Head-neck Postures Research Articles

Postures of the Head, Upper, and Lower Neck in Forward Head Posture: Static and Quasi-static Analyses

Background: Abnormal head and neck postures play a significant role in developing cervical spine dysfunction. Forward head posture (FHP) is one of the most common findings in individuals who experience head and neck disorders. Objectives: This study used a photographic method to analyze the head, upper neck, and lower neck postures in forward head posture in both static and quasi-static states. Since timely diagnosis and appropriate treatment are important in preventing further complications of this kinematic chain disorder, the postural variables of the head and neck were evaluated by focusing on their separate parts in both static and quasi-static states. Methods: This observational-analytical case-control study included 175 individuals with no history of neck pain in the past 6 months, 138 with FHP, and 37 with non-FHP. The postural angles, including the upper cervical, lower cervical, craniovertebral, head posture, and head tilt angles, were measured through photography in both the static state (with the head and neck in a neutral position) and the quasi-static state (while moving the head and neck in the sagittal plane) in a sitting position. The measurements were taken in two groups (FHP and non-FHP). Results: In a static state, the upper cervical angle was higher in the FHP group than in the non-FHP group. The lower cervical measurements were higher in the non-FHP group than in the FHP group. In the quasi-static state, significant differences existed in the changes of the upper cervical, lower cervical, craniovertebral, head postural, and head tilt angles between the two groups (P-value < 0.05). Conclusions: During full flexion to full extension of the neck, subjects with FHP exhibited reduced mobility in the cervical spine, particularly in the lower cervical region. Additionally, the position of the head relative to the neck remained unchanged in this group.

Automated Detection of Ear Tragus and C7 Spinous Process in a Single RGB Image—A Novel Effective Approach

Biophotogrammetric methods for postural analysis have shown effectiveness in the clinical practice because they do not expose individuals to radiation. Furthermore, valid statements can be made about postural weaknesses. Usually, such measurements are collected via markers attached to the subject’s body, which can provide conclusions about the current posture. The craniovertebral angle (CVA) is one of the recognized measurements used for the analysis of human head–neck postures. This study presents a novel method to automate the detection of the landmarks that are required to determine the CVA in RGBs. Different image processing methods are applied together with a neuronal network Openpose to find significant landmarks in a photograph. A prominent key body point is the spinous process of the cervical vertebra C7, which is often visible on the skin. Another visual landmark needed for the calculation of the CVA is the ear tragus. The methods proposed for the automated detection of the C7 spinous process and ear tragus are described and evaluated using a custom dataset. The results indicate the reliability of the proposed detection approach, particularly head postures.

Effect of Different Head-Neck Postures on the Respiratory Function in Healthy Males.

Normal respiration is a very intricate function that comprises mechanical as well as nonmechanical components. It is shown to be affected by various factors including age, lifestyle, disease, and change in posture. With the increased use of hand held devices, everyone is prone to poor sitting postures like forward head posture. The purpose of this study was to evaluate the effect of assumed forward head posture and torticollis on the diaphragm muscle strength. A sample of 15 healthy males, aged 18-35 years, was recruited for this study. All subjects performed spirometry to measure the forced expiratory volume in 1 second (FEV1), the forced vital capacity (FVC), and FEV1/FVC ratio. SNIP was measured during upright sitting, induced forward head posture, and torticollis. Subject's mean age (SD) was 23(6) years. The SNIP score of the subjects during sitting with FHP was lower as compared to that during upright sitting. It decreased significantly during induced right torticollis position. This is the first study exploring the impact of different head and neck positions on respiratory function. Alteration of head and neck positions had an immediate negative impact on respiratory function. Clinicians should be prompted to assess respiratory function when assessing individuals with mal-posture.

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.

Impact of shoulder position and fatigue on the flexion–relaxation response in cervical spine

BackgroundNeck pain is common among general population with a high prevalence among the people who are routinely exposed to prolonged use of static head–neck postures. Prolonged static loading can cause localized muscle fatigue which may impact the stability of the cervical spine. In this study, flexion–relaxation phenomenon was used to study the post fatigue changes in the stability of cervical spine by evaluating the synergistic load sharing between muscles and viscoelastic elements. MethodsThirteen male participants were recruited for data collection. The variables that influence cervical flexion–relaxation were studied pre- and post-fatigue using neutral and shrugged shoulder postures. The Sorensen protocol was used to induce neck extensor fatigue. Surface electromyography and optical motion capture systems were used to record neck muscle activation and head posture, respectively.FindingsThe flexion–relaxation phenomenon was observed only in the neutral shoulder position pre- and post-fatigue. The flexion relaxation ratio decreased significantly post-fatigue in neutral shoulder position but remained unchanged in shrugged shoulder position. The onset and offset angles and the corresponding durations of the silence period were significantly affected by the fatigue causing a post-fatigue expansion of silence period.InterpretationThe muscular fatigue of neck extensors and shoulder position was found to modulate the cervical flexion–relaxation phenomenon. Early shifting of load sharing under fatigued condition indicates increased demands on the passive tissues to stabilize the cervical spine. Shrugging of shoulder seems to alter muscular demands of neck extensors and make cervical flexion–relaxation phenomenon disappear due to continuous activation of the neck extensors.

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.

