Neck mobility measurement by means of the 'Flock of Birds' electromagnetic tracking system

OBJECTIVE: To establish the accuracy and reliability of a six-degrees-of-freedom electromagnetic tracking device, the "Flock of Birds", for measuring neck rotations and to identify the main sources of error. DESIGN: Ten human subjects made the same types of maximal neck rotation, both actively and passively: axial rotation in neutral position, from a flexed position and from an extended position, flexion/extension and lateral flexion. The same movements were mimicked in a 'dummy head' set-up. METHODS: One Flock of Birds receiver was mounted on the thorax, one on the head. By means of a third receiver, mounted on a stylus, bony landmarks on head and thorax were palpated. These served to define two anatomically based local coordinate systems, to which the rotations were referred. RESULTS: Measurements were accurate with a maximal measurement error of 2.5 degrees. No significant difference between active and passive rotation was seen. The intra-subject variation was low within the same session, SD between 2 degrees and 4 degrees. Between sessions the variability was considerable, SD between 5 degrees and 16 degrees. CONCLUSION: The Flock of Birds method is reliable and sufficiently precise. The variability in measured range of motion between sessions is a point of concern in interpreting follow-up studies in patients. RELEVANCE: A reduced range of neck motion is a major complaint in pathologies of the cervical spine or the shoulder. A method is described in which neck rotations are related to well-defined bony landmarks. In combined rotations, e.g. flexion combined with axial rotation, the measured range of motion can sometimes fluctuate strongly (up to 30 degrees ) between measurements, without apparent pathology.     

Normal global motion of the cervical spine: an electrogoniometric study.

OBJECTIVE: Establishment of a normal database and clinical reference of active global cervical spine motion ranges and patterns using a commercial electrogoniometer. DESIGN: Three-dimensional cervical motion ranges and patterns were analyzed in 250 asymptomatic volunteers. BACKGROUND: In vivo out-of-plane motion patterns of the cervical spine have not yet been reported in large populations, but could be of clinical interest. METHODS: In 250 subjects (aged 14-70 yr), motion range and patterns between the first thoracic vertebra and the head were analyzed for flexion-extension, lateral bending, rotation in neutral sagittal plane position and in full flexion using the CA 6000 Spine Motion Analyzer. RESULTS AND CONCLUSIONS: Average motion range in the sagittal plane was 122 degrees (SD: 18 degrees ). Flexion was slightly more important than extension. Out-of-plane components were negligible. Global bending range averaged 88 degrees (SD: 16 degrees ), left and right bending being comparable. Homolateral rotation was associated to lateral bending. Its extent was approximately 40% of the bending range. Global rotation range in neutral sagittal plane position was 144 degrees (SD: 20 degrees ), without significant difference between right and left rotations. Associated motion components were small. During rotation in flexed head position, global range (134 degrees, SD: 24 degrees ) was comparable to the one in neutral flexion. But heterolateral bending, averaging 60% of the primary motion, was associated to flexed rotation. Significant reduction of all primary (but not conjunct) motions with age were obtained. Sex had no influence on cervical motion range. RELEVANCE: Our results agreed with previous observations, validating the methodology used. They thus constitute reference data of cervical out-of-plane motion for clinical applications.     

Variations in the axis of motion during head repositioning--a comparison of subjects with whiplash-associated disorders or non-specific neck pain and healthy controls

