Keywords
lumbrical - cleft hand - variation - plastic surgeon - deformity
Introduction
Cleft hand is a group of hand deformities in which the central digits of the hand
are congenitally absent.[1] This hand deformity is described with many other terms, including split-hand complex,
pincer cleft hand, lobster-claw, crab claw hand, and ectrodactyly. However, currently,
the term cleft hand is the most widely accepted to refer to this deformity.[1]
[2]
[3] Cleft hand may be associated with other congenital deformities. It is the 5th commonest anomaly of the hand. About 2.5% of the children with congenital deformities
of the hand have a cleft hand.[4] Cleft hand is classified into two types; typical cleft hand, characterized by a
V-shaped cleft, and atypical cleft hand, characterized by a U-shaped cleft.[5] The typical cleft hand affects 1 in 90 thousand births, and 1 in 20 thousand from
the general population. On other hand, the atypical cleft hand affects 1 in 150 thousand
births, and 1 in 200 thousand in the general population.[6] The hand deformities are due to chromosomal defects caused by exposure to teratogens
and to maternal metabolic diseases during a critical period of the embryonic development.[2] The soft tissue variations of cleft hand are rarely reported in the literature.[7] In the present case, we report the anatomic variants of a unilateral atypical cleft
hand in an elderly male cadaver.
Case Report
During regular dissection classes, we came across a unilateral atypical cleft hand
in an elderly male cadaver. It was noted during the summer semester teaching for undergraduate
medical students in the year of 2018, in the Department of Human and Clinical Anatomy
of the College of Medicine of the Sultan Qaboos University, Oman. The cleft hand showed
the absence of all of the phalanges of the middle finger. Its metacarpal bone was
of normal size and formed the base of the 2nd web space. There were no associated malformations or deformities of lower limbs,
ears, lips or of the palate. To explore the arrangement of digital tendons and lumbricals,
the hand was carefully dissected. There were four lumbricals and no variation was
found in their origin. The 1st and 2nd lumbricals were inserted into the radial and ulnar sides of the extensor digital
expansion of the index finger, respectively. The 3rd lumbrical close to the base of the 2nd web space was divided into 2 unequal slips; the small radial slip was merged with
the transverse metacarpal ligament over the head of the 3rd metacarpal bone, the larger ulnar slip was inserted into the radial side of the extensor
digital expansion of the ring finger. The 4th lumbrical was inserted into the radial side of the extensor digital expansion of
little finger. Both superficial and deep flexor digital tendons of the missing middle
finger were fused and inserted on the palmar surface of the head of the 3rd metacarpal bone [[Fig. 1]]. The extensor digitorum tendon of the missing finger was inserted on the dorsal
surface of the head of the 3rd metacarpal bone. Just before the insertion site, the tendon had thick tendinous interconnections
with extensor tendons of the index and ring fingers ([Fig. 2]). The palmar digital nerves of the median nerve of the middle finger formed 2 visible
fibrotic masses; radial and ulnar, over the base of the 2nd web space. Of these, the radial mass was formed by fusion of both palmar digital
nerves, as well as a common palmar digital artery from the superficial palmar arch
of the missing finger ([Figs. 1] and [3]). No variations were observed in the left hand ([Fig. 4]).
Fig. 1 Dissection of the right hand showing the distal attachment of four lumbricals (asterisk).
Note the insertion of the flexor digital tendons (DT) over the head of the 3rd metacarpal bone. The two fibrotic masses: ulnar mass (UM) and radial mass (RM) formed
by the fusion of (DN) and (DA) are also seen.
Fig. 2 Dissection of the right hand showing the distal attachment of the extensor digitorum
tendon of the middle finger (DTM) over the head of the 3rd metacarpal bone. Note the tendinous interconnections (asterisk) between the extensor
tendons of the ring finger and the missing middle finger.
Fig. 3 Dissection of the right hand showing the distal attachment of the 2nd lumbrical (2L) and of the 3rd lumbrical (3L). Note the position of the 2 fibrotic masses: ulnar mass (UM) and radial
mass (RM) at the base of the palmar cleft.
Fig. 4 Dissection of the left hand showing the presence of all digits.
Discussion
Although cleft hand has many variations, absence of the central portion of the hand
is the most common feature of this condition. Deficiency of the central portion may
include absence of phalanges, of a whole individual digit, or of all digits. The palmar
cleft can be shallow or deep, depending upon the growth of the remaining metacarpal
bones. Usually, the wider clefts are associated with an overly adducted or deficient
thumb.[4] Classically, the cleft hand is classified into two types: typical and atypical.
The typical cleft hand is usually V-shaped, bilateral, involves the foot and is presented
as a syndrome along with other anomalies such as anencephaly, cleft lip, and cleft
palate. This type of anomaly usually displays a familial inheritance. On the other
hand, the atypical cleft hand is usually U-shaped, unilateral, sporadic, only involves
one limb, and often the metacarpals are absent and the thumb and little finger are
hypoplastic. It is not associated with any other anomalies.[3] Currently, the atypical cleft hand is referred to as symbrachydactyly.[4] The condition is mainly due to a developmental arrest in the formation of the phalanges
and of the metacarpals, and usually two central digits are involved.[2] The remains of the missing finger will still possess some active movement. The present
case may fall under the atypical category due to it being unilateral and having a
U-shaped cleft. However, in the present case, contrary to the classical atypical cleft
hand, the thumb, the ring and little fingers are of normal size.
In cleft hand deformity, the bone abnormalities are more frequent than those of soft
tissues. They include fusion of adjacent metacarpals, bony bridges across the digits,
and proximal phalanx having articulation with two metacarpals. Carpal bones may also
show abnormalities.[7] In our case, the three phalanges of the middle finger were absent. There were no
other bony abnormalities. Generally, the flexor and extensor tendons of the missing
fingers fuse with each other to form tendinous loops over the rudimental carpal or
metacarpal bones. The altered bony configuration may lead to extrinsic and intrinsic
muscle abnormalities.[7] In our case, the flexor and extensor digital tendons are inserted over the head
of the metacarpal bone of the missing middle finger. The 2nd and 3rd lumbricals showed variations in their distal attachment.
Angiography studies on cleft hand have demonstrated the normal development of digital
arteries.[8] However, they are variable in number, with normal origin pattern from the radial
and ulnar arteries.[7] In our case, there were two fibrotic masses at the base of the palmar cleft. They
are formed by the fusion of the palmar digital artery with the palmar digital nerve
(median nerve). More research is warranted to understand the embryological basis for
occurrence of these fibrotic masses.
The functional limitation and psychiatric morbidity are the main concerns in patients
with cleft hand deformity. Plastic surgery followed by rehabilitation with or without
prosthesis is preferred in these patients to restore the active movements and pinch.[9] The reported soft tissue abnormalities in the present case are accidental during
cadaveric dissection and are of academic interest. The knowledge of these abnormalities
will be helpful to plastic surgeons working in this field for successful management.
To the best of our knowledge, the fibrotic masses reported in the present case are
unique and these masses may cause diagnostic errors during angiographic procedures.
