Updated: 10/11/2016

Thumb Hypoplasia

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Introduction
  • Congenital underdevelopment of the thumb frequently associated with partial or complete absence of the radius
  • Epidemiology
    • incidence
      • 1/100,000 live births
    • demographics
      • male = female
    • location
      • bilateral involvement in ~60% of patients
      • right hand more common than left
  • 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
  • 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
  • Opponensplasty


Type IIIA
  • Musculotendinous and osseous deficiencies
  • CMC joint intact
  • Absence of active motion at the MCP or IP joint

Type IIIB


  • Musculotendinous and osseous deficiencies.
  • Basal metacarpal aplasia with deficient CMC joint q
  • 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
Type V
  • Complete absence of the thumb

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
Surgical 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? Tested Concept

QID: 3094
FIGURES:
1

Stability of the carpometacarpal joint

85%

(3017/3547)

2

Functional ROM of the wrist

1%

(21/3547)

3

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

4%

(137/3547)

4

Skin contracture of the first web space

2%

(69/3547)

5

Absence of a thumb interphalangeal joint

8%

(278/3547)

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? Tested Concept

QID: 1142
1

contralateral thumb function

4%

(133/3400)

2

thenar muscle function

7%

(222/3400)

3

presence of an extensor pollicis longus tendon

3%

(99/3400)

4

carpometacarpal joint stability

78%

(2644/3400)

5

metacarpophalangeal joint stability

8%

(286/3400)

L 1 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? Tested Concept

QID: 1225
1

Presence of complete osseous structures

9%

(281/3192)

2

Presence of intact musculotendinous structures

5%

(153/3192)

3

Carpometacarpal joint stability

72%

(2303/3192)

4

Metacarpophalangeal joint stability

11%

(354/3192)

5

Presence of an extensor pollicis longus tendon

2%

(77/3192)

L 2 D

Select Answer to see Preferred Response

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