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Updated: May 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
      • 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
      • 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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