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A Peer Reviewed Publication of the College of Allied Health & Nursing at Nova Southeastern University |
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Correspondence:
Leah Nof, PT, PhD
Citation:
During normal development, most infants achieve the stereotypical motor milestones and develop postural control from practicing transitions between developmental positions repeatedly. The different systems affecting postural control mature at varying intervals.2 In the early stages of development, the infant props him/herself on arms, in a position that permits the elevation of the chest from a surface. Spinal extension strengthens in the antigravity prone position and proceeds in a cephalic to caudal direction from the cervical to the thoracic spine promoting stability in the upper quadrant.
The sequential progression of
cephalic to caudal strengthening influences the achievement of optimal
biomechanical alignment necessary for efficient and effective motor function
in the upper and lower quadrants, trunk and cervical regions.4
Development of
postural control in infancy and early childhood is critical for underlying
stability for performance of mobility and skilled motor tasks throughout
childhood, adolescence, and later on as adults.5,6 Prone
weight-bearing positions contribute to upper truncal and spinal stability,
facilitate strengthening of glenohumeral and scapular muscles, and promote
postural alignment.7
Concurrently,
dynamic movements occurring in the upper extremities, as the infant gains
voluntary control, also affects upper quadrant strengthening and postural
stability. The attainment of postural alignment is dependent on complex
interactions between intact neurological and musculoskeletal systems
resulting in balance between flexor and extensor muscle groups.5,7
Postural alignment
is difficult to achieve and maintain when imbalance exists between flexor
and extensor muscles of the trunk. Scapulae and
shoulder girdle stability of the trunk are provided by the surrounding
musculature, such as the rhomboids and trapezi. During infancy,
strengthening of these muscles is stimulated during closed-chain kinetic
activities in prone developmental positions.7 It follows that
infants who spend less time performing closed-chain strengthening may be at
risk for inadequate stability, impaired postural control, and malalignment
with consequential clinical impairment and symptomology. Walking at early
ages may shorten the time that normally developing infants spend statically
and dynamically weight-bearing on the upper extremities. This may lead to
inadequate strengthening of the upper quadrant musculature.7 The
long-term effects of the resultant weakness may substantially compromise the
stability of the upper quadrant and consequently, affect upright postures,
specifically, the alignment of the upper trunk, thoracic and cervical
spines.15, 16 In contrast, greater time spent practicing
closed-chain activities during motor development may result in adequate
muscle control to promote correct postural alignment and stability around
joints, permitting normal, pain-free movement. The overall purpose of this study was to identify clinical signs that can be used as predictors of TMD. Based on clinical observations, variables consisting of the onset of independent walking, upper quadrant muscle strength, distance of the scapulae from the spine, and head posture were examined. The questions we wanted to answer included: First, was there a difference in the ages when subjects began independent walking, head position, and upper quadrant muscle strength in persons who were symptomatic of TMD as compared to those who were asymptomatic? Second, can TMD be correctly predicted from the age someone began independent walking, the strength of their upper quadrant musculature, and head posture? In order to answer these questions, subjects were considered to have TMD if they had a history of unilateral or bilateral TMJ pain, clicking, deviations with mouth opening, and/or asymmetrical lateral movement. For purposes of this study, subjects were also considered as having TMD if any aspect of the screening process consisting of interview questions and a physical examination conducted by an experienced physical therapist indicated positive clinical signs of TMD.
