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PubMed1984

Prediction of mandibular rotation: an empirical test of clinician performance.

An experiment was conducted in an attempt to determine empirically how effective a number of expert clinicians were at differentiating "backward rotators" from "forward rotators" on the basis of head-film information which might reasonably have been available to them prior to instituting treatment for the correction of Class II malocclusion. As a result of a previously reported ongoing study, pre- and posttreatment head films were available for 188 patients treated in the mixed dentition for the correction of Class II malocclusion and for 50 untreated Class II subjects. These subjects were divided into 14 groups (average size of group, 17; range, 6 to 23) solely on the basis of type of treatment and the clinician from whose clinic the records had originated. From within each group, we selected the two or three subjects who had exhibited the most extreme backward rotation and the two or three subjects who had exhibited the most extreme forward rotation of the mandible during the interval between films. The sole criterion for classification was magnitude of change in the mandibular plane angle of Downs between the pre- and posttreatment films of each patient. The resulting sample contained 32 backward-rotator subjects and 32 forward-rotator subjects. Five expert judges (mean clinical experience, 28 years) were asked to identify the backward-rotator subjects by examination of the pretreatment films. The findings may be summarized as follows: (1) No judge performed significantly better than chance. (2) There was strong evidence that the judges used a shared, though relatively ineffective, set of rules in making their discriminations between forward and backward rotators. (3) Statistical analysis of the predictive power of a set of standard cephalometric measurements which had previously been made for this set of subjects indicated that the numerical data also failed to identify potential backward rotators at a rate significantly better than chance. We infer from these findings that the ability of clinicians to identify backward rotators on the basis of information available at the outset of treatment is poor. Hence, we believe that it is unlikely that such predictions play any consequential operational role in the planning of successful orthodontic therapy at the present state of the art.

Cephalometry↗

PubMed2000

Biological function of the LH receptor is associated with slow receptor rotational diffusion.

The biological activity of luteinizing hormone (LH) receptors can be affected by modifications to the receptor's amino acid sequence or by binding of hormone antagonists such as deglycosylated hCG. Here we have compared rotational diffusion of LH receptors capable of activating adenylate cyclase with that of non-functional hormone-occupied receptors at 4 degrees C and 37 degrees C using time-resolved phosphorescence anisotropy techniques. Binding of hCG to the rat wild-type receptor expressed on 293 cells (LHR-wt cells) or to the LH receptor on MA-10 cells produces functional receptors which exhibit rotational correlation times longer than 1000 micros. However, modification of the LH receptor by substitution of Lys583-->Arg (LHR-K583R) results in a receptor that is non-functional and which has a significantly shorter rotational correlation time of 130+/-12 micros following binding of hCG. When these receptors are treated with deglycosylated hCG, an inactive form of hCG, the rotational correlation times for the LH receptors on LHR-wt and MA-10 cells are also shorter, namely 64+/-8 and 76+/-14 micros, respectively. Finally, a biologically active truncated form of the rat LH receptor expressed in 293 cells (LHR-t631) has slow rotational diffusion, greater than 1000 micros, when occupied by hCG and a significantly shorter rotational correlation time of 103+/-12 micros when occupied by deglycosylated hCG. The effects of rat LH binding to LH receptors on these various cell lines were similar to those of hCG although the magnitude of the changes in receptor rotational diffusion were less pronounced. We suggest that functional LH receptors are present in membrane complexes that exhibit slow rotational diffusion or are rotationally immobile. Shorter rotational correlation times for non-functional hormone-receptor complexes may reflect the absence of essential interactions between these complexes and other membrane proteins.

Animals↗

PubMed1995

Comparison of rotation models for describing DNA conformations: application to static and polymorphic forms.

