What is Radioulnar Synostosis?

Radioulnar synostosis is a condition where there is an unusual connection between two bones in the forearm, the radius and ulna. These two bones, which are usually linked by a membrane, work together to help twist the forearm inwards and outwards. The abnormal link, or synostosis, might be present from birth (congenital), caused by medical treatment (iatrogenic), or result from an injury (posttraumatic). The connection could be bony or fibrous.

This condition can disrupt the normal structure of the forearm and limit its movement. This can lead to substantial challenges for the affected person, as it may cause considerable loss of function and lead to significant discomfort and health issues.

What Causes Radioulnar Synostosis?

Congenital radioulnar synotosis refers to a rare medical condition present from birth, where the two bones in the forearm – the radius and the ulna – are fused together. However, it’s unclear exactly why this condition occurs. This issue may be linked to some genetic disorders such as Tetrasomy X, Poland, Cornelia de Lange, Holt-Oram, Crouzon, and Apert syndromes.

Radioulnar synostosis might be related to a deficiency in a specific protein called SMAD6. This protein helps to control how our bones form and grow. During the seventh week of pregnancy, the developing baby’s limb usually splits into different sections. If this doesn’t happen properly, it could result in the radius and ulna bones in the forearm sticking together from birth.

While it’s possible that this condition runs in families, it’s not confirmed, and researchers have been unable to identify a consistent pattern of inheritance or a definite cause.

Radioulnar synostosis can also occur as a result of injury or trauma. This is known as posttraumatic variant of radioulnar synostosis. This could happen following any injury or fracture to the radius, ulna, or elbow bone known as the olecranon.

Cases have been reported where patients developed this condition after undergoing surgical repair of an elbow fracture or a tear in the distal biceps tendon. A higher risk of this condition might happen with fractures involving both the radius and ulna, and with greater severity of the fracture.

The development of this condition also tends to increase with the severity of the tissue damage around the fracture, and if the membrane between forearm bones is disrupted during surgery. A head injury coinciding with a forearm fracture is also a significant risk factor. However, the reasons for this are not clearly understood.

Risk Factors and Frequency for Radioulnar Synostosis

Congenital or syndromic radioulnar synostosis is a very rare condition, with fewer than 700 cases reported in medical literature. This condition mostly affects young children, causing trouble with daily activities due to functional deficiencies. Unilateral cases, where only one arm is affected, can sometimes be overlooked or diagnosed late because motions at the shoulder or wrist make up for the rotational deficits caused by the synostosis. People with synostosis in both arms often have uneven symptoms and functional deficits. It was previously thought that this condition was more common in males, but recent data shows no difference between the genders.

Posttraumatic radioulnar synostosis occurs in 1.2% to 6.2% of patients suffering from combined fractures in the radius and ulna, the two bones in the forearm. However, this is likely an underestimate as several cases may have been missed due to incomplete follow-ups or if the synostosis doesn’t cause any symptoms. Synostosis occurring after trauma is less likely to be symptomless compared to congenital ones, as adults are less able to compensate for the limitations than children.

There is a higher chance of developing posttraumatic radioulnar synostosis if the initial injury is associated with a neurological or traumatic head injury. For example, a study reported that all three patients with a combined radial and ulnar fracture who also had a spinal cord injury developed posttraumatic radioulnar synostosis.

Signs and Symptoms of Radioulnar Synostosis

Radioulnar synostosis is a condition that affects the forearm’s rotation ability. This can be present in people of all ages, but it usually shows in children around six years old. This is when daily tasks that need rotation, such as turning door knobs or throwing a ball, start to be impacted. The particular issue posed is dependent on the level of fusion in the child’s forearm. If a child is stuck in a pronounced position, they may have trouble with tasks that need supination, such as washing their face, brushing their teeth, eating, or catching a ball. But if a child has a fixed supination deformity, activities requiring pronation, such as typing, writing, or any tabletop activity that requires the palms to face downward, become challenging.

The diagnosis can be missed or delayed until the teenage years if the affected child can compensate for the lack of forearm rotation by adjusting their shoulder, elbow, or wrist movements. There have been cases where adults who didn’t realize they had the condition were diagnosed after noticing limitations in their motion range. However, this is considered quite rare.

Patients with posttraumatic radioulnar synostosis might come forward right after surgery, or even several years later, depending on how much their activities are impacted. The development of synostosis is usually discovered during routine imaging following surgery to check on the healing of a fracture. However, the exact extent of the hindrance caused by synostosis may not be clear until the patient’s fractures completely heal and their post-surgery pain goes away.

Patients who come to medical attention outside of the immediate post-surgical period might recall receiving an injury to their elbow, forearm, or wrist which needed surgical intervention. They may report a progressive lack of motion in their radial and ulnar fractures despite non-surgical treatment. This limited and painless pronation and supination affects their daily activities and work-related tasks.

A physical examination will show a limited range of motion in patients with radioulnar synostosis. Patients with complete bone fusion usually do not experience pain but have a limited range of motion at the forearm. However, those with partial fusion might have some amount of motion left and might experience some discomfort. These symptoms are common in both innate and posttraumatic cases.

Testing for Radioulnar Synostosis

After collecting your health history and conducting a detailed physical exam, your doctor may use images of your elbow, forearm, and wrist to track the progress of a condition called posttraumatic radioulnar synostosis. The condition is typically followed using regular X-ray examinations to decide when surgery might be necessary. However, blood tests or lab work don’t really help in diagnosing or predicting the outcome of this condition.

