Head-neck Posture Research Articles

First evolutionary insights into the human otolithic system

The human otolithic system (utricle and saccule), housed within the bony vestibule of the inner ear, establishes our sense of balance in conjunction with the semicircular canals. Yet, while the morphological evolution of the semicircular canals is actively explored, comparative morphological analyses of the otolithic system are lacking. This is regrettable because functional links with head orientation suggest the otolithic system could be used to track postural change throughout human evolution and across primates more broadly. In this context, we present the first analysis of the evolution of the human otolithic system within an anthropoid primate setting. Using the vestibule as a morphological proxy for the utricle and saccule, we compare humans to 13 other extant anthropoid species, and use phylogenetically-informed methods to find correlations with body size, endocranial flexion, and head-neck posture. Our results, obtained through micro-CT of 136 inner ears, reveal two major evolutionary transitions in hominoids, leading to distinctive vestibular morphology in humans, characterized by otolithic morphology resembling squirrel monkeys (possibly due to reversal), with a pronounced supraovalic fossa. Finally, we find a positional signal embedded in the anthropoid bony vestibule, providing the foundation to further explore the evolution of human head-neck posture using inner ear morphology.

An Extended Neck Position is Likely to Produce Cervical Spine Injuries Through Buckling in Accidental Head-First Impacts During Rugby Tackling

Catastrophic cervical spine injuries in rugby often occur during tackling. The underlying mechanisms leading to these injuries remain unclear, with neck hyperflexion and buckling both proposed as the causative factor in the injury prevention literature. The aim of this study was to evaluate the effect of pre-impact head–neck posture on intervertebral neck loads and motions during a head-first rugby tackle. Using a validated, subject-specific musculoskeletal model of a rugby player, and computer simulations driven by in vivo and in vitro data, we examined the dynamic response of the cervical spine under such impact conditions. The simulations demonstrated that the initial head–neck sagittal-plane posture affected intervertebral loads and kinematics, with an extended neck resulting in buckling and supraphysiologic intervertebral shear and flexion loads and motions, typical of bilateral facet dislocation injuries. In contrast, an initially flexed neck increased axial compression forces and flexion angles without exceeding intervertebral physiological limits. These findings provide objective evidence that can inform injury prevention strategies or rugby law changes to improve the safety of the game of rugby.

The effects of dual screen layout on neck-shoulder muscle activity and head-neck posture variability during computer tasks.

Larger dual screens have been widely used during office work and their biomechanical exposure should be explored. To investigate the biomechanical effect of two dual screen layouts on neck-shoulder muscle activity and the variability of head-neck posture in computer users. A preliminary study of the user-preferred dual screen angles was carried out in V-shaped and L-shaped layouts. Twenty healthy participants aged 19 to 26 years were recruited and assigned to perform reading, typing, and searching tasks for 30 minutes in both workstation layouts. Electromyography was measured at bilateral cervical erector spinae (CES), sternocleidomastoid (SCM), and upper trapezius (UT). The head-neck lateral bending, rotation, and flexion angles were recorded. The visual analog scale (VAS) was used to evaluate visual strain. The muscle activity at the left UT and right CES sites when using the V-shaped layout was significantly higher than the L-shaped. There were significant differences in head-neck rotation and flexion angles between the two layouts in reading and typing tasks. In the searching task, there was no significant difference in the head-neck rotation and flexion angles between the two layouts. The visual strain score was significantly higher in the V-shaped layout. The CES and UT muscles displayed higher levels of activation while using the V-shaped layout in comparison to the L-shaped layout. The head-neck rotation and flexion angles differed due to varied types of work when using V-shaped and L-shaped layouts.

Holistic Approach for Markerless Head-Neck Posture Assessment

Holistic Approach for Markerless Head-Neck Posture Assessment

Neck proprioception assessment with a laser beam device: reliability in participants without neck pain and differences between participants with and without neck pain

