Infants with DS obtained significantly lower scores (z-score) on the TIMP in comparison to children from the control group at every age (Table 1). Mean performance of the control group at every age was within the average range for the reference population (mean = 0; SD = 1), ranging from a low of z = −0.13 (SD = 1.08) at 4 to 5 weeks of age to a high of z = 0.80 (SD = 0.49) at 16 to 17 weeks. On the other hand, the average performance of children with DS in every age bracket was more than 1 SD below the reference mean of zero for the US population-based sample. On the basis of the results of the observed items of spontaneous activity scored 0/1 on the first part of the test, children with DS obtained significantly lower results than children from the control group. Statistically significant differences in distributions of these variables were observed for the following items: 1, Head in Midline; 4, Fingers Object/Surfaces on Right; 5, Fingers Object/Surfaces on Left; 6, Bilateral Hip and Knee Flexion; 9, Reciprocal Kicking; 10, Fidgety Movements; 11, Ballistic Movements of the Arms or Legs; and 12, Oscillation of Arm or Leg During Movement. Taking into account all of the observed items, item number 10 was achieved by the fewest number of children. As expected, no child with DS up to the adjusted age of 9 weeks passed this item. Only 26% of children with DS over 9 weeks adjusted age demonstrated the presence of fidgety movements on item 10. Forty-two percent of the control group children passed item 10, of which 85% were children above 9 weeks adjusted age. On the remaining 5 items (items 2, 3, 7, 8, and 13), no statistically significant differences between groups were identified. The results of the items with quantitative ratings scales, items 14 to 42, expressed as a percentage of ability achieved in relation to the maximum score possible on the given item, show that children with DS also obtain lower results than children from the control group in items involving handling to stimulate movement.
Because the analysis was conducted in relation to the average age of all tested groups, no item was assessed above 90% of the obtainable scores, because the youngest groups never receive the maximum scores of the items from 14 to 42. The biggest difference of the obtained scores in both groups is related to the items measuring head control (14-20, 32), the quality of movement in response to visual (23/24) and auditory stimulation (38/39), behavioral response to a cloth placed over the face (26), and most of the items measuring trunk control in space and the quality of antigravitational postural patterns (27-31, 33-37, and 40-42) (Figure 3).
The analysis of the items measuring head control in space, items 14 to 17, shows that older age is associated with higher scores in both groups. Some of the items proved to be difficult even for children from the control group (ie, children whose motor development was free from disorders according to pediatricians). These activities include items 20, 32, 33, and 34. On the basis of a previous Rasch analysis of item difficulty, the first 2 of these items are of medium difficulty whereas items 33 to 34 are among the hardest items on the test.4 One item caused no difficulties for infants from either group. This was item 22, which assesses the ability to control the head in the midline in response to visual stimulation. The obtained z-score was analyzed depending on the subjects' age (divided into 8 age groups) in both groups (Figure 4). The lowest scores (z-score) were obtained by children with DS examined in the 2nd to 3rd weeks of life (age group 1), the 12th to 13th weeks of life (age group 6), and the 16th to 17th weeks of life (age group 8). Children from the control group achieved the highest z-score in comparison with reference values from the US sample in the 16th to 17th weeks of life.
In the first months of life, children with DS show significant delay in motor development. The development of posture and locomotion proceeds according to patterns that differ from those in children with TD. The profiles of psychomotor development at the beginning of therapy in children with DS show significant delay.11–13 In examinations performed with the use of the TIMP, significant delay was identified in relation to the achievement of particular motor abilities in the first 4 months of life by children with DS in comparison to children from the control group.
As stated by Campbell, the TIMP is sensitive to changes in motor development in relation to the child's age and ability. Studies carried out in 1995 and 2005 show that the age of the examined infants is highly correlated with the obtained scores (r = 0.83 and 0.81, respectively).10,14
A substantial portion of the TIMP items is based on the assessment of the quality of the observed posture and movement patterns in any activity. The quality of head and trunk control in space, as assessed with the TIMP items, is considerably lower in children with DS than in children from the control group. Because increasingly younger infants are admitted to rehabilitation centers dealing with developmental disorders, monitoring the child's development in the first trimester of life has become more common.
