The reproducibility of natural head posture: a methodological study

Repeatability over time of posture, radiograph positioning, and radiograph line drawing: an analysis of six control groups

BACKGROUND

There is debate concerning the repeatability of posture over time, radiograph positioning repeatability, and radiograph line drawing reliability. These ideas seem to negate the use of before-and-after spinal radiographic imaging to detect and correct vertebral subluxations.

OBJECTIVE

To review the results of control groups in 6 clinical control trials with before-and-after radiographic measurements taken days, weeks, months, or years apart to accept or reject the hypothesis that radiographic analysis procedures are not repeatable, reliable, or reproducible.

DATA SOURCES

Six published control groups from original data. Other data were obtained from searches on MEDLINE, CHIROLARS, MANTIS, and CINAHL on radiographic reliability, posture, and positioning.

RESULTS

Comparison of initial and follow-up radiographic data for 6 control groups indicate that measured angles and distances between initial and follow-up radiograph measurements on lateral and anterior to posterior radiographs are not significantly different when utilizing Chiropractic Biophysics radiographic procedures. In 48 out of 50 measurements, the differences between initial and follow-up radiographs are less than 1.5 degrees and 2 mm. These measurements indicate that posture is repeatable, radiographic positioning is repeatable, and radiographic line drawing analysis for spinal displacement is highly reliable. The scientific literature on these topics also indicates the repeatability of posture, radiographic positioning, and radiographic line drawing.

CONCLUSIONS

Posture, radiographic positioning, and radiographic line drawing are all very reliable/repeatable. When Chiropractic Biophysics standardized procedures are used, any pre-to-post alignment changes in treatment groups are a result of the treatment procedures applied. These results contradict common claims made by several researchers and clinicians in the indexed literature. Chiropractic radiologic education and publications should reflect the recent literature, provide more support for posture analysis, radiographic positioning, radiographic line drawing analyses, and applications of posture and radiographic procedures for measuring spinal displacement on plain radiographs.

Head posture and deprivation of visual stimuli

INTRODUCTION

Natural head position (NHP) has been defined as the cranial position that is attained when individuals stand with their visual axes in the true horizontal plane. The visual axis is considered to be a key component in establishing, and maintaining NHP so that, in the absence of visual stimuli, gravitation and muscular proprioception chiefly control head position.

SUBJECTS AND METHODS

In this study, the natural head positions of a group of normal sighted subjects were measured in a well-lighted room. The findings were compared to similar observations made in the same subjects when they were placed in a completely dark environment. Measurements of cranio-cervical angulation were made on adults (N = 30, males = 17, females = 13) by means of an electronic inclinometer. Sitting Head Position (SIHP), Standing Head Position (STHP), and Orthoposition (OP) were determined for each subject in a well-lighted room, and subsequently, in a completely dark room.

RESULTS

The data indicate that there were statistically significant differences between Standing Head Position, and Orthoposition, measured in the light and in the dark. There were no statistically significant differences between Sitting Head Position measured in the light and in the dark.

CONCLUSION

The results indicate that craniocervical angulation is more extended in the dark than it is in the light. This finding suggests that head position responds to visual stimuli, and that when this sensory input is not present, there is a tendency for subjects to extend their heads.

Soft tissue cephalometric analysis: diagnosis and treatment planning of dentofacial deformity

This article will present a new soft tissue cephalometric analysis tool. This analysis may be used by the orthodontist and surgeon as an aid in diagnosis and treatment planning. The analysis is a radiographic instrument that was developed directly from the philosophy expressed in Arnett and Bergman "Facial keys to orthodontic diagnosis and treatment planning, Parts I and II" (Am J Orthop Dentofacial Orthod 1993; 103:299-312 and 395-411). The novelty of this approach, as with the "Facial Keys" articles, is an emphasis on soft tissue facial measurement.

Fifteen-year reproducibility of natural head posture: A longitudinal study

Natural head posture continues to be widely used as the logical reference position for the evaluation of craniofacial morphology. The basic underlying premise is that the long-term clinical reproducibility (variability) of natural head posture is significantly less than the variability of conventional reference planes with respect to the vertical. This study reports the 15-year longitudinal reproducibility of natural head posture. Twenty Chinese adults in Hong Kong, who had initial natural head posture radiographs at age 12 years, were followed up and had repeated cephalograms after 15 years. The method error (reproducibility) after 15 years was 2.2 degrees, which compared favorably with the 5-year reproducibility (method error = 3.0 degrees ) and the 5 to 10 minutes reproducibility (method error = 1.9 degrees ). The individual variability of natural head posture reproducibility increased slightly over time. After 15 years the variance of natural head posture (4.8 degrees [= 2.2(2)]) remains significantly less than the variance of intracranial reference planes to the vertical (25 degrees to 36 degrees ). Cephalometric analyses based on natural head posture therefore remain valid over time.

