Polydactyly

　　The etiology is unknown, and part of the cases are due to genetic factors, with the phenomenon of intergenerational inheritance.

　　Environmental factors can affect embryonic development, such as certain drugs, viral infections, trauma, and stimulation by radioactive substances, especially the pollution from modern industry, which can all be teratogenic factors. Damage to the early differentiation of the limb bud germ base is an important cause of polydactyly. Polydactyly of the thumb is due to the abnormal development of the ectodermal acrospine, the extension of the thumb side towards the proximal and its delayed retraction.

　　The most common complications of polydactyly are associated with cardiovascular, nervous system, or urinary system malformations, such as congenital heart disease, congenital brain maldevelopment, etc. For children with suspected conditions, a comprehensive and systematic physical examination should be conducted.

　　1. Angular deformity: Due to scar contracture after the excision of polydactyly, the distal phalanx of the thumb is pulled to one side, causing the interphalangeal joints to be uneven and forming a certain degree of bending angle, so the thumb cannot be straightened.

　　2. Instability of interphalangeal joints: After the operation, the interphalangeal joints of the thumb can only perform flexion and extension movements, and cannot swing left and right. Therefore, there will be weakness in pinching objects and instability in holding a pen, which is due to the fact that the collateral ligaments are not repaired during the excision of polydactyly.

　　3. Bone spur formation: During the excision of polydactyly, if the child is too young, the phalanx of the polydactyly cannot be fully excised, leaving a residual end, or the periosteum left after the excision of the polydactyly gradually ossifies, and with the growth of age, it forms a 'recurrent polydactyly' again.

　　4. Appearance of being small: If only one finger is simply excised for 'twin thumbs', the remaining thumb will necessarily be smaller than the opposite side, with an unattractive appearance.

　　5. 'Z' deformity: This mainly occurs during the excision of complex polydactyly, where some delicate 'processes' are ignored, resulting in the interphalangeal joints being skewed after surgery, forming a 'Z' deformity. This is the most complex type of deformity after the excision of polydactyly.

　　Polydactyly is mainly divided into three types according to its occurrence and anatomical location: preaxial type of thumb polydactyly (also known as radial polydactyly, preaxial polydactyly, and duplicated thumb deformity), central type of polydactyly and postaxial type of little finger polydactyly (also known as ulnar polydactyly, postaxial polydactyly), and the classification of thumb polydactyly. Currently, the Wassel classification method based on pathological anatomical shape abnormalities is commonly used, which is divided into seven types: distal phalanx type, middle phalanx bone type, and metacarpal type. Each type of malformation is further divided into two types based on the degree of separation of the duplicated fingers: the bifurcated type with bony fusion and the duplicated type with joint fusion. In addition, there is a 7th type with 3 phalanges of the thumb. Among them, type IV is the most common, accounting for about 47%, type VII accounts for 23%, and type II accounts for 15%. This classification method is concise and summarizes the pathological and anatomical rules. The classification of little finger polydactyly often adopts the Stelling-Twrek classification method, which divides it into three types: type I is the supernumerary finger, type II has partial bony structure, and type III is the complete polydactyly including the metacarpal bone. Central polydactyly is rare and is the duplication deformity of the index, middle, and ring fingers. These three fingers rarely appear as simple duplicated fingers but always contain complex syndactyly deformities. The most common polydactyly is the syndactyly hidden in the middle and ring fingers.

　　Polydactyly is a congenital malformation, so the prevention of polydactyly should focus on prenatal health care and nutrition. During pregnancy, it is necessary to avoid respiratory tract infections, gastrointestinal infections, rubella, measles, chickenpox, mumps, and other viral infections. It is also important to avoid contact with radiation and drugs that may cause embryonic malformation. The prevention of malformations can be achieved through premarital examinations, genetic counseling, and prenatal health care. Additionally, the prevention of malformed infants can be done through amniocentesis, chorionic villus sampling, ultrasound, and fetal镜, etc. Early diagnosis and intrauterine treatment can reduce the production of malformed infants.

　　10. Congenital polydactyly can be diagnosed clearly based on the medical history and clinical physical examination. Auxiliary examinations mainly include X-ray photography to determine the type and growth of the skeletal joints of the polydactyly, providing a basis for the selection of treatment plans. For complex and difficult cases, spiral CT examination and three-dimensional reconstruction can also be performed to further clarify the type and degree of deformity.

　　7. The diet of patients with polydactyly deformity should be light, easy to digest, and include more vegetables and fruits, with a reasonable diet arrangement and attention to sufficient nutrition. In addition, patients should also avoid spicy, greasy, and cold foods.

　　4. The principle of Western treatment is to resect the supernumerary fingers and preserve the normal fingers. In addition to X-ray examination, clinical observation of finger function is also needed to determine the normal and supernumerary fingers. Surgery is best performed after 1 year, and a few still need a longer period of observation of hand function to ensure the accurate preservation of the normal finger and the resection of the supernumerary finger.

