Deformational Plagiocephaly More Frequent in Multiple-Birth Infants

Jennifer C. Cherney, M.S.; Timothy R. Littlefield, M.S.


Introduction:

The skulls of neonates and young infants are extremely malleable and external pressures consistently applied to the head during these periods can cause permanent deformations. These deformations typically include cranial asymmetry, ear misalignment and facial asymmetry. This condition is called positional or deformational plagiocephaly.

The incidence of deformational plagiocephaly has risen dramatically since 1992, when the American Academy of Pediatrics (AAP) released their "Back-to-Sleep" campaign, in an attempt to reduce the risk of sudden infant death syndrome (SIDS) [1-4]. While stomach sleeping distributes the weight of the head over the many bones in the face [4], back sleeping places the force on one or two bones that are not held firmly together and are not yet constructed of mature bone. When an infant is repeatedly placed on his/her back in the same position, a flattening begins in the occipital-parietal region (Figure 1 ). As the child is continually placed in the same position, the flattened area will gradually increase. As the flat spot increases, the ipsilat-eral ear and forehead will shift forward and facial asymmetry will develop [5].

Figure 1

The development of deformational plagio-cephaly, however, is very often due to the compilation of several risk factors rather than one specific cause. Other risk factors that influence the development of deformational plagiocephaly include congenital muscular torticollis [6,7], low birth weight [8], premature birth [2,9], intrauterine position [2,10-14] and intrauterine constraint [7,15,16]. No matter what the cause, once the flattening of the occipital-parietal region begins, the infant will be more comfortable resting his/her head on the flat spot rather than balancing the head on a point [3,11,12]. As the head rests on that spot for long periods of time, the condition perpetuates.

Previous studies have shown that multiple-birth infants have a higher incidence of deformational plagiocephaly than single-birth infants. This apparent predisposition of multiple-birth infants is believed to be due to their exposure to multiple risk factors, such as low birth weight, premature birth and intrauterine constraint [11,12]. The purpose of this study was to expand on previous research and retrospectively review the number and history of multiples treated in our Phoenix clinic from 1993 through 2000.

Results:

From 1993 through 2000, 163 multiple-birth infants were referred to our clinic. Fifteen of those infants were eliminated from the study; five had cranio-synostosis and ten were referred from out-of-state. Statistics were completed on the remaining 148 patients.

The 148 infants represented 112 sets of multiples consisting of 100 sets of twins, eight sets of triplets and four sets of quadruplets. Out of a total of 240 multiple-birth infants, 148 (61.7%) were treated for deformational plagiocephaly. One hundred and thirty of the 200 twins (65.0%) were treated; twelve of the 24 triplets (50.0%) were treated and six of the 16 quadruplets (37.5%) were treated in those eight years.

Sixty-two percent of the treatment population was male and 55.8% had right-sided plagiocephaly (flattening in the right occipital-parietal region). Parents reported the zygosity of 103 of the patients, 82.1% of which were fraternal. A majority (71.8%) of the infants in the multiple-birth treatment population had some form of neck involvement, ranging from a consistent head tilt or favoritism to turn to one-side to congenital muscular torticollis. Parents reported birth orders for 135 of the 148 patients. Over half (57.0%) of these patients were the lower in utero infant (baby A), while 40.0% were baby B, 2.2% baby C and 0.8% were baby D. Parents of 88 of the 148 patients reported the children's birth weights. Of those 88 patients, 55.7% were born at a low-birth-weight.

Chi-square analyses were conducted to determine whether infants from multiple-births occurred more frequently in the treatment population than Arizona's population, as reported in the Arizona Health Status and Vital Statistics. The two populations were significantly different in all eight of the years (Table 1).

Discussion:

This investigation found 8.7% of the patients treated for deformational plagiocephaly originated from multiple-births. This value is slightly higher than the 7.5% reported by Little-field et al. [11] and the 7.7% reported by Kane et al. [2], due to the increase in the number of multiples treated in 1999 and 2000. All three of these studies indicate that a higher number of multiple-birth infants develop deformational plagiocephaly. These infants are believed to be more susceptible to the condition because they are exposed to more of the risk factors associated with this condition[11,12]. Those risk factors include neck dysfunction, low birth weight, back sleeping and intrauterine constraint.

Table 1. x2 analysis demonstrating that deformational plagiocephaly occurs in multiple-birth infants at a higher incidence than would be expected in the patients treated at the Phoenix clinic. * Differences considered significant if P & 0.05.
Year Arizona Plural/Total % Treatment Plural/Total % x2Value P
1993 1519/69037 2.2% 11/117 9.4% 27.998 0.0000
1994 1631/70896 2.3% 13 / 200 6.5% 15.570 0.0001
1995 1737 / 72386 2.4% 18/239 7.5% 26.603 0.0000
1996 1877/75094 2.5% 18/245 7.4% 23.402 0.0000
1997 1889/75563 2.5% 11/219 5.0% 5.686 0.0171
1998 2026 / 77940 2.6% 21 / 237 8.9% 36.328 0.0010
1999 2093 / 80505 2.6% 25 / 225 11.1% 60.335 0.0000
2000 2295 / 84985 2.7% 31/221 14.0% 102.277 0.0000

Congenital muscular torticollis is a well-established risk for the development of deformational plagiocephaly. A high percentage (71.8%) of this investigation's population had some sort of neck dysfunction. The definition of congenital muscular torticollis is inconsistent throughout the literature; therefore, it is difficult to compare this result to the results of other authors. The percentage of low birth weight infants in this study's population was equivalent to the percentage of multiples who were born with low birth weight in Arizona in the corresponding years. Approximately 5.5% of singleton infants were born with low birth weight compared to 55.7% of multiple-birth infants. Therefore, multiples are at a much higher risk for being born at low birth weight.

The ratio of male to female patients in the current population is similar to those reported by other authors [17]. The percentage of infants with right occipital plagiocephaly (55.8%) was slightly lower than the values reported by other sources (61% to 79.2%) [13,14,17]. Previous research proposes that the high percentage of right-sided plagiocephaly can be attributed to the most common birth presentation for single-birth infants, which is left occipital anterior (LOA). In this position, the right occiput and the left frontal region of the infant's head are wedged in the mother's pelvis, which may flatten those areas [10,13,14].

As was seen in previous studies, the infant lowest in the womb was more likely to develop plagiocephaly [12]. As shown in Figure 2 , the lower infant, whose head was reportedly engaged in his mother's pelvis, developed deforma-tional plagiocephaly; whereas his sister, who was on top, did not develop plagiocephaly. The lower infant is at a higher risk for several reasons. Infant A frequently engages in the pelvis earlier than normal, which places the head against the mother's pelvis for a longer period of time. In addition, the weight of the higher sibling increases the forces on the lower infant's head and the lower infant is typically unable to alter position.

The percentage of multiple-birth infants in the population treated in the Phoenix clinic was compared to the percentage of multiples born in Arizona's population (Table 1). The clinic's treatment population had a significantly higher percentage of multiple-births than the normal population; therefore, multiple-birth infants develop deformational plagiocephaly at a higher incidence than singletons.

This study supports other findings that indicate that multiples are more likely to develop deformational plagiocephaly than infants born singly. Like singletons, a majority of multiples have neck dysfunction and sleep on their backs. Unlike singleton infants, however, multiples are frequently born at low birth weight and are subject to intrauterine constraint. Both of these factors are believed to contribute to or even cause deformational plagiocephaly. Therefore, infants from sets of twins, triplets and other multiples are exposed to a higher number of the risks associated with the development of deformational plagiocephaly, which explains why a high number of multiples present with this condition.

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