Swan Neck Deformity
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| Swan-neck deformity often begins with flexor synovitis, which
increases the flexor pull on the MP joint. Constant efforts to extend the
finger against this pull lead to stretching of the collateral ligaments
and the volar plate at the PIP joint. In a normal finger, intrinsic muscles
insert into the lateral bands and serve as flexors of the MP joint and extensors
of the PIP and DIP joints by being located volar to the MP joint axis and
dorsal to the PIP and DIP joint axes. When swan neck deformity is present,
the lateral bands are remain dorsal to the axis of the PIP joint. In this
position, the lateral bands increase the pull of the long extensor tendon's
central slip, which attaches to the dorsal base of the middle phalanx. The
increase of flexor profundus tension resulting from hyperextension of the
PIP joint leads to a flexion of the DIP joint. The same type of phenomenon
can happen after mallet deformity. If left untreated, this can lead to a
secondary swan neck deformity. Corrective splinting is essential is the
early stages to prevent progression of the deformity. |
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A typical swan neck deformity |
Custom Finger Gutter with PIP in 30 degrees flexion
and DIP in slight hyperextension |
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