Congenital Radioulnar Synostosis: Why Is Child’s Forearm Stuck in One Position?

A child can bend their elbow, move their wrist and grip objects normally, yet struggle to turn their palm upwards.

One possible reason is congenital radioulnar synostosis, a rare condition in which two forearm bones are abnormally joined from birth.

This restriction can make everyday activities such as eating, dressing, washing and playing more difficult.

Some children adapt without major problems, while others experience limitations as they grow and become more independent.

Understanding this condition helps parents recognize the signs, seek the right assessment and understand how pediatric physiotherapy, occupational therapy and orthopedic treatment can support their child.

What Is Congenital Radioulnar Synostosis?

Congenital radioulnar synostosis is a rare birth condition in which the two bones of the forearm, the radius and ulna, are abnormally connected near the elbow.

Normally, these bones move in relation to each other, allowing the forearm to rotate. This movement helps the palm face upwards or downwards.

In congenital radioulnar synostosis, an abnormal bony or fibrous connection restricts this movement. The forearm may remain fixed in a turned-in position, with the palm facing downwards.

The condition develops before birth when the radius and ulna do not separate normally during fetal development.

It may affect one arm or both arms, and the degree of restriction varies between children.

Although congenital radioulnar synostosis is usually painless, it can affect how a child positions their hand and performs everyday activities (Alabau-Rodriguez et al., 2024).

How Does Normal Forearm Rotation Work?

To understand why this condition affects hand movement, it helps to know how the forearm normally rotates.

There are two important movements:

• Pronation: Rotating the forearm so the palm faces downwards.
• Supination: Rotating the forearm so the palm faces upwards.

These movements are essential for positioning the hand during daily activities.

For example, a child needs supination to hold a bowl with the palm facing upwards or receive an object in an open hand.

Pronation helps position the palm downwards when placing a hand on a table or performing certain writing activities.

The radius rotates around the ulna through the proximal and distal radioulnar joints.

When these bones are abnormally fused, normal rotation between them becomes restricted.

The wrist, fingers and shoulder may still move normally.

However, these joints cannot fully replace the rotational movement that normally occurs between the radius and ulna.

Early Signs of Congenital Radioulnar Synostosis?

The signs depend on how much forearm rotation is restricted and the position in which the forearm is fixed.

Some children have mild limitations that go unnoticed for years. Others experience difficulties during early childhood.

1. Difficulty Turning the Palm Upwards

One of the most characteristic signs is difficulty rotating the palm towards the ceiling.

A child may struggle to hold an object with the palm facing upwards, receive something in their hand or position their hand comfortably during certain activities.

2. The Forearm Appears Fixed in One Position

The affected forearm may remain turned inwards, with the palm facing downwards.

Parents may notice that their child moves the entire arm or shoulder instead of rotating the forearm when reaching for objects.

3. Difficulty With Everyday Activities

Restricted forearm rotation can affect several routine activities, including:

• Eating with a spoon or holding a bowl.
• Washing the face and hands.
• Putting on clothes and managing sleeves.
• Receiving objects in an open palm.
• Turning certain handles or doorknobs.
• Catching and throwing a ball.

The impact depends on the position of the forearm and the child’s ability to compensate.

4. Unusual Shoulder or Wrist Movements

Children often develop alternative movement strategies to complete activities.

For example, they may rotate the shoulder, move the elbow or adjust the wrist to position the palm where they need it.

These compensatory movements can make the condition less noticeable during early childhood.

5. Difficulty With Two-Handed Activities

When both forearms are affected, children may find some activities involving both hands more challenging.

Holding a container while opening it, manipulating toys or positioning objects may require additional adjustments.

However, bilateral involvement does not automatically mean that a child will have significant functional difficulties.

Why Can Some Children Have Congenital Radioulnar Synostosis Without Obvious Symptoms?

The presence of bone fusion alone does not determine how severely a child will be affected.

The position in which the forearm is fixed plays an important role.

A child whose forearm rests close to a neutral position may manage many everyday activities comfortably.

A child whose forearm is fixed in a more pronounced pronated position may struggle with tasks requiring the palm to face upwards.

Children can also compensate using movements at the shoulder, wrist and hand. These adaptations may help them complete activities even though normal forearm rotation is absent.

