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