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A triphalangeal thumb (TPT) has three phalanges instead of two, and therefore, the thumb is long and similar in appearance to a finger. This congenital abnormality is rare and of uncertain pathogenesis. Wood reported that triphalangeal thumb was inherited by a simple autosomal dominant inheritance pattern.5  Zuidam et al have noted that there is a area in The Netherlands where triphalangeal thumb has been linked to chromesome 7q36.3  Triphalangeal thumb  may occur in isolation, in association with other hand and foot malformations, or as a feature of various syndromes. In about two-thirds of all cases, there is a genetic component. There are two types of isolated TPT: opposable and non-opposable. Isolated TPT may occur as a sporadic disorder, but it is usually inherited in an autosomal dominant manner. Sporadic cases are opposable and unilateral. Autosomal dominant cases are mostly non-opposable and bilateral. Owing to the rarity of the condition, there are vast differences of opinion about disease characteristics, etiology, and classification systems.1-5


Theories include:

  • Failure of fusion of the middle and distal phalanges (persistence of middle phalanx) in first digit (Abnormal digit is opposable)
  • Duplication of the index finger in association with absence of the thumb (Abnormal digit is non-opposable)
  • Arrested attempt at formation of a bifid thumb (Abnormal digit is opposable)

Incidence and Related Conditions

  • Only about 140 cases of TPT have been reported worldwide in the past century. 
  • An incidence of one case of triphalangeal thumb per 25,000 live births has been reported.5
  • The frequency with which TPT is associated with bifid thumb, pre-axial polydactyly, and the split-hand (“lobster claw”) deformity suggests a close pathogenetic relationship among these anomalies.
  • The relationship between triphalangeal thumb and bifid thumb (radial polydactyly) is strong.  Reports of the percentage of triphalangeal thumb associated with thumb polyddacyly varies from 11% to 32%.
  • Other associated deformities include brachyectrodactyly syndrome and preaxial polydactyly of the feet.

Exam Findings, Signs and Positive Tests

  • Persistence of a middle phalanx: long, slender thumbs with slight flexion and ulnar deviation of the distal phalanges
  • Absence of thumb/duplication of index finger:  5-fingered hand with all fingers triphalangeal and in the same plane
  • Incomplete duplication of thumb: ulnar digit has a small third phalanx interposed between the nail and the proximal phalanx on its radial aspect
  • Thumb strength is significantly diminished but activities of daily living functions remain intact.
  • Thenar muscles may be underdeveloped, though functional
  • There may be no mobility at the proximal or distal interphalangeal joints (PIPs, DIPs)
  • The metacarpophalangeal (MP) joint is usually stable.

Work-Up Options

  • X-rays
    • Persistence of a middle phalanx: 3 normally formed phalangeal elements in each thumb, with an epiphysis at each end of the first metacarpal
    • Absence of thumb/duplication of index finger: 3 phalanges in all 5 digits
    • Incomplete duplication of thumb: bifid thumb
  • The work-up may be extensive depending on suspected associated syndromes. For example, to check for Blackfan-Diamond syndrome, laboratory studies would look for:
    • Macrocytic anaemia with no other significant cytopenias
    • Reticulocytopenia
    • Normal marrow cellularity with a paucity of erythroid precursors

Differential Diagnosis

More than 50 malformations, syndromes, and teratogens have been associated with TPT. Here is a partial listing:

  • Aase syndrome
  • Absence of pectoralis muscle
  • Blackfan-Diamond syndrome
  • Fanconi pancytopenia
  • Holt-Oram syndrome
  • Phenytoin (dilantin)
  • Polydactyly-syndactyly
  • Radial hypoplasia, thrombocytopathy, and sensorineural hearing impairment
ICD-10 Codes

    Diagnostic Guide Name


    ICD 10 Diagnosis, Single Code, Left Code, Right Code and Bilateral Code


    ICD-10 Reference

    Reproduced from the International statistical classification of diseases and related health problems, 10th revision, Fifth edition, 2016. Geneva, World Health Organization, 2016

Weak pinch and grip
Abnormal appearance with long thin thumbs noted
Angulatory deformities of the thumb and unacceptable appearance
Typical History

TPT is frequently bilateral and associated with a positive family history. Due to the rarity of the condition, little else is known.

Positive Tests, Exams or Signs
Work-up Options
Images (X-Ray, MRI, etc.)
Triphalangeal Thumb
  • Hypoplastic triphalangeal thumb: 1.distal phalanx; 2.middle phalangeal; 3. proximal phalanx;  M-thumb metacarpal
    Hypoplastic triphalangeal thumb: 1.distal phalanx; 2.middle phalangeal; 3. proximal phalanx; M-thumb metacarpal
Treatment Options
Treatment Goals
  • Improve thumb appearance
  • Improve thumb function
  • Inform patient and/or parents that the thumb will be weaker than normal but typically not weak enough to affect the patient’s capacity to perform activities of daily living.
  • Observation
  • Zuidam et al report that untreated patients with triphalangeal thumb(s) are weaker but function adequately. 
  • This team also reports that thumb apearance is the patients major concern.

