Updated: 8/15/2017


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  • Congenital digital flexion deformity that usually occurs in the PIP joint of the small finger
  • Epidemiology
    • prevalence
      • less than 1%
    • location
      • unilateral (33%) or bilateral (66%)
        • if bilateral, can be symmetric or asymmetric
  • Pathophysiology
    • typically caused by either
      • abnormal lumbrical insertion/origin   
      • abnormal (adherent, hypoplastic) FDS insertion 
      • other less common causes include
        • abnormal central slip
        • abnormal extensor hood
        • abnormal volar plate
        • skin, subcutaneous tissue, or dermis contracture
  • Genetics
    • most often sporadic
    • can be inherited with autosomal dominant inheritance with incomplete penetrance/variable expressivity
  • Associated conditons
    • can be associated with more widespread developmental dysmorphology syndromes
•If full PIP extension can be achieved actively with MCP held in flexion, digit can be explored and abnormal tendon transferred to radial lateral band
Benson Classification
Characteristics Treatment  
Type I

 • Isolated anomaly of little finger, presents in infancy and affects males and females equally
 • Most common form

Type II

 • Same clinical features as Type I, presents in adolescence
 • Affects girls more often than boys 

From abnormal lumbrical insertion, abnormal FDS origin or insertion

If full PIP extension can be achieved actively with MCP held in flexion, digit can be explored and abnormal FDS tendon transferred to radial lateral band
Type III  • Severe contractures, multiple digits involved, presents at birth
 • Usually associated with a syndrome 
Non-operative (unless functional deficit exists after skeletal maturity), then consider corrective osteotomy/fusion
Kirner's Deformity  • Specific deformity of small finger distal phalanx with volar-radial curvature (apex dorsal-ulnar)
 •  Often affects preadolescent girls
 •  Often bilateral
 •  Usually no functional deficits
  • Symptoms
    • often goes unnoticed as usually only affects small finger and is very rarely associated with any significant compromise in function
    • typically painless and without motor/sensory deficits
  • Physical exam
    • flexion deformity of small finger PIP joint
      • flexible (correctable) or fixed (non-correctable) deformity
      • progressively worsens over time if untreated
      • may rapidly worsen during growth spurts
    • normal strength, sensation, perfusion
    • usually normal DIP and MCP joint alignment, however compensatory contractures can develop
    • no swelling, erythema, or warmth; not associated with inflammation
  • Radiographs
    • often normal, especially in early stages
    • later stages: possible decrease in P1 head convexity; possible volar subluxation and flattening of base of P2
  • Nonoperative
    • passive stretching, splinting
      • indications
        • nonoperative treatment is favored in most cases   
        • best for PIP contracture < 30 degrees
      • technique
        • passive stretching + static splinting
      • outcomes
        • variable outcomes
        • best outcomes with early intervention
  • Operative
    • FDS tenotomy +/- FDS transfer
      • indications
        • progressive deformity leading to functional impairment
      • technique
        • must address all abnormal anatomy
        • passive (correctable) deformities
          • FDS tenotomy, or
          • FDS transfer to radial lateral band if full active PIP extension can be achieved with MCP flexion
    • osteotomy vs. arthrodesis
      • indications
        • severe fixed deformities
      • outcomes
        • variable outcomes
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