Motor Development of Infants with Positional Plagiocephaly

Abstract

Concurrent with recommendations to place infants to sleep in supine, there has been a dramatic increase in the number of infants with positional plagiocephaly (PP). Recent evidence suggests that infants who have decreased exposure to prone position may have a higher incidence of PP and may be at risk for a delay in the acquisition of certain motor skills. The purpose of this study was to compare motor development between infants with PP and matched peers without PP. We also examined differences in infant positioning practices when asleep and awake between the two groups. Twenty-seven infants with PP, 3 to 8 months of age, were matched by age, gender, and race to infants without PP. Motor performance was evaluated using the Alberta Infant Motor Scale (AIMS) and the Peabody Developmental Motor Scales (PDMS). Parents completed a diary that recorded infant positioning over a 3-day period. Mean AIMS percentile score for infants with PP was 31.1 ± 21.6 as compared with 42.7 ± 20.2 in infants without PP (p =. 06). Better performance on the AIMS was positively correlated with the amount of time in prone position when awake, for both groups of children (PP r =. 52, no PP r =. 44, p <. 05). Therapists should be aware of a risk of a motor delay when evaluating infants with PP. It is also important for parents to be informed about the importance of supervised prone playtime to enhance the development of early motor skills.

KEYWORDS:

• Plagiocephaly
• infant
• motor development
• prone positioning

Occipital plagiocephaly is a term used to describe asymmetry of the infant skull arising in the prenatal or perinatal period that is characterized by unilateral occipital flattening with ipsilateral frontal prominence. The ear on the affected side is displaced anteriorly and inferiorly (Dias & Klein, 1996). Positional torticollis is often associated with the plagiocephaly (Bruneteau & Mulliken, 1992; Rout & Price, 1978). The head is usually turned so that the chin points to the side opposite to the occipital flattening and the head is tilted to the same side as the flattening. There are two types of occipital plagiocephaly. The first type is associated with a true fusion of the lambdoid suture resulting in a craniosynostosis. This type of deformity usually requires surgical management. The second and more common type of plagiocephaly is positional plagiocephaly (PP). This involves a similar deformity but with maintenance of a patent suture. Thus, brain growth is not inhibited (Dias & Klein, 1996).

The cause of PP is somewhat controversial. Two possible mechanisms have been proposed. The first mechanism is that of fetal head constraint by the maternal pelvis during the latter stages of pregnancy. The second proposed mechanism, and perhaps the one under most scrutiny in recent years, is that of postnatal positioning of the infant (Bialocerkowski, Vladusic, & Ng, 2008; Dias & Klein, 1996). Young infants placed predominantly in the supine position tend to posture their heads preferentially to one side due to lack of head control. Prolonged exposure to this position causes molding of the skull that can result in PP.

Prior to 1992, the incidence of PP in North America was reported to be one in 300 live births (Clarren, Smith, & Hanson, 1979). In 1992, the American Academy of Pediatrics issued a position statement on the association of the prone sleep position with sudden infant death syndrome (Kattwinkle, Brooks, & Myerberg, 1992). This was closely followed by the “Back to Sleep Campaign,” which urged parents to use the supine position as the sleep position of choice for healthy children (Turk, McCarthy, Thorne, & Wisoff, 1996) Subsequent to this campaign, several craniofacial and neurosurgical centers reported a dramatic increase in the number of referrals for plagiocephaly (Kane, Mitchell, Gavin, & Marsh, 1996; Turk et al., 1996).

More recently, there have been reports of delayed development and poor head control in children with occipital plagiocephaly. Pople, Sanford, and Muhlbauer (1996) reported that four out of 46 children, for whom psychomotor development was assessed, presented with a delay in development and poor head control. Kane et al. (1996) examined 269 infants with the diagnosis of PP. They determined that 4.4% of their sample of infants presented with poor head control. Francel et al. (2000) compared the performance of 42 infants with PP and a matched sample of 42 infants with typical development using the Bayley scales. Thirty-two percent of infants with PP demonstrated a delay on the psychomotor index compared with only 12% of the infants with typical development. In a retrospective chart review of 48 children with PP referred to physical therapy for neck range of motion and positioning exercises, Kennedy (1997) reported that 24% of the infants were determined as having some degree of motor delay on initial evaluation. The majority of the studies reviewed did not indicate how motor development was assessed. Furthermore, the relationship between motor scores with positioning practices while the infant is awake and actively practicing gross motor skills has not been examined.