Methodology
Subjects A total of sixty-seven volunteers participated in this study. All subjects gave written informed consent. Children signed an assent form in addition to the parental informed consent. All forms and tests used had approval of the Institutional Review Board (IRB) at Nova Southeastern University, Fort Lauderdale, Florida. Participants were screened for presence or absence of common TMD symptomology. A questionnaire and physical examination form (see Appendix A), developed and commonly used by the NSU dental clinic to screen for TMD, was modified for our study and utilized by one of two physical therapist researchers, who performed all measurements for the study. A first physical therapist with over 25 years experience assessing and treating patients with TMD, conducted the screening and physical examinations. Questions inquired as to limited or painful mouth opening; clicking or locking of the jaw; pain with chewing; previous injury to the jaw, head or neck; and previous treatment for TMD. Physical examination was inclusive of palpation of TMJ during mouth opening and lateral deviation movements. Of those screened, 22 were found to clearly have positive TMJ symptoms, (mean age = 22.5; range 12-28 years) and 25 subjects were clearly symptom-free (mean age 22.6; range between 9-29 years). An additional 20 volunteers denied TMD symptoms but displayed inconsistent symptomology during physical examination. These subjects were excluded from the study as not meeting inclusion criteria. Our 47 subjects ranged in ages from 9 to 29 years (9 children from 9-18 years of age; 38 adults from 19-29 years of age). In addition to the clear absence or presence of clinical signs and symptoms of TMD, subjects were asked to consult with their parents or directly access their childhood/medical records wherein was documented information identifying the age in months, they began independent walking. Exclusion criteria included history of trauma to their TMJ, neuromuscular disorder, pathology or orthopedic surgery involving the TMJ, cervical spine, the upper quadrant area, thoracic spine or lower extremities.
Measurements Figure 1: Markings on inferior angle of scapula and corresponding spinal process in preparation for measurement of scapulae distance from corresponding spinal process
Scapula winging was determined by measuring, in millimeters, the distance of the inferior angles from the posterior thoracic wall. For this measurement, the arms were positioned in full shoulder internal rotation, with the dorsum of the hands positioned over the lumbar area. An observational posture examination was performed and a photograph of the relaxed standing posture was taken for all subjects. Anterior head position was recorded as nominal data. Subjects were assigned to one of two groups: normal alignment or forward head posture. A subject was considered to have forward head posture based on a photograph of the subject’s to the shoulder and mid-thoracic trunk (Figure 2).lateral views, where a line from the external meatus fell anterior to a line traveling down anterior Figure 2: Forward head posture determined by drawing a straight line down from the external meatus; the line falls anterior to the shoulder and mid-thoracic trunk
Muscle strength of the rhomboids, lower trapezi, and serratus anterior muscles were graded in accordance with standard muscle testing protocols used by clinicians as outlined by Kendall.22 The average of three maximal efforts, for each muscle by subjects, was evaluated as having MMT grades of 0-5 and for statistical purposes of this study, assigned corresponding numerical value, such that MMT grades of 5/5 = 5.0; 5 minus/5 = 4.75; 4 plus/5 = 4.25, 4/5 = 4.0; 4 minus/5 = 3.75; 3 plus/5 = 3.25; 3/5 = 3.0; 3 minus = 2.75; 2 plus = 2.25. The averages of muscle strength measurements for each subject per muscle tested were then collapsed into two groups. For this study, “good” muscle strength was defined as a score of 4 or greater; “weak” muscle strength was defined as a score of 3.75 or lower. The second physical therapist performed the postural screening and muscle testing for all subjects. Each therapist was blinded to measurements taken and data recorded by the other as well as subject group assignment. Data Analysis
Descriptive statistics were used
for demographics of sample size, number of adults and children. Differences
in ages of independent walking and scapulae distance in groups with and
without TMD were analyzed using a 2-tailed t-test. A Mann-Whitney U test
was used to determine differences in muscle strength data obtained from the
two subject groups. Differences in head posture were analyzed by
Chi-Square. Age of walking, head posture and scapulae distance data were
analyzed for predictive value using a correlation matrix for independent
variables. Probability ratios that the three variables can predict TMD were
determined by logistic regression statistics. Data were compiled and assigned to groups based on presence or absence of clinical signs and symptoms of TMD in subject participants. Descriptive statistics were used to describe the characteristics of the study subjects assigned to either the group with TMD or without TMD (Table 1). Our first research question as to whether there was a difference in the ages when subjects began independent walking, head posture, and upper quadrant strength in persons who presented with clinical symptoms as compared to those who were asymptomatic was answered. The mean walking age for the 22 subjects with TMD pathology was 10.0 months (SD 1.995), as compared to 11.8 months (SD 1.668) for the 25 subjects exhibiting normal, asymptomatic TMD function. Comparison of the average means of walking age between the subject groups (with and without TMD) was analyzed using a 2-tailed t-test with alpha set at the .05 level. The results of the t-test showed there was a significant difference between the groups as to the age of walking, with p=.002 (Table 2). Our results demonstrate a significantly higher prevalence of TMD pathology in our subjects, who began walking independently before the accepted motor milestone range of 12 to 15 months.23 Table 1: Demographic Data
Table 2: Group
Statistics
aTMD = Temporomandibular Dysfunction Comparison of means
t-test (relating walking age to TMD pathology) Of the 22 subjects with positive TMD symptoms, the frequency of forward head posture (cervical hyperlordosis) was found in 16 of the 22 subjects with TMD and 9 of the 25 subjects without TMD. Head position in the two subject groups was analyzed using a Chi-Square test, with significance set at the .05 level (Table 3).