As a result, congenital radioulnar synostosis may not become obvious until a child starts school, participates in sports or performs more complex self-care activities (Rutkowski and Samora, 2021).

Why Does Congenital Radioulnar Synostosis Develop?

Congenital radioulnar synostosis develops during fetal growth because the radius and ulna do not separate normally near the elbow.

The exact cause is not fully understood.

Most cases occur without an identified family history. However, familial cases have been reported, suggesting that genetic factors may contribute in some children.

The condition may occur independently or alongside other congenital differences. A specialist may recommend additional evaluation if a child has other physical findings or developmental concerns.

Importantly, congenital radioulnar synostosis is not caused by poor posture, incorrect sleeping positions, lack of exercise or something parents did during pregnancy (Alabau-Rodriguez et al., 2024).

Can Congenital Radioulnar Synostosis Affect a Child’s Development?

Yes. Restricted forearm rotation can affect specific movement skills and everyday independence.

However, it does not automatically mean that a child has delayed overall development.

The functional impact depends on whether one or both arms are affected, the fixed position of the forearm and the child’s ability to compensate.

Area of daily life	Possible difficulty
Eating	Positioning the palm and utensils comfortably
Dressing	Managing sleeves and clothing fasteners
Personal hygiene	Washing the face and hands
School activities	Positioning the hand for writing, drawing or classroom materials
Play	Catching, throwing and handling toys
Sports	Activities requiring different hand positions

Some children manage these activities independently. Others may need additional time, adapted techniques or assistance.

How Is Congenital Radioulnar Synostosis Diagnosed?

Diagnosis usually involves a clinical examination and X-rays.

Clinical Examination

A pediatric orthopedic specialist may assess:

• The resting position of the forearm.
• Available pronation and supination.
• Elbow, wrist and shoulder movement.
• Hand function and grip.
• Compensatory movement patterns.
• Difficulties with everyday activities.

Both arms may be examined, even if only one appears affected.

This helps establish how much the condition affects function rather than relying only on the appearance of the forearm.

X-ray Examination

X-rays help confirm the abnormal connection between the radius and ulna.

They also provide information about the location and pattern of the fusion, the shape of the bones and the position of the radial head.

Additional imaging, such as CT or MRI, may be considered when more anatomical detail is required for treatment planning.

The diagnosis is based on clinical findings and imaging together. The radiographic appearance alone does not determine whether a child needs surgery (Alabau-Rodriguez et al., 2024).

What Are the Treatment Options for Congenital Radioulnar Synostosis?

Treatment depends on how much the fixed forearm position interferes with daily activities.

Not every child requires surgery. Some children manage comfortably with their available movement and practical adaptations.

1. Observation and Functional Adaptation

Children with mild restrictions and good functional ability may be managed without surgery.

The specialist may recommend periodic follow-up to monitor function as the child grows.

Parents can also learn practical ways to adapt everyday activities, such as changing how objects are positioned or encouraging comfortable hand positions.

2. Surgical Treatment

Surgery may be considered when the fixed position significantly affects daily activities.

One commonly used procedure is a derotational osteotomy.

During this procedure, the surgeon cuts and repositions one or both forearm bones to place the hand in a more functional position.

The aim is to improve the resting orientation of the hand and make activities such as eating, washing and dressing easier.

An important point for parents is that this operation generally does not restore normal forearm rotation. It changes the fixed position of the forearm to improve function.

Simply separating the fused bones has often produced disappointing results because the abnormal connection may recur and other anatomical differences can continue to restrict rotation.

Surgery also carries risks, including nerve injury, compartment syndrome, problems with bone healing and loss of correction.

Therefore, the decision should be individualized according to the child’s functional limitations, anatomy and potential surgical risks (Zarantonello et al., 2025)

What Is the Role of Pediatric Physiotherapy?

Pediatric physiotherapy has a supportive role in managing congenital radioulnar synostosis, but its limitations must be understood.

Physiotherapy cannot separate the radius and ulna or reverse the structural fusion.

Repeated stretching and strengthening exercises cannot restore normal pronation and supination across the fused segment.

However, physiotherapy may help assess functional movement, identify compensatory patterns and support rehabilitation when required after surgery.

