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At least 163 records · Page 9Linked to original sources
PubMed2005

Effect of head restraint backset on head-neck kinematics in whiplash.

Although head restraints were introduced in the 1960s as a countermeasure for whiplash, their limited effectiveness has been attributed to incorrect positioning. The effect of backset on cervical segmental angulations, which were previously correlated with spinal injury, has not been delineated. Therefore, the practical restraint position to minimize injury remains unclear. A parametric study of increasing head restraint backset between 0 and 140mm was conducted using a comprehensively validated computational model. Head retraction values increased with increasing backset, reaching a maximum value of 53.5mm for backsets greater than 60mm. Segmental angulation magnitudes, greatest at levels C5-C6 and C6-C7, reached maximum values during the retraction phase and increased with increasing backset. Results were compared to a previously published head restraint rating system, wherein lower cervical extension magnitudes from this study exceeded mean physiologic limits for restraint positions rated good, acceptable, marginal, and poor. As head restraint contact was the limiting factor in head retraction and segmental angulations, the present study indicates that minimizing whiplash injury may be accomplished by limiting head restraint backset to less than 60mm either passively or actively after impact.

Biomechanical Phenomena↗
PubMed2002

Heading in the right direction? An innovative approach toward proper patient head positioning.

An in-house-manufactured modification of the standard A-F foam rubber head-neck supports (aka. Timo Supports) was designed to eliminate clinical setup problems with head immobilization and instability during treatment, thus providing for a more comfortable head rest for the patient. The custom design of this head holder seeks to eliminate superior-to-inferior shift, and minimize the lateral right-to-left rotational movement of the head when coupled with an AquaPlast casting system. By focusing attention to the seating of the occipital portion of the head and contour of the patient's neck, the aforementioned problems of movement were addressed, while adhering to the interests of patient comfort in this modified head support system.

Equipment Design↗
PubMed1991

[The role of mechanical stress on the femoral head in the occurrence of femoral head lesions in spontaneously hypertensive rats].

Using spontaneously hypertensive rats (SHRs), attempts were made to decide whether or not mechanical stress on the femoral head plays a role in the occurrence of the femoral head lesions, namely, avascular necrosis and ossification disturbance. The following measures were taken to reduce mechanical stress: severing of the sciatic nerve, severing of both the sciatic and femoral nerves, and amputation of the hind limb on one side. The frequency of the femoral head lesions was highest in the control group (85%). It was lower in the sciatic nerve severance group, sciatic and femoral nerve severance group, and hind limb amputation group, in that order, showing a direct correlation with the level of mechanical stress. Moreover, histological abnormalities of the growth plate were observed frequently in the outer portion of the femoral head in SHRs with femoral head lesions. These findings indicate that mechanical stress causes an impairment of the femoral head cartilage, resulting in the obstruction of blood vessels leading to the epiphyseal nucleus of the femoral head.

Animals↗
PubMed1999

Developmental morphology of the head mesoderm and reevaluation of segmental theories of the vertebrate head: evidence from embryos of an agnathan vertebrate, Lampetra japonica.

Due to the peculiar morphology of its preotic head, lampreys have long been treated as an intermediate animal which links amphioxus and gnathostomes. To reevaluate the segmental theory of classical comparative embryology, mesodermal development was observed in embryos of a lamprey, Lampetra japonica, by scanning electron microscopy and immunohistochemistry. Signs of segmentation are visible in future postotic somites at an early neurula stage, whereas the rostral mesoderm is unsegmented and rostromedially confluent with the prechordal plate. The premandibular and mandibular mesoderm develop from the prechordal plate in a caudal to rostral direction and can be called the preaxial mesoderm as opposed to the caudally developing gastral mesoderm. With the exception of the premandibular mesoderm, the head mesodermal sheet is secondarily regionalized by the otocyst and pharyngeal pouches into the mandibular mesoderm, hyoid mesoderm, and somite 0. The head mesodermal components never develop into cephalic myotomes, but the latter develop only from postotic somites. These results show that the lamprey embryo shows a typical vertebrate phylotype and that the basic mesodermal configuration of vertebrates already existed prior to the split of agnatha-gnathostomata; lamprey does not represent an intermediate state between amphioxus and gnathostomes. Unlike interpretations of theories of head segmentation that the mesodermal segments are primarily equivalent along the axis, there is no evidence in vertebrate embryos for the presence of preotic myotomes. We conclude that mesomere-based theories of head metamerism are inappropriate and that the formulated vertebrate head should possess the distinction between primarily unsegmented head mesoderm which includes preaxial components at least in part and somites in the trunk which are shared in all the known vertebrate embryos as the vertebrate phylotype.