Increase of the vertical occlusal dimension by means of a removable orthodontic appliance and its effect on craniocervical relationships and position of the cervical spine in children

The aim of this study was to determine the effect of the increase in the occlusal vertical dimension by means of an orthodontic appliance on craniocervical relationships and position of the cervical spine. Thirty children presenting malocclusion were divided into two groups of 15 (a study and a control group). Those in the study group wore an orthodontic appliance to correct cross-bite. The children in the control group had no treatment during the experimental period. Two lateral craniocervical radiographs were taken for each child. The first one was taken in the intercuspal position in both groups. The second radiograph was taken of the study group after four months of wearing the appliance and also of the control group after four months. Cephalometric analysis in the study group showed a significant forward cervical spine position. There were no significant changes in the control group. The changes found in the study group suggest that when there are signs and symptoms of cervical dysfunction in children undergoing long-term orthodontic treatment, it is necessary to make an evaluation of the cervical column position after the insertion of any orthodontic appliance which increases the occlusal vertical dimension.

The relationship between ortho head posture and head posture measured during walking

Murphy, Preston, and Evans recognized the dynamic nature of head posture and developed instrumentation capable of measuring and recording this posture in a continuous manner. The aim of the current project was to use the newly developed instrumentation to determine whether the difference is statistically significant between the mean natural head ortho posture, measured in a controlled manner, and the mean dynamic head posture obtained during 5 minutes of walking activity in an experimental situation. The mean ortho head posture and the mean walking head posture were measured in each of 30 men. The differences between these two sets of mean head postures were statistically significant (p < or = 0.05). In 23 persons, the mean walking head posture was tipped backward relative to the mean natural head ortho position.

Immediate postural responses to total nasal obstruction

Twenty-five nasal breathing adults were radiographically examined before and after their nasal respiratory pattern had been artificially eliminated for a period of 1 hour. Six angular and six linear variables were measured to determine the extent of the postural reflexive behavior of the cranium, mandible, hyoid bone, tongue, and lips. All subjects coped in their own individual way with the environmental impact. The most generalized findings were parting of the lips (p < 0.05), a drop in mandibular position (p < 0.001), and a downward movement of the hyoid bone (p < 0.05). Cranial extension did not reach statistical significance (p = 0.06). The relevance of these findings relative to primate experiments and human clinical research is discussed. If the same postural reactions are maintained over a long-term period, they may be instrumental in influencing the vertical craniofacial growth pattern.

Sleep, breathing, and cephalometrics in older children and young adults. Part II -- Response to nasal occlusion

STUDY OBJECTIVES

We postulated that nasal occlusion would provide a challenge enabling us to assess factors predisposing development of sleep apnea in older children/adolescents and young adults. Factors of interest included sex, age, body mass index (BMI), tonsillar hypertrophy, and cephalometric measurements.

DESIGN

Sleep and breathing variables were examined and compared for four groups of subjects between one baseline night and one night of nasal occlusion in a sleep research laboratory.

SUBJECTS

Healthy, normal boys (n=23, mean age=13.3+/-2.1 years), girls (n=22, mean age=13.8+/-1.8 years), men (n=23, mean age=22.2+/-1.5 years), and women (n=24, mean age=22.4+/-1.8 years) were studied.

MEASUREMENTS AND RESULTS

The following sleep and sleep-related breathing measures showed significant increases in all four groups from baseline to occlusion: percentage of stage 1, number of transient arousals, transient arousal index, apnea index, respiratory disturbance index (RDI), and mean apnea length. No significant relationships were found between occlusion-night RDI and tonsillar size, cephalometric variables, or BMI, either singly or in combination.

CONCLUSIONS

Subjects' responses to nasal occlusion varied: most demonstrated a minimal and clinically insignificant increase in RDI; few showed a marked increase in RDI. Significant increases of sleep fragmentation -- even in the absence of frankly disturbed breathing -- indicate that nasal occlusion may secondarily affect waking function if prolonged over a series of nights.

Sleep, breathing, and cephalometrics in older children and young adults. Part I -- Normative values

STUDY OBJECTIVES

Aims were (1) to provide normative values for sleep and sleep-related breathing variables and physical features (cephalometrics, body mass index [BMI], and tonsillar size) in older children/adolescents and young adults, (2) to describe sex and age group differences, and (3) to evaluate relationships between physical features and sleep-related breathing variables.

