Brachydactyly Type A3​

50-year-old female presenting with short 5th finger. What is the diagnosis? • Xray of the Week

Figure 1. Frontal bilateral hand X-ray. What is the diagnosis?

Figure 2. Frontal bilateral hand X-ray:  Severe shortening of the middle phalanx of the fifth digit (red arrows). The phalanx measures less than 50% of the length of the adjacent fourth middle phalanx, satisfying the Hertzog criteria for Brachydactyly Type A3. A mild radial clinodactyly is present, secondary to the wedge-shaped morphology of the middle phalanx.

Discussion

Brachydactyly (BD) refers to disproportionately short fingers and toes, classified by the Julia Bell system into five primary types (A–E) based on anatomical involvement. Type A3 (BDA3), also known as brachymesophalangy V, is the most common isolated hand anomaly.[1] 

Imaging Findings and Analysis

Radiographs of this 50-year-old female (Fig 1, 2) reveal isolated, bilateral shortening of the middle phalanx of the fifth digit. The definitive diagnosis is established using the Hertzog criterion, which mandates that the longitudinal length of the fifth middle phalanx must be less than 50% of the longitudinal length of the fourth middle phalanx.[1] Morphologically, the affected phalanx exhibits a characteristic rhomboid or wedge-shaped configuration. The radial side of the phalanx is significantly shorter than the ulnar side, creating a slanted distal articular surface that drives radial clinodactyly (radial deflection of the distal phalanx toward the fourth digit). 

Pathophysiological and Genetic Mechanisms

BDA3 is an autosomal dominant disorder arising from disrupted cartilage ossification during early embryonic development (blastogenesis), with some cases mapped to the chromosome 13q33 region.[1] 

Epidemiology and Biocultural Insights

The prevalence of BDA3 varies significantly by ethnicity; it is a common variant in Asian populations, occurring in 21% to 25.6% of Japanese children, but remains rare in populations of European or African descent (<2%).[7][8] 

Growth and Development

Although BDA3 is more frequently identified in children with short stature, it does not negatively impact the efficacy of growth hormone therapy, indicating that the local physis disruption does not represent global resistance to growth signals.[4]  

Syndromic Associations and Differentials

Radiologists should view BDA3 as a clinical marker for broader genetic conditions, most notably Down syndrome (present in ~60%) and Turner syndrome.[9] Differential considerations include Kirner deformity (palmo-radial bowing of the distal phalanx shaft) and Camptodactyly (a soft-tissue flexion contracture of the PIP joint).[5]  

Genetic Counseling

Inheritance is typically autosomal dominant with a 50% recurrence risk for offspring; however, for isolated cases, patients should be reassured that BDA3 is a benign anatomical variant.[1]  

Management and Prognosis

Isolated BDA3 is almost universally asymptomatic and requires no medical or surgical intervention. The functional prognosis is excellent, as the shortening of the little finger does not typically affect manual dexterity or grip strength.[5]

Corrective surgical procedures, such as osteotomy, are extremely rare and indicated only for severe clinodactyly that causes functional impairment or significant cosmetic distress.[1] 

Key Learning Points

• Diagnostic Standard: BDA3 is confirmed when the fifth middle phalanx length is <50% of the fourth (Hertzog criterion).[1]  

• Radiographic Features: Look for a wedge-shaped middle phalanx and associated radial clinodactyly.  

• Population Variant: High prevalence in Japanese and other Asian populations should be noted as a common anatomical variation.[7][8]

• Clinical Marker: Identification of BDA3 warrants screening for Down and Turner syndromes, particularly if associated with metacarpal shortening.[9]  

• Management: Isolated BDA3 is benign; functional impairment is rare, though corrective options exist for severe cases.[5]  

References

1. Temtamy SA, Aglan MS. Brachydactyly. Orphanet J Rare Dis. 2008;3:15. doi:10.1186/1750-1172-3-15

2. Garn SM, Hertzog KP, Poznanski AK, Nagy JM. Metacarpophalangeal length in the evaluation of skeletal malformation. Radiology. 1972;105(2):375-381. doi:10.1148/105.2.375

3. Wu H, Wu H, Li Y, Li H. Brachydactyly Type A3 Is More Commonly Seen in Children With Short Stature But Does Not Affect Their Height Improvement by Growth Hormone Therapy. Front Endocrinol (Lausanne). 2022;13:824315. doi:10.3389/fendo.2022.824315

4. Nguyen ML, Jones N. Undergrowth: brachydactyly. Hand Clin. 2009;25(2):247-255. doi:10.1016/j.hcl.2009.02.003

5. Everman DB. The brachydactylies. In: Stevenson RE, Hall JG, eds. Human Malformations and Related Anomalies. 2nd ed. Oxford University Press; 2006:968-983.

6. Zhang W, Li K, Zhang Q, et al. Epidemiology of brachydactyly type A3 in China: a nationwide multicentre population-based study among children aged 3–17 years. BMJ Open. 2025;15(11):e099166. doi:10.1136/bmjopen-2025-099166

7. Wu HH, Zhang YQ, Yu CD, et al. Brachydactyly type A3 may be associated with shorter stature: An observation from a Chinese pediatric sample. PLoS One. 2025;20(11):e0336913. doi:10.1371/journal.pone.0336913

8. Kang MJ, Kanakatti Shankar R, Jee YH. Phalangeal bone growth and implications in Turner syndrome. Front Endocrinol (Lausanne). 2026;16:1735962. doi:10.3389/fendo.2025.1735962.

9. Castriota-Scanderbeg A, Dallapiccola B. Abnormal Skeletal Phenotypes: From Sameness to Differential Diagnosis. Springer; 2006. doi:10.1007/3-540-30361-8 

10. Cleveland Clinic. Brachydactyly. Accessed January 20, 2026. https://my.clevelandclinic.org/health/diseases/24081-brachydactyly 

Kevin M. Rice, MD is the president of Global Radiology CME and is a radiologist with Cape Radiology Group. He has held several leadership positions including Board Member and Chief of Staff at Valley Presbyterian Hospital in Los Angeles, California. Dr. Rice has made several media appearances as part of his ongoing commitment to public education. Dr. Rice's passion for state-of-the-art radiology and teaching includes acting as a guest lecturer at UCLA. In 2015, Dr. Rice and Natalie Rice founded Global Radiology CME to provide innovative radiology education at exciting international destinations, with the world's foremost authorities in their field. In 2016, Dr. Rice was nominated and became a semifinalist for a "Minnie" Award for the Most Effective Radiology Educator. He was once again a semifinalist for a "Minnie" for 2021's Most Effective Radiology Educator by AuntMinnie.com. He has continued to teach by mentoring medical students interested in radiology. Everyone he has mentored has been accepted into top programs across the country, including Harvard, UC San Diego, Northwestern, Vanderbilt, and Thomas Jefferson.

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