Animals↗
PubMed1994

Activity of neurons in Forel's field H during orienting head movements in alert head-free cats.

Single unit activities were recorded in Forel's field H (FFH) at the mesodiencephalic junction during orienting head movements in two alert cats under head-free conditions. Recordings were made of 63 neurons of which 20 showed phasic firing that preceded the onset of head movements by 20-100 ms and was temporally related to the dynamic phase of the orienting head movement. Nineteen of these neurons showed a preference for upward movements, while the remaining neuron preferred downward movements. Activities during orienting movements in eight different directions (each separated by 45 degrees) were systematically analyzed for 12 of the 19 upward-preferring neurons. The activities were broadly tuned; in most of the neurons, maximum activity was observed for direct upward movements (+90 degrees), but significant activity was also observed for ipsilateral and contralateral oblique upward movements (+45 degrees and +135 degrees). In these cases, the increase in activity preceded the onset of the movement. Some increase in activity was also observed for ipsilateral and contralateral horizontal, oblique downward and downward movements. However, the increase in activity in the latter cases occurred simultaneously with or lagged behind the onset of the movement and was often preceded by a decrease in activity. The same pattern of directional tuning was observed in the EMG of the biventer cervicis muscle, a target of FFH neurons. The preferred directions of the 12 upward-preferring neurons were estimated by calculating the vector sum of the activity and were distributed between +68 degrees and +108 degrees. The same amount of activity was observed for ipsilateral and contralateral oblique upward movements, suggesting that FFH neurons on both sides of the brainstem are equally activated even during oblique orienting. Input from the ipsilateral superior colliculus was investigated in 18 neurons, all of which were orthodromically activated with a latency of 0.8-1.8 ms, suggestive of a mono- or disynaptic excitatory connection. Seven neurons were identified as descending projection neurons by antidromic activation from the ipsilateral medullary reticular formation. Repetitive microstimulation of unilateral FFH induced oblique upward head movements and an accompanying torsional component, while simultaneous bilateral stimulation at comparable stimulus strength induced purely upward head movements. These results strongly suggest that the vertical component of orienting head movements is encoded by equal bilateral activation of the FFH.

Animals↗
PubMed2006

Head-bobbing and non-bobbing walking of black-headed gulls (Larus ridibundus).

Head-bobbing walking (HBW) and non-bobbing walking (NBW) of black-headed gulls were compared from kinematic and behavioral/environmental viewpoints. The birds walked with a longer stride length and lower stride frequency during the HBW than during the NBW. With respect to these two parameters, the HBW of black-headed gulls was similar to that of other head-bobbers, and the NBW was similar to that of other non-bobbers. The stride length and the amplitude of head bobbing were correlated. These results suggest that the head-bobbing and gait parameters are related. From a behavioral viewpoint, HBW was observed during seeking-type foraging by wading, and NBW was observed during waiting-type foraging on a flat substrate. The type of foraging behavior and/or substrate condition probably determines whether the birds walk with or without head bobbing.

Animals↗
PubMed1991

Assessment of total head excursion and resting head posture.