DESIGN

Standard polysomnographic variables describing sleep and breathing were measured during a single night. Cephalometric measures were obtained from a standing lateral skull radiograph.

SUBJECTS

Normal, healthy boys (n=23; mean age=13.3+/-2.1 years), girls (n=22; mean age =13.8+/-1.8 years), men (n=23; mean age=22.2+/-1.5 years), and women (n=24; mean age=22.4+/-1.8 years) with BMI less than 27 were evaluated.

RESULTS

Sleep variables showed age group and sex differences consistent with published norms. Slow-wave sleep and rapid eye movement (REM) latency declined with age; transient arousals increased with age. Sleep-related breathing variables showed few changes related to age group or sex; small but statistically significant sex differences were found for arterial oxygen saturation nadir (lower in male subjects) and respiration disturbance index in non-REM sleep (greater in male subjects). Differences in cephalometric measures largely reflected normal growth and expected sex differences. No significant relationships between sleep-related breathing variables and physical findings were observed.

CONCLUSIONS

These data provide well-controlled normative values for sleep, breathing, and cephalometrics in a group of normal older children, adolescents, and young adults. The data provide useful reference points for patients of these ages in whom sleep apnea is suspected, particularly since such clinical studies are normally based on first-night polysomnography. Furthermore, these values represent developmentally appropriate grouping of the data.

New television technique for natural head and body posture analysis

A new television technique that proved to be faster than conventional photographic analysis has been developed and applied to the evaluation of the head and body natural standing posture in 303 healthy children, ages 6 to 11, and in 186 healthy young adults. In the lateral plane all subjects had extended head (soft tissue Frankfurt plane), with parallel Camper's and occlusal planes. The neck was halfway between the horizontal and vertical planes. Most angles significantly correlated with each other. The occlusal and neck angles showed a significant effect of age, being larger in children than in adults. In children the neck was more flexed, and the occlusal plane was more inclined downward. The results were in accord with previous photographic evaluations showing that the applied method was reliable and could be usefully employed in postural investigations. The results also confirmed that in healthy subjects, regardless of age, the soft tissue Frankfurt plane is extended, not horizontal.

The Frankfort horizontal as a basis for cephalometric analysis

A random sample of 79 British 12-year-old children was studied from tracings registered in the natural head position (NHP). The angle between the Frankfort horizontal (FH) and the horizontal at right angles to the plumb line was measured. Two experienced assessors checked every tracing; for those children perceived to show unnatural head position this was adjusted to what they considered to be the natural head orientation (NHO). The NHO was defined as the head orientation of the subject perceived by the clinician, based on general experience, as the NHP in a standing, relaxed body and head posture, when the subject is looking at a distant point at eye level. The FHK horizontal angle was then measured, now related to the corrected head position. The standard deviation for the latter angle was smaller than that of the uncorrected, but still too large for the FH to be considered reliable as a basis for clinical cephalometric analysis. No statistically significant difference in variability as found between FH and the sella-nasion line. The extracranial horizontal plane related to NHO was recommended as the least variable of the references studied.

Relative position of porion and tragus in orthodontic patients

In order to assess the relationship between the hard (porion-orbitale) and soft (tragus-orbitale) tissue Frankfurt planes, the relative positions of porion, orbitale, and tragus were evaluated on cephalometric radiographs. A 5-mm radiopaque disk was fixed on the right tragus of 160 white orthodontic patients (65 males aged 7 to 28 years, and 95 females aged 7 to 36 years), and a pre-treatment lateral cephalometric radiograph was taken. In every film the positions of orbitale, porion, and tragus were digitized, and the linear distances between the points, as well as the position of tragus relative to the skeletal structures, were calculated. The linear distances porion-orbitale and tragus-orbitale progressively increased with age, with a low variability in all age classes. The linear distances were always larger in the males than in the females. The tragus was always lower and more anterior than the porion, with vertical distances ranging from 1.2 to 19.8 mm. When the porion-tragus distance was expressed as a percentage of the porion-orbitale distance, the variability decreased. In the age classes, mean percentage horizontal projections from porion ranged from 18 to 23% of the porion-orbitale distance, mean percentage vertical projections ranged from 8 to 15%. Unfortunately, sample variability was large, and, in a single patient, the position of tragus relative to the skeletal structures could be predicted only with a large approximation.