1. Assessing Functional Arm Movement

A paediatric physiotherapist may evaluate:

• Shoulder, elbow and wrist mobility.
• Hand function and grip.
• Reaching, grasping and releasing objects.
• Two-handed coordination.
• Posture and upper-limb movement patterns.
• Activities that the child finds difficult.

This assessment helps identify whether the child is relying excessively on shoulder or wrist movements to compensate for restricted forearm rotation.

2. Supporting Comfortable Movement Strategies

The focus should be on helping the child use their available movement effectively.

Depending on individual needs, therapy may involve practicing everyday tasks with appropriate hand positioning and comfortable movement strategies.

Activities should be meaningful and age-appropriate. They should not attempt to force rotation through the fused bones.

3. Supporting Rehabilitation After Surgery

Physiotherapy may form part of the recovery program following a derotational osteotomy.

The program depends on the procedure, bone healing and the surgeon’s instructions.

Rehabilitation may include:

• Gradual movement of permitted joints.
• Functional reaching and grasping activities.
• Progressive strengthening when cleared.
• Hand and arm coordination activities.
• Practicing age-appropriate daily activities.
• Gradual return to school, play and sports.

The physiotherapist should follow the orthopaedic team’s guidance on immobilisation, movement restrictions and progression.

4. Working Alongside Occupational Therapy

Occupational therapy may be particularly useful when the condition affects self-care, school participation or hand positioning.

An occupational therapist can help with:

• Adapting dressing and eating techniques.
• Modifying how a child holds classroom materials.
• Finding practical ways to complete two-handed tasks.
• Recommending suitable equipment or activity adaptations.

Physiotherapy and occupational therapy may work together when a child has both movement and everyday functional difficulties.

Can Exercises Correct Congenital Radioulnar Synostosis?

No. Exercises cannot separate the radius and ulna when they are structurally fused.

Stretching, strengthening and repeated attempts to turn the palm upwards will not remove the abnormal connection.

Forcing the forearm into rotation may cause discomfort and place unnecessary stress on surrounding joints.

The purpose of therapy is to support comfortable functional movement, develop useful compensatory strategies and assist recovery after surgery when indicated.

Children should not be given a universal exercise program without an individual assessment.

What Can Parents Do at Home?

Parents can support their child’s independence without trying to correct the fixed forearm position themselves.

Helpful approaches include:

• Allowing the child to complete tasks using comfortable hand positions.
• Placing toys and everyday objects where they can be reached easily.
• Encouraging age-appropriate two-handed play.
• Giving extra time for dressing and eating.
• Avoiding forceful stretching or attempts to rotate the forearm.
• Following advice from the treating orthopedic and rehabilitation team.

The aim is to encourage participation rather than make the child perform movements that their anatomy does not allow.

When Should Parents Consult a Specialist?

Consider an assessment if your child:

• Consistently struggles to turn the palm upwards.
• Appears to have one forearm fixed in a turned-in position.
• Has difficulty with eating, dressing or washing.
• Uses unusual shoulder or wrist movements to compensate.
• Has restricted movement in both forearms.
• Experiences difficulties with school, play or daily independence.

Congenital radioulnar synostosis is generally painless.

However, new pain, swelling, redness, sudden loss of movement or symptoms following an injury should not automatically be attributed to the condition.

These changes require medical assessment.

Early evaluation helps establish the cause of restricted movement and identify whether observation, functional adaptations or surgical consultation is appropriate.

Conclusion

Congenital radioulnar synostosis is a rare condition in which the radius and ulna are abnormally connected, restricting the forearm’s ability to rotate.

Some children adapt well, while others experience difficulties with eating, dressing, washing, writing and play.

Treatment depends on how much the fixed forearm position affects everyday function.

Children with mild limitations may only need observation and practical adaptations, while those with significant difficulties may be considered for surgery.

Pediatric physiotherapy can support functional assessment and postoperative rehabilitation, but it cannot reverse the bony fusion itself.

Occupational therapy may also help children develop practical ways to manage daily activities.

The goal is not simply to improve a movement that the bones cannot perform.

It is to help each child use their arms comfortably, safely and as independently as possible.

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