BackgroundProprioception deficits have previously been reported in patients with non-specific chronic neck pain (NSCNP), with a comprehensive and valid battery of tests still required. This study aimed to investigate the test-retest and inter-rater reliability of cervical proprioception in participants without NSCNP and to examine differences in proprioception between participants with and without NSCNP. Twenty participants without NSCNP and 20 age- and sex-matched participants with NSCNP were recruited. Proprioception tests were sequentially performed in random order, in four head-to-neutral movement directions (starting positions at mid-flexion, mid-extension and mid-right/mid-left rotation head-neck positions and end position at neutral head-neck posture) and two head-to-target movement directions (starting position from neutral head-neck posture and end positions at right and left 45° rotation), with a laser beam device secured onto their forehead. Participants performed all tests in sitting at a 1-m distance from a whiteboard. The average deviations of the laser beam mark from set targets marked on the whiteboard represented proprioception deficits. The two-way random, absolute agreement model of the intraclass correlation coefficient (ICC), the standard error of the measurement (SEM) and the smallest detectable difference (SDD) were used as measures of reliability. Between-group differences were examined with the independent samples t test.ResultsThe reliability of the laser beam device in participants without neck pain varied from poor to good. The following tests demonstrated good reliability: test-retest ‘Head-to-neutral from flexion’ (ICC: 0.77–0.78; SDD: 5.73–6.84 cm), inter-rater ‘Head-to-neutral from flexion’ (ICC: 0.80–0.82; SDD: 6.20–6.45 cm) and inter-rater ‘Head-to-neutral from right/left rotation’ (ICC: 0.80–0.84; SDD: 5.92–6.81 cm). Differences between participants with and without NSCNP were found only in head-to-neutral from flexion (4.10–4.70 cm); however, those were within the limits of the SDD values of the HtN from flexion test.ConclusionsThe laser beam device can be reliably used in clinical practice only in the aforementioned head-neck movement directions, based on the findings of the present study. The between-group differences noted involved only the head mid-flexion to neutral test, possibly denoting proprioception deficits only in this movement direction, for reasons that require further evaluation.

Neck Strength and Endurance and Associated Personal and Work-Related Factors.

The present study aimed to establish a normative database of neck strength and endurance while exploring personal and work-related factors that can significantly influence neck strength and endurance. A normative database combining both neck strength and endurance and delineating how they are affected by personal and work-related factors is currently lacking. It is needed for the development of tools and guidelines for designing work requiring head-neck exertions to contain the risk of occupational neck pain. Forty healthy participants (20 males and 20 females) performed sustained-till-exhaustion head-neck exertions, while seated, at 50% and 100% of their maximal efforts in anterior, anterior-superior, and posterior-superior directions in neutral, 40° extended, and 40° flexed neck postures. Exertion force and endurance time data from 38 participants were recorded and analyzed using regression models. Overall, multiple regression analyses of the neck strength and endurance database revealed that head-neck posture is the most significant determinant of both neck strength and endurance. The time of day significantly influenced neck endurance. Among the personal factors, a significant sex effect on neck strength and significant age and body mass index (BMI) effects on neck endurance were identified. The work-related factors play a more significant role in shaping both neck strength and endurance than personal factors and therefore are more important modifiable factors in meeting the physical demands of work. The study findings can aid in work design as well as in pre-employment screening to reduce the incidence of neck pain in the workplace.

The influence of different head posture on occlusal contacts and its importance in restorative prosthodontics -A short term study

Aim: To investigate the effect of sagittal plane head-neck posture on initial tooth contacts. Alteration of the position of the head will influence the neck and stomatognathic system, bringing the changes in occlusal stress distribution. Objective: To evaluate the various head positions in an attempt to elucidate the head posture and occlusal contacts. Materials and Methods: 20 subjects from 16 to 25 years of age with reasonable volunteer to participate in the study. The occlusal contacts are quantified by using occlusal indicator (okklean spray). Subjects with the head-neck in 450 dorsiflexion, 300 ventroflexion and in upright position. The head position is standardized by using pendulum goniometer. Conclusion: Occlusal contacts position have significance in the analysis of dental health. The evaluation of the area and force of occlusal contact is helpful for diagnosing the occlusal state of patients. The selection of appropriate occlusal indicator for this purpose enables the dentist to work with precision and provides valuable information on occlusion refinement. Keywords: Head position, occluasal contacts, ventroflexion, dorsiflexion and upright position.

Correlation between Trunk Posture and Neck Reposition Sense among Subjects with Forward Head Neck Postures.

