Updated: 5/22/2021

Thumb Hypoplasia

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  • summary
    • Thumb Hypoplasia is the congenital underdevelopment of the thumb frequently associated with partial or complete absence of the radius.
    • Diagnosis is made clinically with hypoplasia of the thumb and thenar musculature. Radiographs are helpful in determining musculotendinous versus osseous deficiencies.
    • Treatment may be observation, soft tissue reconstruction, pollicization, or amputation depending on the level of the deficit and presence of carpometacarpal joint instability.
  • Epidemiology
    • Incidence
      • 1/100,000 live births
    • Demographics
      • male = female
    • Anatomic location
      • bilateral involvement in ~60% of patients
      • right hand more common than left
  • Etiology
    • Pathophysiology
      • exact cause during embryologic development has yet to be elucidated
    • Associated anomalies
      • greater than 80% of patients will have associated anomalies including
        • VACTERL
        • Holt-Oram
        • thrombocytopenia-absent radius (TAR)
        • Fanconi anemia
  • Classification
    • Treatment algorithm depends on presence of carpometacarpal joint stability
    • Blauth Classification
      Type
      Description
      Treatment
      Type I
      • Minor hypoplasia
      • All musculoskeletal and neurovascular components of the digit are present, just small in size
      No surgical treatment required
      Type II
      • All of the osseous structures are present (may be small) 
      • MCP joint ulnar collateral ligament instability
      • Thenar hypoplasia
      Stabilization of MCP joint
      Release of first web space
      Oppensplasty
      Type IIIA
      • Musculotendinous and osseous deficiencies
      • CMC joint intact
      • Absence of active motion at the MCP or IP joint
      Stabilization of MCP joint
      Release of first web space
      Oppensplasty
      Type IIIB
      • Musculotendinous and osseous deficiencies.
      • Basal metacarpal aplasia with deficient CMC joint 
      • Absence of active motion at the MCP or IP joint.
      Thumb amputation & pollicization
      Type IV
      • Floating thumb
      • Attachment to the hand by the skin and digital neurovascular structures
      Thumb amputation & pollicization
      Type V
      • Complete absence of the thumb
      Thumb amputation & pollicization
  • Presentation
    • Physical exam
      • inspection
        • extrinsic tendon abnormalities
          • pollex abductus
            • flexor pollicus longus attaches to normal insertion and the extensor tendon
          • hypoplasia of thenar musculature
        • absence of skin creases indicates muscle or tendon abnormalities
        • excessive abduction of MCP joint
      • range of motion and instability
        • ulnar collateral ligament laxity
        • web-space tightness
      • evaluation for associated anomalies is essential
        • cardiac
          • auscultation
          • echocardiography
        • kidneys
          • ultrasound
        • abdomen
          • ultrasound
  • Imaging
    • Radiographs
      • recommended views
        • bilateral films of hand, wrist and forearm
  • Studies
    • Labs
      • peripheral blood smear and complete blood count
        • important to rule out Fanconi anemia
    • Additional studies
      • chromosomal challenge test
        • detects Fanconi anemia before bone marrow failure
  • Treatment
    • Nonoperative
      • observation
        • indications
          • Type I hypoplasia where augmentation of thenar musculature (thumb abduction) is not necessary
    • Operative
      • opposition tendon transfer (opponensplasty)
        • indications
          • Type I hypoplasia with insufficient thumb abduction
      • release of first web space, opposition transfer, stabilization of MCP joint
        • indications
          • Type II and IIIA hypoplasia
      • pollicization
        • indications
          • Type IIIB, IV, V hypoplasia
  • Techniques
    • Opponensplasty (opposition transfer)
      • technique
        • performed using
          • flexor digitorum superficialis or
          • abductor digiti minimi
    • First web space deepening
      • technique
        • usually performed with Z-plasty
    • Stabilization of MCP joint
      • technique
        • three options
          • fusion
          • reconstruction of UCL with FDS
          • reconstruction of UCL with free tendon graft
    • Pollicization
      • technique
        • plan skin incision to avoid skin grafts
        • isolate index finger on its neurovascular bundles
        • detach first dorsal and palmar interosseous muscles
        • shorten digit by removing index finger metacarpal and epiphyseal plate
        • stabilize index MCP joint
        • reattach and balance musculotendinous units
        • reconstruct long extensor tendons
        • rebalance flexor tendons

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Questions (3)

(OBQ10.6) The parents of a newly adopted 3-year-old boy bring the child to the office for evaluation of his thumb. A clinical photograph is provided in figure A. Which of the following is the most important factor in determining thumb reconstruction versus ablation and pollicization?

QID: 3094
FIGURES:
1

Stability of the carpometacarpal joint

84%

(3215/3826)

2

Functional ROM of the wrist

1%

(25/3826)

3

Functional ROM of the index, middle, ring, and small fingers

4%

(150/3826)

4

Skin contracture of the first web space

2%

(78/3826)

5

Absence of a thumb interphalangeal joint

9%

(328/3826)

L 1 B

Select Answer to see Preferred Response

(OBQ05.256) What is the most important variable when deciding between reconstruction versus ablation of a hypoplastic thumb?

QID: 1142
1

contralateral thumb function

4%

(155/3742)

2

thenar muscle function

7%

(259/3742)

3

presence of an extensor pollicis longus tendon

3%

(116/3742)

4

carpometacarpal joint stability

77%

(2883/3742)

5

metacarpophalangeal joint stability

8%

(312/3742)

L 2 C

Select Answer to see Preferred Response

(OBQ04.120) Using the Blauth classification of thumb hypoplasia, grade IIIA can be treated with thumb reconstruction whereas grade IIIB is treated with thumb amputation & pollicization. What is the key difference between these two grades?

QID: 1225
1

Presence of complete osseous structures

9%

(301/3364)

2

Presence of intact musculotendinous structures

5%

(164/3364)

3

Carpometacarpal joint stability

72%

(2421/3364)

4

Metacarpophalangeal joint stability

11%

(371/3364)

5

Presence of an extensor pollicis longus tendon

2%

(83/3364)

L 2 D

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