Syndactyly

What is Syndactyly?

Syndactyly is one of the most common birth defects affecting the limbs. It’s a condition where the skin and/or bones of neighboring fingers or toes are fused together, leading to the appearance of “webbed” or “super” digits. The severity of the condition varies. In “simple” syndactyly, only the skin between the digits is joined, while in “complex” syndactyly, the bones are also connected. “Complete” syndactyly means the fusion extends to the very tips of the digits, including the area around nails, and “incomplete” syndactyly doesn’t go the entire length of the digit. There’s also a “complicated” form of syndactyly where extra or abnormal bones develop in the conjoined digits.

It’s most common to see syndactyly between the second and third toes, or between the middle and ring fingers. While it can occur as a standalone condition (usually as a result of certain genes inherited from the parents which don’t always cause the condition), it can also be seen in various genetic disorders like Apert and Poland syndromes. Syndactyly usually causes fewer problems in the feet than in the hands, where we need the fingers to move independently more often.

Unless it’s only a very mild case, surgery is often recommended to separate the fused fingers or toes. This is particularly important for the hand, where it can greatly improve function.

What Causes Syndactyly?

In a growing human body, all the fingers and toes initially are attached together by a layer of soft and loose tissue. If these digits don’t properly separate, a condition known as syndactyly occurs. The process of the limbs starting to grow begins in the fifth week of pregnancy, underneath an area of skin tissue known as the apical ectodermal ridge (AER). This AER is important because it’s responsible for the length-wise growth of limbs.

The process of limb growth starts when certain cells in the somatic lateral mesoderm, a specific layer of the embryo, get activated. Hand development begins in the sixth week, when this soft tissue starts forming the bones of the fingers. The feet undergo a similar process in the seventh week of pregnancy.

The formation of individual digits is prompted by the sonic hedgehog protein (SHH), which is released from an area called the zone of polarizing activity (ZPA). Higher concentrations of SHH result in the formation of the inner side of the limb, while lower concentrations lead to the development of the outer side of the limb. The dorsal (back) and volar (palm or sole) structures of the limb are then developed by the dorsal and volar skin tissues.

As the limbs continue to grow, “notches” form between the digits at the AER. These notches then extend inward as the previously connected soft tissue undergoes apoptosis, which is a controlled, natural process of cell death that helps separate the digits. These digits are fully formed by the end of the eighth week of pregnancy.

If the soft tissue doesn’t undergo apoptosis or if the notches don’t form in the AER, then syndactyly develops. In cases where syndactyly is not part of a syndrome – like the constrictive ring syndrome, Poland syndrome, Apert syndrome, or Carpenter syndrome – it’s typically inherited in an autosomal dominant pattern. This means that you only need one copy of the abnormal gene from one parent for the condition to develop. Syndactyly has been linked to defects on the second chromosome.

Risk Factors and Frequency for Syndactyly

Syndactyly, a condition where some or all of the fingers or toes are joined together, is relatively common, affecting around 1 in 2000 babies at birth. It’s responsible for about 20% of all birth defects relating to the hands. This condition is more commonly found in feet than hands, and in about half of all cases, it affects both hands or both feet.

Most often, syndactyly is an inherited trait, passed down from parents to their children. However, this gene doesn’t always express itself, which is why not everyone who has the gene has the condition – this is known as incomplete penetrance. Interestingly, this condition seems to occur less often in women than in men, and men are almost twice as likely to have syndactyly. It also seems to occur more in White people compared to other races.

In some cases, syndactyly can occur randomly without a clear genetic cause (spontaneous). Additionally, syndactyly can be part of genetic disorders like Poland syndrome, Apert syndrome, Carpenter syndrome, and constrictive ring syndrome.

• Syndactyly happens in about 1 in 2000 newborns.
• It accounts for 20% of congenital hand deformities.
• The condition affects the feet more often than the hands.
• About 50% of cases occur on both sides (both hands or both feet).
• Syndactyly is usually inherited but can occur spontaneously.
• Men are nearly twice as likely to be affected as women.
• This condition is more common in White people compared to other races.
• Syndactyly can also be associated with certain genetic conditions like Poland syndrome, Apert syndrome, Carpenter syndrome, and constrictive ring syndrome.

Signs and Symptoms of Syndactyly

When a child comes in with syndactyly (fused fingers or toes), the doctor should perform a complete history and physical exam. This includes asking about any family history of syndactyly. Sometimes, syndactyly can “skip” a generation due to incomplete penetrance. It’s also important to know about any issues during pregnancy or at birth. The child should have a complete newborn orthopedic exam, particularly if they’re a newborn or infant, to look for any signs of a possible underlying syndrome. It’s crucial to understand, though, that isolated simple syndactyly is usually not connected to any genetic syndrome. Additional tests might be needed, such as tests for hip dysplasia, infantile reflexes, curvature of the foot, sacral dimpling, and spine examination. If there’s a chance the child could have an undiagnosed genetic syndrome or a complicated syndactyly, a geneticist consultation is recommended.

