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Swan Neck Deformity following Excision of FDS

Discussion

  • may result from complete excision of the flexor digitorum sublimis;
  • it is especially likely to occur in patients with a hyperextensible PIP joint;
  • major vinculum exists at the insertion of the sublimis tendon;
  • when tendon is exised to to its insertion, the vinculum is violated, creating major source of adhesion formation for reconstructed tendon;
  • check rein effect on the joint is lost, allowing hyperextension;
    • this creates a relative lengthening of the extensor apparatus, causing terminal phalanx to drop into flexion;
    • lateral bands displace dorsally;

Prevention

  • do not excise sublimis distally farther than neck of middle phalanx or just proximal to vinculum;
    • if possible, the remaining sublimis should be left even longer