When your baby is born and you notice that your middle finger and ring finger are growing together and cannot be separated, as if they were one finger, your obstetrician will tell you that your baby has congenital syndactyly. You may be unfamiliar with the term “syndactyly” and would like to know everything about it, especially how it will affect your baby in the future. There is a lot to know about syndactyly, but here are a few things you should know about this congenital condition.
According to the literature, the incidence of congenital syndactyly is 1/2000, which means that one out of 2000 newborns has congenital syndactyly, and the chance of boys having syndactyly is twice as high as that of girls, and syndactyly is one of the most common congenital malformations of the hand. In our young patients, we find that most of the syndactyly is bilateral, that is, both hands have syndactyly, and the syndactyly is not always the same on both sides. The middle finger and ring finger together is the most common, followed by the ring finger and pinky finger, the index finger and the middle finger, the most rare is the thumb and index finger together.
2, the formation of parallel fingers: how does parallel fingers occur? At present, the cause of syndactyly is still unclear, but the process of syndactyly formation has been basically figured out. First of all, you need to understand a term: finger webbing. Most of our exposure to the word “webbing” began when we were learning about the body structure of small animals. Amphibians basically have webbing, the membrane-like structure that connects the fingers, while in humans this webbing is only visible at the base of the fingers. In the earliest stages of new life formation, the human fetus has a similar morphology to animals because we are genetically similar to most other animals, and initially the fetal hands are joined together. So how are our fingers separated? During the 5th-6th weeks of the life course, interactions between certain embryonic structures cause the soft tissue cells between the fingers to begin to die gradually programmed from the tips of the fingers toward the base, and our fingers separate when the webs descend into their proper position. If this process is disturbed, it can lead to the occurrence of syndactyly.
3. Genetic characteristics of syndactyly: In our patients, many parents of children with syndactyly also have syndactyly, and even most members of a family have syndactyly, which we call a syndactyly family line. This suggests that there is a genetic link to juxtaposition. Geneticists have identified nine types of syndactyly, five of which have been identified, most of which are autosomal dominant, meaning that if one parent has syndactyly, there is a high probability that the child will also have syndactyly, but there are also three types that are recessive. This means that although the child carries the gene for the disease, the final form of the gene is not completely faithful to the parent’s form of gene presentation, which in genetic terminology means that it has an incomplete epistasis. According to research, autosomal dominant syndactyly types generally have a variety of expressions, but the performance is generally mild; autosomal recessive syndactyly types have stable expressions, but are generally more serious.
4. Performance and typing of syndactyly: As mentioned above, the manifestations of syndactyly are diverse, and the severe ones can have five fingers in syndactyly, and the small hands become shovel-like or fist-like.
Considering the diversity of the syndactyly, clinicians have made a classification of syndactyly to guide the treatment of syndactyly. There are many ways to classify syndactyly, but two of them are simple and easy to understand and help parents understand the manifestations of syndactyly. The first one is that the syndactyly can be divided into complete and incomplete, which is well understood. Complete syndactyly is when the two fingers are completely joined together from the base to the end, and incomplete is when the fingers are partially joined. The second type of juxtaposition is simple and complex. Simple juxtaposition means that the juxtaposition of the fingers is limited to the soft tissues and does not involve the bony tissues, while complex juxtaposition means that there is bony fusion between the fingers. It seems that the juxtaposition of the fingers is not simple, because not only the skin is connected, but also the blood vessels that supply blood to the fingers, the nerves that innervate the senses, the joints, the finger bones, the nails, etc. The separation of these structures is not simple, which makes the juxtaposition surgery difficult. In addition, the syndactyly can take on more complex forms, such as a short syndactylic finger, which is called a short syndactylic finger. If one of the fingers is redundant, it is called a multifinger syndactyly.
Syndactyly can occur alone or in combination with disease in other parts of the body, with the latter manifesting as a syndrome. Syndactyly is simply understood as the presence of multiple disease manifestations in the patient, and the causes of these manifestations are related. Scientists have now discovered that syndactyly is one of more than 300 hereditary syndromes. Common syndromes that include syndactyly are Apert syndrome and Poland syndrome. This feature of syndactyly is important for parents to know. Because the syndactyly is externally obvious and easily recognized, some disease manifestations are not easily detected, such as heart disease, and if the syndrome is diagnosed, then the syndactyly will lead the physicians to the hidden disease. For example, when we encounter a child with short finger syndactyly, we will habitually check the ipsilateral chest wall of the child, and if we find that one side of the chest wall is depressed, it suggests that the pectoralis major muscle is not developed, and then we can basically diagnose Poland syndrome.