When examining the syndactyly, the doctor should see which digits are fused and identify if it’s just soft tissue fusion or a combination of bone and soft tissue fusion. The degree of the fusion and the presence of subtle incomplete syndactyly should also be checked. A physical examination in the sagittal plane (a side view) can help with this. Normally, the spaces between fingers are angled about 45 degrees with one finger extended and the adjacent one flexed. Examination of any flexion and extension creases in the affected digits can indicate potential bone fusion and affect digit function. It is necessary to assess independent finger motion. If there’s no independent motion, it might indicate a more complex or complicated syndactyly scenario. Noticing length differences between the fused digits is also important. Both hands and feet should be checked for any other instances of syndactyly or extra digits.

Finally, it is important to communicate with the patient and their family about the possibility of a 30% skin shortage around the fused digits. This means skin grafting might be needed when the fused digits are separated, to ensure the skin can close without tension.

For patients who have had prior treatment or surgery, obtaining previously recorded medical history and operation reports is crucial. Preoperative photographs or pictures showing any post-surgical changes could be useful. Moreover, the skin should be checked for scars and skin donor sites, which could affect future surgeries. Sensory and vascular examinations should be thoroughly conducted in revisions.

Testing for Syndactyly

If your doctor suspects that you have a problem with one of your hands or feet, they will most likely start by taking several X-rays of the affected area from different angles. These X-rays can reveal if any of your finger or toe bones, also known as phalanges and metacarpals, have started to fuse or grow together. The X-ray can also sometimes show additional digits that might not have been noticed during the physical exam.

Once your doctor has checked you over and the X-ray results are available, they can classify the type of issue you’re experiencing. They might use terms like ‘incomplete’ or ‘complete’, which refer to whether the issue affects the whole length of the digit, ‘simple’ or ‘complex’ to describe whether or not your bones are fusing, and ‘complicated’, which means there are extra or abnormal bones.

Another common method for classification is the Tentamy and McKusick system. The types include:

• Type I: Most common, usually affects the middle and ring fingers on your hand or the second and third toes on your foot
• Type II: This type affects the same fingers as Type I but also includes an extra digit between the fused fingers
• Type III: This type typically affects the ring and little finger
• Type IV: Involves all fingers being fused together.
• Type V: This type involves the fusion of metacarpals or metatarsals, the bones in your hand and feet, often seen in the ring and little fingers or third and fourth toes

If you have a simple condition, where there’s no extra or abnormal bone, you probably won’t need any more tests. But if your condition is more complicated, you might need an MRI, a more detailed scanning method, before deciding on any surgical treatment. This scan can help your doctor see where your tendons and nerve and blood vessels are located, so they can plan any surgery more accurately.

Treatment Options for Syndactyly

Syndactyly, a condition where two or more digits are fused together, can be managed both through surgery and non-surgical methods. If the condition isn’t affecting functionality and is just a concern cosmetically, such as in the case of syndactyly of the toes, non-surgical management is often chosen. This also applies in cases where surgery might not improve the condition or might yield unsatisfactory results, such as in ‘superdigits’ (one oversized digit supported by two bones or multiple digits supported by a single bone) or complex cases where the whole hand works as a single unit or there’s no muscular control.

However, surgical intervention is typically chosen when it can result in improved function of the hand or foot. If surgery is needed, it’s generally performed when the child is between 12 to 18 months old. This is done to reduce the risk of scar contractures (shortening of the skin due to a scar) as the child grows. However, in some cases, like when smaller digits are fused with longer ones or multiple fusions are involved, the surgery might be performed earlier, around 6 months, to avoid deformities and for early development of coordination.

The procedure for surgical correction, called surgical release, involves careful dissection of the fused digits to separate them while preserving the sensitive nerves and blood vessels. The surgery aims to create new nail folds, develop the skin between the digits, and create a new web space (the skin between the fingers or toes). Following the dissection, the incisions are closed in a manner to minimize tension. If necessary, skin grafts from other parts of the body, like the inside of the wrist or elbow or the instep of the foot, are used to fill any gaps.

In the case of incomplete syndactyly (where the fusion doesn’t extend fully along the digits), a modified surgical technique can be used that focuses on successfully reconstructing the web space. If multiple digits are involved, the surgical releases are carried out in stages to prevent any potential risk to the blood supply. For example, if all fingers except the thumb are fused, first, the index and little finger would be separated, and after approximately six months, the remaining fingers get separated.