BACKGROUND: The ability to reproduce head position can be affected in patients after a neck injury. The repositioning error is commonly used as a measure of proprioception, but variations in the movement might provide additional information. METHODS: The axis of motion and target performance were analyzed during a head repositioning task (flexion, extension and side rotations) for 24 control subjects, 22 subjects with whiplash-associated disorders and 21 with non-specific neck pain. Questionnaires regarding pain intensity and fear avoidance were collected. Head position and axis of motion parameters were calculated using a helical axis model with a moving window of 4 degrees . FINDINGS: During flexion the whiplash group had a larger constant repositioning error than the control group (-1.8(2.9) degrees vs. 0.1(2.4) degrees , P=0.04). The axis was more inferior in both neck pain groups (12.0(1.6)cm vs. 14.5(2.0)cm, P<0.05) indicating movement at a lower level in the spine. Including pain intensity from shoulder and neck region as covariates showed an effect on the axis position (P=0.03 and 0.04). During axial rotation to the left there was more variation in axis direction for neckpain groups as compared with controls (4.0(1.7) degrees and 3.7(2.4) degrees vs. 2.3(1.9) degrees , P=0.01 and 0.05). No significant difference in fear avoidance was found between the two neck pain groups. INTERPRETATION: Measuring variation in the axis of motion together with target performance gives objective measures on proprioceptive ability that are difficult to quantify by visual inspection. Repositioning errors were in general small, suggesting it is not sufficient as a single measurement variable in a clinical situation, but should be measured in combination with other tests, such as range of motion.     

Acute neck pain: cervical spine range of motion and position sense prior to and after joint mobilization

Despite the relatively high prevalence of cervical spine pain, the efficacy of treatment procedures is limited. In the current study, range of motion and proprioception was assessed prior to and after specific cervical spine mobilisation techniques. A 44-year-old male office worker presented with a history of cervical pain of 1 day duration. He had woken with pain, stiffness and a loss of range of motion. Examination findings indicated pain to be at C5–6 on the left side. Measurement of maximal three-dimensional cervical motion was undertaken using a Zebris system. A position matching task tested the individual's ability to actively reposition their head and neck. The treatment undertaken involved grade III down-slope mobilisations on the left side at C5–6 and C6–7 in supine lying. This technique was then progressed by placing the subject in an upright sitting position, and sustained natural apophyseal glides were performed at C6.Immediately following the treatment, the patient reported a considerable decrease in pain, less difficulty in movement and reduced stiffness. Motion analyses showed the most marked percentage improvements in range of motion after treatment were in flexion (55%), extension (35%), left rotation (56%), and left lateral flexion (22%). Ipsilateral lateral flexion with axial rotation was also notably improved following treatment. No change in proprioceptive ability was found following the treatment. The findings showed that the application of standardised specific mobilisation techniques led to substantial improvements in the range of motion and the restitution of normal coupled motion.     

Physiotherapist observation of head and neck alignment

Objective: To determine the reliability of physiotherapists' visual observation of head and neck alignment. Design: An interrater reliability study with an evaluation of concurrent validity using a gold standard. Setting: Physiotherapy Research Laboratory, Princess Alexandra Hospital. Participants: Three physiotherapist raters, one male model exhibiting 53 test positions. Main outcome measures: Assessment of head and neck alignment required rating the direction of deviation (in each of the three planes of movement), and the magnitude of deviation. Results: All three assessors were correct across all domains of direction and magnitude of deviation for only 10 of the 53 test positions. There was a mean of 2 total errors (out of a possible 12) per position. The more planes of deviation involved in a position, the more total errors there were. Most errors were made in the axial rotation (transverse) plane. Where a lateral flexion (coronal) plane of deviation was involved, there were more total errors; however, this plane itself had the fewest number of errors. Positions with a combination of both lateral flexion and axial rotation deviations were often mistaken for a flexion/extension (sagittal plane) deviation. Fewer errors were recorded for positions of 10-degree deviation compared to 5-degree deviations. Conclusions: Visual assessment of head and neck alignment by physiotherapists is of questionable validity for identifying deviations in the order of 5 degrees from neutral. For deviations of 10 degrees in a single plane visual, observation is comparable to other clinically available tools.     

Do flexion/extension postures affect the in vivo passive lumbar spine response to applied axial twist moments?