In 2004, Mazzone, Mugno, and Mazzone9 began to study the development of the youngest children with DS. The researchers analyzed the quality of global movements presented by infants with DS. Twenty-three infants from birth to the 6th month of life were examined using the The General Movements test. The General Movements assessment using the Prechtl method is a diagnostic tool used to perform a functional assessment of the young nervous system.15 The test results were compared with the global movements presented by children of the same age without developmental disorders. It was stated that global movements in children with DS are disordered and distinguished by slow pace, high or moderate movement range, sudden start and sudden stop, and rare spontaneous movements. It was stated that movement quality improves with age, but the group of children with DS was heterogeneous in comparison to children who are healthy. The global movements presented by children with DS correlate with the condition of the central nervous system and the condition of the movement characteristic of trisomy 21. A thesis was advanced that the assessment of global movements may be an early marker of future developmental disorders. In the first part of the TIMP, item 10 relates to the assessment of global fidgety movements, which are observed in TD from about the 9th week of life after the date of expected delivery. In this study, 50% of the children with DS were older than 9 weeks at the time of assessment. Only 26% of the infants with DS received a score of 1 for the quality of movement.
Tudella et al16 analyzed motor development of 19 children with DS from 3 to 12 months old. They identified difficulties both in performance and acquiring motor skills in prone, supine, sitting, and standing positions. They concluded that infants with DS need more time than children with TD to acquire skills, mainly antigravitational ones. Delayed development of antigravity movements, motor incoordination, and the presence of muscle hypotonia17,18 are confirmed in the results of TIMP testing for this group. Low scores on the TIMP items assessing the quality of antigravitational patterns (ie, the items related to the quality of head and trunk control in space [items 14, 15, 16, 17, and 18] and the quality of straightening reactions [items 19, 20, 33, 34, 41, and 42]) support this hypothesis. Rigoldi et al19 analyzed postural control in standing in 3 groups: children, teenagers, and adults with DS. Several parameters differed between the control and adult participants with DS, but divergence in postural control between the groups began in childhood.
The TIMP is sensitive to small changes in posture and movement patterns, making it useful for assessing early motor development of children with DS. This fact allows early implementation of intervention, which may contribute to development of balance reactions and motor coordination. Some of the children with trisomy 21 have reached significantly low scores in the item regarding supine neck rotation—use of visual tracking to elicit head turning to the side. Therapy for this group of children should take into account facilitating the infant's visual tracking, by improvement of head movements in horizontal and vertical directions, activation of the neck and trunk flexors, and elongation of the spinal extensors.20
Comparison of the results of the z-scores of children with DS in different age groups may prove that infants with DS develop disharmoniously and that during development periods of increased and decreased pace of achieving the individual abilities and motor behaviors occur. Commensurate with this conjecture is the fact that our mathematical models of head control (items 14, 15, 16, and 17) showed linear regression fit for the improvement of motor abilities as a function of time. Of course, this is the first approximation at modeling developmental change over time and the hypothesis needs to be further tested with a longitudinal study with a new sample of children.
The results of this study apply only to children from central of Poland with life conditions typical for proper development. In future research on assessment of motor development in children with DS, the effects of sociodemographic differences could be investigated.
The TIMP is a sensitive measure of delayed motor development in infants with DS that can be used to confirm the need for therapy. Analysis of item performance can identify specific areas of impaired postural control that can be used to design plans of care for improving motor outcomes of children with DS.
The authors gratefully acknowledge the participation of therapists, physicians, and nurses in the Early Intervention Center in Warsaw and Outpatient Clinic for Children in Warsaw (ZOZ Warszawa Wola). We thank Kryspina Czerny-Sieradzinska for creating the process of data collection. We especially thank the families who allowed their babies to be tested to benefit other children in the future.
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Keywords:Copyright © 2016 Academy of Pediatric Physical Therapy of the American Physical Therapy Association
child; developmental disabilities; Down syndrome; infant; motor skills; neuropsychological tests