Head posture and cephalometric analyses: an integrated photographic/radiographic technique

A photographic technique for natural head posture (NHP) recording that can be associated to standard radiographic exposures is presented. It allows the evaluation of radiographs, according to both the standard intracranial references and NHP. On the NHP photograph, the angle between the soft tissue nasion-pogonion line and the true vertical is calculated, and this value is used to rotate the standard radiograph around the Bolton point. The technique has been applied to 40 private orthodontic patients (24 females and 16 males, aged 7 to 20 years, mean 12.9 years). The hard tissue Frankfurt plane in NHP showed a wide variation: 80% of the patients had orbitale lower than porion (mean angle -6 degrees relative to the ground), 20% had orbitale higher than porion (mean angle 4 degrees). The position of this plane in NHP seemed to be different in the two sexes, with more males having the Frankfurt plane going upwards than females. The soft tissue Frankfurt plane (tragus-orbitale) in NHP was directed upwards (head extended) in 53% of patients. The two Frankfurt planes were never coincident in all subjects; the tragus was always lower and more anterior than porion. On average, the angle tragus-orbitale-porion was about 6 degrees. In young orthodontic patients NHP is therefore highly variable, gender dependent, and cannot be deduced from mean population values. Nevertheless, the evaluation of head position should be performed in each young patient before and during the treatment, to verify how the combined effects of therapy and growth act.

[The assessment of the facial profile in relation to head posture]

On the basis of Schwarz's [21] facial typology, soft tissue facial profile was evaluated in relation to 3 head positions: natural head position, head position according to the Frankfurter Horizontal, and head position according to a subjective personal appraisal of an aesthetically pleasing profile, i.e. aesthetic head position. Forty children (20 girls and 20 boys) and 40 adults (20 women and 20 men) with varying occlusal relationships constituted the study group. Facial photos oriented according to the above 3 head positions were evaluated. The results revealed that head posture had a decisive impact on the outcome of the facial profile evaluation. Significant differences existed between natural head position on the one hand and Frankfurter Horizontal and aesthetic head position on the other. Due to the relatively large methodological error in the registration of natural head position, and the resulting effect of this error on profile evaluation, natural head position can lead to misleading results. The advantage of Frankfurter Horizontal as opposed to aesthetic head position is the result of a subjective appraisal. Thus, when using Schwarz's method in evaluating facial profile, Frankfurter Horizontal still appears to be quite appropriate.

Effect of head posture on cephalometric sagittal angular measures

The definitions of cephalometric landmarks include relative terms that are dependent on the orientation of the head (e.g., lowest, most posterior) and head orientation differ widely during cephalometry (e.g., Frankfort plane horizontal, natural head posture). The purpose of this study was to quantify the effect of head posture changes on the commonly used sagittal angular measures SNA, SNB, and SNPogonion (SNPg). The sample comprised 30 Chinese skulls. Cephalograms were taken in a purpose designed skull holder with the Frankfort plane horizontal and at +10 degrees, +20 degrees, +30 degrees, -10 degrees, -20 degrees, and -30 degrees. A geometric grid was used to locate the deepest landmarks, and the landmarks were digitized followed by computer superimposition on the S-N line. To compare the values of the SNA, SNB, and SNPg angles in the different head postures, t tests were used. Head (skull) posture changes produced significant effects on the cephalometric values even at +/- 10 degrees of tilting. Overall, the angles were underestimated by approximately 1 degrees. In general, the angular differences and their standard deviations increased as the skull rotation increased with most of the differences for the SNB and the SNPg angles being clinically significant and also statistically significant at the 0.1% level. It was concluded that head posture needs to be standardized during cephalometry. Changes in posture significantly affect the location of some landmarks and the subsequent data obtained.

A natural head position technique for radiographic cephalometry

A three-part study was designed in order to test the applicability of the fluid-level method for registration of natural head position. In the first part the fluid-level method was utilized to make two repeated cephalometric radiographs of 33 young adults. The reproducibility of the craniovertical, craniocervical and cervicohorizontal relationships was comparable with previous results with the mirror method. In the second part, the fluid-level method was compared with the mirror method when used by two radiographers for repeated radiographs in 40 subjects. The reproducibility of the craniocervical and cervicohorizontal angles was less accurate with both methods and the only difference between them was a slightly better reproducibility of the craniovertical angle with the fluid-level method for one of the radiographers. In the third part, it was shown that using the fluid level, a patient can be transferred from a standing to a sitting position in the cephalostat without any systematic change in craniovertical, craniocervical or cervicohorizontal relationships.