Radioulnar synostosis is a condition where the two bones in the forearm, the radius and ulna, are fused together. There are several categorizations or “classification systems” for this condition based on the features seen in X-rays.

For congenital (meaning present at birth) radioulnar synostosis, the most popularly used classification today is the “Cleary classification.” This system, which is a more detailed version of the earlier “Wilkie classification,” describes four types of congenital synostosis. Type 1 is where the bones are fused together by a tissue called fibrous tissue and the radial bone’s head is in its correct location. In Type 2, the fusion of the bones is firmer, with a bone-like connection, and the head of the radius bone is in its correct location. In Type 3, this bone-like connection exists, but the head of the radial bone is misplaced and underdeveloped. Type 4 is similar, but the head of the radius bone is dislocated forward and may appear “mushroom-shaped.”

Posttraumatic radioulnar synostosis, which occurs after injury, is usually classified using the “Hastings-Graham system.” This system describes six types of radioulnar synostosis based on the area where the condition has occurred.

In addition to regular X-ray examinations, other imaging techniques such as computed tomography (CT) scans or bone scans can be used. CT scans provide further details about the type and location of the fusion of the bones, which could be useful in planning surgery. Meanwhile, bone scans are useful to understand the maturity of the condition that has developed after an injury, which can help decide the best time for surgery to minimize the risk of the condition recurring after surgery.

Treatment Options for Radioulnar Synostosis

Treating a radioulnar synostosis, which is a condition where the two bones in the forearm have fused together, can be done in two ways: non-surgically or surgically. The choice depends on the nature of the fusion, its location, how much movement the patient has lost, the positioning of the forearm, and whether it’s a birth defect or not. Typically, if the patient was born with it, we often choose non-surgical treatment, but if it happened after an injury, surgical intervention is usually needed.

The non-surgical treatment is usually chosen if the patient still has a good range of motion in the arm or only has minor functional deficits. The main components of this approach are extensive physical and occupational therapy. These therapies can help improve function, but to what degree depends on the individual patient. The patient’s needs and demands dictate whether they can tolerate a fixed pronation deformity, which is where the palm of the hand faces down, as opposed to a fixed supination where the palm faces up. A hand therapist can help immensely with this process.

If the forearm is stuck in a less-than-optimal position or it inhibits movement, surgical intervention may be required. There are two main types of surgery that can be performed: “mobilization” or “repositioning”. Mobilization involves removing the bony fusion and placing various grafts into the area. Repositioning involves cutting and realigning the bones. However, results vary, and there is no one-size-fits-all technique that works best for everyone. The right surgical approach depends on individual circumstances of each patient.

The timing of surgery is also important to reduce the chance of the bones fusing together again. It’s typically best to wait until the fusion has fully matured before performing surgery. Depending on the specific area of fusion, different surgical techniques can be recommended. For instance, elbow arthroplasty might be used for fusions in Area 1, or a radial head resection could be employed for fusions in Area 2.

Some doctors use adjuvant therapies in conjunction with surgery to minimize the chance of the synostosis recurring, though this isn’t well-studied. In these cases, patients might undergo radiation therapy on the day of the surgery and then take indomethacin, an anti-inflammatory medicine, for two weeks after the operation.

Regardless of the treatment path chosen, physical and occupational therapy are essential post-treatment steps to achieve the best functional outcome. Working with a specialized hand therapist can be especially beneficial.

When a doctor is trying to diagnose radioulnar synostosis, which is a condition where the two bones in the forearm are fused together, there are other conditions that can have similar symptoms. These conditions could be:

Contracture of the soft tissues, which is when the tissues that connect, support, or surround other structures and organs of the body become less flexible.
Fracture malunion, which is a healing bone that is not correctly aligned.
A neurologic deficit, which is a problem with the nervous system.

It’s important that these conditions are considered to make sure the correct diagnosis is made.

What to expect with Radioulnar Synostosis

The outcome of congenital (present at birth) and posttraumatic (caused by an injury) radioulnar synostosis largely depends on how much the condition affects normal function. Radioulnar synostosis is a condition where two bones in the forearm, the radius and ulna, are fused together. If one is born with this condition, intensive hand therapy can help improve hand function and deliver good results.

Surgery can also be an option for treatment, aiming to either reposition the bones or to increase mobility. However, surgical treatments can have varying and unpredictable results. After surgery for posttraumatic radioulnar synostosis, the prognosis is usually excellent, meaning a complete or nearly complete recovery is expected. However, there’s still a high chance of the condition recurring if the surgical procedure isn’t carried out properly.

Possible Complications When Diagnosed with Radioulnar Synostosis

Surgery for radioulnar synostosis, a condition where the two bones in the forearm are fused together, is generally well-received by patients. But like any surgery, it has its risks. These risks can include typical concerns linked with all types of surgery, such as pain, bleeding, potential infections, and complications due to the anesthesia. Additionally, the specific risks involved with this particular operation can include:

A return of the synostosis or unnatural bone rotation
Neurological damage
Compartment syndrome, which is a severe condition that can occur after bone-cutting surgery
Broken bones
Bones not healing properly or healing in incorrect positions
Soft tissue stiffening or contracting excessively

Preventing Radioulnar Synostosis

Unfortunately, there’s no way to prevent syndromic congenital radioulnar synostosis, a condition in which the two bones in the forearm are fused together from birth. However, there’s a different type of this condition, posttraumatic radioulnar synostosis, which can occur after a trauma, such as a forearm, elbow, or wrist fracture. This can potentially be prevented by using the right surgical techniques when treating these fractures.