BACKGROUND: The injury potential and mechanical effects of combining axial rotation with non-neutral flexion/extension postures in vivo remains poorly understood, despite being identified as a risk factor in epidemiological and in vitro studies. The purpose of this experiment was to quantify the passive axial twist motion of the lumbar spine in various postures, and to assess whether non-neutral flexion/extension postures cause a detectable change in the range of twist motion and/or spine rotational stiffness. METHODS: Ten healthy male participants were passively rotated three times from a neutral and six flexed/extended starting postures (maximum-, mid-, mild-), while the moment-angle relationships were measured. The upper body was fixed to an adjustable rigid harness and the lower body was fixed to a cradle that rested on a frictionless table, thereby isolating the lumbar spine. FINDINGS: The lumbar spine stiffness and rotational range of motion were modulated by the different flexion/extension postures. The average maximum rotational stiffness values were smallest in maximum-flexion (81.0%, SD 16.6), and largest in maximum-/mid-extension postures at 125.4% (SD 24.4, P<0.0001) of the neutral stiffness magnitude. The axial twist angle was significantly different for each posture (P<0.0001), with 13.8% (SD 8.9) greater rotation in the maximum-flexion and 23.8% (SD 7.8) less rotation in the maximum-extension posture. The lateral bend coupled motion with axial twist was significantly different (P<0.0001) between the maximum-flexion (11.4 degrees , SD 6.3), mid-flexion/maximum-extension/mid-extension (6.5 degrees , SD 4.5), and mid-extension/mild-flexion/mild-extension postures (4.4 degrees , SD 3.8). INTERPRETATION: The lumbar spine stiffness and rotational range were modified by flexed-extended postures. The postural mechanism observed may be due to a change in the initial distance separating the facets prior to rotation. This information will be useful in determining spine rotational injury mechanisms through comparison with in vitro literature and for patient positioning during diagnostic tests.     

Validity and Intertester Reliability of Cervical Range of Motion Using Inclinometer Measurements

Abstract

Several procedures have been developed for using inclinometers to measure cervical range of motion. The purpose of this study was to evaluate the validity and reliability of three such methods. The subjects were thirty-four practicing physical therapists. Three individuals, who served as models, had their cervical range of motion measured by the thirty-four physical therapists using a single, double, and stabilization inclinometer method. X-ray films were then taken of the models in flexion, extension, and right and left lateral flexion. A computerized axial tomography scan was used for measuring cervical spine rotation. Results indicate that the single and double methods in flexion and single and stabilization methods in flexion were valid. Inclinometer measurements of cervical flexion, extension, lateral flexion, and rotation were found to be reliable for all three methods with ICCs ranging from .89 to .94. Although inclinometry yields consistent results, there validly is questionable. Sources of error were identified and suggestions given for improving validity and reliability of cervical range of motion while using inclinometers.     

Lower lumbar spine axial rotation is reduced in end-range sagittal postures when compared to a neutral spine posture

Sports such as rowing, gymnastics, cycling and fast bowling in cricket that combine rotation with spine flexion and extension are known to carry greater risk of low back pain (LBP). Few studies have investigated the capacity of the lumbar spine to rotate in various sagittal positions, and further, these studies have generated disparate conclusions. The purpose of this study was to determine whether the range of lower lumbar axial rotation (L3–S2) is decreased in end-range flexion and extension postures when compared to the neutral spine posture. Eighteen adolescent female rowers (mean age=14.9 years) with no history of LBP were recruited for this study. Lower lumbar axial rotation was measured by an electromagnetic tracking system (3-Space Fastrak™) in end-range flexion, extension and neutral postures, in sitting and standing positions. There was a reduction in the range of lower lumbar axial rotation in both end-range extension and flexion (p<0.001) postures when compared to neutral. Further, the range of lower lumbar axial rotation measurements in flexion when sitting was reduced when compared to standing (p=0.013). These findings are likely due to the anatomical limitations of the passive structures in end-range sagittal postures.     

