INCIDENCE AND NATURAL HISTORY

According to G. Watson, 14% of the adult population of the USA suffered from some kind of cranial deformity in 1971. These figures go against the popular belief that positional plagiocephaly did not exist before 1992, and that such deformities went away by themselves so there was no need for concern. On a day-to-day basis we see adults with misshapen heads, and parents of affected children often say they would like to have the treatment themselves.
Sterling K. Clarren (1981) assures that 10% of infant plagiocephaly cases are likely to persist in the form of a permanent deformity.
In Spain we have only one prospective study on a series of 186 healthy babies at a local health clinic (Panero,1999). In the study, 22 cases of plagiocephaly were detected (11,8%) at an average age of 2.6 months. During the follow-up (Age up to 4 years) all cases of plagiocephaly were resolved by the age of 11.4 months (range 4-27 months). Clinical experience would question these conclusions. The criteria for inclusion and evaluation were subjective, with no measurements taken nor photos and it is not stated if the observer was always the same person.
A more recent and completely objective study was carried out  (Hutchison, 2004) using anthropometric measurements as  basic criteria in a similar sample (200) with the following results:

Conclusion: in an advanced western society with supine sleep position used for many years 3.3% of healthy children reach 2 years of age with some kind of plagiocephaly and/or brachycephaly not resolved. It would be interesting to know how this group of children evolve over the next few years and we hope Hutchison is keeping a close eye on them. A criticism of the study might be that had the criteria for inclusion not been so permissive, the results would have been substantially worse.
For example, Hutchison considers a brachycephaly case to be positive when the cranial index is ≥ 93, despite the accepted value being = 80 ± 4, according to all anthropological and anatomical manuals. The cases of brachycephaly are most abundant in the CI group 84-93 and it is precisely this group which, in Hutchison's study, are not counted.
As for the calibration of plagiocephaly, we personally prefer to use absolute cranial dimensions expressed in millimetres rather than proportion, since 15 mm. of asymmetry at 4 months or at 20 years are very different proportionally but at 20 few people want their head 1.5 cm flatter on one side than the other.

Further studies are needed with respect to the long-term evolution of cases of plagiocephaly.

Other data reported in the same study may shed light upon the evolution of plagiocephaly according to the age at diagnosis.

Such a high percentage (with average at 3,3%) of babies condemned to suffer plagiocephaly for the rest of their lives should be considered unacceptable.
Any patient reaching the age of 2 years with plagiocephaly, brachycephaly or scaphocephaly will have to resort to surgery.
There is still a lack of information concerning the functional deficits as stated recently by Kordestani (2006) and we are still in the dark about what percentage of these are transitory and which permanent.