　　1. The surgical treatment of polydactyly not only requires obvious cosmetic effects but more importantly, the reconstruction of hand function. The surgical resection of polydactyly is not difficult, but it needs to be considered comprehensively based on the shape, position, structure, and relationship with the normal fingers of the supernumerary fingers, combined with X-ray examination, to determine the site and method of resection of the supernumerary fingers. Simple polydactyly requires resection and local skin整形; complex polydactyly requires not only resection but also the full or partial resection of supernumerary metacarpals. The amount of metacarpal resection needs to be determined according to the shape and functional reconstruction requirements of the affected hand. In addition to resecting the supernumerary fingers, sometimes joint and skeletal deformity correction, joint ligament repair, and skin整形 are also needed.

　　2. The timing of surgery for supernumerary digits that are only connected to the normal fingers by a narrow and elongated pedicle can be simply resected and can be performed immediately after birth; for simple polydactyly, especially ulnar polydactyly, surgery is better between 3 to 6 months after birth; for complex polydactyly with severe deformity and tissue defects, microsurgical techniques can be used to perform polydactyly resection after 1 year, reconstructing function through tissue transplantation or transfer, and regular follow-up until the period of development stops. Osteotomy and correction of the palm and phalanges should be performed after 1 year; for reconstruction of the palm function, it is better to do so after 3 years, and the transfer of the palmaris longus tendon is often performed.

　　3. The anatomical variation of polydactyly is significant, and its treatment is often much more complex than imagined. Simple resection often leads to deformity, joint instability, and functional impairment, so the surgical plan should be determined according to different situations. In principle, the thumb with a more normal appearance and better function should be preserved. If the fingers to be resected have a main nerve and vascular bundle, they should be carefully separated and not damaged, and preserved; if there are main tendons or intrinsic muscle insertion points, they should also be transferred to the corresponding position of the preserved thumb. When resecting the polydactyly located within the palmar or interphalangeal joint capsules, the joint capsules and ligamentous tissues of the polydactyly should be preserved to repair the thumb joint capsule and maintain joint stability. When the preserved thumb is too oblique, it is necessary to perform joint fusion or osteotomy correction after the ossification of the epiphysis is basically stopped.

　　4. The bifurcation deformity of the distal phalanx of the thumb has little impact on function, but it affects appearance. Starting from improving the appearance, the bony and skin bridge between the two thumbs can be wedge excised, and the two preserved sides can be directly sutured to form a thumb. If the distal thumb is connected to one side and is smaller, it can be excised, and the defect can be covered with a palmar skin flap and inverted sutured to reconstruct the nail groove.

　　5. Polydactyly thumb deformity can be corrected through finger thumbization surgery. Single thumb or little finger triangular phalanx deformity has minor functional impairment, and most patients seek improvement in appearance. Wood (1977) performed central osteotomy on the triangular phalanx and then corrected the deformity with wedge osteotomies. Reverse wedge osteotomy and bone grafting can also be used, which involves making a wedge osteotomy on the long side of the triangular phalanx at its interface and transplanting it to the short side of the interface to correct the angular deformity of the finger.

　　6. The excision of polydactyly on the ulnar side of the little finger generally does not involve the repair of the joint capsule and tendons. When there is a supernumerary metacarpal, it should be excised at the same time.

　　7. During the excision of central polydactyly, due to the frequent occurrence of syndactyly deformity, vascular and nerve variations often occur. The excision should avoid damaging the blood supply and nerve supply of the remaining fingers to prevent necrosis of the remaining fingers, and can be performed in stages if necessary.

　　8. During the excision of the middle phalanx type of polydactyly, the focus of the operation is on orthopedic correction and functional reconstruction. It is necessary to preserve the joint capsule and collateral ligaments attached to the supernumerary finger, suture the intrinsic muscles of the hand firmly to the proximal base of the preserved finger after excising the supernumerary finger, and re-restore the joint capsule and ligaments to maintain the stability of the finger joint. During the excision of polydactyly, the extensor and flexor tendons of the finger can be preserved to strengthen the extension and flexion function of the preserved finger, or used for the reconstruction of collateral ligaments. In cases of congenital defects of extensor and flexor tendons of the preserved finger, the extensor tendons of the index finger and the superficial flexor tendons of the ring finger can be transferred and reconstructed at the same time as the excision of polydactyly to restore the function of the preserved finger.

　　9. The excision of polydactyly should be thorough to avoid residual deformities that affect appearance. At the same time, since the operation is often performed before school age, attention should be paid not to damage the epiphysis, which may affect development.

　　10. Early efficacy of long-term follow-up for polydactyly is generally satisfactory, but with the development of the child, a few may appear secondary deformities. Therefore, long-term regular follow-up should be carried out after surgery until the growth period stops.