Helmet therapy in infants with positional skull deformation: randomised controlled trial

The researchers compared two approaches for treating positional skull deformation (flat head syndrome) in infants:

**Intervention group:** Infants wore a custom-moulded helmet for 23 hours per day for 6 months. The helmet was designed to guide skull growth by applying gentle pressure to prominent areas while leaving room for flattened areas to expand.

**Control group:** Infants received no treatment — parents were instructed to avoid any intervention for skull deformation and simply let the condition follow its natural course.

The primary outcome was change in skull shape measured at 24 months of age (roughly 18 months after the intervention period ended). Two specific shape indices were tracked:

**Plagiocephaly** (asymmetry where one side of the back of the head is flatter than the other) — measured as the Oblique Diameter Difference Index (ODDI), where a value of 1.00 means perfectly symmetrical and higher values indicate more asymmetry.

**Brachycephaly** (a wide, flat back of the head) — measured as the CranioProportional Index (CPI), where higher values indicate a wider, flatter head shape relative to length.

Secondary outcomes included ear deviation, facial asymmetry, occipital lift (a measure of how much the skull base is tilted), motor development, quality of life for both infant and parents, parental satisfaction, and parental anxiety.

**Sample size:** 84 infants (42 randomised to helmet therapy, 42 to natural course)

**Age at enrolment:** 5–6 months old

**Inclusion criteria:** Moderate to severe positional skull deformation (confirmed by plagiocephalometry), born after 36 weeks gestation

**Exclusion criteria:** Muscular torticollis (tight neck muscle causing head tilt), craniosynostosis (premature fusion of skull bones), or any dysmorphic features (suggesting a genetic syndrome)

**Setting:** 29 paediatric physiotherapy practices in the Netherlands; helmet therapy was administered at four specialised centres

**Final analysis:** 39 infants in the helmet group and 40 in the control group completed the 24-month follow-up (5 dropouts total)

The primary measurement tool was **plagiocephalometry** — a non-invasive anthropometric method using a flexible measuring tape and callipers to capture skull dimensions. This is a validated, low-cost alternative to 3D scanning or CT imaging.

**Oblique Diameter Difference Index (ODDI):** Ratio of the longer diagonal skull diameter to the shorter diagonal. A value of 1.00 = perfect symmetry. Higher values = more asymmetry (plagiocephaly). The threshold for "moderate" deformity was ODDI ≥ 1.06.

**CranioProportional Index (CPI):** Ratio of skull width to skull length, multiplied by 100. Higher values = wider, flatter head shape (brachycephaly). The threshold for "moderate" deformity was CPI ≥ 90%.

**Full recovery** was defined as ODDI < 1.04 AND CPI < 90% at 24 months — essentially returning to within a normal range.

Secondary outcomes were measured using:

**Ear deviation and facial asymmetry:** Measured with callipers and a goniometer (angle measurement tool)

**Occipital lift:** Measured with a specially designed device that quantifies the tilt of the skull base

**Motor development:** Alberta Infant Motor Scale (AIMS), a validated observational assessment

**Infant quality of life:** TNO-AZL Infant Quality of Life questionnaire (TAPQOL), parent-reported

**Parental quality of life, satisfaction, and anxiety:** Standardised questionnaires including the State-Trait Anxiety Inventory (STAI)

Measurements were taken at baseline (5–6 months), then at 8 months, 12 months, and 24 months of age.

**Study design:** Pragmatic, single-blinded, randomised controlled trial (RCT) nested within a prospective cohort study. This is a "pragmatic" trial, meaning it was designed to test how the intervention works in real-world conditions rather than in a tightly controlled laboratory setting.

**Randomisation:** Infants were randomly assigned to helmet therapy or natural course using a randomisation plan with blocks of eight. Block randomisation ensures equal group sizes throughout the enrolment period, preventing seasonal or temporal biases. The allocation was concealed — meaning the person enrolling the infant did not know which group the next infant would be assigned to — which prevents selection bias.

**Blinding:** The primary outcome assessment at 24 months was blinded. The person measuring skull shape did not know which group the infant had been in. This is critical because knowledge of treatment assignment can unconsciously influence measurements. However, parents and treating clinicians obviously knew which group the infant was in — this is unavoidable with a physical device like a helmet. The single-blind design (blinded assessor only) is the best that can be achieved in this context.