Clinicians typically evaluate head posture and cervical range of motion in both standing and sitting positions. There are currently few quantitative data available regarding resting head posture (RHP) or total head excursion (THE), a retraction-protraction gliding range of head motion in the sagittal plane, and where the RHP lies within THE. The purposes of this study were to describe quick and simple methods to determine quantitative measurements of THE, RHP while sitting, and RHP while standing, to provide preliminary data on these postural measurements for men and women in four age categories; and to determine the effects of gender and age on these measurements. Subjects included 218 able-bodied adults. Measurements of THE, RHP while sitting, and RHP while standing were taken. A two-way multivariate analysis of variance followed by two-way analyses of variance showed only the main effect of gender to be significant (p less than .05) for each of the dependent measurements. Across the age groups, men had a greater excursion distance from retraction to protraction than women. Within THE, women held their heads more forward than men. Men held their heads farther from the vertical than women while standing. These results indicate that normal head and neck posture is different for men and women and should not be judged by the same standard. The methods used in this study are clinically advantageous in that they produce objective, quantitative measurements of THE and RHP that may be obtained quickly and with minimal equipment.

Adult↗
PubMed1989

Multiple primary cancer in patients with cancer of the head and neck: second cancer of the head and neck, esophagus, and lung.

Squamous cell carcinoma of the head and neck is complicated by a second primary carcinoma of the head and neck, esophagus (the upper aerodigestive tract, or UADT), or lung in 10-40% of patients. Routine panendoscopy will identify a simultaneous second primary in 9-14% of the patients. Metachronous second cancers most often involve the esophagus or lung, whereas synchronous second cancers are more common in the head and neck as occult lesions. For the highest-risk subgroups, second primary cancers occur in 4% of patients per year. In cancer of the floor of the mouth the excess mortality rate is 5-6% per year. Risk is independent of stage of the first primary and the survival impact is the greatest in groups of patients with early-stage disease. Head and neck cancer almost always results from the heavy use of tobacco for many years, either with or without the concomitant heavy use of alcohol, and these same agents are directly responsible for the second cancers of the UADT and lung. All head and neck cancer patients should be advised to avoid these agents. The clinician must diagnose and treat second cancers to extend the survival of patients with a good prognosis for control of the initial head and neck cancer. We need further progress in eliminating the use of known carcinogens in these patients, paradigms for cost-effective diagnosis and treatment of second primary cancers, effective treatment of the head and neck primary cancer devoid of long-lasting tissue toxicities, effective chemopreventive agents to retard established processes of carcinogenesis that place the patient at continued risk after cigarette and alcohol use has been eliminated, and continued efforts to control the medical illnesses to which these patients are susceptible.

Carcinoma, Squamous Cell↗
PubMed2001

Experimental control of eye and head positions prior to head-unrestrained gaze shifts in monkey.

A coordinated movement of the eyes and head in the head-unrestrained condition is often used to change orientation between targets. Under natural conditions, these gaze shifts are typically generated with the eyes roughly centered in the orbits. To achieve experimental control of eye and head positions, a miniature laser was mounted on the head implants of monkeys that were trained to point the head to one target and direct gaze to another before generating a head-unrestrained gaze shift to a third target (dissociation paradigm). For comparison, monkeys were also required to make gaze shifts between stimuli, without any constraints on eye and head positions (standard paradigm). Analyses indicated that movement parameters, limited to horizontal gaze shifts, were similar for both behavioral conditions. Thus, the proposed technique and behavioral paradigm, when used in conjunction with electrophysiological and pharmacological experiments, may facilitate the study of neural control of gaze.

Animals↗
PubMed2003

The neuropsychology of heading and head trauma in Association Football (soccer): a review.

Association Football (soccer) is the most popular and widespread sport in the world. A significant proportion of the injuries suffered in football are head injuries involving trauma to the brain. In normal play, head trauma frequently arises from collisions, but some researchers have claimed that it also may arise as a consequence of heading the ball. Although assessments based on biomechanical analyses are equivocal on the potential for brain injury due to football heading, a growing literature seems to support the claim that neuropsychological impairment results from general football play and football heading in particular. However, this review suggests a distinction is required between the neuropsychological effects of concussive and subconcussive head trauma and that all of the neuropsychological studies conducted so far suffer from methodological problems. At best, a few of these studies may be regarded as exploratory. The review concludes that presently, although there is exploratory evidence of subclinical neuropsychological impairment as a consequence of football-related concussions, there is no reliable and certainly no definitive evidence that such impairment occurs as a result of general football play or normal football heading. The neuropsychological consequences of football-related subconcussive effects await confirmatory investigation.