It has been proposed that PP can develop as a result of persistent positioning of the infant in supine position with preferential head turning to one side (Dias & Klein, 1996). Several studies have demonstrated that children who adopt the supine sleep position are more likely to exhibit gross motor lags and may have delays in the acquisition of gross motor milestones when compared with infants who sleep in prone position (Monson, Deitz, & Kartin, 2003; Salls, Silverman, & Gatty, 2002). Jantz, Blosser, and Fruechting (1997) noted a change in findings for developmental screening of infants in their pediatric practice beginning 1 year after the American Academy's recommendations regarding sleep position. Davis, Ottolani, Moon, Saachs, and Ottolini (1998) determined that infants who slept in supine position had delayed acquisition of rolling and tripod sitting, among other motor milestones, when compared with infants who adopted the prone position for sleep. Majnemer and Barr (2005) provided empirical evidence demonstrating that exposure to prone position while awake is positively associated with performance on gross motor assessments at both 4 and 6 months of age. It is unknown whether infants with PP are at enhanced risk for delays in early motor development due to prolonged supine exposure.

The purpose of this study was to (1) to compare motor development of infants with PP with a matched group of infants without PP, and (2) to examine the association between infant positioning practices and motor development. We hypothesized that the infants with PP would have an increased exposure to supine while asleep and awake when compared with their matched peers. We further hypothesized that this preference for prolonged supine positioning would not only be associated with the PP but would also be associated with a delay in motor development.

METHODS

Participants

A sample size calculation was performed to identify the number of infant pairs that were required to test the hypotheses. To detect a difference of at least 25 percentiles on the Alberta Infant Motor Scale (AIMS; Piper & Darrah, 1994), using α =. 05, β =. 20 and power of. 80, it was determined that a minimum of 16 subjects per group would be adequate. The number was increased by 10% to allow for analysis of each confounding variable and a further 20% was added to accommodate for missing data and withdrawals from the study. This brought the total number of subjects required to 25 infants per group.

Term infants between the ages of 3 and 8 months with a diagnosis of PP that was confirmed by both radiographic and clinical examination by a neurosurgeon with craniofacial expertise were recruited into the study from the neurosurgery clinics of the Montreal Children's Hospital. Each infant with PP was matched by age (± 2 weeks), gender, and race with a comparison infant that was recruited from the general practices of pediatricians associated with the hospital. The study was approved by the hospital's institutional review board and informed consent was signed by a parent for each participant.

A total of 27 infant pairs participated in the study. There were 16 males and 11 females in each group. Paired t-tests were performed to analyze the differences in descriptive characteristics between the two groups (Table 1). There was no statistically significant difference in gestational age, birth weight, or age at evaluation between the two groups. The mean difference in age at evaluation was 6 days, which was not thought to be clinically meaningful. There was no significant difference in socioeconomic status between two groups, as represented by maternal educational level. Cranial measurements were carried out on each comparison infant to rule out the possibility of undetected PP.

TABLE 1 Characteristics of Infants with Positional Plagiocephaly and Comparison Group of Infants Matched for Age (n = 27)

	PP group	Comparison group	Paired analysis (p value)
Gestational age (weeks)	39.8 (± 1.2)	39.4 (± 1.1)	.17
Birth weight (in grams)	3557.6 (± 473.6)	3663.5 (± 487.9)	.43
Age at evaluation (in months)	5.0 (± 1.5)	5.2 (± 1.4)	.07

* Mean (standard deviation).

