|Year : 2017 | Volume
| Issue : 1 | Page : 29-33
Influence of gestational age on muscle tone of healthy preterm indian infants at 40 weeks postconceptional age: An objective assessment
Rajni Farmania1, S Sitaraman1, Rashmi Ranjan Das2
1 Department of Pediatrics, Sir Padampat Mother and Child Health Institute, Jaipur, India
2 Department of Pediatrics, All India Institute of Medical Sciences, Bhubaneswar, India
|Date of Web Publication||8-Feb-2017|
Dr. Rajni Farmania
Department of Pediatrics, Sir Padampat Mother and Child Health Institute, Jaipur - 302004
Source of Support: None, Conflict of Interest: None
Objectives: To provide baseline values of muscle tone of healthy preterm appropriate for gestational age (AGA) infants and to study the influence of gestational age (GA) on muscle tone of healthy preterm infants compared to full term (FT) at 40 weeks postconceptional age (PCA) in Indian scenario. Methods: The muscle tone of 204 healthy preterm and 74 term infants with normal perinatal course was measured within 72 h of life with the help of a goniometer. Out of 75 preterms followed up till 40 weeks PCA, 61 completed the study. The cohort was subdivided into two groups: Group 1= <35 weeks gestation (n = 23) and Group 2= ≥35 weeks gestation (n = 38). Each group was compared to term infants at 40 weeks PCA. Statistical analysis was performed using SPSS software. Results: The adductor angle, arm recoil, popliteal angle, wrist flexion and dorsiflexion angles of both preterm groups were significantly less mature than the FT (P < 0.05). Scarf sign was significantly lower in Group 1 but not in Group 2 when compared to FT individually. Heel-to-ear angle and posture of both groups were not significantly different to the FT. Conclusions: Objective assessment provides a normative data for healthy preterm infants. Maturation of heel to ear angle and posture is independent of GA at birth and can be taken as marker of muscle tone maturity. Deviation in these indicators can be taken as a marker for delayed maturation and follow up is advisable in these cases.
Keywords: Gestational age, muscle tone, neurological maturity, objective assessment, preterm
|How to cite this article:|
Farmania R, Sitaraman S, Das RR. Influence of gestational age on muscle tone of healthy preterm indian infants at 40 weeks postconceptional age: An objective assessment. J Clin Neonatol 2017;6:29-33
|How to cite this URL:|
Farmania R, Sitaraman S, Das RR. Influence of gestational age on muscle tone of healthy preterm indian infants at 40 weeks postconceptional age: An objective assessment. J Clin Neonatol [serial online] 2017 [cited 2019 Nov 15];6:29-33. Available from: http://www.jcnonweb.com/text.asp?2017/6/1/29/199754
| Introduction|| |
Preterm mortality has decreased in the last decade due to advancement in the field of neonatology. Despite the technological and scientific progress, newborns requiring neonatal intensive assistance are estimated to be at higher risk to develop neurological problems., The importance of birth weight (BW) and gestational age (GA) in the prognosis of preterm infants is justified as both represent systemic organ structural and functional maturation. Muscle tone is classified into active and passive components. Active muscle tone (motility, activity, or efforts at righting oneself) is markedly affected by states of illness, recent maternal medications, acute perinatal compromise, and level of alertness. Hence, active muscle tone is not consistently useful in evaluating baseline neuromuscular maturity. Passive tone essentially is unscathed by these factors that profoundly affect active tone. Passive tone can be measured by a scientifically accurate method using goniometer.
As clinicians become more involved in preventative, screening, assessment, and treatment of newborns and infants, an increasing need exists for baseline, goniometric values describing normal joint ranges of this population. The range of motion characteristics that are unique to newborns are described predominantly in qualitative terms, but quantitative data are scarce. Literature reports on neonatal assessment provide numerical values for the full-term , and some values for preterm newborns. No study has so far been done to provide baseline goniometric angles for the preterm that to from Indian sub-continent.