Human head–neck models in whole-body vibration: Effect of posture

This work presents passive and muscle-based models to predict the biodynamical response of the human head–neck under fore-aft and combined-axis whole-body vibration considering four head–neck postures: neutral, flexion, lateral flexion, and lateral rotation. The passive model consists of one link, a three-rotational-degrees-of-freedom joint, and traditional spring-mass-damper elements. The muscle-based model is similar to the passive model but has additional muscle components. The additional muscle component comprises spring-mass-damper elements to capture the effects of changes in displacement, velocity, acceleration, and jerk. Eleven male participants were tested under white-noise random vibration input signals at the seat level with a frequency range of 0.5–10Hz and magnitudes of 1.5m/s2 RMS for the fore-aft condition and 1.0m/s2 RMS in each direction for the combined-axis condition. The proposed models were able to reasonably predict the frequency content and acceleration of the head–neck for the postures under investigation, with the muscle-based model performing better.

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.

EFFECTS OF RANDOM WHOLE-BODY VIBRATION ON POSTURAL CONTROL, MUSCLE PERFORMANCE AND MOBILITY IN ELDERLY PEOPLE

This work presents passive and muscle-based models to predict the biodynamical response of the human head–neck under fore-aft and combined-axis whole-body vibration considering four head–neck postures: neutral, flexion, lateral flexion, and lateral rotation. The passive model consists of one link, a three-rotational-degrees-of-freedom joint, and traditional spring-mass-damper elements. The muscle-based model is similar to the passive model but has additional muscle components. The additional muscle component comprises spring-mass-damper elements to capture the effects of changes in displacement, velocity, acceleration, and jerk. Eleven male participants were tested under white-noise random vibration input signals at the seat level with a frequency range of 0.5–10 Hz and magnitudes of 1.5 m/s2 RMS for the fore-aft condition and 1.0 m/s2 RMS in each direction for the combined-axis condition. The proposed models were able to reasonably predict the frequency content and acceleration of the head–neck for the postures under investigation, with the muscle-based model performing better.

Cervical root compression monitoring by flexor carpi radialis H-reflex in healthy subjects.

One-group, pretest-postest experimental research with repeated measures. To determine the effect of head postural modification on the flexor carpi radialis H-reflex in healthy subjects. H-reflex testing has been reported to be useful in evaluating and treating patients with lumbosacral and cervical radiculopathy. The idea behind this technique is that postural modification can cause further H-reflex inhibition, indicating more compression of the impinged nerve root, or recovery, indicating decompression of the root. Such assumptions cannot be supported unless the influence of normal head postural modification on the H-reflex in healthy subjects is studied. Twenty-two healthy subjects participated in this study (14 men, 8 women; mean age, 39 +/- 9 years). The median nerve of the subjects at the cubital fossa was electrically stimulated (0.5 msec; 0.2 pulses per second [pps] at H-max), whereas the flexor carpi radialis muscle H-reflex was recorded by electromyography. The H-reflexes were recorded after the subject randomly maintained the end range of head-forward flexion, backward extension, rotation to the right and the left, lateral bending to the right and the left, retraction and protraction. These were compared with the H-reflex recorded during comfortable neutral positions. Data were recorded after the subject maintained the position for 30 seconds, to avoid the effect of dynamic postural modification on the H-reflex. Four traces were recorded in each position. During recording, the H-reflex was monitored by the M-response to avoid any changes in the stimulation-recording condition. Repeated multivariate analysis of variance was used to evaluate the significance of the difference among the H-reflex, amplitude, and latency, in various head positions. The H-reflex amplitude showed statistically significant changes (P < 0.001) with head postural modification. All head positions, except flexion, facilitated the H-reflex. Extension, lateral bending, and rotation toward the side of the recording produced higher reflex facilitation than the other positions. These results indicate that H-reflex changes may be caused by spinal root compression-decompression mechanisms. It may also indicate that relative spinal root decompression occurs in most head-neck postures except forward flexion. Head postural modification significantly influences the H-reflex amplitude but not the latency. This indicates that the H-reflex is a more sensitive predictor of normal physiologic changes than are latencies. The H-reflex modulation in various head positions may be-caused by relative spinal root compression-decompression mechanisms.

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.

Sagittal-plane mobility of the cat cervical spine

The present study was conducted to evaluate the nature of sagittal-plane motion across cervical vertebral joints and to identify the centers of rotation for each joint in anaesthetized cats X-rayed in a range of head-neck postures. Relative positions of adjacent pairs of vertebrae were assessed by constructing transparent templates for each vertebra that could be overlaid onto different X-rays, and then by digitizing the locations of three markers attached at a distance from each template. The finite centers of rotation for each joint were estimated using a rigid-body method. The errors associated with the estimates were quantified further by using a method in which the positions of digitized markers were fitted to concentric circles using a least-squares approach. The center of rotation between the skull and C1 was located at the cranial articular facets between the two bones. The center of rotation between C1 and C2 was situated near the tip of the odontoid process close to the site of attachment of the transverse ligaments. Centers of rotation for the other cervical vertebral joints were located in the region of the intervertebral disc. A similar range of values was obtained for centers of rotation when extended or flexed postures were used for the calculations, suggesting that the centers of rotation may not move markedly throughout a range of sagittal-plane rotations of approximately 90° at the skull-C1 joint and about 15–30° at the other cervical joints. These results showed that all cervical joints rotated during sagittal-plane motion. A minimal representation of the musculoskeletal mechanics of the feline neck probably requires multiple segments, each corresponding to a single vertebral bone.