Alcoholism↗
PubMed2001

Comparison of femoral head penetration rates between cementless acetabular components with 22-mm and 28-mm heads.

Between April 1993 and July 1994, the senior author (R.C.J.) performed 151 consecutive primary total hip arthroplasties using a Harris-Galante II acetabular component and a polished Iowa femoral component. In 105 hips, 22-mm head components were used, and in 46 hips, 28-mm head components were used. Femoral head penetration into the acetabular shell was measured using digital edge detection techniques. The group average penetration for the initial 2-year bedding-in period was 0.35 mm/y for the 22-mm and 0.31 mm/y for the 28-mm head components. The long-term rate of penetration into the shell was 0.11 mm/y for the 22-mm heads and 0.17 mm/y for the 28-mm heads, a significant difference (P=.029). The dislocation rate was significantly higher, however, with the 22-mm heads (P=.001). The 22-mm components showed significantly less wear but at the expense of an increase in the prevalence of dislocation.

Acetabulum↗
PubMed1999

A sensor-weighted overlapping-sphere head model and exhaustive head model comparison for MEG.

The spherical head model has been used in magnetoencephalography (MEG) as a simple forward model for calculating the external magnetic fields resulting from neural activity. For more realistic head shapes, the boundary element method (BEM) or similar numerical methods are used, but at greatly increased computational cost. We introduce a sensor-weighted overlapping-sphere (OS) head model for rapid calculation of more realistic head shapes. The volume currents associated with primary neural activity are used to fit spherical head models for each individual MEG sensor such that the head is more realistically modelled as a set of overlapping spheres, rather than a single sphere. To assist in the evaluation of this OS model with BEM and other head models, we also introduce a novel comparison technique that is based on a generalized eigenvalue decomposition and accounts for the presence of noise in the MEG data. With this technique we can examine the worst possible errors for thousands of dipole locations in a realistic brain volume. We test the traditional single-sphere model, three-shell and single-shell BEM, and the new OS model. The results show that the OS model has accuracy similar to the BEM but is orders of magnitude faster to compute.

Brain↗
PubMed1999

The head midline as a reliable reference frame for encoding head-on-body orientation.

Twelve right-handed male subjects were asked to use each hand to point accurately toward the center of their forehead, determining the correct position according to their mental representation, while the head was either aligned with the trunk or tilted 30 degrees to the right or left. Analysis of end-positions of pointing revealed that the right hand exhibited a slight leftward bias with respect to the putative head midline passing through the center of the glabella and the center of the fissure between the two upper central incisors, regardless of the head-on-body orientation, whereas the left hand proved very accurate when the head was aligned with the trunk but, when the head was tilted either way, it deviated to the opposite side. These results lead to the conclusion that the head midline appears to act as a reliable reference frame for encoding head-on-body orientation when pointing is carried out by the dominant hand.

Adult↗
PubMed1993

Long-term outcome of head injuries: a 23 year follow up study of children with head injuries.

The purpose of the 23 year follow up study was to determine the relationship between trauma variables including measures of head injury and very long-term sequelae. The study included 159 individuals with a mean age 31.40 years, of whom approximately 90% were admitted to hospital with a mild head injury during childhood (mean age 7.96). Extent of head injury was determined by unconsciousness, neurological status, skull fracture, EEG, post-traumatic seizures and a composite measure. The composite measure of neurological variables was the best predictor of long-term outcome. In addition, IQ recorded in the post-acute phase was a reliable predictor of long-term outcome. Of the sample, 32.7% reported physical complaints and 17.6% reported current psychological/psychiatric problems unrelated to the head injury. Subjective sequelae (physical, intellectual and emotional) specified as due to the head injury were reported by 31% of the sample, and the sequelae were found to be related to the extent of the head injury and initial IQ. There were no discernible relationships between attribute variables including premorbid status and age with subjective sequelae. There were, however, significant relationships between subjective sequelae and objective, psychosocial measures of adaptation including educational lag, unemployment, current psychological/psychiatric problems and relationships with family members. Finally, there appeared to be continuity of complaints elicited during the five year follow up of the original project and current sequelae. The severity of the head injury was identified as the primary contributory factor in the reconstitution process and in the prediction of long term outcomes.

