Hand Surgery Source

Swan neck deformity - observation

Test, Exam and Signs

Historical Overview

  • In 1676, swan neck deformity was possibly first described by Thomas Sydenham. There are also examples of swan neck deformity in Rubens’ paintings from the seventeenth century.1,2

Description

  • Swan neck deformity is diagnosed primarily by observation of proximal interphalangeal (PIP) joint hyperextension and distal interphalangeal (DIP) joint flexion.3 The patient’s finger will have a “kink”, which resembles a swan’s neck while in flight.
  • Swan neck deformity may also involve volar plate insufficiency and tendon imbalance.3

Pathophysiology

  • Swan neck deformity often arises from chronic mallet finger or rheumatoid arthritis (RA). It is important to distinguish posttraumatic cases from cases involving RA, because the treatment options are different.4
  • In children, swan neck deformity is often related to neurologic disorders such as cerebral palsy.1,5
  • Swan neck deformity may also be associated with some connective tissue disorders, such as Ehlers Danlos syndrome.

Instructions

  1. Obtain an accurate and complete patient history. Ask the patient to rate on a scale from 1 to 10, how much pain s/he usually experiences in the affected finger(s).
  2. Check the patient’s fingers for swelling, hyperextension and inflammation in the PIP joints. 
  3. Observe for snapping, clicking, or locking of the fingers in hyperextension.
  4. Check the patient’s fingers for DIP joint flexion.
  5. Examine the contralateral hand.

Variations

  • In swan neck deformity, the lateral bands migrate dorsal and the transverse retinacular ligament will elongate and attenuate.6

Related Signs and Tests

  • Mallet finger observation
  • Bunnell test1
  • Collateral ligament stability and tenderness
  • Extensor tendon exam
  • Flexor tendon exam
  • Joint exam
  • Hyperligamentous laxity
  • Range of motion (ROM), active
  • ROM, passive
  • Intrinsic plus test7
  • Volar plate stability
  • Volar plate tenderness 
  • Radiographs
  • Magnetic resonance imaging (MRI), without contrast 

Diagnostic Performance Characteristics

  • In addition to other physical tests and radiographs, use MRI without contrast, to improve reliability.
Definition of Positive Result
  • A positive result occurs when one or more of the patient’s fingers shows PIP joint hyperextension and DIP joint flexion.
Definition of Negative Result
  • A negative result occurs when the patient’s fingers do not show PIP joint hyperextension and DIP joint flexion. 
Comments and Pearls
  • In swan neck deformity with cerebral palsy, surgery aims to correct the underlying muscle imbalance.8
  • For patients with RA who have swan neck deformity, the hand surgeon should coordinate treatment with the rheumatologist and any other orthopedic surgeons.7
Diagnoses Associated with Tests, Exams and Signs
References
  1. Dreyfus JN, Schnitzer TJ. Pathogenesis and differential diagnosis of the swan-neck deformity. Semin Arthritis Rheum1983;13(2):200-11. PMID: 6673115
  2. Appelboom T, de Boelpaepe C, Ehrlich GE, Famaey JP. Rubens and the question of antiquity of rheumatoid arthritis. JAMA1981;245:483-6. PMID: 7005475
  3. Culp R, Jacoby S. Musculoskeletal Examination of the Elbow, Wrist and Hand: Making the Complex Simple. New Jersey: SLACK Incorporated, 2012
  4. McKeon KE, Lee DH. Posttraumatic boutonnière and swan neck deformities. J Am AcadOrthop Surg2015;23(10):623-32. PMID: 26320165
  5. Tran PC, Witt P. An unusual case of swan neck deformity in a child. Plast Reconstr SurgGlob Open2015;3(8):e478. PMID: 26495191
  6. Rayan G, Akelman E. The Hand: Anatomy, Examination and Diagnosis. Philadelphia: Lippincott Williams & Wilkins, 2012
  7. Rizio L, Belsky MR. Finger deformities in rheumatoid arthritis. Hand Clin1996;12(3):531-40. PMID: 8842717
  8. Carlson EJ, Carlson MG. Treatment of swan neck deformity in cerebral palsy. J Hand Surg Am2014;39(4):768-72. PMID: 24613587