guidebook. - Fanconi Anemia Research Fund

Chapter 5: Hand and Arm Differences in FA
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Thumb duplication involves more than the bony elements,
since the parts may share common nails, tendons,
ligaments, joints, and neurovascular structures.
Treatment requires using portions of each component
to construct a properly aligned and functional thumb.
This decision is not always straightforward and requires
careful examination. The soft tissues from the ablated
thumb are used to augment the retained thumb, including
the collateral ligament and muscles. Articular
surface modification via osteotomy or joint recontouring
and tendon realignment are necessary to optimize
thumb function. Irrespective of treatment, the reconstructed
thumb will be smaller than a normal thumb and
usually will lack some motion.
Table 2: Classification of Duplicated Thumbs
Type Duplicated Elements
I
Bifid distal phalanx
II
Duplicated distal phalanx
III
Bifid proximal phalanx
IV
Duplicated proximal phalanx*
V
Bifid metacarpal phalanx
VI
Duplicated metacarpal phalanx
VII
Triphalangeal component
* Most common type
Adapted from Wassel et al.
Radial Deficiency
The radius can be slightly smaller, considerably smaller,
or absent. The severity of radial deficiency is graded
from I through IV, and based on x-ray interpretation
(Table 3). Ossification of the radius is delayed in radial
deficiency, and the differentiation between total and
partial absence (Types III and IV) cannot be established
until approximately three years of age. Complete