Objective. To assess the correlation of abnormal trunk postures and reposition sense of subjects with forward head neck posture (FHP). Methods. In all, postures of 41 subjects were evaluated and the FHP and trunk posture including shoulder, scapular level, pelvic side, and anterior tilting degrees were analyzed. We used the head repositioning accuracy (HRA) test to evaluate neck position senses of neck flexion, neck extension, neck right and left side flexion, and neck right and left rotation and calculated the root mean square error in trials for each subject. Spearman's rank correlation coefficients and regression analysis were used to assess the degree of correlation between the trunk posture and HRA value, and a significance level of α = 0.05 was considered. Results. There were significant correlations between the HRA value of right side neck flexion and pelvic side tilt angle (p < 0.05). If pelvic side tilting angle increases by 1 degree, right side neck flexion increased by 0.76 degrees (p = 0.026). However, there were no significant correlations between other neck motions and trunk postures. Conclusion. Verifying pelvic postures should be prioritized when movement is limited due to the vitiation of the proprioceptive sense of neck caused by FHP.

Application of wireless inertial measurement units and EMG sensors for studying deglutition - Preliminary results.

Different types of sensors are being used to study deglutition and mastication. These often suffer from problems related to portability, cost, reliability, comfort etc. that make it difficult to use for long term studies. An inertial measurement based sensor seems a good fit in this application; however its use has not been explored much for the specific application of deglutition research. In this paper, we present a system comprised of an IMU and EMG sensor that are integrated together as a single system. With a preliminary experiment, we determine that the system can be used for measuring the head-neck posture during swallowing in addition to other parameters during the swallowing phase. The EMG sensor may not always be a reliable source of physiological data especially for small clustered muscles like the ones responsible for swallowing. In this case, we explore the possibility of using gyroscopic data for the recognition of deglutition events.

Neck Postures and Cervical Spine Loading Among Microsurgeons Operating with Loupes and Headlamp

OCCUPATIONAL APPLICATIONS Surgical tasks performed using loupes and headlamps were examined to identify exposures to physical risk factors for work-related musculoskeletal disorders in the neck among microsurgeons. Surgeons who use loupes and headlamps were found to spend extensive time periods working in non-neutral head–neck postures. These postures, and the use of loupes and headlamps, were found to be associated with an increased loading of the cervical spine, which might cumulatively contribute to occupational neck musculoskeletal disorders. To develop effective control strategies, future studies should focus on the impact of design features of loupes (e.g., mount angles, weight, and shape) on head–neck postures during surgical tasks. TECHNICAL ABSTRACT Background: Work-related musculoskeletal disorders in the neck are common among microsurgeons who operate with loupes and headlamps. Published surveys indicate that microsurgeons across many subspecialties believe that loupes contribute to neck musculoskeletal disorders. However, objective data on head–neck posture and cervical loading during surgical tasks performed using loupes and headlamps are currently lacking. Purpose: This study will assess exposures to physical risk factors for neck musculoskeletal disorders during surgical tasks performed using loupes and headlamp. Methods: A field study was performed in operating rooms to measure the head–neck postures commonly used by three ophthalmic plastic surgeons; a subset of microsurgeons. Posture data were used as input to a biomechanical model to estimate cervical spine loading. Results: During nearly 85% of the time spent operating, surgeons adopted asymmetrical head–neck postures characterized by either bending or rotation of >15°, coupled with flexion of >15°. Postures consisting of flexion ≥45°, 15°–30° bending, and 15°–45° rotation produced significantly higher biomechanical loading of the cervical spine compared to near-neutral postures (i.e., flexion, bending and rotation between 0° and 15°). This loading was further exaggerated by the weight of loupes and headlamp. Conclusions: Non-neutral head–neck postures demanded by the dexterous operating tasks performed using loupes and headlamps could be important biomechanical risk factors for cervical musculoskeletal disorders among microsurgeons.

