Keywords
radial polydactyly - congenital anomalies - cadaver - hand
Introduction
Polydactyly is one of the frequently observed congenital anomalies of the hand and
foot. In this anomaly, a rudimentary or fully developed additional digit is seen along
with the usual digits. The anomaly is also referred as polydactylia, polydactylism,
or hyperdactyly.[1] It can occur as a part of a syndrome or isolatedly.[2] Polydactyly of the hand or of the foot are categorized into preaxial, postaxial
and central types.[3] Thumb polydactyly is the most common type of polydactyly in the hand. Currently,
the classification of thumb polydactyly proposed by Wassel[4] is in clinical use. In the present case, we report an unusual type of preaxial polydactyly
and discuss its structural components.
Discussion
The pathogenesis of preaxial polydactyly has been studied in both experimental animals[5]
[6] and in men.[7] Yasuda has studied 13 human embryos and demonstrated the morphological features
in the early pathogenesis of preaxial polydactyly.[7] In this study, it is concluded that the interaction between the ectoderm and the
mesoderm of the limb plays a crucial role in the development of preaxial polydactyly.[7] In both white and black populations, the incidence of thumb polydactyly is found
to occur in 8 in 100,000 individuals.[8]
[9] The Wassel classification[4] is proposed based on the level of bifurcation or duplication, and is widely accepted
clinically. According to Wassel, the pathoanatomy of thumb polydactyly can be divided
into 7 groups; type I: bifid distal phalanx; type II: duplicated distal phalanx; type
III: bifid proximal phalanx; type IV: duplication of the proximal phalanx that rests
on the broad metacarpal; type V: bifid metacarpal; type VI: duplicated metacarpal;
and type VII: triphalangism.[4] The occurrence of type IV is more common when compared with other types.[4] In the present case, we report an unusual type of thumb polydactyly in which the
additional thumb was found to be devoid of skeletal, muscle and tendon components.
In the Wassel[4] classification of thumb polydactyly, the reported type has not been described. The
documentation of this rare type may be clinically important. In an immature hand,
due to the presence of the cartilaginous epiphysis, the identification of the level
of bifurcation between the duplicated components is difficult.[3] This can possibly explain why sometimes the clinically diagnosed type of polydactyly
is different from the findings encountered in the surgery and, in such cases, the
classification may not be appropriate to deal with.[3] A radiographic examination is usually recommended to evaluate the presence of the
skeletal component in the additional digit, before planning the surgery.[3] For the better reconstruction outcome and to avoid or reduce complications in operations,
the components of the additional digit such as skin, nail, bone, and the ligaments
should be evaluated and treated in a simultaneous manner.[9]
[10] The additional digit observed in the present case was non-functional and there were
no skeletal, muscle and tendon components in it. The presence of a thick cord of connective
tissue formed by the fibrous flexor sheath of the flexor pollicis longus tendon reported
here may be clinically significant during the diagnosis, treatment and while planning
the surgery and reconstruction procedures.