- To provide baseline values of muscle tone of healthy preterm appropriate for GA (AGA) infants
- To study the influence of GA on muscle tone of healthy preterm infants compared to full-term (FT) at 40 weeks postconceptional age (PCA).
| Methods|| |
The study was a prospective longitudinal study of a birth cohort of preterm and FT infants conducted from August 2009 to November 2010 in a tertiary care teaching hospital of North India. The study protocol was approved by Research and Ethics Committee of the hospital, and written informed consent was obtained from parents before enrollment of the subjects. Two hundred and four preterm infants of GA 28 weeks to 37 completed weeks, AGA with the normal perinatal course were enrolled for the study along with 74 term infants with the normal perinatal course. Small for GA, presence of congenital anomalies, abnormal neurological examination at term, those delivered by breech, use of mechanical ventilation, and abandonment of study before 40 weeks were excluded. Assessment of GA was performed by New Ballard score. The nutritional status (BW) in relation to GA was classified in accordance to Lubchenco scales. PCA was calculated as GA plus days/weeks of extrauterine life.
The muscle tone of preterm AGA and FT AGA infants was measured within 72 h of life with the help of a goniometer by a single observer. Preterm infants were followed at PCA of 40 weeks for a second assessment. The second assessment was done in the ward or in Child Development Centre outpatient clinic, if the subject is discharged within 72 h. FT infants were subjected to single examination. The infant was assessed in a quiet room when the baby was not hungry, sleepy, or irritable 1 h after feed. The resistance of an extremity to manipulation was measured by recording the angle formed at the joint by this movement, using a goniometer. The following angles were measured: adductor angle, popliteal angle, dorsiflexion angle, the difference in rapid and slow angle, heel-to-ear angle, arm recoil, wrist flexion, scarf sign, and posture. Muscle tone evaluation was adapted from Saint-Anne Dargassies, Ballard et al. and Amiel-Tison.,, Five posture patterns were evaluated in the infants. Posture was measured through scores graduated from 0 to 4, in this graduation, lower scores were related to immaturity. Following angles were measured with the goniometer in degrees, larger angles were related to immaturity: Wrist flexion and dorsiflexion angles (from 90°-0°), and arm recoil (180°-0°). Smaller angles indicated immaturity in popliteal and heel to ear angle measured as 0°-180°. Interpersonal error is avoided as the measurement of angles was done by a single person in both first and the follow-up assessment.
The database was mounted in the Excel program, and the statistical analysis was performed with SPSS (Version 16.0. Chicago, SPSS Inc.). The comparison of preterm infants, matched to term at 40 weeks PCA was analyzed through the variation analysis (ANOVA-one-way). The localization of differences between the groups was determined through the test of multiple comparisons. Sample size was previously estimated to reach the significance level adopted of <0.05. The comparison of muscle tone development in preterm at first and second assessment at 40 weeks was made with a nonparametric test (Wilcoxon for paired samples).
| Results|| |
A total of 204 preterm (m:f = 1:1) and 74 full-term babies underwent first assessment within 72 h of life. 75 preterm infants were enrolled for follow-up till 40 weeks PCA, of which 14 were excluded (PDA = 3, hypoglycemic seizures in the 1st week of life = 3, asymmetry of the popliteal and heel to ear angles = 2, died due to SIDS at home = 2, and lost to follow-up = 4). The mean GA of preterm infants (n = 204) at their first assessment was 34.29 ± 1.71 weeks. They were examined at mean age of 24.00 ± 13.88 h (between 28 and 30 [n = 0]; 30–32 [n = 19]; 32–34 [n = 38]; 34–36 [n = 85]; 36–37 [n = 62]). Out of 204 preterm infants, 135 were born by vaginal delivery and 69 by lower segment cesarean section. The descriptive statistics of individual angle is shown in [Table 1].
