Radioulnar Synostosis - Types, Causes, Symptoms, and Treatment

Introduction

Radioulnar synostosis is a skeletal anomaly. Synostosis means the fusion of two or more bones to form a single bone. In this condition, there is an abnormal fusion of the radius and ulna present from birth. The radius and the ulna are the two long bones in the upper limb region extending from the elbow to the wrist. It is caused by the improper development of the bones in the forearm. However, the underlying cause of the condition remains unknown. The symptoms of the condition depend on the severity of the malformation. This article will discuss radioulnar synostosis and its causes, symptoms, and treatment in detail.

What Are the Types of Radioulnar Synostosis?

Based on the condition's etiology, they are divided into the following categories.

1. Congenital Radioulnar Synostosis: This is a rare condition with approximately 350 evident cases reported in the literature. It is one of the most common congenital disorders of the elbow joint. They are further classified based on the presence of malformation in the hands into the following categories.

• Unilateral - Presence of radioulnar synostosis in a single hand.

• Bilateral - Presence of radioulnar synostosis in both the arms, which is seen in most cases (60 percent) of congenital radioulnar synostosis.

Types of congenital radioulnar synostosis based on the radiographic findings:

• Fibrous synostosis.

• Osseous synostosis.

• Osseous synostosis with the ends of the radius bone forced out of the normal position posteriorly.

• Osseous synostosis with the ends of the radius bone forced out of the normal position anteriorly.

2. Post-traumatic Radioulnar Synostosis: Some cases of operatively treated forearm fractures are more likely to develop this condition. They are further classified according to the location of the fusion.

• Distal forearm.

• Mid forearm.

• Proximal forearm.

What Is the Cause of Radioulnar Synostosis?

This condition occurs during the embryonic development of the fetus’s arm during the fifth to eighth week of pregnancy. During the early stages of development, the radius and ulna are typically connected. However, later they separate to become two discrete long bones. The bone fails to separate in people with this condition, and they are born with fused forearm bones. In most cases, the underlying cause of this condition is unknown. Sometimes, they develop the disease by genetically inheriting it in an autosomal dominant pattern.

In some cases, they occur due to some abnormalities with the chromosome or in association with genetic syndromes such as:

• Klinefelter's syndrome (an inherited condition that affects physical and intellectual development).

• Carpenter’s syndrome (an inherited condition causing premature fusion of the skull bones).

• Apert syndrome (a genetic condition causing skeletal deformities).

• Arthrogryposis (a group of conditions affecting the joints).

What Are the Symptoms of Radioulnar Synostosis?

Symptoms of radioulnar synostosis typically begin to occur at the age of one to 23 months or between the ages of two to eleven years. Mostly the condition is asymptomatic until noticed by the parents and teachers during school age. Various symptoms of this condition are as follows.

• Limited movements of the elbow joint.

• Abnormality in the shape of the forearm bone.

• The limitation of rotation of the forearm in its longitudinal axis affects day-to-day activities such as eating, performing personal hygiene, catching a ball, typing, etc.

• Abnormalities in the muscles of the upper arm.

• Dislocation of the radial head (the head of the radius bone is forced out of its normal position either anteriorly or posteriorly).

• Physical discomfort or unpleasant pain in the shoulder region.

• Shortening of the forearm.

• Pain in the wrist region.

• Presence of supernumerary numbers of toes and fingers present from birth.

• Webbing or fusion of the fingers and toes.

• Other associated skeletal problems such as hip dislocation and knee abnormalities.

How Common Is Radioulnar Synostosis?

There have been only a few hundred cases of congenital radioulnar synostosis reported in the literature. In 60 percent of the cases, abnormal fusion in the forearm occurs in both hands. Recent studies reported the occurrence of this condition seen more in males than in females, with a ratio of 3:2.

How Is Radioulnar Synostosis Diagnosed?

The diagnosis of radioulnar synostosis may be delayed due to its late onset of symptoms. The clinical presentation may become more prominent only after the adolescent stage. The clinician may perform a detailed history and physical examination of the patients, and familial history may be addressed. The clinical presentation of the condition varies from person to person. The most effective way to diagnose this condition is through radiological investigations.

1. Plain X-ray imaging in the posteroanterior and lateral view of the forearm is recommended in diagnosing radioulnar synostosis.

2. A radiological examination of the patient may reveal the following findings:

   • Presence of proximal fusion of the forearm bone.

   • Wide and bow-shaped radius bone.

   • Straight and tapered ulna bone.

   • Dislocation in the head of the radius bone.

3. The doctor may refer the infant and the family for genetic counseling.

What Is the Treatment for Radioulnar Synostosis?

Treatment for this condition is based on the extent of symptoms in the patients.

• Patients with no symptoms and unilateral presence of abnormality are recommended to be kept under observation and indicated for treatment only when the child starts having difficulties performing various activities.

• Surgical management of this condition is advised when the patient has bilateral synostosis and excessive limitations in performing daily functional activities.

• Surgical repositioning osteotomy: The procedure is a simple and safe method involving the surgical cutting of the forearm bone and repositioning and securing them properly with plates and pins.

• Another surgical technique is the surgical excision of the synostosis with soft tissue interposition of vascularized fascia-fat graft.

• Post-surgical management with splinting or casting in maximum pronation and supination.

• Patients are referred to physical therapy after surgical management to regain the maximum range of motion.

What Are the Complications of Radioulnar Synostosis?

• There is a high chance of synostosis recurrence after surgical management.

• Patients may develop neurological deficits such as posterior interosseous and radial nerve palsy.

• Patients with a significant rotational correction of more than 60 percent may develop compartment syndrome.

Conclusion

Radioulnar synostosis is an extremely rare condition that is present from birth or occurs after a surgical procedure for a forearm fracture. Rarely this condition occurs in association with other syndromes or as a result of genetic inheritance of the disease. An abnormal fusion of the forearm bones characterizes the state. The diagnosis of the condition is confirmed through radiological investigation of the patients. The most effective treatment method is the surgical management of the synostosis in the forearm.