Influence of an eccentric load added at the back of the head on head-neck posture

A biomechanical study of the head-neck complex in seated subjects was conducted to verify whether a slight load, applied at the back of the head, could beneficially affect the head-neck posture, one of the factors of postural neck pain. An eccentric load of 0.5kg was applied to the subjects’ head by means of a special cap. A group of asymptomatic subjects (n=10, 28.9±12.1yrs), and a group of subjects that had experienced mild, occasional neck pain (n=10, 39.6±18.4yrs) were compared. They were analyzed while maintaining a still posture that was periodically perturbed to avoid habituation. A 3D motion analyzer and reflective markers placed over the head, the neck and the trunk, were used to compute head inclination and translation and head/neck flexion angle in different conditions: before, during and after having had the load applied for 15min. Although the moment induced by the load was extensor, a forward-oriented movement of the head was observed in both groups. However, the forward displacement, in relation to the initial position, was smaller in the mild neck pain group than in the asymptomatic group (5.7±4.7mm vs. 8.9±5.5mm, P<0.05 and 2.6±5.9mm vs. 11.0±9.0mm after 15min, P<0.05). After removing the load, the mild neck pain subjects assumed a retracted position (−3.8±2.7mm) while the asymptomatic subjects stayed protracted (+3.5±5.1mm, P<0.01). These unexpected findings suggest that a slight load added to the head can influence the postural control mechanisms and, in symptomatic subjects, lead to a new strategy aimed at a reduction of the neck extensor muscle contraction.

The Impact of Use of Dual Monitor Screens on 3D Head–Neck Posture and Activity of Neck Muscles

OCCUPATIONAL APPLICATIONS Computers with dual monitor screens are being increasingly used at many workplaces. Altered screen layout and increased viewing space associated with dual monitor screens may affect head–neck working postures and the activity of neck muscles. However, this problem has not been investigated in the past, and standard guidelines based on empirical data are not available for setting up a computer workstation with dual monitor screens. The present study compared the effects of single versus dual monitor screens on 3D head–neck postures and the activity of neck muscles in computer users. The results of this study have demonstrated that working on a video display unit workstation with dual monitor screens involved more rotated, asymmetric head–neck postures and higher activation of the anterior neck muscles than a video display unit workstation with a single monitor screen. TECHNICAL ABSTRACT Background: Among workstation design factors, placement of the computer monitor screen is the most frequently identified risk factor for neck and shoulder pain among video display unit users. One of the recent changes in video display unit workstation design that may influence the position of computer monitor screens is the use of dual monitors. Some studies have shown that user performance and efficiency was positively affected by the use of dual monitor screens; however, the effect of use of dual monitor screens on the biomechanical behavior of the head-neck region is currently unknown. Purpose: This study was aimed at understanding the effect of single versus dual monitor screens on 3D head–neck postures and the activity of neck muscles. Method: Ten healthy participants performed three types of video display unit tasks: (1) reading for 10 minutes, (2) typing for 5 minutes, and (3) performing search and find tasks for 10 minutes using single and dual monitor screens. An inertial motion-capture system was used to measure 3D head–neck postures. Activity of sternocleidomastoid and cervical trapezius muscles was recorded bilaterally using surface electromyography. Results: Use of dual monitor screens significantly increased head–neck rotation by 9.0° compared to the single monitor screen. The range of motion of head–neck rotation increased significantly by 8.4° using dual monitor screens compared to the single monitor screen. Corresponding to the increase in the head–neck rotation, a contralateral increase in the activity of the right sternocleidomastoid muscle was observed with the dual monitor screen layout. Activity of cervical trapezius muscle was not affected by the type of monitor layout. Conclusions: Increased activation of anterior neck muscles caused by asymmetrical, more rotated head–neck postures while operating a video display unit workstation with dual monitor screens may increase the risk of neck musculoskeletal disorders, especially with prolonged computer use.

Predictive discomfort of non-neutral head–neck postures in fore–aft whole-body vibration

It seems obvious that human head–neck posture in whole-body vibration (WBV) contributes to discomfort and injury risk. While current mechanical measures such as transmissibility have shown good correlation with the subjective-reported discomfort, they showed difficulties in predicting discomfort for non-neutral postures. A new biomechanically based methodology is introduced in this work to predict discomfort due to non-neutral head–neck postures. Altogether, 10 seated subjects with four head–neck postures—neutral, head-up, head-down and head-to-side—were subjected to WBV in the fore–aft direction using discrete sinusoidal frequencies of 2, 3, 4, 5, 6, 7 and 8 Hz and their subjective responses were recorded using the Borg CR-10 scale. All vibrations were run at constant acceleration of 0.8 m/s2 and 1.15 m/s2. The results have shown that the subjective-reported discomfort increases with head-down and decreases with head-up and head-to-side postures. The proposed predictive discomfort has closely followed the reported discomfort measures for all postures and rides under investigation. Statement of Relevance: Many occupational studies have shown strong relevance between non-neutral postures, discomfort and injury risk in WBV. With advances in computer human modelling, the proposed predictive discomfort may provide efficient ways for developing reliable biodynamic models. It may also be used to assess discomfort and modify designs inside moving vehicles.

