A retrospective study based on electronic medical records of 77,108 children in primary care showed that infants diagnosed with plagiocephaly before 12 months had 1.5 times higher risk (adjusted OR: 1.50; 95% CI: 1.32–1.70) of presenting developmental delays compared to those without this condition.

Furthermore, the diagnosis of plagiocephaly preceded that of delay in 92.6% of cases where both conditions coexisted, suggesting it could act as an early indicator of functional neurological risk.

A comparative study in school-age children showed that children with moderate to severe positional plagiocephaly and/or brachycephaly (PPB) during early childhood scored lower on cognitive and academic tests compared to controls. The differences were significant only in moderate to severe cases, while in mild cases the associations were negligible. The authors suggest that PPB could act as a marker of developmental risk, without necessarily implying a causal relationship.

Study evaluating cognitive and psychomotor delays in children with single-suture craniosynostosis or plagiocephaly without synostosis using the Bayley-II scales. 63 children were analyzed before intervention, revealing significant delays in psychomotor development (PDI), particularly in craniosynostosis. Post-treatment follow-up is recommended to assess improvements.

A pioneering follow-up study revealed that a very important percentage of school-aged children with a history of deformational plagiocephaly subsequently required special education services, occupational therapy, or physical therapy. The results suggest it serves as an early marker of functional delays.

A prospective clinical study on 110 infants demonstrated that, before any intervention, patients with deformational plagiocephaly showed significant delays in both mental and psychomotor development (assessed with Bayley scales) compared to the standard population.

Neurological evaluation of 49 infants with plagiocephaly compared to 50 healthy controls. A statistically significant difference was highlighted in general scores, with a predominance of muscle tone alterations (abnormally variable tone, both high and low), confirming functional neurological vulnerability.

Research comparing infants with plagiocephaly to healthy children concluded that affected patients scored significantly lower on all Bayley scales (particularly in the motor aspect). This strongly suggests that plagiocephaly is a marker of high risk for delay in neurodevelopment.

A prospective study on 48 infants with plagiocephaly evaluated the effect of physical therapy, cranial orthoses, and family postural exercises on psychomotor development. The results indicate that plagiocephaly is a marker of risk for delay (especially in motor and language domains), and that this delay can improve with treatment.

A systematic review of 19 articles found a consistent positive association between plagiocephaly and developmental delay (primarily motor). Early referral to physical therapy and early intervention are recommended to mitigate long-term risks.

Study on language acquisition in children with single-suture craniosynostosis and posterior deformational plagiocephaly, which showed a high risk of speech and language disorders (21% with severe alterations, 3 times more than the general population). Children with sagittal synostosis showed better linguistic development, while those with posterior plagiocephaly (operated or not) also showed delays, contradicting the previous belief that the risk was limited to craniosynostosis.

3D computed tomography study on 14 patients with uncorrected congenital muscular torticollis (from 1 month to 24 years): cranial and skull base deformation appears as early as infancy (especially in the posterior cranial fossa), while facial asymmetry (jaw, maxilla, orbit) develops from 5 years of age, worsening with age. Early muscle release is recommended to prevent craniofacial deformations.

An electrophysiological study demonstrates that infants with plagiocephaly show reduced amplitudes in auditory ERPs (P150/N250), confirming for the first time early neuro-auditory involvement and a high risk of suffering from sound processing disorders.

Study on 40 infants with posterior plagiocephaly: 35% had constriction of the visual hemifields (≥20°) and 17.5% had asymmetry ≥20°. No correlation was found between the laterality of visual defects and cranial deformation, but plagiocephaly may affect the development of the visual field.

Observational study: in deformational plagiocephaly, there is no higher prevalence of strabismus (only <1% with esotropia), but there is a higher prevalence of astigmatism (9% unilateral, 15% bilateral). In plagiocephaly due to craniosynostosis, there is a higher prevalence of strabismus (7% exotropia) and astigmatism (7% unilateral, 21% bilateral).

A systematic review by the Congress of Neurological Surgeons concludes that cranial molding orthosis (helmet) therapy offers more significant and faster improvement in skull shape in infants with positional plagiocephaly, compared to conservative therapy, especially in severe cases and when applied during the optimal period of early infancy.

However, specific criteria for measuring and quantifying the deformation, as well as the most appropriate time to initiate treatment, remain to be defined. In general, infants with more severe deformations and those who wear the helmet from an early age achieve more notable correction (even normalization) of head shape.

Plagiocephaly can cause mechanical complications at the maxillofacial or cervicobrachial level, or even cognitive ones.

Indeed, since the early 1990s and their mass adoption, these practices are responsible for skull deformations called "plagiocephalies," associated with disorders of varying severity, which sometimes cause significant damage to the psychical, cerebral, or physical development of infants. These disorders, difficult to overcome after two and a half years, can lead to a reduced development coefficient in some children. The identified problems are biomechanical, physiological, aesthetic, and psychological.

Indeed, according to two specialist physicians in France, Bernadette de Gasquet and Thierry Marck, authors of the book "My Baby Won't Have a Flat Head: How to Prevent and Treat Plagiocephaly in Babies" (Albin Michel, 2015), it is possible to achieve improvement, even near-total disappearance of these undesirable effects harmful to a child's normal development, while maintaining the recommendations aimed at combating sudden infant death. However, there seems to exist a certain indifference, ignorance, or denial of this reality within a medical community that limits itself to recognizing the undeniable benefits of these practices.