Evaluation of efficacy and 3D kinematic characteristics of cervical orthoses

BACKGROUND: Cervical orthoses are often prescribed for both extrication stabilization of trauma patients and a treatment option of injuries to the cervical spine. The objective of this study was to compare effectiveness of two new and two established cervical orthoses in restricting 3D range of motion in the cervical spine. METHODS: Twenty healthy males and females (ten each) participated in the study. Two new cervical collars, C-Breeze and XTW and two established collars, Miami J and Aspen, were examined. A 3-camera Vicon system was used to collect 3D kinematic data. Subjects performed three trials in each of the 15 test conditions wearing no collar and the four cervical collars and performing three different head movements: flexion-extension, left-right lateral flexion, and left-right axial rotation. FINDINGS: The results comparing with the unbraced movements indicated that the Miami J and C-Breeze collars had significantly greater percent reduction on range of motion in flexion than the XTW collar. For both extension and lateral bending, all three collars showed greater percent reduction than the Miami J. The XTW also showed greater reduction than the C-Breeze and Aspen in extension. Finally, the C-Breeze collar showed a significantly more reduction in axial rotation than the Miami J collar. INTERPRETATION: The results suggested that C-Breeze and XTW along with the Miami J and Aspen collars are effective in restricting range of motion in the cervical spine. The two new cervical orthoses also performed either comparably as or better than the two established cervical orthoses.     

Spinal reflex excitability changes after lumbar spine passive flexion mobilization

BACKGROUND: Flexion distraction has gained increased credibility as a therapeutic modality for treatment of low back pain. Although important work in the area has elucidated the intradiskal pressure profiles during flexion distraction, the accompanying neural responses have yet to be described. OBJECTIVE: The purpose of this pilot study was to assess neural reflex responses to motion with 3 degrees of freedom applied to the lumbar spine and to evaluate H-reflex responses of the soleus. METHODS: Subjects (n = 12) were measured for H-maximum reflexes determined from stimulus response recruitment curves measured in neutral prone position. The mean of 10 evoked H-waves (at H-maximum stimulus intensity) were measured in neutral position, flexion, left and right lateral flexion, and axial rotation of the trunk on an adjusting table. H-reflexes were expressed as a percentage of maximal M-wave for the criterion measure. Spinal range of motion was quantified by digitization. RESULTS: The data showed variation in some movement ranges, notwithstanding identical table positioning for all subjects. Mean H-reflex amplitude was decreased (15.2 +/- 5.8 mV to 13.8 +/- 5.8 mV), and the H/M ratio was also decreased in flexion compared with neutral (55.0% +/- 19.1% to 50.3% +/- 19.4%; P <.05). CONCLUSIONS: Trunk flexion is accompanied by inhibition of the motor neuron pool. Slight perturbations in numerous afferent receptors are known to significantly alter the H-reflex. The absence of measurable changes in lateral flexion and trunk rotation may indicate that both slow- and fast-adapting receptors could be involved in lumbar motion. These preliminary findings suggest the need for further dynamic motion studies of the flexion distraction neurophysiologic condition.     

Three-dimensional analysis of active head and cervical spine range of motion: effect of age in healthy male subjects

OBJECTIVE: To assess the effect of age on active head-cervical range of motion in healthy men. DESIGN: Three-dimensional cervical motion ranges and patterns were measured in 70 men. BACKGROUND: The effect of age on cervical range of motion is still discussed. METHOD: Twenty adolescent (mean age 16 year), 30 young adult (mean age 23 year), and 20 mid-aged (mean age 37 year) men performed maximal head and cervical spine flexion-extension, lateral bending, and axial rotation. Movements were detected using a digital optoelectronic instrument. Maximum head-cervical spine and thoracic motions were separated. RESULTS: Flexion and extension were larger in the adolescents and young adults (130-132 degrees ) than in the mid-aged men (117 degrees ). Thoracic movement increased as a function of age. Lateral bending was symmetric, associated with head-cervical rotation and extension, and larger in adolescents (85 degrees ) than in young (77 degrees ) and mid-aged adults (79 degrees ). Axial rotation was symmetric, associated with flexion-extension and lateral bending, and similar in the three age groups (respectively, 160 degrees, 155 degrees, 153 degrees ). CONCLUSIONS: Active head-cervical range of motion reduced between 15 and 45 years of age in men.Relevance The present data can be used as a reference for cervical range in motion in men between 15 and 45 years.     