Posture, muscle activity and muscle fatigue in prolonged VDT work at different screen height settings

With the increasing use of video display terminals (VDTs), there is growing concern over the corresponding increase in the number of health problems reported. Although much research has focused on identifying the optimal screen height, there is to date no consensus. This study aimed to investigate the effect of prolonged (89 min) VDT work at four different screen heights on head-neck posture, muscle activity and the development of muscle fatigue. The results show that lowering screen height, starting from 15 cm above the baseline (i.e. top of the screen level with eye height while sitting), decreased the ear-eye angle, increased the viewing angle, increased the viewing angle relative to the ear-eye line, and increased the muscle activity of the neck extensor muscles. There were also some significant time effects on postural angles and muscle activity. In this study there were only rare occurrences of muscle fatigue, defined as a simultaneous increase in EMG amplitude and a shift of the EMG power spectrum to lower frequencies. Muscle activity increased significantly in some muscles and for certain screen heights.

VDT WORKSTATION PREFERRED SETTINGS: COMPARISON BETWEEN PC AND CAD WORKSTATION FOR TAIWANESE USERS

ABSTRACT A laboratory study was conducted to assess the preferred settings of the Taiwanese VDT users for both PC and CAD workstations. Thirty experienced VDT users from a semiconductor manufacture company participated in the study. A preferred backward leaning posture with upper arm slightly elevated and with a downward gaze angle was observed for most of the subjects on both workstations. The main differences on preferred settings between PC and CAD workstation were head-neck posture and gaze angle which were due to the difference in monitor size. Since neither the desk height and the monitor stand height, nor the seat height showed significant difference between the two types of workstations, similar adjustable dimensions may be specified for the design of both workstations. Except that the CAD workstation should allow for greater monitor screen to desk edge distance.

Influence of head-neck posture on airflow and pulmonary mechanics in preterm neonates.

The influence of head-neck posture (neutral, 15 degrees, 30 degrees, and 45 degrees extension and flexion) on airflow and pulmonary mechanics was evaluated in 10 spontaneously breathing healthy preterm neonates (mean +/- SD; birth weight, 1.32 +/- 0.23 kg; gestational age, 29.4 +/- 2.4 weeks; study age, 36.6 +/- 1.6 weeks) who had had respiratory distress syndrome. Head-neck postures were quantified using specially constructed wooden wedges. Airflow was measured by a pneumotachometer via face mask. Lung compliance (CL) and resistance (RL) were measured using an esophageal balloon. Airflow interruption was designated as mild (10-40%), moderate (40-80%), and severe (> 80-100%) decrease of airflow. At neutral head-neck posture, 42.8 +/- 7.5% SEM of breaths had airflow interruption (71.4% mild, 19.9% moderate, 8.7% severe). There was no significant change with 15 degrees and 30 degrees head-neck flexion and extension. However, at 45 degrees flexion the overall incidence of airflow interruption (77.3 +/- 4.8%, P < 0.05) and RL (86.6 +/- 6.7 vs. 64.2 +/- 3.9 cmH2O/L/s, mean +/- SEM; P < 0.05) significantly increased. Extension to 45 degrees caused severe airflow interruption and increased RL in some infants, but no statistically significant change for the whole group. The incidence of severe airflow interruption significantly increased (P < 0.05) from 8.7% at neutral head-neck posture to 26.3% at hyperflexion (45 degrees). No changes in CL were observed. We conclude that minor (15-30 degrees) deviations from neutral neck posture are insignificant, whereas hyperflexion, and in some infants, hyperextension, can significantly affect airflow and pulmonary mechanics.