Table 3: Difference in Head Posture
F = 6.340 (df1). Statistically significant at alpha <.012 level Based on our study, subjects with TMD were significantly more likely to have forward head posture (p=.012) than subjects without TMD. The average means of bilateral scapulae distance from the spine in asymptomatic and symptomatic study subjects were analyzed using 2-tailed t-tests with alpha set at the .05 level. Significant differences comparing left and right scapulae distance existed in the groups, with p = .002 (left) and p = .006 (right) (Table 4). The average mean distance of the scapulae from the spinal processes in subjects with TMD was significantly greater than in subjects without TMD pathology. Muscle strength of the serratus anterior, lower trapezius and rhomboid muscles in the subject groups was compared using the Mann-Whitney U Test, significance set at p=.05. Our results support significant differences in the strength only in the rhomboid muscles of subjects, with p=.0009 (left) and p=.019 (right) (Table 5). We found no significant differences in strength in the other upper quadrant muscles tested. Table 4: Scapula Distance and
TMD
Table 5: Muscle Strength and TMD
We were able to answer our second and third research inquiries. This study revealed a relationship among the variables: age of independent walking, the strength of their upper quadrant musculature and head posture in our subjects. The data further support that TMD can be correctly predicted from the age an individual began independent walking, the strength of their upper quadrant musculature and head posture. Logistic regression analysis was used to determine whether the variables of age of walking, scapula distance, and forward head position, could predict the presence or absence of TMD in our study subjects. Of our initial 47 subjects, we were able to predict the presence of TMD or no TMD in 39 of the subjects. Of the 25 subjects without TMD, our model (using the variables of age of walking, forward head posture, and increased scapulae distance) predicted 21 of the group not to have TMD. Of the 22 subjects with TMD, our model correctly predicted 18 members of the group to be positive. In our subjects, the model using the variables of age of walking, scapula distance, and forward head position was accurate in predicting group membership 81% of the time (Table 6a). Table 6a: Prediction of TMD Based on Age of Independent Walking, Scapulae Distance and Head Posture
Table 6b: Logistic Regression Table for Probability of TMD
Odds ratios, as demonstrated in
Table 6b, derived from our data demonstrated that: 1) the odds of having TMD
are less likely the later independent walking begins; 2) odds are less
likely to develop TMD the reduced degree of forward head position; and 3)
the odds are more likely to develop TMD the greater the scapulae distance.
Discussion
In our study, the average age reported for independent walking in subjects without TMD was comparable to the typical milestone. In comparison, subjects with TMD on the average began walking almost two months earlier. We theorize that early independent walking shortens the time the child would spend creeping. The preference for upright walking rather than creeping in early-walking infants, would decrease the exposure to the potential benefits to upper quadrant strengthening achieved through weight-bearing. Subsequently, this reduces the upper quadrant stability, which is needed for postural control and proper alignment, and can lead to forward head posture, malalignment of the TMJ and positive signs and symptoms of TMD.