**Duration:** The intervention period lasted 6 months (from age 5–6 months to age 11–12 months). Follow-up continued until 24 months of age — a full 12–13 months after the helmet was removed. This long follow-up is important because it captures the final shape after natural growth has had time to remodel the skull, rather than just measuring the immediate effect of the helmet.

**Statistical approach:** Analysis of covariance (ANCOVA) was used, with baseline values as a covariate. This is appropriate because it adjusts for any pre-existing differences between groups and increases statistical power. The primary analysis was intention-to-treat — meaning infants were analysed in the group they were assigned to, regardless of whether they actually wore the helmet. This preserves the benefits of randomisation and reflects real-world effectiveness (some infants may not tolerate the helmet).

**What this design can and cannot prove:**

**Can prove:** Causal effectiveness (or lack thereof) of helmet therapy compared to natural history. Because of randomisation, any difference between groups at 24 months can be attributed to the helmet rather than to pre-existing differences between infants. The blinded outcome assessment prevents measurement bias.

**Cannot prove:** Whether helmet therapy works for more severe deformities (the study only included moderate-to-severe cases). Whether it works if started earlier or later (only 5–6 month olds were enrolled). Whether it works for deformities caused by torticollis (these infants were excluded). Long-term effects beyond 24 months (skull growth continues into adolescence, though most remodelling happens in the first year).

**Major methodological strength:** The pragmatic design means the results reflect what happens in real clinical practice, not just in an idealised research setting.

**Major methodological weakness:** The sample size is relatively small (84 randomised, 79 analysed). While the confidence intervals are narrow enough to rule out clinically meaningful effects, a larger study could detect smaller differences. Also, parents in the control group were told to avoid any treatment — but we don't know if some sought treatment elsewhere (though the authors report this was monitored and compliance was good).

**Primary outcome — change in skull shape from baseline to 24 months:**

**Plagiocephaly (ODDI change score):** Mean difference between groups = -0.2 (95% CI: -1.6 to 1.2, p = 0.80). This means the helmet group improved by only 0.2 points more on the ODDI scale than the natural course group — a trivial difference that is statistically indistinguishable from zero.

**Brachycephaly (CPI change score):** Mean difference between groups = 0.2 (95% CI: -1.7 to 2.2, p = 0.81). Again, essentially no difference.

**Full recovery at 24 months:** 10/39 (26%) in the helmet group vs 9/40 (23%) in the natural course group. Odds ratio = 1.2 (95% CI: 0.4 to 3.3, p = 0.74). This means the odds of full recovery were only 1.2 times higher with the helmet — and the confidence interval includes 1.0, meaning the result is not statistically significant.

**Secondary outcomes:**

**Ear deviation, facial asymmetry, occipital lift:** No statistically significant differences between groups at any time point. The natural course of growth corrected these asymmetries just as well as the helmet.

**Motor development (AIMS):** No difference between groups at any time point. Helmet therapy did not impair or improve motor development.

**Quality of life (infant and parent):** No significant differences between groups.

**Parental satisfaction:** Parents in the helmet group reported higher satisfaction with treatment (which is expected — they invested time and money), but this did not translate into better outcomes for the infant.

**Parental anxiety:** No difference between groups. Parents were not more anxious in the control group, suggesting the "wait and see" approach did not cause undue distress.

**Side effects:** All 42 parents in the helmet group reported one or more side effects. The most common were:

Skin irritation or pressure marks (reported in most infants)

Sweating and overheating

Difficulty fitting the helmet as the infant grew (requiring adjustments)

Discomfort and crying when the helmet was first applied

Bad smell from the helmet (due to sweat and skin oils)

The results translate into plain English as follows:

If you put a helmet on an infant with moderate-to-severe flat head syndrome for 6 months, the chance of achieving a normal head shape by age 2 is about 26%. If you do nothing, the chance is about 23%. That's a 3 percentage point difference — meaning you would need to treat 33 infants with helmets to get one additional "cure" beyond what nature would achieve on its own.

The actual numerical improvement in skull shape indices was so small that it falls within the measurement error of the plagiocephalometry technique. In other words, the difference between groups is smaller than the uncertainty in the measurement itself.

To put it in perspective: the natural course of skull deformation from age 5–6 months to 24 months produces substantial improvement on its own — the skull rounds out as the brain grows and the infant spends less time lying on their back. The helmet adds essentially nothing to this natural remodelling process.

The side effects, however, are universal — every single infant in the helmet group experienced at least one adverse effect. So the trade-off is: no benefit, guaranteed discomfort.