Sixty-one preterm infants (32 male and 27 female) with GA range ≥30 to <38 weeks completed the study and were followed till 40 weeks PCA. The mean GA of these babies at their first assessment was 34.85 ± 1.33 weeks. They were examined at mean age of 25.95 ± 16.31 h. They were sub-grouped according to GA from 28 to 30 weeks (n = 0); 30–32 weeks (n = 3); 32–34 weeks (n = 5); 34–36 weeks (n = 30); and 36–38 weeks (n = 23). No infant between 28 and 30 weeks met the inclusion criteria. The mean age of examination of term infants was 18.13 ± 7.15 h.
Preterm infants when compared to term at first assessment showed immaturity at all the muscle tone indicators as expected. Comparison of preterm infants with term at PCA of 40 weeks demonstrated no significant difference in posture, heel-to-ear angle and scarf sign. Adductor angle, popliteal angle, arm recoil were significantly lower in preterm newborns at 40 weeks PCA. Wrist flexion and dorsiflexion angles were significantly low in full-term than preterm infants at 40 weeks PCA [Table 2]. The difference between rapid and slow dorsiflexion angle showed no difference. Both preterm and full-term infants had score <10°. The non-parametric data is shown in [Table 3].
The cohort was subdivided into two groups: Group 1= <35 weeks gestation (n = 23), and Group 2= ≥35 weeks gestation (n = 38). Muscle tone indicators of both groups were compared with the FT individually at 40 weeks PCA and was computed post hoc. The adductor angle, arm recoil and popliteal angle of both preterm groups were significantly lower than the FT individually. The heel-to-ear angle, posture of both preterm groups was not significantly related to the FT. The weight, occipitofrontal circumference (OFC) and scarf sign of the Group 1 infants were significantly lower than the full-term at 40 weeks PCA. These parameters were not significantly related in the Group 2 infants [Table 4].
| Discussion|| |
The current study shows that preterm AGA infants have similar physical growth in terms of weight and OFC, but decreased muscle tone than their full-term counterparts. The study showed significantly reduced flexor tone (popliteal angle, arm recoil, wrist flexion and dorsiflexion) and adductor angle in preterm infants at 40 weeks when compared to full-term; while, posture, heel-to-ear angle and scarf sign were not found to be significantly different.
Few studies have compared premature infants at 40 weeks PCA to full-term infants., Saint-Anne–Dargassies describes that preterm infant at 40 weeks PCA exhibit lower muscle tone, greater range of motion, so that their motility is more varied and of greater amplitude than the FT infant. Howard and associates had found preterm infants to have a greater number of weak responses, especially on items involving muscle tone, despite their higher level of arousal.
With respect to posture, we found no significant difference between preterm and term infants. This corroborated with the findings of other studies.,,, One study observed muscle tone assessment of preterm infants not to be influenced by birth-weight, though the evolution is clearly related to PCA. When preterm infants were compared to term at 40 weeks, all indicators except Posture, Heel to ear and Scarf sign were significantly low in preterm infants. In this study, the preterm infants were evaluated between 7 and 14 days of life and the term infants between 24 and 48 h of life to avoid stress of delivery and more severe clinical instability, while in our study, we examined the infants at <72 h of life. Posture in our study was not significantly different suggesting that stress of delivery may not play the influential role on maturation of posture. In another study, the authors did not observe any posture that characterizes a specific gestational age. Other authors have agreed that posture is not age-dependent. A recent study using Sheehan Disability scale found a similar result. A study by Palmer et al. found that the preterm infants reaching 40 weeks showed less flexion in their posture, and less arm traction, arm recoil, and leg recoil than the full-term infants on day 1 and day 5 of assessment. Differences in posture between our study and the former can be explained as 34% of the preterm infants evaluated by former had gestational age <32 weeks compared to 8% in present study. The difference may be explained by the fact that the infants examined in the present study were more mature at the first assessment.
