selects one direction from them to rotate, and that is self-organization of rotational motion. Interpretation of the transition between the two stable rotational states as the chemotactic reversals of the flagellar motor is also discussed.

Bacterial Physiological Phenomena↗
PubMed2004

Direct manipulation and observation of the rotational motion of single optically trapped microparticles and biological cells in microvortices.

This paper describes a method for manipulating and monitoring the rotational motion of single, optically trapped microparticles and living cells in a microvortex. To induce rotation, we placed the microparticle at the center of rotation of the vortex and used the recirculating fluid flow to drive rotation. We have monitored the rotation of single beads (which ranged in diameter from a few micrometers to tens of micrometers) and living cells in a microvortex. To follow the rotation of a smooth and symmetrically shaped bead, we first ablated a small region ( approximately 1 microm) on the bead. An Ar(+) laser was then tightly focused ( approximately 0.5-microm spot size) onto the bead, and rotation was tracked by recording changes in the level of backscattered laser light as the ablated region repeatedly transited the laser focus. Using this method, we have followed bead rotation that varied in frequency from 0.15 to 100 Hz and have studied the effect of bead diameter on the rate of rotation at a given fluid flow rate. To monitor the rotation of single living cells, we selectively stained portions of B-lymphocytes with the fluorescent dye DiOC(6). We observed rotation by following changes in the fluorescence signal as the dye-stained region transited the laser focal volume. This technique provides a simple and sensitive method for controlling and monitoring the rotational motion of microparticles in a microfluidic environment.

Animals↗
PubMed2005

Habituation of horizontal nystagmus of the eyes in pigeons in conditions of alternating central and eccentric rotations.

Intact pigeons (n=19) were rotated in the dark in the horizontal plane in different orientations relative to the axis of rotation. In central (evoking habituation) rotations, the animal's head was located on the axis of rotation; in eccentric rotations, the animal's head was 0.6 m from the axis of rotation. Pigeons were subjected to series of alternating central and eccentric rotations; rotation directions were also alternated. Series consisted of 2-5 rotation using a trapezoidal program. Each stimulus evoking habituation was used no more than 14 times during the experiment. Eccentric rotations were found not to prevent the gradual decrease in the peak rates of the slow components of primary nystagmus occurring on the transition from one series of central rotations to another in 17 individuals (group 1); these were increased in two individuals (group 2). Group 1 showed direct relationships between changes in this measure of primary nystagmus, changes in the duration of nystagmus, and changes in the peak rates of secondary nystagmus. Modifications of nystagmus within series varied. When two identical stimuli did not follow immediately one after the other, the second stimulus induced the same changes in nystagmus as observed in the individual in the first and next series of central rotations. If two identical stimuli followed one immediately after the other, the second stimulus in the pair often induced increases in the peak rates of primary and secondary nystagmus, along with increases in the time taken to reach the peak rate of primary nystagmus. These changes were non-random at a probability of >95%.

Animals↗
PubMed1975

Rotation of spin-cast hydrogel lenses.

This study was designed to determine if spin-cast hydrogel contact lenses rotate on the eye, and if so, to investigate the parameters which influence rotation. If these lenses do rotate, correction of residual astigmatism may be difficult, if not impossible. We monitored the lens rotation associated with 12 specially marked B and L Soflens TM contact lenses on six corneas after insertion and 30 minutes later by use of high speed motion pictures. To analyze lens rotation, the film was projected with a stop action projector and the amount of rotation measured with a protractor. Thirty-one percent of the 144 observations made showed some lens rotation, the majority of which was encyclorotation. Most of the lenses showed little or no change in rotation between the two time periods. Corneal curvature was the only lens or eye parameter associated with rotation. Why lenses were more likely to rotate on steeper corneas is not fully understood. Our findings indicate that Softlenses TM may rotate, but there is no definite way of determining in advance if a given lens will rotate on a given eye. This emphasizes the need for individualized lens fitting and proper patient monitoring.

Adult↗
PubMed2006

Biomechanical analysis of rotational motions after disc arthroplasty: implications for patients with adult deformities.

STUDY DESIGN: An anatomic and biomechanical bench-top basic scientific comparative analysis to determine the appropriateness of total disc replacement (TDR) in a lumbar spine with scoliotic tendencies. OBJECTIVES: Only limited data are currently available studying the application of disc replacement adjacent to scoliosis fusions. Theoretically, motion preservation should help delay the continuum of lumbar degeneration adjacent to scoliosis fusions and rotationally unstable lumbar segments. SUMMARY OF BACKGROUND DATA: As a tertiary referral center for failed TDR, we noticed an alarming number of lumbar spinal rotational iatrogenic instability patterns but none occurring in the cervical spine. It is appropriate to analyze the bench-top rotational stability of disc replacement to predict whether this new technology is feasible for a larger prospective clinical study in the treatment of degenerative scoliosis. METHODS: Measurements were taken from 60 human specimens from the Hamann-Todd Osteological Collection: 1) to determine the rotational arc of influence (AOI) = the angle formed from the center of axial rotation to the outermost extent of the facet joints; and 2) to determine the relative anatomic size discrepancy between the left and right facets proportionately with the cross-sectional area of the intervertebral disc = facet/endplate ratio (FER). Biomechanical testing was performed using fresh frozen human cadaveric spines with the following conditions to determine the rotational stability: 1) intact; 2) resection of ALL, anulus, disc, and PLL simulating the preparation for a TDR; 3) a more radical anular resection; 4) entire 360 degrees anular resection; and 4) insertion of the respective unconstrained-type disc replacement. Using a 6 degrees of freedom spine simulator, unconstrained pure moments of +/-8.0 Nm (lumbar) and +/-3.0 Nm (cervical) were used for axial rotation with quantification of the operative level range of motion and neutral zone, with data normalized to the intact spine condition. RESULTS: There were anatomic limitations in the lumbar spine that make it less desirable to apply uncon-strained disc replacements; indeed, the spine was at risk for iatrogenic lumbar scoliosis. The anulus fibrosis, anterior longitudinal ligament, and the posterior longitudinal ligament are critical structures in preventing iatrogenic scoliosis. The lumbar facet joints are more posteriorly located and are smaller relative to the intervertebral disc, compared with this association in the cervical spine. Because the facet capsular ligaments are mechanically less effective with lower tensile strength in the lumbar spine, multiple-level arthroplasty tends to accentuate scoliotic tendencies; this is independent of prosthetic design and surgical technique. DISCUSSION: Implantation of the lumbar TDR never restored the motion segment back to the rotational stability of the intact segment achieving a range of 120% to 140% rotational range of motion compared with the intact condition. This rotational instability proved to be additive as a two-level lumbar TDR resulted in between 240% and 260% increase in rotational instability compared with the intact condition. CONCLUSION: The neutral zone of the intact cervical spine was restored even using an unconstrained cervical TDR. The greater inherent rotational constraints of the cervical spine make it more amenable to stable multilevel arthroplasty compared with the lumbar spine.

Adult↗