A new method, based on a space-fixed rotation axis, or local helix axis, is proposed for the calculation of the relative orientation variables for a sequence of base pairs. With this method, orientation variables are determined through the rotation of a base pair about this axis. These variables uniquely determine a set of helical variables, similar to the roll, tilt, and twist, commonly used for a description of spatial orientations of internally rigid base pairs. The proposed identification of roll and tilt with the direction cosines of the space-fixed rotation axis agrees well with their customary definitions as the openings of the angles between adjoining base pairs toward the minor groove and toward the ascending (5' to 3') backbone strand, respectively. These new variables permit a more direct physical comprehension of DNA conformations and also the behavior of self-complementary sequences. These direction cosines, together with the rotation angle about the space-fixed axis, form a set of three independent orientation variables of the bases that afford some advantages over the variously defined twist, roll, and tilt angles, either for static or average forms. An example for the static form of these variables is shown through their use to interpret crystal coordinates. An example for the average of orientation variables is based on statistical calculations. In this example, the orientation variables, together with the translational variables that describe the relative displacements of a pair of adjacent base pairs, form a canonically distributed ensemble in phase space spanned by these variables. Two sets of conformational variables are generated by using two different methods for performing rotation operations on the sequences of base pairs. The first method is based on the new single rotation about a space-fixed axis of rotation. This space-fixed axis of rotation is, in fact, the local helical axis as constructed previously by others. The second method is based on three consecutive rotations by Euler angles. Because of large flexibilities and anisotropies along various conformational variables of DNA base pairs, the two sets of generated conformational variables, based on these two different methods of performing rotation operations, lead to slightly different sets of structurally different, but energetically equivalent, spatial arrangements of the base pairs.

Base Composition↗

PubMed1999

Correlation and quantification of projected 2-dimensional radiographic images with actual 3-dimensional Y-axis vertebral rotations.

BACKGROUND: Historically, measurement of 2-dimensional (2-D) radiographic images on the anteroposterior radiograph has been made to assess 3-dimensional (3-D) y-axis vertebral rotations. OBJECTIVES: To correlate and quantify measurements of the projected 2-D radiographic image with the degree of 3-D y-axis rotation. STUDY DESIGN: A computer model was positioned in a simulated x-ray beam. Points of model contact with the simulated beam were projected onto a line in the neutral position and the first 7 degrees of both positive and negative y-axis rotation using two different axes of rotation. A larger model, a shape-altered model, and a decreased source-object-distance model were also studied. RESULTS: 3-D y-axis rotation of vertebrae causes an off-center displacement of the 2-D projected lamina junction in relation to the projected vertebral body. The magnitude of displacement increases with increasing degrees of rotation. In our model, no clinically significant difference was found in the amount of the projected off-center displacement of the lamina junction between either of our two chosen axes of rotation. However, significant differences in the projected offset were found between vertebrae with the same degree of rotation as a result of changes in vertebral shape, size, and positioning. The projected lamina junction off-centering at a given rotation is quantified for our model. CONCLUSION: Use of millimetric measurement of the projected lamina offset on the anteroposterior radiograph is an inaccurate method for the assessment of the degree of 3-D y-axis vertebral rotation.

Biomechanical Phenomena↗

PubMed2001

Kinematics of rotational mobilisation of the lumbar spine.

OBJECTIVE: The purposes of this study were to measure the movements of the lumbar spine produced by rotational mobilisation, and to study the effects of different grades of mobilisation on the movements produced. DESIGN: Kinematics of rotational mobilisation was assessed with an electromagnetic tracking device. BACKGROUND: Rotational mobilisation is frequently used in the treatment of back pain, but there was no information on its mechanical effects. METHODS: Movements of the lumbar spine were measured in 14 healthy volunteers when they were subjected to grades I to IV left rotational mobilisation. RESULTS: In the starting positions, the spines were found to be flexed, axially rotated to the left and laterally bent to the right. As the mobilisation grade increased, the spine was axially rotated further into the range. Rotational mobilisation was found to produce oscillatory movements of the lumbar spine in all three anatomical planes. It produced axial rotation which was accompanied by lateral bending in the opposite direction and sagittal rotation. The mean frequency of the oscillatory movements was 1.4 Hz. The amplitude of the oscillations was small, and was found to be increased in grades II and III mobilisation. CONCLUSION: Rotational mobilisation may be able to restore lost movements of the lumbar spine in any of the three anatomical planes.

Adult↗

PubMedDate not supplied

Use of vertebral levels to measure presumed internal rotation at the shoulder: a radiographic analysis.