Most of the previous studies have assessed heel to ear angle subjectively as scores. We measured it objectively by goniometer. Comparing heel-to-ear angle of preterm at 40 weeks PCA to FT showed no significant difference, indicating the maturity of distal muscles. This is a well-established fact that maturation of passive tone occurs in the caudo-cephalic pattern. A study has shown the evolution of tone and reflexes from 25 weeks postmenstrual age to term. Lower extremity flexor tone was first detectable at 29 weeks postmenstrual age by the popliteal angle and heel-to-ear maneuvers. Lower limb tone appears 2–3 weeks earlier than the upper limb tone. Two patterns of normal development are seen in the preterm infants. Tone and reflexes emerge in a caudo-cephalad (lower extremities to upper extremities) and centripetal (distal to proximal) manner.
Dorsiflexion angle of preterm infants at 40 weeks PCA was 41.38 ± 7.60 and of term was 28.08 ± 11.44. All newborns showed <10° difference between the rapid and slow angle. This is in accordance with the Amiel-Tison which states that in the newborn period, the angle itself depends on the gestational age at the time of birth and ranges from 50° to 60° in very premature infants to nearly 0° in full-term.
To find whether certain muscle tone variables influenced by PCA can be attributed to gestational-age, further analysis of the data was performed by dividing preterm infants into two groups: group 1, <35 weeks gestation (n = 23) and Group 2, ≥35 weeks gestation (n = 38). Each group was matched to term infants at 40 weeks PCA. The result showed that heel-to-ear angle and posture is not significant in both the groups and Scarf sign is significantly low (P< 0.05) at <35 weeks gestation but not at ≥35 gestation. Thus, maturity of scarf sign is related to gestational-age and matures after 35 weeks. This is in accordance with a study which showed that shoulder tone (37–38 weeks) is preceded by hip tone (35–37 weeks).
Group 1 showed significantly less growth than full-term at 40 weeks PCA as evidenced by weight and OFC, which was significantly less than Group 2. This implies postnatal physical growth of preterm infants (<35 weeks) is dependent on the GA. As physical growth occurs, the muscle tone also matures, but not identically. Two parameters of muscle tone (heel-to-ear and posture) of both groups were comparable to the full-term at 40 weeks PCA. In other words, maturation of these muscle tone parameters is dependent on conceptional age regardless of GA at birth.
The functional anatomic approach by Sarnat explains the caudo-cephalic maturation. There are two systems in the central control of motor function: The corticospinal, which originates from the motor and premotor cortex, and the sub-corticospinal, from the reticular formation, the vestibular nuclei and the tectum. Myelination (the most visible indicator of maturation in motor pathways) shows that the timing and direction of development differ in these two systems. The sub-corticospinal system myelinates early and in an upward or caudocephalic, direction (very rapid changes are observed from 24 to 34 weeks' gestation). By 34 weeks, some of these pathways (medial) are fully myelinated, whereas others (lateral) are partially myelinated. Antigravity activity is dependent on the lower system.
Only few studies have used goniometer in past to measure the muscle tone angles in preterm infants. The present study is one of the first to measure the muscle tone of preterm infants with goniometer. Furthermore, heel-to-ear is quantified and not scored which provides more objective assessment. This study hypothesizes that heel-to-ear angle and posture can optimally be taken as the marker of muscle tone maturity of preterm infants at 40 weeks PCA, irrespective of the gestation at birth. Any deviation can be taken as a marker for delayed maturation, and follow up is advisable in these cases. Further studies with larger sample of lower gestational-age are required to validate the hypothesis.
| Conclusions|| |
Objective assessment provides a normative data for healthy preterm infants. Maturation of heel to ear angle and posture is independent of GA at birth and can be taken as marker of muscle tone maturity. Deviation in these indicators can be taken as a marker for delayed maturation and follow up is advisable in these cases.
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Conflicts of interest
There are no conflicts of interest.
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[Table 1], [Table 2], [Table 3], [Table 4]