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PubMed This is a summary of 11 peer-reviewed journal articles Updated
Pediatrics · Postaxial Polydactyly

The Diagnostic Process: Distinguishing Type A vs. Type B

At a Glance

To safely treat an extra digit, doctors use an X-ray to determine if it contains bone (Type A) or is purely soft tissue (Type B). This diagnosis confirms the right surgical approach and helps decide if further genetic screening is needed.

When a baby is born with an extra digit, the medical team needs to determine exactly how that digit is formed. Confirming whether the digit is Type A or Type B is critical because it dictates the safest treatment plan and helps doctors know if further health screenings are needed [1][2].

Why an X-ray is Necessary

While a doctor can often guess the type just by looking, an X-ray (radiograph) is the gold standard for diagnosis [1]. Even a small “skin tag” can sometimes hide a tiny piece of bone or a connection to a joint that isn’t visible from the outside [3].

An X-ray allows the surgeon to:

  1. See the internal structure: Confirm if there are ossified (bony) elements inside the digit [1][4].
  2. Identify connections: Determine if the extra digit shares a joint or a bone with the rest of the hand or foot [1][2].
  3. Plan the procedure: If there is a bony connection, a simple bedside procedure could be painful or lead to complications. Knowing the anatomy beforehand ensures the right surgical technique is chosen to protect the function of the hand or foot [2][3].

If the X-ray confirms there is no bone and the digit is purely soft tissue, the diagnosis of Postaxial Polydactyly Type B is confirmed. If bone and joints are present, it is considered a Type A digit, which requires a different, more involved surgical approach [5][4].

When to Consider Further Testing

For most babies with Type B polydactyly, the extra digit is an “isolated” finding, meaning there are no other underlying medical issues [6][7]. However, doctors may recommend a more thorough evaluation or genetic testing in specific situations:

  • Type A Diagnosis: Type A digits are statistically more likely to be associated with rare genetic conditions than Type B [6][7].
  • Other Physical Findings: If the baby has other unusual features, such as heart issues, kidney abnormalities, or distinctive facial features, a genetic workup may be suggested [8][9]. Fortunately, if a syndrome is present, pediatricians usually spot these other obvious physical symptoms right away.
  • Family History: If multiple family members have had complex extra digits or other health concerns, genetic counseling may provide more clarity [10][11].

In many cases, the pediatrician will simply perform a detailed physical exam. If everything else looks healthy, the focus shifts entirely to the best way to remove the extra digit, which you can explore in our Treatment Options guide.

Common questions in this guide

Why does my baby need an X-ray for an extra digit?
An X-ray is necessary to see if there are any bones or joint connections inside the extra digit. Even small digits that look like skin tags can hide tiny pieces of bone that aren't visible from the outside.
What is the difference between Type A and Type B polydactyly?
Type A polydactyly contains bone and joint connections, requiring a more involved surgical approach. Type B is made purely of soft tissue and has no bone, making it simpler to remove.
Does having an extra finger mean my baby has a genetic condition?
In most cases, especially with Type B polydactyly, the extra digit is an isolated finding with no underlying medical issues. However, if the baby has other unusual physical features, a Type A diagnosis, or a family history of health concerns, genetic testing may be recommended.

Questions to Ask Your Doctor

Curated prompts to bring to your next appointment.

  1. 1.Does the X-ray show any bone or joint connections between the extra digit and the rest of the hand or foot?
  2. 2.Given the imaging and physical appearance, do you definitively categorize this as Type A or Type B?
  3. 3.If you suspect a syndrome based on other physical findings, which specific specialist referrals (like a geneticist) do you recommend?

Questions For You

Tap a prompt to share your answer — we'll use it plus this page's context to start a tailored conversation.

References

References (11)
  1. 1

    The CoULD Ulnar Polydactyly Classification: A Multicenter Analysis.

    Mendenhall SD, Cordray H, Steinman SE, et al.

    Plastic and reconstructive surgery 2026; (157(2)):315-325 doi:10.1097/PRS.0000000000012224.

    PMID: 40489747
  2. 2

    Morphologic Changes in Postaxial Polydactyly of the Foot: A Standardized Quantitative Analysis Using the Watanabe-Fujita Classification.

    Makino A, Saito S

    Plastic and reconstructive surgery 2024; (153(1)):170e-180e doi:10.1097/PRS.0000000000010565.

    PMID: 37075280
  3. 3

    Surgical Procedures Based on the Arthrographic Findings of the Fifth MTP Joint With Proximal Phalanx Duplication in Postaxial Polydactyly of the Foot.

    Kurokawa T, Iba K, Hanaka M, et al.

    The Journal of foot and ankle surgery : official publication of the American College of Foot and Ankle Surgeons 2021; (60(5)):983-989 doi:10.1053/j.jfas.2021.04.011.

    PMID: 34006434
  4. 4

    A Rare Presentation of Postaxial Polydactyly in a 2-Year-Old Female with Ellis-van Creveld Syndrome.

    Anthony T, Nguyen ET, Moyer B, et al.

    Journal of hand surgery global online 2023; (5(6)):852-855 doi:10.1016/j.jhsg.2023.08.007.

    PMID: 38106942
  5. 5

    Bilateral Postaxial Polydactyly of the Feet in an Adult: Surgical Management and Outcomes.

    Aljefri A, Batouk OA, Esmaiel AA, et al.

    Cureus 2026; (18(1)):e101428 doi:10.7759/cureus.101428.

    PMID: 41694918
  6. 6

    Predictors of Syndromic Association in Ulnar Polydactyly: Analysis of a Multicenter Congenital Hand Differences Registry in the United States.

    McQuillan T, Antonellis H, Wall L, et al.

    The Journal of hand surgery 2026; (51(3)):292-300 doi:10.1016/j.jhsa.2025.03.019.

    PMID: 40377505
  7. 7

    Polydactyly, postaxial, type B.

    Holmes LB, Nasri H, Hunt AT, et al.

    Birth defects research 2018; (110(2)):134-141 doi:10.1002/bdr2.1184.

    PMID: 29377639
  8. 8

    Early prenatal detection of Bardet-Biedl syndrome in a case with postaxial polydactyly and hyperechoic kidneys confirmed by next generation sequencing.

    Li QY, Huang LY, Li DZ

    Congenital anomalies 2019; (59(4)):142-144 doi:10.1111/cga.12306.

    PMID: 30073714
  9. 9

    Orofaciodigital syndrome type II (Mohr syndrome): a case report.

    Malekianzadeh B, Vosoughi F, Zargarbashi R

    BMC musculoskeletal disorders 2020; (21(1)):793 doi:10.1186/s12891-020-03825-x.

    PMID: 33256699
  10. 10

    Case Report: A case of Culler-Jones syndrome caused by GLI2 gene mutation.

    Xie X, Wei Y, Li Y, et al.

    Frontiers in pediatrics 2025; (13()):1699082 doi:10.3389/fped.2025.1699082.

    PMID: 41488893
  11. 11

    Third case of Bardet-Biedl syndrome caused by a biallelic variant predicted to affect splicing of IFT74.

    Mardy AH, Hodoglugil U, Yip T, Slavotinek AM

    Clinical genetics 2021; (100(1)):93-99 doi:10.1111/cge.13962.

    PMID: 33748949

This page provides educational information about diagnosing postaxial polydactyly in infants. It is not a substitute for professional medical advice, imaging, or diagnosis from your child's pediatrician or surgeon.

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