Measures

Motor skill acquisition was assessed using AIMS (Piper & Darrah, 1994) and the gross and fine motor subscales of the Peabody Developmental Motor Scales (PDMS) (Folio & Fewel, 1983). The AIMS is a norm-referenced observational measure that describes the movement abilities of infants from birth to walking. Domains include prone, supine, sit, and standing positions. Items within each domain are scored on specific criteria (weight bearing, antigravity movements, postural alignment). The PDMS is a norm-referenced measure of motor skills mastered or emerging in infants and young children. A gross motor and fine motor quotients may be separately derived. At the time of initial recruitment for this study, version 2 of the PDMS was not yet available. Both the AIMS and PDMS tests have evidence of reliability and validity and are widely used in clinical practice (Boulton et al., 1995; Darrah, Piper, & Watt, 1998a; Gebhard, Ottenbacher, & Lane, 1994; Hinderer, Richardson, & Atwater, 1989; Piper, Pinnell, Darrah, Maguire, & Byrne, 1992; Piper & Darrah, 1994; Stokes, Deitz, & Crowe, 1990).

Time spent in prone and supine positions was measured using prospective recording in a standardized diary (Barr et al., 1988). Time spent in prone, supine, and other positions was calculated in minutes per day and averaged over 3 days. A parental diary was used to record this time. This method has been found to be a valid and reliable measure of behaviors associated with infant state and position (Barr, Kramer, Pless, Boisjoly, & Leduc, 1989; St. James-Roberts, Hurry, & Bowyer, 1993). Reporting for 3 days consecutively has been reported to substantially reduce variability due to day of sampling (personal communication, Dr. R. Barr).

Procedure

Parents were provided with instruction on the completion of the diary and were asked to fill it in on 3 consecutive days during next week. During the same week, the AIMS and PDMS were administered in the home of each infant by the same physical therapist, who had experience in the administration and scoring of both the measures. Assessments by the physical therapist took approximately 1 hr to complete. The physical therapist was not aware of the objectives of the study.

Data Analysis

Data were analyzed using the statistical package SPSS for Windows, version 11 (Chicago: SPSS Inc.). α was set at p <. 05. Performance on motor measures was compared between infants in the PP and comparison group using paired t-tests and chi-square analysis. The association between the amount of awake time spent in prone position and motor performance (AIMS absolute motor scores) was examined by correlation analyses (univariate) and subsequently using multiple regression models whereby additional independent variables including maternal education, birth order, and age at assessment were considered. We also computed multiple conditional linear regression analysis, which enabled us to examine factors associated with pair differences in motor scores (PP infant compared with its matched control) as the dependent variable.

RESULTS

Motor Development

The mean percentile score on the AIMS was 31.1 ± 21.6 for infants with PP group and 42.7 ± 20.2 for infants in the comparison group, a difference that was not significant (p =. 06). The mean percentile score for both groups was below the 50th percentile. Five of the 27 infants with PP (18.5%) and one infant in the comparison group (3.7%) had scores below the 10th percentile on the AIMS. On chi-square analysis, the difference between the number of infants with PP and the ones in the comparison group with scores ≤ 10th percentile was not significant (p =. 08).

The mean developmental motor quotient (DMQ) for the Peabody gross motor scale was 85.8 ± 9.9 for infants with PP and 88.0 ± 11.5 for infants in the comparison group, a difference that was not significant (p =. 38). The mean DMQ for Peabody fine motor scale was 86.8 ± 11.4 for infants with PP and 89.3 ± 9.1 for infants in the comparison group, a difference that was not significant (p =. 20). The mean DMQs for both groups of infants were lower than the normative mean of 100 for the gross motor and fine motor scales. Six of the 27 (22.2%) infants with PP and four (14.8%) infants in the comparison group had a DMQ ≥ 1.5 standard deviation below the mean on the Peabody gross motor scale, a gross motor scale of the PDMS, a difference that was not significant (p =. 88). Six of the 27 (22.2%) infants with PP had a fine motor DMQ ≥ −1.5 standard deviation below the mean while only three of the 27 (11.3%) comparison infants had a fine motor DMQ ≥ −1.5 standard deviation, a difference that was not significant (p =. 62). Multiple regression analyses did not reveal any association between birth order or maternal education and Peabody gross motor and fine motor DMQs.

Positioning and Motor Performance

The amount of time infants spent in each position is summarized in Table 2. There was no significant difference between the two groups. On average, infants with PP and infants in the comparison group spent less than 30 min per day in the prone position while awake. Fifteen (60%) of the infants with PP and nine (36%) infants in the comparison group spent 5 min or less per day in the prone position while awake.

