Positional plagiocephaly, also known as deformational plagiocephaly, is a condition where the skull becomes asymmetrically deformed because of external pressure, without craniosynostosis [1]. The condition may have both prenatal and postnatal causes, but is most commonly associated with infants spending extended periods in the supine position [2,3]. Severe flattening of the posterior region of the head is often accompanied by ipsilateral frontal bossing and anterior displacement of the ear (Fig. 1A). While repositioning therapy can be an effective treatment for infants under 4 months of age, helmet therapy may be considered if the deformity is severe or if repositioning is unsuccessful, after ruling out other conditions such as lambdoid synostosis (Fig. 1B) [4,5]. The effectiveness of helmet therapy is controversial, with some studies reporting significant improvement and others finding no clinically meaningful difference [6-8]. While skull deformation is commonly perceived as a cosmetic issue, studies have suggested an association between infants with positional plagiocephaly and various health concerns, such as delays in psychomotor development, jaw asymmetry, and low self-esteem [9,10]. Therefore, parents have become increasingly attentive to their infants' head shape, leading to a surge in pediatrician visits [11,12]. However, few studies have investigated the treatment of positional plagiocephaly, and there is limited evidence regarding the effectiveness of helmet therapy for infants with this condition. Therefore, the treatment for positional plagiocephaly primarily depends on clinical experience and varies greatly [6,13]. The lack of consensus among medical professionals regarding treatment options can create uncertainty for parents. This study aimed to evaluate the effectiveness of helmet therapy in infants with moderate to severe positional plagiocephaly, while also examing the influence of different initiation ages, degree of head asymmetry and daily duration of helmet wear on treatment outcomes.

Helmet therapy was shown to be an effective tool for infants with moderate to severe positional plagiocephaly. Better treatment outcomes were achieved when the treatment was started earlier than 9 months of age and the helmet was worn for more than 15 hours per day.

Positional plagiocephaly is a condition where an infant's head becomes flattened in one area because of prolonged pressure on that area of the skull. This can occur when infants spend a lot of time lying on their backs, in a car seat, or in a rocker. The incidence of positional plagiocephaly increased after the American Academy of Pediatrics initiated the "Back to Sleep" campaign in 1992, which advised parents to avoid putting infants in a prone position while sleeping to decrease the occurrence of sudden infant death syndrome [14]. Prior to the campaign, instances of positional plagiocephaly occurred in 1:300 infants, whereas after the campaign, instances increased to 1:60 infants [15,16].

Early physical and repositioning therapy is highly effective in correcting positional plagiocephaly if it is detected at an early age (within 4 months of age) [17]. Repositioning therapy typically entails maintaining an infant's head in a preferred position, while parents are counseled to enhance supervised tummy time and limit time spent in car seats and rockers [18]. In milder cases, where the diagnosis is made early, cranial deformation can be managed by stretching exercises and a regular prone position.In most severe cases, the use of a helmet may be necessary (Fig. 5) [8,12,19]. The objective of helmet therapy is to reposition the developing skull in regions where it has become flattened [20]. During the first year of life, the infant’s skull grows rapidly; thus, early intervention is considered important for more successful treatment of skull deformation [8,21]. Since it was first introduced by Clarren et al., helmet therapy has been widely applied [22,23]. Many studies have examined the effectiveness of helmet therapy; however, no definite conclusions have been reported [9,15,24,25]. In 2014, van Wijk et al. studied 84 infants and reported no differences in the change score of skull deformity between helmet therapy and natural course groups [6]. In 2015, Rowland and Das [13] conducted a study that compared the helmet therapy and no-intervention groups comprising 84 infants with moderate to severe positional plagiocephaly. They reported that improvement in skull shape was almost the same in the helmet therapy and control groups. Despite some disagreement, most studies reported that helmet therapy is effective in improving and preventing the progression of positional plagiocephaly [9-12]. According to recent reports, the effectiveness of helmet therapy is influenced primarily by the age at which the therapy is initiated and the severity of the asymmetry [19,20,26]. Moreover, it has been reported that the earlier the helmet is applied, the more rapid and complete the correction will be [6]. Some studies have suggested that helmet therapy initiated before 6 months of age is preferable [11,15]. However, infants younger than 4 months old usually lack the cervical muscle strength to tolerate the helmet [11]. In contrast, helmet therapy after 1 year of age is generally less effective because the skull thickens and cranial growth slows down [9,24,25].

The findings of our study are consistent with those of previous research, demonstrating a negative relationship between the effectiveness of helmet therapy and the age of treatment initiation [11,15]. Infants who received treatment before the age of 9 months exhibited a more significant decrease in CVA/CVAI, with a reduction of 6.0 mm/4.7%, than those who began treatment later and had a reduction of 2.7 mm/2.0%. Additionally, the success rate of helmet therapy varied notably across different age groups. Group 1 (≤5 months) had a success rate of 38.8%, group 2 (5–7 months) of 45.9%, group 3 (7–9 months) of 18.2%, and group 4 (>9 months) of 0.0%. Therefore, it is critical to initiate helmet therapy after 4 months of age, when the infant can withstand the weight of the helmet, but before 9 months of age, to obtain the best treatment outcomes. These findings are of paramount significance for clinical practice and emphasize the importance of early intervention in managing plagiocephaly [15,24].

The effectiveness of helmet therapy in correcting positional plagiocephaly is dependent on the severity of the initial head shape asymmetry, with more severe cases being less likely to achieve complete correction and with a limited extent of correction [11,12]. In this study, a full correction was almost achieved in 40.9% of the infants in the moderate group, compared with only 8.3% in the severe group, with longer treatment duration in the latter. Thus, the initial head shape asymmetry severity is a critical determinant of the success of helmet therapy, affecting the likelihood and extent of achieving complete correction. Infants with more severe cases require longer treatment duration, as evidence shows that severe cases require 7.9 months and moderate cases require 5.8 months [11,12].

Furthermore, our study observed that compliance with wearing the helmet for more than 15 hours per day was linked to a higher rate of successful treatment, whereas inadequate compliance resulted in no successful outcomes [15]. Although some common side effects, such as sweating, odor, and skin rash, were reported, the therapy was generally well-tolerated, and no severe complications, including skin ulcer, occurred. The cost of helmet therapy in South Korea is approximately United States dolloar 2500.

This study had some limitations that should be considered when interpreting the results. First, there was a selection bias as only patients with positive outcomes and without complications were included in the study, and the study lacked a well-established validated scale for measuring head deformation. Additionally, a control group was not available for comparison owing to the retrospective nature of the chart review. Second, the study focused solely on plagiocephaly and excluded brachycephaly from the analysis. Future studies can be improved by including patients with brachycephaly. Moreover, recent concerns have emerged regarding the potential adverse effects of moderate to severe positional plagiocephaly on cognitive and academic outcomes [12]. Therefore, future research should incorporate long-term evaluations of psychomotor development in infants who receive helmet therapy and parental feedback on their child's quality of life after treatment.

In conclusion, with increasing parental concerns about their baby’s head shape, the use of helmet therapy has increased recently. For proper helmet therapy, accurate anthropometric measurements of the head are crucial, and it is important to rule out conditions that require surgical treatment, such as craniosynostosis. Helmet therapy is effective for infants with moderate to severe positional plagiocephaly. The rate of change in CVA/CVAI through helmet therapy is significantly influenced by the age at which the therapy is initiated, duration of daily wear, and severity of the initial condition. Therefore, pediatricians should have a strong understanding of the indications for helmet therapy and assist parents in making informed decision regarding whether to pursue this treatment for their child.