Facial keys to orthodontic diagnosis and treatment planning. Part I

The purpose of this article is twofold (1) to present an organized, comprehensive clinical facial analysis and (2) to discuss the soft tissue changes associated with orthodontic and surgical treatments of malocclusion. Facial examination leads to avoidance of potential orthodontic and surgical facial balance decline and enhances diagnosis, treatment planning, treatment, and quality of results. Patients are examined in natural head position, centric relation, and relaxed lip posture. Nineteen key facial traits are analyzed. By examining the patient in this format, reliable facial-skeletal traits can be recorded that enhance all aspects of care. Orthodontics and surgery used to correct the bite alter facial traits; alteration should reverse negative traits and maintain positive traits. This cannot be achieved without a complete understanding of the face before treatment. Tooth movement (orthodontic or surgical) used to correct the bite can negatively impact facial esthetics, especially if pretreatment esthetics are not defined before treatment. Treating the bite based on model analysis or on osseous cephalometric standards without examination of the face is not adequate. Three questions are asked regarding the 19 facial traits before treatment: (1) What is the quality of the existing facial traits? (2) How will orthodontic tooth movement to correct the bite affect the existing traits (positively or negatively)? (3) How will surgical bone movement to correct the bite affect the existing traits (positively or negatively)? This article is for orthodontists, and yet, much surgical information is included. This is intentional. We only treat what we are educated to see. The more we see, the better the treatment we render our patients.

Reproducibility of natural head position

The orientation of the head, when the natural head position was adopted, was measured relative to the true vertical on standardized black and white profile photographs. Two methods of obtaining the natural head position were compared and their reproducibility tested. No statistically significant difference was found between the two different methods or at different sittings.

Proportional analysis of the facial profile in natural head position in Caucasian and Chinese children

A proportional analysis of the facial soft tissue profile in natural head position involving 11 indices (ratios), was applied to 80 Caucasian, and 80 Chinese male and female 12-year-old children in Hong Kong. The analysis is based on the true horizontal and the porion vertical, and has the advantage that its foundation lies on a more stable (less growth affected) region of the head compared to profile soft tissue landmarks. Measurements were made on cephalograms recorded in natural head position. Male subjects were larger than the females for most of the horizontal measurements, but for both population samples the vertical measurements displayed virtually no significant intersex differences at 12 years. No very significant intersex differences were found for the proportional indices. Ethnic differences were mainly found with the horizontal measurements. Relative to the porion vertical the Caucasian children were more protrusive over soft tissue nasion, nose tip, and sulcus labialis superior, whilst the Chinese displayed more protrusion over the lower lip and sulcus labialis inferior. Ethnic proportional differences relative to nasion were combined with a shorter porion-nasion distance in the Chinese as compared with the Caucasian children. The sella-nasion line was found to be more forwards-upwards inclined in Chinese than Caucasian children. It was concluded that a proportional soft tissue profile analysis, based on natural head position, is a useful method for the comparison of ethnic population groups. This study amplified ethnic differences previously reported by Cooke (1986) and Cooke and Wei (1989).

Five-year reproducibility of natural head posture: a longitudinal study

Natural head posture (NHP) is being increasingly used as the logical reference position for the evaluation of craniofacial morphology. The basic premise underlying its use is that the long-term clinical reproducibility (variability) of NHP is significantly less than the variability of conventional intracranial reference planes with respect to the vertical. This study reports the results of a 5-year longitudinal study evaluating the reproducibility over time of NHP lateral cephalometric radiographs. The subjects were 126 randomly selected Chinese children in Hong Kong who were first assessed at the age of 12 years. Thirty subjects were recorded after 5 years. NHP reproducibility deteriorated over time but showed signs of stabilizing after 1 to 1 1/2 years. The method error was 1.93 degrees after 1 to 2 hours, 2.34 degrees after 3 to 6 months, and 3.04 degrees after 5 years. The individual variability of NHP reproducibility also increased over time. The standard deviation of the SN/vertical angulation was 2.61 degrees after 1 to 2 hours, 3.16 degrees after 3 to 6 months, and 4.20 degrees after 5 years. Further longitudinal data are required to determine whether NHP reproducibility continues to deteriorate after 5 years. After 5 years, however, the variance of NHP (9.24 degrees [= 3.04(2)]) remains significantly less than the variance of intracranial reference planes to the vertical (25 degrees to 36 degrees).

Intersex differences in craniocervical morphology and posture in southern Chinese and British Caucasians

The aim of this study was to compare intersex differences in the angular relationships of the head, the cervical column, and the true vertical in natural head posture (the "postural variables") for unselected samples of southern Chinese (n = 240) and British Caucasian (n = 80) 12-year-old children in Hong Kong. For both samples the cervical spine was angulated significantly more forwardly in the females (P less than or equal to 0.001) and the head held higher relative to the spine. Cervical lordosis was also greater in the females and the cervical column of greater relative length. Our findings are in agreement with comparable data previously reported for a northern Finnish population.