Internal rotation of the shoulder is frequently measured by noting the maximal vertebral level reached by the patient's thumb, but it is not at all certain that this maneuver is strictly measuring internal rotation. We analyzed this maneuver with computed tomographic scans of the shoulder in differing positions. We also analyzed extension of the glenohumeral joint and scapulothoracic articulation with scapular lateral radiographs. Finally, we used posteroanterior radiographs to analyze elbow flexion at the limits of internal rotation behind the back. We found that maximal internal rotation behind the back occurs in approximately a 2 : 1 ratio between the glenohumeral joint and the scapulothoracic articulation. However, the scapulothoracic articulation was more significant in placing the arm behind the back, whereas the glenohumeral joint performed most of the internal rotation in front of the body. The scapulothoracic articulation assists in this motion by both extension and internal rotation of the scapula on the thorax. The limits of internal rotation behind the back are reached with a significant contribution from elbow flexion. We conclude that measuring shoulder internal rotation by the maximal vertebral level reached by the patient's thumb greatly oversimplifies the concept of internal rotation and that limitations in this motion may not be strictly due to a loss of internal rotation at the glenohumeral joint.

Adult↗

PubMedDate not supplied

Anatomy and dimensions of rotator cuff insertions.

The purpose of this study was to devise and implement an accurate and reproducible method of measuring the area and dimensions of the rotator cuff tendon insertions and their distance from the articular surface. Twenty fresh-frozen cadaveric upper-extremity specimens were divided into 2 groups of 10. In group 1 the specimens were dissected, leaving only the most distal rotator cuff tendons attached to the humerus. The periphery of the insertion onto the greater tuberosity was marked at 3-mm intervals. The specimens were then mounted onto a custom jig, and the insertion was mapped by a 3-space digitizer. In group 2 the specimens were prepared by removing all tissues except the rotator cuff muscles and tendons and the joint capsule. The interval between the muscles of the rotator cuff was identified and marked. The rotator cuff muscles and tendons were then removed, leaving only the most distal tendons attached to the tuberosities. The periphery of the individual cuff insertions was then marked as in group 1 and mapped in the same fashion. The articular margin also was marked at similar intervals and mapped with the same technique. The area of insertion of the 3 tendons on the greater tuberosity averaged 6.24 cm(2) (SD, 2.04 cm(2)) in group 1. The mean minimum transverse dimension across the cuff insertion occurred in the mid portion of the supraspinatus, with a mean distance of 14.7 mm (SD, 3.22 mm). In group 2 the mean area of insertion of the supraspinatus was 1.55 cm(2) (range, 0.68-2.64 cm(2); SD, 0.66 cm(2)) and the mean area of insertion for the infraspinatus was 1.76 cm(2) (range, 1.23-2.53 cm(2); SD, 0.40 cm(2)). The distance from the articular margin to the most medial rotator cuff fibers was less than 1 mm along the anterior-most 2.1 cm of the cuff insertion onto the greater tuberosity. No correlation could be made between humeral head dimension and the dimensions of the rotator cuff insertions. The mean minimum medial-to-lateral distance across the rotator cuff insertion was sizeable, at 14.7 mm. This represents the minimum possible distance, as the mathematical calculation to determine the dimensions used a perpendicular measurement. The rotator cuff inserts very closely to the articular margin along the anterior 2.1 cm of the greater tuberosity. These anatomic measurements may be useful in evaluating and reattaching the rotator cuff to the humerus.

Aged↗

PubMed2006

Distinct patterns of viewpoint-dependent BOLD activity during common-object recognition and mental rotation.

A fundamental but unanswered question about the human visual system concerns the way in which misoriented objects are recognized. One hypothesis maintains that representations of incoming stimuli are transformed via parietally based spatial normalization mechanisms (eg mental rotation) to match view-specific representations in long-term memory. Using fMRI, we tested this hypothesis by directly comparing patterns of brain activity evoked during classic mental rotation and misoriented object recognition involving everyday objects. BOLD activity increased systematically with stimulus rotation within the ventral visual stream during object recognition and within the dorsal visual stream during mental rotation. More specifically, viewpoint-dependent activity was significantly greater in the right superior parietal lobule during mental rotation than during object recognition. In contrast, viewpoint-dependent activity was significantly greater in the right fusiform gyrus during object recognition than during mental rotation. In addition to these differences in viewpoint-dependent activity, object recognition and mental rotation produced distinct patterns of brain activity, independent of stimulus rotation: object recognition resulted in greater overall activity within ventral stream visual areas and mental rotation resulted in greater overall activity within dorsal stream visual areas. The present results are inconsistent with the hypothesis that misoriented object recognition is mediated by structures within the parietal lobe that are known to be involved in mental rotation.