Measuring range of active cervical rotation in a position of full head flexion using the 3D Fastrak measurement system: an intra-tester reliability study

Most external assessments of cervical range of motion assess the upper and lower cervical regions simultaneously. This study investigated the within and between days reliability of the clinical method used to bias this movement to the upper cervical region, namely measuring rotation of the head and neck in a position of full cervical flexion. Measurements were made using the Fastrak measurement system and were conducted by one operator. Results indicated high levels of within and between days repeatability (range of ICC2,1 values: 0.85-0.95). The ranges of axial rotation to right and left, measured with the neck positioned in full flexion, were approximately 56% and 50%, respectively of total cervical rotation, which relates well to the proportional division of rotation in the upper and lower cervical regions. These results suggest that this method of measuring rotation would be appropriate for use in subject studies where movement dysfunction is present in the upper cervical region, such as those with cervicogenic headache.     

Validation of a Method to Assess Range of Motion of the Cervical Spine Using a Tape Measure

Objective

The purposes of this study were to validate a tape measure method for measuring cervical spine range of motion compared with a universal goniometer in all planes of motion and to derive equations to convert a linear measurement to an angular distance.

Methods

Participants were healthy volunteers. Measurements of flexion/extension, rotation, and lateral flexion were made with the universal goniometer and tape measure, in the neutral position, extreme of motion, and 2 positions between. Measurements from the 2 techniques were compared with Pearson correlation coefficient and simple linear regression to determine R², the regression coefficient and the regression equation. Reliability was assessed using the intraclass correlation coefficient.

Results

There were 40 participants with a mean age of 30.5 (SD, 9.1) years. Goniometer measurements had good to excellent correlation with both absolute and percentage change in tape measurement (correlation coefficients, 0.74-0.94 and 0.75-0.91, respectively). Correlation was highest for flexion and extension, lowest for rotation and lateral flexion. The amount of variability in the data explained by the linear regression models (R²) varied from 55% to 89%. Intraclass correlation coefficient ranged from 0.44 to 0.69 and 0.38 to 0.59 for intrarater and interrater reliability, respectively. Reliability was greatest for flexion and extension, lowest for rotation and lateral flexion.

Conclusion

This study demonstrated that tape measurements correlated well with a universal goniometer. The tape measure may be useful for measuring cervical spine range of motion where availability, simplicity, and low cost are important considerations such as with conduct of research or patient management.     

Assessment of the cervical range of motion over time, differences between results of the Flock of Birds and the EDI-320: a comparison between an electromagnetic tracking system and an electronic inclinometer

The objective of this study was to analyse cervical range of motion, assessed over time by means of a digital inclinometer (EDI-320) and a three-dimensional electromagnetic tracking device (Flock of Birds). The maximum active cervical range of motion was assessed with two measurement devices in three sessions over time, with 6-week intervals. In total, 26 women and 24 men (mean age: 44.4, SD: 9.9) without known pathology of the cervical spine participated. Four movements were measured axial rotation with the cervical spine in a flexed and in an extended position, flexion-extension, and lateral bending. The results showed that the factor time was significant for rotation in extension and rotation in flexion. The factor device was significant for all movements measured, and the interaction term between time and device was significant for all movements except rotation in extension. The Flock of Birds measured significantly higher ranges of motion on all motions except for lateral bending. A substantial variation in cervical range of motion was observed over time (ranging from -5.6 to 8.1) as well as between devices (ranging from -13.1 to 29.9). Substantial and significant differences in cervical range of motion were found over time as well as differences between the Flock of Birds and the EDI-320.     