Adolescent↗
PubMed2006

Head replacement, head rotation, and surface damage effects on metal-on-metal total hip replacements: a hip simulator study.

The possibility of replacing the femoral head alone, in either solid or articular surface replacement form, during revision operations on metal-on-metal total hip replacements remains an attractive feature of such implants. In the present investigation, laboratory simulator studies of the influence upon volumetric wear of inserting a new femoral head, of introducing some head rotation, and of damaging the femoral head by scratches have all been explored. New and rotated heads both involve an additional running-in period, but the experimental studies show that the volumetric wear associated with this process is less than the initial running-in wear. The beneficial effects upon volumetric wear of small clearances have been confirmed, while the processing of high-carbon Co-Cr-Mo materials appears to be much less influential. Scratches did not affect wear as much as head replacement or head rotation, but the ongoing wear rates were somewhat higher.

Biocompatible Materials↗
PubMed1999

Target-directed head movements in a head-coupled virtual environment: predicting the effects of lags using Fitts' law.

Two experiments have investigated the effects of lag on discrete target-directed head movements in a virtual environment. Both the target and a head-slaved pointer (subjected to lag) were presented on a head-mounted display. Target-directed head movements in the presence of a constant time lag were shown to obey Fitts' law (R2 > .93). A previously reported interaction between the effects of lag and the effects of index-of-difficulty on hand movement time could not be found in head movement time when the target width was kept constant. Further experiments suggested that there is a significant interaction between the effects of target width and lag but not between target distance and lag. A model predicting head movement strategy in the presence of lag is proposed to explain the experimental findings. This model predicts, and experiments verified, that for a target width from 1 degree to 8 degrees and a target distance range of 2.5 degrees to 30 degrees, the effect of lag (up to 267 ms) on target-directed head movement is independent of target distance but dependent on target width. Actual or potential applications of this research include the design of virtual control panel and its layout in a Virtual Reality simulator.

Adult↗
PubMed2005

Use of the head shake-sensory organization test as an outcome measure in the rehabilitation of an individual with head movement provoked symptoms of imbalance.

BACKGROUND AND PURPOSE: The purpose of this case report is to highlight the Head Shake (HS) Sensory Organization Test (SOT) (HS-SOT) as an outcome measure in the rehabilitation of a patient with head movement provoked symptoms of dysequilibrium. Despite complaints of imbalance and head movement provoked symptoms, there are individuals who are able to score within normal limits on measures such as the SOT and Berg Functional Balance Test. The HS modification to the SOT can objectively identify abnormal vestibular inputs associated with head motion and maintaining balance. METHODS: This case report describes the examination, intervention, and outcomes for a 71-year old female with a history of imbalance and decreased ambulatory endurance. During examination, the patient presented with SOT scores within functional limits. The HS-SOT was then implemented to assess vestibular function during head motion in standing, with eyes closed. The intervention included balance retraining, dynamic gait activities, lower extremity strengthening, and instruction in a home exercise program. RESULTS: Improvements were noted for all measures. Initially, during the HS-SOT, the patient fell during all 6 trials of the HS modification to condition 5 and her equilibrium score was 12.Posttreatment, she was able to maintain her balance in 5 out of 6 trials and her score increased to 55. The patient reported increased ambulatory endurance and independence with functional activities (ie, walking and turning her head, and stair negotiation without use of a railing). CONCLUSIONS: The HS-SOT quantified the complaint of head movement provoked symptoms for this individual with dysequilibrium and was useful in measuring success of an intervention.

Aged↗