**What the authors acknowledge:**

The sample size was calculated to detect a clinically meaningful difference, but the study may have been underpowered to detect very small effects. However, the confidence intervals are narrow enough to rule out any effect that would be worth the cost and side effects.

Blinding was only possible for the primary outcome assessor at 24 months. Parents and clinicians knew the treatment assignment, which could have influenced secondary outcomes like quality of life ratings (though these showed no difference).

The study excluded infants with torticollis, so results may not apply to that subgroup (though torticollis is often treatable with physiotherapy).

The pragmatic design means helmet fitting and compliance were not tightly controlled — some infants may have worn the helmet less than the prescribed 23 hours/day.

**What a critical reader would note:**

The study was funded by a Dutch health insurance company and the Netherlands Organisation for Health Research and Development — no helmet manufacturer funding, which is a strength.

The primary outcome was measured at 24 months, but skull growth continues until adolescence. It's theoretically possible that the helmet group could diverge from controls later, though this seems unlikely given that the helmet was only worn for 6 months and the groups were identical at 24 months.

The definition of "full recovery" (ODDI < 1.04 and CPI < 90%) is somewhat arbitrary. A different threshold could change the recovery rates, but the continuous measures (ODDI and CPI change scores) also showed no difference.

The study did not measure whether helmets reduced the need for later treatments (e.g., surgery for craniosynostosis), but this is extremely rare in positional deformation anyway.

The control group was told to avoid any treatment, but some parents may have used repositioning techniques (e.g., tummy time, alternating head position). This would actually bias the results against the helmet — if repositioning works, the control group would improve more, making the helmet look worse. But the control group's improvement was substantial, suggesting repositioning may be effective (or natural history alone is sufficient).

For someone running their own n=1 experiment (e.g., a parent considering helmet therapy for their infant):

**What to test:**

The intervention itself: custom-moulded helmet therapy worn 23 hours/day for 6 months, starting at age 5–6 months

The comparator: natural course (no treatment, but continue normal repositioning and tummy time)

Note: This is not a self-experiment you can easily run on yourself — it's for your infant. But the principles of testing a treatment against doing nothing apply.

**Minimum meaningful duration:**

The study used 6 months of helmet wear with follow-up to 24 months of age. A shorter trial (e.g., 3 months) would not capture the full effect, as skull remodelling is slow.

For a personal experiment, you would need to commit to at least 6 months of helmet use and measure outcomes at 24 months — a total commitment of about 18 months from start to final assessment.

**What to measure (specific metrics):**

**Primary metric:** Skull shape asymmetry — measure the difference between the two diagonal skull diameters using a flexible measuring tape. A difference of >6 mm is considered moderate. Track this monthly.

**Secondary metrics:** Head width-to-length ratio (measure width at the widest point and length from forehead to back of head). Ear position (are the ears aligned when viewed from above?). Facial symmetry (is one cheek fuller than the other?).

**Subjective metrics:** Infant comfort (crying, fussiness during helmet wear), skin condition (redness, irritation, rashes), sleep quality (does the infant sleep worse with the helmet?).

**Photographic documentation:** Take standardised photos from above (bird's-eye view), from the side, and from the front at the same distance and lighting each month.

**Key confounds to control for:**

**Age at start:** The study only tested 5–6 month olds. Starting earlier or later may produce different results, but the evidence only supports this age window.

**Torticollis:** If your infant has a tight neck muscle, treat that first with physiotherapy before considering a helmet. The study excluded these infants.

**Sleep position:** Always place the infant on their back to sleep (SIDS prevention). Do not use positioning devices or wedges — these are not recommended and can be dangerous.

**Tummy time:** Ensure at least 30–60 minutes of supervised tummy time per day by 3–4 months of age. This strengthens neck muscles and reduces pressure on the back of the head.

**Car seats, swings, and bouncers:** Minimise time in devices that put pressure on the back of the head. Alternate head position during supervised awake time.

**Measurement consistency:** Use the same person to take measurements each time, at the same time of day, with the same technique. Measurement error is substantial with manual methods.

**What a positive result would look like:**

A positive result for helmet therapy would be: the ODDI (asymmetry index) decreases by at least 0.06 more than the natural course over 6 months, AND the CPI (width-to-length ratio) decreases by at least 3% more than natural course.

In practical terms: the difference between the two diagonal skull diameters should decrease by at least 6 mm more than what happens without the helmet. The head should become visibly more symmetrical when viewed from above.

Given the study results, a positive result