In more complex cases where the bones of the fused digits are joined, more planning and additional steps are required to maintain as much normal anatomy as possible. In certain complex cases, it might be more beneficial to amputate a non-functional digit than to proceed with a difficult reconstruction.

What else can Syndactyly be?

Syndactyly, a condition where fingers or toes are fused together, can usually be diagnosed through a physical exam. However, when examining a child for syndactyly, it’s important to keep in mind other possible conditions linked to abnormal hand shape and various syndromes. These can include:

• Poland syndrome
• Apert syndrome
• Ectrodactyly (also known as cleft hand)
• Constriction band syndrome
• Synpolydactyly
• Carpenter syndrome
• Oculodentodigital dysplasia

What to expect with Syndactyly

The outcome for patients with syndactyly, a condition in which two or more fingers or toes are fused together, largely depends on the severity of the condition and the treatment plan. Complex cases of syndactyly tend to have less favorable results, and often need multiple surgeries. On the other hand, patients with simpler forms of syndactyly generally have good short and long-term results.

Despite this, it’s worth noting that as many as 10% of patients who undergo surgery for syndactyly may require additional surgery in the future.

Possible Complications When Diagnosed with Syndactyly

Just like any operation, there’s a chance of infection after surgery for syndactyly, which is when some or all of the fingers or toes are joined together. Infections aren’t common – they happen in about 1.6% of cases – but they can cause major problems if they’re not treated quickly with antibiotics or another surgery. Infections are most common in patients with multiple pre-existing health conditions or forms of syndactyly.

Other potential problems after surgery include scarring, tissue tightening, or bone growth in the surgery area. These complications can be avoided by using full-thickness skin grafts when possible. In some cases, the webspace (the area between the fingers or toes) can move further down the digit as the patient gets older, which can lead to a progressive hand deformity. The age at which the patient has the operation could play a part in this, so they should have regular check-ups to spot this complication early.

There could also be damage to the blood vessels or nerves in the digit. To avoid this, only one side of the digit should be operated on to ensure the digit keeps a working artery. If the blood vessels are damaged it could lead to longer healing and recovery times, and in extreme cases, the need for amputation. If the nerves are damaged various techniques can be used to repair them, such as primary nerve repair, repair with a nerve conduit, and nerve grafting. Still, even after repair, there could be loss or reduction of feeling in the digit.

If surgery isn’t carried out, the hands may not work as well and the patient may have less dexterity. If the syndactyly isn’t treated, and the digits are different lengths, the shorter digit may pull the longer digit into an angular deformity towards the shorter digit and cause it to bend.

Potential Complications:

• Infection
• Scarring and tissue tightening
• Progressive hand deformity
• Damage to blood vessels or nerves
• Extended healing and recovery times
• Loss or reduction of feeling in the digit
• Less hand function and dexterity with non-surgical treatment
• Increased deformity and growth disturbance

Recovery from Syndactyly

After surgery, the patient’s hand is typically wrapped in a large, soft dressing, or placed in a splint or cast. The choice depends on the complexity of the surgery, the preferences of the surgeon, and factors individual to the patient’s post-operative care compliance. This dressing is usually removed after about two weeks.

Once the surgical cut has healed, the patient is encouraged to start moving their hand actively and massage the area of the scar. Hand therapy can be beneficial, as it helps the patient learn scar massage techniques and assists in regaining hand movement.

In young or growing patients, ongoing check-ups are important to look out for complications such as ‘web creep’, or the excessive growth of skin between the fingers. A technique involving measuring the height ratios of the webspace, or the space between the fingers, on X-rays, has been proposed to keep track of this potential issue.

Preventing Syndactyly

In previous sections, we’ve talked about the importance of discussing with parents whether and when surgery may be needed. For a condition known as syndactyly, which is when two or more fingers or toes are fused together, surgery is recommended if it can improve the functioning of the affected hand or foot.

It’s also important to share with parents that waiting until the child is older before performing the surgery generally leads to better outcomes, unless there are specific situations like the involvement of an important (border) digit, or multiple fused digits. In these cases, the surgery might need to be done earlier.

Even though having to do the surgery again is quite rare, it’s also important to discuss potential complications with the family. These can include things like scar formation and contracture, which is a shortening of the muscle or joint. Other complications that may occur are webspace creep, where the space between the fingers or toes decreases or increases, potential loss of blood supply to the digit, and digital nerve injury, which is damage to the nerves of the fingers or toes that could affect sensation and movement.