As a result of this preliminary study, it may
not be advisable for parents to stimulate and encourage upright postures
before infants are truly ready for them and have developed sufficient upper
quadrant strength and stability to independently assume and maintain
postural alignment in such position. In our society, it is common to
position infants in upright positions before they have the appropriate
stability. The use of mobility devices such as baby-walkers and
ringed-walkers, and even jumpers, may actually contribute to upper quadrant
instability, since the infant is unlikely to prefer the all-fours position
for locomotion and play after experiencing the freedom to move in an upright
position, having their hands free. Parents desirous of stimulating gross
motor advancement in infants, not exhibiting delays, should be educated as
to the potentially negative effects of such activities. They should find
comfort in the fact that their child is not an early walker and may be
further developing upper quadrant stability while spending longer times
creeping. Our conclusions may appear contrary to the conclusion reached by
Leonard, which supports incorporating upright postures early in development
before the second year of life, for the purpose of promoting and preserving
central pattern generation (CPG) of stepping leading to normal gait.24
This study can be distinguished from ours in that Leonard’s subjects had
neurological deficits and did not examine the effects of early upright
positioning on posture, strength or presence of TMD.
Our study utilized a sample of convenience
consisting of young adults (college-age students) and only a small number of
children and adolescents. Many of the subjects, in both symptomatic and
asymptomatic groups, were in their early twenties and led typically active
lifestyles participating in recreational sports activities and/or fitness
routines. No information was gathered regarding the duration, frequency or
types of exercises and activities performed by subjects, which may have
affected upper trunk strength and postural alignment. The sample size was smaller than originally anticipated since many of the potential subjects, who claimed to be normal and asymptomatic, when screened, exhibited one or more of the commonly accepted clinical signs that may over time result in TMD. The two physical therapists who took all measurements, were blinded to each other’s examination findings, but not in all cases as to whether or not a subject had TMD. Knowledge of this information may have influenced the results. However, the therapists, having about 50 years of experiences between them performing similar measurements on various patient populations, took care to obtain objective and repeatable measurements. To minimize discrepancies in muscle grading, an average of three maximal efforts by each subject was recorded to minimize bias and error. In many instances, we relied upon verbal reporting to provide us with the age at which their child began to walk independently. It is possible a parent may have inaccurately recalled and thus reported incorrectly, the onset of independent walking and this may have skewed our results. A number of the subjects in both groups had been treated with orthodontic bracing, which may have affected the alignment of the TMJ. In all cases, such bracing was completed years earlier, during adolescence. Therefore, it was felt that the bracing would have a remote, if any, influence on our results.
Conclusions
Our results demonstrated that subjects exhibiting TMD, on average, started to walk at an earlier age than those who did not exhibit clinical signs or symptoms consistent with TMD. Additionally, those subjects with clinical TMD may have some upper quadrant weakness in the rhomboids, which may explain the greater scapulae displacement on the posterior chest wall with arm movements. This upper quadrant weakness may have also been a factor contributing to the development of the forward head posturing observed in our subjects. Our findings of hyperlordosis of the cervical spine confirm and support results of earlier studies, which indicated the presence of forward head posturing in persons with TMD.
Although a significant difference of 1.8 months (10.0 vs. 11.8 months) found in subjects with respect to age at onset of walking is generally not considered clinically relevant, in terms of later onset of TMD our study seems to indicate otherwise.
From our results, infants who spend shorter times in quadruped, consequently reduce benefits obtained from closed-chain strengthening of the upper quadrant musculature. This may place these infants at higher risk of ensuing upper quadrant instability and developing postural changes related to TMD. The variables of age of walking, forward head posture and abducted scapulae position appear to be promising predictors of later onset of TMD. References
Appendix A
SCREENING QUESTIONS
SCREENING TEST
Name:_______________________ Date of Birth: _________________ Male: _______ Female:________
Anterior teeth: Horizontal Overlap ________mm Vertical Overlap ________mm
Range of movement: ______mm (R); __________mm (L); Opening _________mm
TMJ Sounds: __None __Right __Left Muscle Pain: __No __Yes Joint Pain: __No __Yes __Right Side __Left Side
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