Adolescent↗

PubMed2005

ATP-driven stepwise rotation of FoF1-ATP synthase.

FoF1-ATP synthase (FoF1) is a motor enzyme that couples ATP synthesis/hydrolysis with a transmembrane proton translocation. F1, a water-soluble ATPase portion of FoF1, rotates by repeating ATP-waiting dwell, 80 degrees substep rotation, catalytic dwell, and 40 degrees -substep rotation. Compared with F1, rotation of FoF1 has yet been poorly understood, and, here, we analyzed ATP-driven rotations of FoF1. Rotation was probed with an 80-nm bead attached to the ring of c subunits in the immobilized FoF1 and recorded with a submillisecond fast camera. The rotation rates at various ATP concentrations obeyed the curve defined by a Km of approximately 30 microM and a Vmax of approximately 350 revolutions per second (at 37 degrees C). At low ATP, ATP-waiting dwell was seen and the kon-ATP was estimated to be 3.6 x 10(7) M(-1) x s(-1). At high ATP, fast, poorly defined stepwise motions were observed that probably reflect the catalytic dwells. When a slowly hydrolyzable substrate, adenosine 5'-[gamma-thio]triphosphate, was used, the catalytic dwells consisting of two events were seen more clearly at the angular position of approximately 80 degrees . The rotational behavior of FoF1 resembles that of F1. This finding indicates that "friction" in Fo motor is negligible during the ATP-driven rotation. Tributyltin chloride, a specific inhibitor of proton translocation, slowed the rotation rate by 96%. However, dwells at clearly defined angular positions were not observed under these conditions, indicating that inhibition by tributyltin chloride is complex.

Adenosine Triphosphate↗

PubMed2004

Ergonomics and biology of spinal rotation.

Spinal rotation, though being a very common motion of the body, is poorly understood. Furthermore, this motion and the extent of its development is unique to the human. Beyond the extent of its need in common activities, spinal rotation is a destabilizating motion for an inherently unstable structure. Spinal rotation has been argued to be an essential feature for an efficient bipedal gait. Also, it provides leverage to the upper extremities in delivering a forceful impact. An artificial restriction/elimination of spinal rotation resulted in significantly shorter stride length, slower walking velocity, and higher energy consumption in walking (p < 0.05). Spinal rotation also decreases the amount of force the spinal muscles can generate (to 25% of spinal extension). However, its extensive employment in industrial activities has been associated with 60.4% of back injuries. It is further stated that the amount of scientific information currently available is inadequate to biomechanically model the spinal response in a working environment. For example, when the spine is pre-rotated, a further rotation in the direction of pre-rotation decreases the force production significantly (p < 0.01) and increases the EMG activity significantly (p < 0.01) but the pattern changes with effort in the opposite direction. This and other properties (described in the paper) render biomechanical models inadequate. Muscle activation pattern and neuromotor behaviour of spinal muscles in flexion/extension and rotation of the spine are significantly different from each other (p < 0.01). The localized fatigue in different spinal muscles in the same contraction is significantly different and has been called differential fatigue. Finally, the trunk rotation, being pivotal for bipedal locomotion has brought many back problems to the human race.

Abdominal Muscles↗

PubMed2004

Influence of pelvis rotation styles on baseball pitching mechanics.

