Introduction:
Additional digits appear in about 0.05 % of the people. About 50 % of them appear on both hands or feet. It may occur in infants with a family history, as it can be inherited, and it is more common in African American infants.
What Are Supernumerary Digits?
The little finger is frequently linked to an extra digit. There could be bone under the extra digit, or it could just be flesh and skin. It might appear floating (known as a nubbin) and attached by a stalk with a typical-looking nail at the end. It could appear alone at birth or associated with other features. When it occurs with other elements, it could result from a chromosomal disorder involving an extra piece or the entire chromosome. The additional digit may or may not be visible on a prenatal ultrasound.
Typically a diagnosis of polydactyly; a condition where an infant is born with one or more fingers is readily apparent. The extra digit may include either bony and soft tissue features or both. However, in the case of rudimentary digits, there is usually only soft tissue; a differential diagnosis must be that of acquired digital fibrokeratoma (a rare, benign fibrous tumor appearing on the fingers and toes).
How Does Supernumerary Digit Develop?
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The interactions of many signaling molecules during limb development in an embryo determine the normal pattern of digit development.
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On one or both hands and feet, extra digits can develop when one or more of these signaling molecules are upregulated or downregulated.
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Genetic mistakes in a number of potential chromosomal locations are often the cause of this up or down-regulation.
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The ulnar side of the hand is more frequently affected by polydactyly than the radial side.
Is Supernumerary Digit Familial?
Thorough family history is crucial since polydactyly is a congenital condition that frequently manifests in familial patterns. Patients who appear with polydactyly will have an additional finger or toe, which is most frequently identified in the newborn's first few days after birth.
The main theory behind polydactyly is that digit control throughout development fails. Between four and eight weeks following conception, the typical limb growth takes place. The signaling hubs that control limb and digit growth are many.
The most notably active polydactyl signaling molecule is Sonic Hedgehog (SHH), which functions from the zone of polarizing activity (ZPA). The development of the anterior-posterior (radial-ulnar) axis is controlled by the ZPA. SHH is vital to digit number and type development. The apical ectodermal ridge sends fibroblast growth factor signals that control limb length during normal hand development. The bone morphogenetic protein (BMP) family and SHH control the radial-ulnar axis, which determines how digits develop.
SHH is more abundant radially than elsewhere, which facilitates digit distinction. Due to increased SHH expression in the developing limb, mutations in the LMBR1 gene have also been linked to polydactyly. An SHH antagonist known as glioma-associated oncogene homolog 3 (Gli3) has a missense mutation in a population of individuals with Greig cephalopolysyndactyly (a genetic mutation that is inherited congenitally).
What Are the Types of Supernumerary Digits?
The Wassel classification is used for the hand's preaxial (radial) polydactyly.
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Type I: It involves a bifid distal phalanx.
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Type II: The distal phalanx is duplicated.
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Type III: It is characterized by bifid proximal phalanges.
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Type IV: It is the most typical type with duplicated proximal phalanx.
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Type V: It includes a bifid metacarpal.
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Type VI: Duplicated metacarpals.
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Type VII: Consists of triphalangeal digits.
How Are Supernumerary Digits Treated?
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The goal of treatment is to enhance hand cosmesis and function. When necessary, surgical management might be started after a diagnosis has been obtained. The expected role of the extra digit serves as the main factor in deciding whether to have surgery or nonoperative care.
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Nonoperative management is frequently taken into account if the finger has completely developed skeletal components and is not expected to affect hand function. There are numerous surgical methods available to treat polydactyly of the hand.
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A few general guidelines must be followed, such as keeping healthy skin flaps, safeguarding ligamentous structures to keep the finger stable, and surgical planning to preserve a tight pinch grasp.
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The most common time to treat central polydactyly is between the ages of six and 12 months. Form and function are once again the primary considerations. The most common surgical techniques are excision or ligation of the most primitive digits.
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Several small investigations on the results of surgery for central polydactyly have suggested that instead of constructing a five-fingered hand, it is preferable to generate an opposable thumb and three functional digits. Again, the focus of foot polydactyly treatment is on function and esthetic results.
The following guiding concepts apply to surgical care:
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Recreating a normal foot contour.
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Maintaining physeal alignment.
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Keeping proper soft tissue tension around the joints of the toes.
What Are the Postoperative Complications of Supernumerary Digits?
Multiple potential problems could arise during polydactyly surgical therapy. Suture ligation frequently results in a painful neuroma. Cyst development has also been connected to suture ligation. Angulated growth, growth stops, joint stiffness, infection, painful scarring, joint instability, and nail bed abnormalities are some other reported side effects associated with the treatment of polydactyly. According to one study, preaxial polydactyly revision rates are 19 %, usually due to discomfort or instability.
What to Do at Home?
An interdisciplinary medical team approach is necessary for the clinical evaluation, care, and follow-up of patients with supernumerary digits. The diagnosis is typically made early in life by a primary doctor, and timely referral to an orthopedic expert can enable early intervention when appropriate. If surgical intervention is chosen, one of the numerous specialists, such as orthopedic surgeons, plastic surgeons, and anesthesiologists, may be engaged.
It is essential for all medical practitioners to be aware that polydactyly can appear as a symptom of a condition, in which case a genetic specialist may need to be consulted. Physical and occupational therapists can also be part of the team to help with strengthening and developing motor skills. Communication between team members is crucial to achieving the best patient results, just like it is in all other aspects of interprofessional management.
Conclusion:
Polydactyly has esthetic and functional implications. The primary concerns with polydactyly center around its impact on fine motor development and function. With appropriate and well-timed intervention, the vast majority of cases of polydactyly have good functional outcomes, and the overall prognosis is favorable. It is essential to have early conversations with the parents of a patient with polydactyly. As early intervention can lead to more optimal outcomes, parents should be educated about the etiology, results, and potential complications of polydactyly and its management. Parents need to understand that surgical complications are generally uncommon, and painful scarring, growth disturbances, and neuroma formation can occur.