Normal range of motion of the cervical spine

To evaluate the normal range of motion of the cervical spine, 70 healthy subjects were studied using radiography and clinical examination. An equal number of men and women were studied; age ranged from 12 to 79 years. Radiographs were taken in the lateral projection during maximal flexion and extension. In the frontal projection, radiographs were taken during maximal bending to the left and right. The radiographs were analyzed on a digitizing tablet linked to a computer, using preset points to indicate the motion between the vertebrae. The intraobserver error of measurement was +/- 1.8 degrees. The range of axial rotation was measured with the aid of a compass placed on the subject's head. The intraobserver error of measurement with this technique was +/- 6 degrees. The largest intersegmental flexion-extension motion occurred between C4/C5 and C5/C6. A linear decrease of motion in all directions, except in flexion, was found with age. There was no statistically significant difference in motion for men and women. The reliability of methods is discussed.     

Quantification of isometric cervical strength at different ranges of flexion and extension

BACKGROUND: Studies have demonstrated that cervical strength is affected by injury to the neck. Cervical strength measurements are influenced by the protocol used for the measurements. Previous studies have determined the isometric cervical strength only at a few degrees of range of neck motion. The present study was aimed at quantifying cervical strength at neutral, 25%, 50% and 75% of flexion and extension. METHODS: Using a correlation study design, 39 volunteers in the age range of 18-30 years were recruited in two sessions, one for flexion and the other extension. Their sequence was randomized. The cervical strength was measured using a force measuring device. The device was firmly bolted in the floor. A rotating metal tube was pivoted, adjustably counterweighted and attached to the device at one end and an immovable object with a load cell in its path at the other. The neck was positioned in the desired posture and isometric efforts were exerted on the horizontal resistance arm. FINDINGS: Cervical strength was found to be highest in the neutral posture for both flexion (19.8 N females and 31.4 N males) and extension (39.5 females and 45.1 males) and significantly decreased with an increasing angular deviation of the neck (P<0.01). Males exerted significantly higher forces than females. The overall flexion-extension ratio was 1:1.7 (P<0.01). INTERPRETATION: The maximum force was exerted in the neutral posture of the neck and it was directionally dependent being less in flexion than extension (P<0.01). Males were stronger than females. The findings may assist in targeting rehabilitation goals.     

Reproducibility and instrument validity of a new ultrasonography-based system for measuring cervical spine kinematics

OBJECTIVE: To report instrument validity of CMS 70P, a new ultrasonography-based system for spatial kinematic analysis of the spine and its application in studying the reproducibility of cervical motion findings in healthy subjects. BACKGROUND: Reproducibility of cervical motion has been investigated using various instruments and consisting in most cases of short test-retest time intervals of between minutes to days. METHODS: Performance of the instrument was validated against a digital inclinometer, at ranges of motion compatible with actual cervical motion. To study reproducibility, 25 healthy individuals, 22 women and 3 men aged 26-48 were tested twice within an average time interval of 3.3 weeks. Performed in the seated position and at a self-determined pace, cervical motion was defined in terms of head motion relative to a sternal (reference) system, in all six primary motions: flexion, extension, right rotation, left rotation, right lateral flexion and left lateral flexion. RESULTS: The system exhibited excellent agreement with the digital inclinometer, establishing its instrument validity for testing cervical motion. No significant differences were indicated between the test and retest for both the net maximal displacements and average velocities. The correlation coefficients for the single plane motions (e.g. flexion+extension) were higher than those derived for the primary motions, and ranged between 0.78 (sagittal plane) and 0.88 (frontal plane). The magnitude of the standard error of the measurement reflected the same trend with the lowest value recorded for the frontal plane. The self-selected velocity at which these motions were performed was similar in the frontal and saggital planes but was significantly higher for the transverse plane (rotations). CONCLUSIONS: This study indicates that spanned over time intervals that are measured in weeks, cervical motion findings derived from the CMS 70P are well reproducible. Findings also imply the need for a more stringent control of subject positioning and stabilization. RELEVANCE: Reduction of range of motion and average is typically observed in various pathologies of the cervical spine and is regarded, together with pain, as a major impairment. Therefore, valid assessment of cervical motion which is essential for follow-up and treatment outcome strongly depends on reproducibility of the findings. This study indicates that acceptable reproducibility is maintained over periods of time which are clinically meaningful using the system described herewith.