The Effect of Head Posture on Muscle Contact Position Using the T-Scan System of Occlusal Analysis

The purpose of this study is to investigate the effect of sagittal plane head-neck posture on initial tooth contacts (muscle contact position) using the T-Scan system of occlusal analysis. Thirty-five subjects from 14 to 72 years old were selected. Computerized T-Scan occlusal printouts were obtained on each subject with the head-neck in 45 degrees dorsiflexion and 30 degrees ventroflexion. To quantify the location of the contacts on the upper arch, the dotted lines appearing on the printout were assigned numerical values. Low numbers represent distal contacts and the higher the number, the more mesial the contact. Wilcoxon's Rank Sum Test was used to analyze the data. Results indicated that below the age of 30 years no significant relationship was demonstrated between head posture and muscle contact position. However, over the age of 30 there was an increasingly significant relationship between sagittal plane head-neck posture and initial occlusal contacts. Based on these findings, the authors recommend that management of occlusally related problems, i.e., temporomandibular disorders include an assessment of the craniovertebral region especially in patients over the age of 30 years.

Body Posture and Hand Strength of Patients with Temporomandibular Disorder

The aim of this study was to observe the difference between patients of craniocervical muscle pain and nonpatients in head-neck posture, masticatory muscle activity, and the force exerted by the hand. Fifty-one patients and 28 nonpatients were observed. The electric activity of the masseter muscles was recorded when the subjects were doing pinching or grasping with the jaw in positions of rest, clenched, and clenched with gauze. Measurement of right and left tilting or extension and flexion of the head and neck was made from photographs of frontal and lateral views. It was found that the pinching and grasping force was much stronger in men than in women and in nonpatients than in patients with pain. The pinching and grasping force was more powerful with the teeth clenched. Clenching with gauze did not increase, but more often decreased the strength of the hand. The activity of the masseter muscle during clenching was about 10 to 26 times that of the resting activity. The activity decreased slightly when clenching with pinching or grasping. Patients were more likely to have a stretched neck with more extension of the head. Their masseter muscle activity and hand force were significantly weaker than that of the nonpatients.

Aggressive Communication By Larus Glaucescens Part Vi: Interactions of Territory Residents With a Remotely Controled, Locomotory Model

[Defenders maintaining a territory utilize similar strategies in defense when responding to a locomotory model as they do to intruders entering a territory. Model directional movement, body posture, and orientation were found to be highly correlated with subsequent behavioral response by the defender. Directional model movement caused an immediate position adjustment by the defender in most cases. Model towards movement resulted in a defender movement away and subsequent Display (Choke), while model movement Away caused a defender's Approach and subsequent Attack. Body posture was found to influence Attack rate as well as alter other behavioral responses by the defender. The lower head-neck posture was correlated with fewer attacks, thus showing that the low head-neck posture may convey greater threat to interacting birds. The orientation of a defender to the model during Attack was most common at angles greater than 90°. Thus the independent evaluation of orientation using the model shows that defenders as well as intruders are responsible for maintaining a particular orientation. The sex of defending birds interacting with the model was not distributed randomly. Males tended to interact more than females. Evidence supports the observation that male defenders are more aggressive than females. The non-correlation of certain behaviors during normal intruder-defender and model-defender interactions may be significant. It may be that the defender Upright Still and other behaviors are a waiting condition during which the defender plans its strategy under the influence of external threat conditions (i.e., movement, posture, orientation and sex recognition)., Defenders maintaining a territory utilize similar strategies in defense when responding to a locomotory model as they do to intruders entering a territory. Model directional movement, body posture, and orientation were found to be highly correlated with subsequent behavioral response by the defender. Directional model movement caused an immediate position adjustment by the defender in most cases. Model towards movement resulted in a defender movement away and subsequent Display (Choke), while model movement Away caused a defender's Approach and subsequent Attack. Body posture was found to influence Attack rate as well as alter other behavioral responses by the defender. The lower head-neck posture was correlated with fewer attacks, thus showing that the low head-neck posture may convey greater threat to interacting birds. The orientation of a defender to the model during Attack was most common at angles greater than 90°. Thus the independent evaluation of orientation using the model shows that defenders as well as intruders are responsible for maintaining a particular orientation. The sex of defending birds interacting with the model was not distributed randomly. Males tended to interact more than females. Evidence supports the observation that male defenders are more aggressive than females. The non-correlation of certain behaviors during normal intruder-defender and model-defender interactions may be significant. It may be that the defender Upright Still and other behaviors are a waiting condition during which the defender plans its strategy under the influence of external threat conditions (i.e., movement, posture, orientation and sex recognition).]