Efficient, sequential timing is essential for upper level pitching. Interestingly, pitchers vary considerably in timing related elements of pitching style including pelvis rotation, arm cocking, stride leg behaviour, and pitch delivery time. The purpose of this study was to determine whether relationships exist among these elements by examining the overall style of pitchers exhibiting different pelvis rotation patterns. Pitching styles were defined by pelvis orientation at the instant of stride foot contact. Pitchers demonstrating a pelvis orientation greater than 30 degrees were designated as 'early rotators', while pitchers demonstrating a pelvis orientation less than 30 degrees were designated as 'late rotators'. Kinematic and temporal differences were associated with the two styles. During the arm cocking phase, early rotators showed significantly greater shoulder external rotation at the instant of stride foot contact, earlier occurrence of maximum pelvis rotation angular velocity, and shorter time taken to complete the phase. However, by the instant of maximum shoulder external rotation, early and late rotators appeared remarkably similar as no significant difference occurred in pelvis and arm orientations. Therefore, it appears that early and late rotators used different methods to achieve similar results, including throwing velocity. Significant differences in throwing arm kinetics were also found for 10 of the 11 measures in the study. As the pelvis assumed a more open position at stride foot contact, maximum kinetic values were found to both decrease in magnitude and occur at an earlier time within the pitch.

Adolescent↗

PubMed1996

Effect of rotation and knee flexion on radiographic alignment in total knee arthroplasties.

A synthetic femur and tibia were used to create a model resurfacing total knee arthroplasty. The femoral component was placed in 7 degrees valgus; the tibial component was placed in 2 degrees varus with a 5 degrees posterior slope. The overall anatomic alignment was 5 degrees valgus. A series of radiographs were taken on 14 inch x 17 inch plates, in full extension and 10 degrees flexion, with the limb rotated, in 5 degree increments, from 20 degrees external rotation to 25 degrees internal rotation. Seven orthopaedic surgeons independently measured the tibiofemoral angle and tibial alignment for each series of radiographs; interobserver variability was insignificant. Average radiographic anatomic alignment ranged from 2.29 degrees valgus in 20 degrees external rotation and 10 degrees flexion, to 6.73 degrees valgus in 25 degrees internal rotation and 10 degrees flexion. Limb rotation and knee flexion of 10 degrees, either alone or in combination, had a highly statistically significant effect on measured values of the anatomic alignment. Tibial alignment ranged from 5 degrees varus in 20 degrees external rotation to 3 degrees valgus in 25 degrees internal rotation, with the knee flexed 10 degrees. The variability associated with changes in rotation was statistically significant. Changes associated with rotation, when the knee was flexed 10 degrees, were not significantly different than those measured with the knee fully extended. Even in a well aligned total knee arthroplasty, limb positioning at the time of radiographic assessment will alter the apparent alignment indices, making objective evaluation difficult.

Humans↗

PubMed2002

Glenohumeral joint total rotation range of motion in elite tennis players and baseball pitchers.

UNLABELLED: The amount of glenohumeral joint internal and external rotation used during overhead sport activities has been measured experimentally by sports scientists. Clinical measurement of glenohumeral joint internal and external rotation using goniometry is an integral part of a shoulder evaluation after injury or surgery or during preseason or preventative musculoskeletal screenings. PURPOSE: This study measured glenohumeral joint internal and external rotation in two groups of unilaterally dominant upper extremity athletes to compare the total arc of rotational range of motion between the dominant and nondominant extremities. METHODS: A total of 163 elite athletes (117 male junior tennis players and 46 male baseball pitchers) were measured for glenohumeral joint internal and external rotation at 90 degrees of abduction. Total rotation range of motion was calculated by summing internal and external rotation measures in each extremity. RESULTS: An ANOVA with post hoc testing revealed no significant difference (P > 0.05) between extremities in baseball pitchers for total rotation range of motion (145.7 vs 146.9), whereas significantly less (P < 0.001) dominant arm total rotation range of motion was identified in the elite junior tennis players (149.1 vs 158.2). CONCLUSION: This study has identified unique glenohumeral joint rotational patterning in unilaterally dominant upper extremity athletes that has ramifications for rehabilitation after injury and for both injury prevention and performance enhancement.

Adolescent↗

PubMed1996

Axial rotation measurement of scoliotic vertebrae by means of computed tomography scans.