5. Timing of surgery for syndactyly: So does syndactyly need to be treated? How can it be treated? Some parents may ask if two fingers are together and it does not affect the child’s writing, can we not treat it? This depends on the situation. As mentioned above, there are various manifestations of syndactyly. If the manifestation is very mild and the webbing is only slightly shallow and does not affect the function and growth of the fingers, surgery can be avoided. However, a large number of syndactyly will require surgery. We can observe our own hands, the length of each finger is different, the growth of the long fingers is held back by the short fingers that are joined together, if not corrected early, the long fingers will develop scoliosis or flexion deformity. The function of the thumb is very important, accounting for 50% of the hand’s function, so if the thumb and the index finger are parallel, the hand will lose its basic functions such as grasping, gripping and pinching, so early surgery is necessary to correct this.
When is the right time to have surgery? This is probably one of the most frequently asked questions by parents. The timing of surgery has evolved as knowledge of syndactyly has been updated. Initially, doctors generally agreed that it was more appropriate to perform surgery around the age of five. Later, studies of hand function in children showed that the grip of the hand is established by 24 months of age, so the current widely accepted time of surgery is between one and two years of age. For thumb-indicator syndactyly, ring finger pinky syndactyly needs to be corrected early, at around 6 months of age. Complex syndactyly with bony connections need to be corrected before they interfere with normal finger development, which is before the age of one year. For children with bilateral syndactyly, bilateral corrective surgery can be performed at the same time when they are one or two years old, but for older children, the surgery is usually performed on one side at a time.
6, and finger surgery method: perhaps some parents think that finger surgery is very simple, not just from the middle split? In fact, it is not, but the surgery requires a fine pre-operative design and operation, there are many things to pay attention to, and finger surgery has undergone a long history of evolution, and now becomes more mature. The surgery can be divided into three parts: the separation of the finger structure, the reconstruction of the web and the repair of the wound. First of all, the separation of the finger is not simple and there are many factors to consider, the most important of which is the protection of the neurovascular structure of the finger. Because the vascular nerve structure of the juxtaposed fingers has many variants, sometimes two fingers share a common vessel and the splitting can only leave the vessel to one of the fingers, while the other finger can only rely on the vessel on its other side to provide blood flow, so the blood flow on the other side of the finger must be preserved and cannot be operated at the same time. The nerves of the fingers are innervated for sensation, which is very important for the function of the fingers. If it is found intraoperatively that the nerves of the two fingers have a high point of common trunk bifurcation, the operation can only be complicated by splitting the nerves under the microscope to distribute them to the fingers on both sides. After successful separation of the fingers, the surgeon needs to reconstruct the missing web structure. Perhaps few people have looked closely at the normal webbing, which is a 45-degree slope toward the palm side of the hand when viewed from the side, and an hourglass shape when viewed from the dorsal side of the hand. The reconstruction of the webbing is the key to the success of the surgery and to prevent recurrence of the syndactyly. It is mostly done with local flaps and has various design methods and requires a high preoperative design. The last step is to close the trauma. Parents may wonder where the trauma comes from. The sum of the circumference of the two fingers is much larger than the circumference of the two fingers together, so there will be a trauma on the side of the fingers after they are separated. The skin between the fingers is usually designed as an interactive triangular flap to interrupt the straightness of the trauma, which requires careful and reasonable preoperative design. Most of the skin used for skin grafting comes from the abdomen of the child because it is more hidden and the skin is loose enough to provide more skin. Parents must have been distressed by the damage to other parts of the child’s body in order to make the hand, but this is the price that has to be paid for “mending the western wall”. This is how a delicate finger-splitting surgery is completed. But the surgery was complete, the treatment was not over. The transplanted skin piece itself has no blood flow and needs to be nourished by the traumatic substrate to survive, which is not a physiological process in itself. The growth rate of the surviving skin piece cannot catch up with the growth rate of the healthy skin of the finger, so the finger may be “dragged” by the skin piece during the development of the child, resulting in flexion deformity and requiring another surgery. There is a lot more to juxtaposition surgery, and the above is only an overview of simple juxtaposition surgery. If nail and bony connections are involved, the surgery becomes more complex.