Hand Malformations

Hand and finger malformations represent a challenging area of clinical genetics from the standpoint of understanding the classification as well as in understanding the genetic etiologies, which are often due to single-gene mutations. The majority of familial types however are not yet associated with specific genes. In addition, there is terrific variation in expression between affected family members.

Another challenge in studying hand anomalies is that the literature will often refer to certain malformation types (e.g., brachydactyly type E) without defining what this type is. If the reader is not familiar with a visual image of the malformation, then learning may be hindered. Accordingly, the purpose of these diagrams is to present images of the common polydactyly, syndactyly, and brachydactly malformations that have been described.

The Hand Syndactylies: Common Types

Illustration comparing five types of hand syndactyly — This illustration shows five common types of hand syndactyly, with simplified drawings of hands demonstrating where digits are fused. Type I involves webbing between the middle fingers and is the most common form. Type II, also called synpolydactyly, affects digits along the ring and middle finger region and is associated with HOXD13 mutations. Type III involves fusion of the fourth and fifth fingers and is linked to mutations in the GJA1 gene. Types IV and V are rare forms that show more extensive or complex fusion patterns. The diagrams help compare how syndactyly affects different areas of the hand.

Polydactylies, Classification for thumb (preaxial) and little finger (postaxial) types.

These diagrams illustrate the main types of polydactyly. These malformations are usually observed in otherwise normal children, and often have an autosomal dominant pattern of inheritance.

Illustration comparing thumb (preaxial) and little‑finger (postaxial) types of polydactyly. — This figure compares postaxial and preaxial forms of polydactyly, showing where extra digits occur on the little‑finger side or the thumb side of the hand. Postaxial polydactyly is illustrated with Type A, which has a well‑formed additional digit, and Type B, which features a small, rudimentary extra digit. Preaxial types include four variations: Type 1 shows an extra thumb; Type 2 includes a duplicated thumb with a triphalangeal segment; Type 3 displays a duplicated middle digit with triphalangeal features; and Type 4 shows polydactyly of both hands and feet. These diagrams highlight how polydactyly can vary in structure and location.

Brachydactyly Classification Types

Diagramed below is the classification system used to describe hand anomalies associated with shortening of the fingers. Most are autosomal dominant. For some, genes have been identified but genetic heterogeneity is present in all, as well as variable expression. Darkened areas show the main bone findings. For some types, such as in A5 and B, there is an absence of bones (middle phalanges) so that no “dark” areas are indicated.

Illustration comparing types of brachydactyly based on bone shortening patterns — This figure illustrates the major classification types of brachydactyly, showing differences in bone development across the fingers. Each hand diagram highlights specific bones that are shortened or absent. Types A1 through A5 depict patterns involving missing or shortened middle phalanges or radial deviations. Additional types, including B, C, D, and E, show variations such as shortened terminal phalanges, absent bones, or more complex anomalies involving multiple digits. A normal hand is included for comparison. The darkened areas indicate the primary bones affected in each subtype.

Thumb Hypoplasia Classification

These tables and images were adapted from a 2004 paper addressing radial ray digit defects and thumb hypoplasias. See the table below the images for explanation of this classification system.

Images illustrating Blauth and Schneider‑Sickert thumb hypoplasia types — This figure shows the Blauth and Schneider‑Sickert classification system for thumb hypoplasia, ranging from mild underdevelopment to complete absence of the thumb. Type 1 demonstrates mild narrowing and reduced size. Type 2 shows more pronounced underdevelopment with limited motion. Types 3A and 3B illustrate increasing instability at the base of the thumb and partial absence of skeletal structures. Type 4, known as a ‘floating thumb,’ shows minimal bony support with severe functional limitation. Type 5 represents complete absence of the thumb. Photographs and X‑rays are presented together to highlight both clinical appearance and underlying bone structure

Explanation of above classification: