Rethinking Farkas: Updating Cephalic Index Norms in a Large, Diverse Population

UMMS Affiliation

Division of Plastic Surgery, Department of Surgery; Department of Population and Quantitative Health Sciences, Division of Biostatistics and Health Services Research; School of Medicine

Publication Date


Document Type



Congenital, Hereditary, and Neonatal Diseases and Abnormalities | Musculoskeletal Diseases | Plastic Surgery


BACKGROUND: Cephalic index, the ratio of head width to length, is one normative indicator used by insurers to derive criteria for plagiocephaly helmet authorization. Current norms were established by a small sample of white children in the 1987 Farkas and Munro data set. This study establishes updated cephalic index values for infants and children in a large, diverse patient population.

METHODS: Children aged 0 to 3 months, 3 to 6 months, 9 to 12 months, 2 to 3 years, and 12 to 14 years were recruited at their well-child appointment. Cephalic index was calculated for each age group and compared to previously established norms.

RESULTS: Eight hundred seventy patients met inclusion criteria. The means for boys and girls between 0 and 6 months were 83.5 (n = 155, SD 6.01) and 83.5 (n = 191, SD 5.80), respectively. Established means for boys and girls between 0 and 6 months were 74.4 (n = 38, SD 5.2) and 74.3 (n = 49, SD 6.1), respectively. The difference between norms is highly statistically significant (p < 0.0001). For this age range, insurance criteria for a helmet is > 83.7 for boys and > 82.7 for girls. Using previous norms, 74 boys (44.6 percent) and 104 girls (54.5 percent) would meet criteria for a helmet under current guidelines.

CONCLUSIONS: The mean cephalic index of children has changed. The reasons could include diversifying populations in the United States and the introduction of the Back to Sleep campaign. Over 50 percent of children may inappropriately meet criteria for a helmet based on prior norms. Updating norms could change the definition of plagiocephaly for a helmet orthosis.

DOI of Published Version



Phelan AL, Gu G, McCarthy M, Barton BA, McIntyre JK, Lalikos JF. Rethinking Farkas: Updating Cephalic Index Norms in a Large, Diverse Population. Plast Reconstr Surg. 2021 Jun 1;147(6):1369-1376. doi: 10.1097/PRS.0000000000007957. PMID: 33973960. Link to article on publisher's site

Journal/Book/Conference Title

Plastic and reconstructive surgery

PubMed ID


Related Resources

Link to Article in PubMed