STUDY DESIGN: This study evaluated the preconditions for exact axial rotation measurement and the possibility for other parameters to measure axial rotation and mechanical torsion. OBJECTIVES: Quality criteria for axial rotation measurement in computed tomography scans are not established yet. Criteria should be found to improve axial rotation measurement. SUMMARY OF BACKGROUND DATA: To the authors' knowledge, no systematic analysis of the errors of axial rotation measurement based on computed tomography scans has been performed. METHODS: Axial rotation was measured in 259 computed tomography scans of 11 cadaveric vertebrae from scoliotic specimens. The sagittal axial rotation measurement angle of Aaro and Dahlborn and a new rotation parameter were measured with a pencil and ruler. Five landmarks were digitized and consequently five axial rotation parameters were computed. The influence of insufficient visualization of bony landmarks, mechanical torsion of the vertebra itself, and oblique position of the vertebra was evaluated. RESULTS: Accuracy is considerably improved in central computed tomography scans (same distance to the top and bottom of the vertebral body) due to good visualization of landmarks and reduction of effects of mechanical torsion. The oblique vertebral position causes more errors. One mechanical torsion parameter with sufficient reliability is identified. CONCLUSION: The sagittal axial rotation measurement method of Aaro and Dahlborn is superior to other techniques of measurement. It can be improved considerably if computed tomography scans fulfill certain quality criteria.

Anthropometry↗

PubMed1999

Rotations of a helix as a model for correction of the scoliotic spine.

STUDY DESIGN: A prospective study using intraoperative stereophotogrammetry to analyze helical motion of the spine during the correction of scoliosis. OBJECTIVE: To determine whether derotation systems rotate the scoliotic helix. SUMMARY OF BACKGROUND DATA: Scoliosis is a complex three-dimensional deformity that is difficult to visualize on standard radiographs. The use of stereophotogrammetry has allowed study of the deformity in three dimensions during surgical correction. METHODS: Thirty-five patients with right thoracic adolescent idiopathic scoliosis were studied using a stereophotogrammetry technique during surgical correction. Changes in vertebral unique rotations and spinal plane of maximum deformity were measured during three sequential stages of the surgery. RESULTS: The mean preoperative and postoperative Cobb angles were 58 degrees and 19 degrees, respectively. Most rotation occurred at the top and bottom vertebrae in the curve, averaging 10 degrees each but in opposite directions. The apical vertebra rotated the least in the structural curve, with an average rotation of 5 degrees. Much of the rotation occurred during the derotation maneuver with additional rotation occurring during the final distraction. The plane of maximum deformity changed from a mean of 50 degrees before instrumentation to 19 degrees at the end of the procedure. CONCLUSIONS: Multiple rotations of the scoliotic curve occur, and it can be shown when maximum rotations occur during surgery. Posterior derotational systems unwind or rotate the scoliotic helix and reposition the resultant sine wave toward the sagittal plane as described by the change in the plane of maximum deformity.

Adolescent↗

PubMed2004

Kinematics of the upper cervical spine in rotation: in vivo three-dimensional analysis.

STUDY DESIGN: Kinematics of the upper cervical spine during head rotation were investigated using three-dimensional magnetic resonance imaging (MRI) in healthy volunteers. OBJECTIVES: To demonstrate in vivo intervertebral coupled motions of the upper cervical spine. SUMMARY OF BACKGROUND DATA: Although various in vivo and in vitro studies have identified the normal movement patterns of the upper cervical spine, no previous studies have accurately analyzed in vivo three-dimensional intervertebral motions of the upper cervical spine during head rotation. METHODS: Fifteen healthy volunteers underwent three-dimensional MRI of the upper cervical spine using a 1.0-T imager in progressive 15 degrees steps during head rotation. Segmented three-dimensional MRIs of each vertebra in the neutral position were superimposed over images taken at other positions, using voxel-based registration. Relative motions between occiput (Oc) and atlas (C1) and between C1 and axis (C2) were measured and described with 6 degrees of freedom by rigid body Euler angles and translations. RESULTS: Mean (+/- SD) maximum angles of axial rotation in Oc-C1 and C1-C2 were 1.7 +/- 1.5 degrees and 36.2 +/- 4.5 degrees to each side, respectively. Increases in angle of axial rotation in C1-C2 became smaller with increased head rotation, indicating axial rotation in C1-C2 displayed nonlinear motion. Coupled lateral bending with axial rotation was observed in the direction opposition to that of axial rotation in Oc-C1 (mean, 4.1 +/- 1.4 degrees) and C1-C2 (mean, 3.8 +/- 3.0 degrees). Coupled extension with axial rotation occurred at both C0-C1 (mean, 13.3 +/- 4.9 degrees) and C1-C2 (mean, 6.9 +/- 3.0 degrees). CONCLUSIONS: We developed an innovative in vivo three-dimensional motion analysis system using three-dimensional MRI. In vivo coupled motions of the upper cervical spine investigated using this system supported the results of the previous in vitro study.