Many different surgical approaches have been performed. Every case is unique and careful individualized surgical planning is needed. 

Surgical options include:

  • Excision of one phalanx
  • Corrective osteotomy of the metacarpal
  • Interphalangeal arthrodesis
  • Partial and total resection of the triphalangeal thumb when part of a bifid thumb (radial polydactyly)
  • Removal of the triphalangeal thumb and pollicization of the index ray
CPT Codes for Treatment Options

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Common Procedure Name
Supernumerary digit excision and reconstruction
CPT Description
Reconstruction of supernumerary digit soft tissue and bone
CPT Code Number
CPT Code References

The American Medical Association (AMA) and Hand Surgery Resource, LLC have entered into a royalty free agreement which allows Hand Surgery Resource to provide our users with 75 commonly used hand surgery related CPT Codes for educational promises. For procedures associated with this Diagnostic Guide the CPT Codes are provided above. Reference materials for these codes is provided below. If the CPT Codes for the for the procedures associated with this Diagnostic Guide are not listed, then Hand Surgery Resource recommends using the references below to identify the proper CPT Codes.

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Hand Therapy
  • Subsequent deformities may develop (eg, Z deformity with ulnar deviation of the PIP joint and radial deviation of the DIP joint)
  • Weaker than normal pinch and grip despite reconstructiion of the thumb
  • Parents should be advised that with growth secondary surgical reconstructive procedures may be needed
  • Associated syndromes must be identified in order to avoid complictions from the underlying syndrome
  • Infection remains a risk with surgical reconstruction
  • Near-anatomical correction of the deformity is possible.
  • Satisfactory range of motion and functional pinch/grasping can be achieved.
  • Cosmetic improvement is usually achieved with surgical reconstrudtion
Key Educational Points
  • Patients with bifid thumbs (radial polydactyly) usually have duplication of varying parts of their distal phalanx, middle phalanx and thumb metacarpal.  Using the Wassell classification system, bifid thumbs are classified according to number of duplicated halves of each bone in the thumb. With half the distal phalanx is duplicated the Wassell Type is a Type I . If all the distal phalanx is duplicated Wassell class is a Type II and Type III if half the proximal phalanx is partyially duplicated etc.  When one or more of the duplicated thumbs is a triphalangeal thumb, the bifid thumb is classified as a Wassell Type VII which is often further classified by sub-types A-D.
  • Patients with triphalangeal thumb typically do not have limited range of motion.
  • In children, some advise surgical correction at 1–2 years of age, when X-rays show ossification.
  • In adults, surgery should be undertaken only when function is limited and/or the cosmetic situation is limiting the patient's capacity to function in society.
  • Triphalangeal thumb can occur as a result of teratogen (eg, hydantoin) exposure.
  • Triphalangeal thumb(s) can be associated with many different inherited congenital syndromes and a careful work-up to rule out associated problems is critically important.
  • Patients with triphalangeal thumbs have weak pinch and grip compared to individuals with anatomically normal thumbs
  • Patients with triphalangeal thumbs are usually most concern with the appearance of their thumb not its functional limitations.

New Articles

  1. Alrabai HM, Farr S, Girsch W. Triphalangeal thumb reduction osteotomy through a versatile spiral approach. Tech Hand Up Extrem Surg 2016;20(2):54-60. PMID: 26926846
  2. Zuidam JM, Selles RW, de Kraker M, Hovius SE. Outcome of two types of surgical correction of the extra phalanx in triphalangeal thumb: is there a difference. J Hand Surg Eur Vol 2016;41(3):253-7. PMID: 25794887
  3. Zuidam JM, Selles RW, Ananta M, Runia J, Hovius SER.  The classification system of radial polydactyly: inclusion of triphalangeal thumb and triplication.  J Hand Surg AM 2008; 33A:373-377.
  4. Zuidam JM, de Kraker M, Selles RW, Hovius SER.  Evaluation of function and appearance of adults with untreated triphalangeal thumbs.  J Hand Surg AM 2010; 35A(7): 1146–1152
  5. Virchel E. Wood VE.  Polydactyly and the triphalangeal thumb. J Hand Surg Am 1978; 3A(5): 436-444


  1. Pedrazzini A, Pogliacomi F, Colacicco A, et al. Triphalangeal thumb: case report and literature review. Acta Biomed 2015;86(3):290-5. PMID: 26694158
  2. Qazi Q, Kassner EG. Triphalangeal thumb. J Med Genet 1988;25(8):505-20. PMID: 3050097


  1. Abramowitz I. Triphalangeal thumb. A case report and evaluation of its importance in the morphology and function of the thumb. S Afr Med J 1967;41(5):104-6. PMID: 6020465
  2. Milch H. Triphalangeal thumb. J Bone Joint Surg Am 1951;33(3):692-7. PMID:
  3. Virchel E. Wood VE.  Polydactyly and the triphalangeal thumb. J Hand Surg Am 1978; 3A(5): 436-444