TABLE 2 Time (Average Min/24 Hr) Spent in Positions by Infants with Positional Plagiocephaly and Comparison Group of Infants Matched for Age (n = 25)

Position	PP group	Comparison group	Paired analyses (p value)
Prone sleeping	26.6 (± 133.0)	67.4 (± 178.0)	.39
Prone awake	27.8 (± 43.6)	27.3 (± 43.1)	.97
Supine/side-lying sleeping	675.6 (± 198.0)	598.3 (± 243.9)	.19
Supine /side-lying awake	97.7 (± 69.1)	139.3 (± 134.0)	.19
Other awake^#	441.2 (± 151.9)	470.6 (± 119.9)	.40

* Mean (standard deviation); ^# primarily supported sitting positions.

There was a significant correlation between time spent in prone position when awake and AIMS percentile scores for infants with PP (r =. 52, p =. 01) and infants in the comparison group (r =. 44, p =. 05). When time spent in prone position was entered into a multiple regression analysis with birth order, mother's education and age at assessment, time spent in prone position while awake was the only factor that influenced the difference in AIMS percentile scores between pairs (r² =. 40, p =. 01) (Table 3). On simple linear regression analysis, decreased time spent in prone position while awake was associated with a greater difference in AIMS motor scores between pairs (r² =. 32, p <. 01). This association also was significant when prone awake time was entered into a multivariate analysis, with the Peabody gross motor quotient as the dependent variable.

TABLE 3 Conditional Linear Regression (r ² =. 40) with Dependent Variable and Difference in Scores on AIMS Between Matched Pairs of Infants

Exposure	Parameter estimate	Standard error	p value
Maternal education	−7.0	5.1	.19
Awake time in prone	0.3	0.1	.01
Birth order	−8.3	14.3	.57
Age at assessment	2.0	4.4	.65

DISCUSSION

The results do not support our hypothesis that the infants with PP would have delayed motor development and an increased exposure to supine position while asleep and awake when compared with infants without PP matched for age. Our sample of infants with PP had motor scores similar to that of a matched group of infants without PP. Motor development was associated with amount of time spent in the prone position while awake for both groups of infants. Infants with PP who spent less time in prone position while awake had lower motor scores when compared with their matched pairs. The lack of significant difference in the mean percentile score for the AIMS may have been due to the small sample; sample size was calculated based on the expectation of a larger mean difference (effect size) in AIMS scores between the two groups.

Five of the 27 infants with PP had scores at or below the 10th percentile on the AIMS, indicating a potential for a gross motor delay in almost one-fifth of this group. Darrah et al. (1998a) examined the predictive validity of the AIMS in the early identification of infants with either suspect or abnormal motor development at 18 months of age and determined that the 10th percentile was the most clinically relevant predictor of future motor delays. Based on the results of this study, we cannot infer that scores below the 10th percentile are the result of PP, but the finding warrants further investigation on a larger sample.

Speculation that amount of time spent in prone position when awake is associated with improved motor performance is reinforced by the association between daily prone exposure and AIMS percentile scores for both groups of infants. In our study, both the infants with PP and the comparison group spent very little time in prone position while awake. Therefore they were afforded very little time to practice the prone motor skills, such as head lifting, and this might have affected their scores on the motor assessments. Research suggests that the acquisition of motor milestones does not necessarily occur in a predictable sequence (Kamm, Thelen, & Jensen, 1990). It is postulated that development is facilitated by environmental factors such as practice opportunities. Schmidt (1999) and Zelazo, Zelazo, Cohen, and Zelazo (1993) suggest that a motor skill is learned and retained through practice and repetition of that particular skill. The influence of environmental factors on motor development is further elaborated within the dynamical systems theory (Herzia, 1991). According to this theory, movement patterns arise as a result of the cooperation and interaction of many subsystems including sensory, perceptual, and musculoskeletal systems that interact with the environment to produce the desired movements.