Adult↗

PubMed2005

Looking away from whiplash: effect of head rotation in rear impacts.

STUDY DESIGN: Twenty healthy volunteers in a laboratory were subjected to rear-end impacts 4.4, 7.9, 10.9, and 13.1 m/s acceleration, with head rotation to the right and left. OBJECTIVE: The purpose of this study was to determine the response of the cervical muscles to increasing low-velocity rear impacts when the head is rotated at the time of impact. SUMMARY OF BACKGROUND DATA: A previous study of rear impacts with head in neutral posture suggests that the burden of impact is borne primarily by the sternocleidomastoid muscles bilaterally. To improve automobile designs to prevent whiplash injury, we need to understand the response of the cervical muscles to whiplash-type perturbations in less-than-ideal conditions, such as when the head is rotated to the right and left at the time of rear-end impact. METHODS: Triaxial accelerometers recorded the acceleration of the sled, torso at the shoulder level, and head of the participant, while bilateral electromyograms of the sternocleidomastoids, trapezii, and splenii capitis were also recorded. RESULTS: For participants having a rear-end impact, whether having the head rotated to the left or right at the time of impact, the muscle responses increased with increasing levels of acceleration (P < 0.01). The time to onset and time to peak electromyogram for all muscles progressively decreased with increasing levels of acceleration (P < 0.01). Which muscle responded most to a whiplash-type neck perturbation was determined by the direction of head rotation. With the head rotated to the left, the right sternocleidomastoid generated 88% of the maximal voluntary contraction electromyogram (at least triple the response of other muscles). In comparison, the left sternocleidomastoid, both trapezii, and the splenii capitis generated on average only 10% to 30% of the maximal voluntary contraction electromyogram with head rotated to the left. On the other hand, with the head rotated to the right, the left sternocleidomastoid generated 94% of the maximal voluntary contraction electromyogram (again, at least triple the response of other muscles). CONCLUSIONS: If the head is rotated out of neutral posture at the time of rear impact, the injury risk tends to be greater for the sternocleidomastoid muscle contralateral to the side of rotation. Measures to prevent whiplash injury may have to account for the asymmetric response because many victims of whiplash are expected to be looking to the left or right at the time of collision.

Acceleration↗

PubMed2006

Analysis of preexistent vertebral rotation in the normal quadruped spine.

STUDY DESIGN: In this CT study, vertebral rotation was analyzed in the transverse plane of the normal, nonscoliotic canine spine with a computer-based measurement method. OBJECTIVES: To determine if a rotational pattern exists in the normal, nonscoliotic quadruped spine, similar to what is seen in humans. SUMMARY OF BACKGROUND DATA: Idiopathic scoliosis does not occur in quadrupeds. In humans, the normal, nonscoliotic spine shows a preexistent pattern of vertebral rotation, which corresponds to the most prevalent curve types of idiopathic scoliosis. Since this rotational tendency has only been demonstrated in humans, it is not clear if it can be considered as a part of the pathogenesis of idiopathic scoliosis or as a normal anatomic feature. METHODS: CT scans of the thorax of 42 dogs without clinical or radiologic evidence of scoliosis were used to measure axial vertebral rotation from T1-T13 with a previously developed computer-based CT measurement method. RESULTS: The results of this study demonstrated a predominant rotation to the right of the upper, mid, and lower thoracic vertebrae of the normal canine spine. The mean vertebral rotation angles differed significantly from zero degrees rotation at level T1, from level T4-T7, and from T11-T13. CONCLUSIONS: The normal spine of quadrupeds shows rotation of the thoracic vertebrae with a preferred direction to the right, similar to what is seen in humans. Since idiopathic scoliosis does not exist in quadrupeds, this preexistent rotation seems to be a physiologic process in normal spinal development, independent of the pathogenesis of scoliosis.

Animals↗