The positioning practices measured in this study may not have been representative of how infants were positioned prior to the diagnosis of PP. We cannot rule out the possibility that the infants with PP had more limited exposure to the prone position in the weeks or months prior to the diagnosis of the skull deformity. We hypothesized that infants with PP would have a significantly greater exposure to the supine or side-lying position and a decreased exposure to the prone position while asleep and awake than infants in the comparison group. We found no significant difference in positioning practices between the two groups. It is likely that following the diagnosis of PP, parents were cautioned by their pediatrician or family physician to avoid persistent positioning of their infants in supine in order to reduce the compressive forces on the infant's skull. Future studies are needed to investigate this issue prospectively so that infants are recruited soon after birth and before the diagnosis of PP, which typically occurs later in infancy. Thus exposure to the prone position would be measured prospectively, both prior to and following diagnosis of PP. While the infants with PP did not spend a larger amount of time in the supine or side-lying positions than the comparison infants, they did spend an extensive amount of time in the supported sitting position. This time was usually spent in an infant seat or swing. This position still allows for the compressive forces of the weight-bearing surface to affect the symmetry of the skull, thus reinforcing the deformity. Therefore, rehabilitation specialists and pediatricians should make families aware of the potential negative impact of prolonged exposure to the supported sitting positioning.

Neither group of infants spent prolonged periods of playtime in the prone position. This finding supports the work of Mildred, Beard, Dallwitz, and Unwin (1995) who reported that many parents who were aware of the increased risk of sudden infant death syndrome associated with prone sleeping, not only avoided placing their infants in this position for sleep but also avoided positioning their infants in prone position when awake. Infants may develop less tolerance to the prone position, as it requires effort to lift the head against gravity, whereas in the supine position they are free to observe their surroundings without exertion. The lack of exposure to this position while awake may inhibit the development of antigravity trunk and neck extension and therefore delay the acquisition of such motor skills as extended-arm support, four-point crawling, and the transition to the sitting position. This assumption was supported by recent research done by Majnemer and Barr (2005, 2006).

Several limitations were inherent in the design of this study. First, there was not as large an effect of PP on motor development as we had anticipated. It is possible that had the sample size been larger, the findings would have been statistically significant. The results suggested in this study will require further validation by others on larger samples. Furthermore, motor development of infants was assessed only once during the course of this study. Recent studies demonstrate that both PDMS and AIMS scores may fluctuate significantly during the first year of life (Darrah, Hodge, Magill-Evans, & Kembhavi, 2003; Darrah, Magill-Evans, Volden, Hodge, & Kembhavi, 2007; Darrah, Redfern, Magurie, Beaulne, & Watt, 1998b). Prospective studies that evaluate infants periodically during the first year of life may provide evidence supporting the risk for motor delays in infants with PP. Finally, although the evaluator was not aware of the hypotheses of this study, plagiocephaly was apparent in some of the infants. This could possibly have influenced the therapist who was carrying out the motor assessments.

Implications for Practice

Infants with and without PP spent minimal amount of awake time in the prone position. Both the American Academy of Pediatrics and the Canadian Pediatric Society have altered their recommendations to include the necessity of “tummy time” when the child is awake in order to develop prone skills. However, parents in our sample did not appear to be acting upon this message. This message needs to be clearly presented to parents by their pediatricians or family physicians so that they will feel comfortable to use prone position as a supervised play position when the child is awake. Not only will this foster motor development but will also reduce the deforming compressive forces on the infant skull provided by constant exposure to the supine or supported sitting positions. The finding that lower motor scores in both groups of infants were associated with less exposure to prone positioning when awake suggests that therapists should encourage prone positioning while infants are awake and supervised to promote early motor development.

Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.

The authors wish to thank all the infants and families who participated in this study. We are grateful to Alison Steel, physical therapist, for evaluating all the infants. We would also like to thank Nancy Marget and Drs. M. Shiller and A. Chan Yip for their assistance with recruitment of comparison infants and Victoria Stuhec, occupational therapist, for her assistance with data entry and analysis. This study was funded by grants from the Professional Order of Physical Therapy of Quebec (OPPQ) and the Provincial Network for Habilitation and Rehabilitation Research (REPAR).