Humero Radial Synostosis: Causes, Symptoms, and Treatment

Introduction

Synostosis is an abnormal fusion of two or more bones resulting in a single bone. Humero-Radial Synostosis is a congenital skeletal anomaly that causes developmental deformities of the upper limb. The prognosis of the condition is good if the elbow is in a functional position and if it occurs as an isolated entity. The symptoms of the condition depend on the severity of the skeletal defect. This article will discuss Humero-Radial Synostosis, its causes, symptoms, diagnosis, and treatment in detail.

What Is Humero Radial Synostosis?

The primary bones of the upper limb are the humerus, radius, and ulna. The humerus bone is one of the long bones that run from the shoulder joint to the elbow. The radius and ulna are the two long forearm bones extending from the elbow to the wrist region. Humero-Radial Synostosis is an uncommon condition that causes unilateral or bilateral osseous fusion of the humerus and radius bone at the elbow level. Which in turn results in loss of elbow motion in the affected patient. Bowing of the radial bone may be seen in most cases.

What Are the Types of Humero Radial Synostosis?

Humero-Radial Synostosis is generally classified into the following categories.

• The first type is the sporadic condition, which occurs infrequently and is often accompanied by missing or incomplete formation of the upper limb. They occur bilaterally and mostly in association with other syndromes.

• The second type is often an inherited condition with a family history of Humero-Radial Synostosis. They occur as an isolated upper limb skeletal disorder.

What Causes Humero Radial Synostosis?

The upper limb's embryonic development occurs around the fourth to eighth week of gestation. Ossification of the humerus bone occurs on the 54th day. The humerus, ulna, and radius bone are affected by each other and are connected by the same perichondrium during the fifth week of gestation. Any alteration in bone development during this stage may result in a developmental anomaly of the upper limb. It occurs due to improper longitudinal differentiation.

The genetic variant of this condition occurs due to harmful changes or mutations in the DNA material. Humero-Radial Synostosis is inherited in both autosomal recessive and autosomal dominant patterns. Generally, all individuals inherit a pair of copies of most genes. The number of genes necessary to cause the disease affects the inheritance of the condition.

Humero-Radial Synostosis is inherited in both autosomal dominant and autosomal recessive patterns.

• Autosomal inheritance refers to a mutated or altered gene in the non-sex chromosome (22 numbered pairs of chromosomes) except the X and Y chromosome (sex chromosomes).

• For a genetic disorder to be inherited, two copies of an altered gene must cause the disease.

• In autosomal dominant inheritance, a single copy of the mutated gene is enough to cause the condition.

• In autosomal recessive inheritance, two copies of the altered gene are required to inherit the condition.

Some cases of Humero-Radial Synostosis occur in association with other syndromes.

What Are the Symptoms of Humero Radial Synostosis?

The signs and symptoms of Humero-Radial Synostosis begin during pregnancy or after birth in the first four weeks of life. The severity and the extent of the symptoms differ for each individual.

The following findings are present in only some cases. The typical clinical results of Humero-Radial Synostosis are mentioned below.

• Elbow ankylosis: Stiffness and rigidity in the elbow joint due to abnormal joint adhesion.

• Tarsal Synostosis: Tarsal synostosis, also referred to as tarsal fusion, is an abnormal osseous fusion of tarsal bones (seven short bones of the proximal part of the foot) such as the calcaneus, cuboid, talus, navicular, lateral, medial and intermediate cuneiform bones.

• Microcephaly: A condition in which the head of the affected child is smaller than the ideal size. The circumference of the head is below two standard deviations.

• Iris Coloboma: This condition refers to the developmental defects of the iris (the colored tissue present at the front part of the eye and comprises the pupil in the center).

• Meningocele: A neural tube defect forms an abnormal lump or sac in the lower back region or the skull through which the membrane covering the central nervous system (meninges) protrudes.

• Chorioretinal Coloboma: This refers to the congenital developmental defect that causes the absence of a part of the retina (the innermost layer of tissue that lines the back wall of the eye).

• Abnormality of the Wrist: Humero-Radial Synostosis is sometimes accompanied by abnormalities of the wrist region that connects the hand to the forearm.

• Aplasia or Hypoplasia of the Eye: Presence of absence or underdeveloped eye.

• Elbow Dislocation: The elbow joint is where the radius, ulna, and humerus bone meet. In cases of Humero-Radial Synostosis, the distal humerus slips out of its normal position from the elbow joint.

• Limited Joint Motion: These patients have generalized limitations of joint movement.

How Is Humero Radial Synostosis Diagnosed?

Humero-Radial Synostosis is diagnosed through detailed history taking and thorough physical examination of the patient. The clinician may address the familial history of the patient. The clinical findings of the case vary for each patient. The effective investigation method for Humero-Radial Synostosis is through imaging studies. Imaging studies such as plain X-ray radiography of posteroanterior and lateral views may be performed to evaluate the upper arm and forearm.

• The radiographic findings may reveal a shortening or contracture of the upper limbs.

• Bilateral and symmetrical fusion of humerus and radial bone.

How Is Humero Radial Synostosis Treated?

• Asymptomatic patients and the presence of unilateral fusion of the radius and humerus bone are kept in observation. They are indicated for treatment only when the affected child has functional difficulties.

• Surgical management of Humero-Radial Synostosis is indicated to improve the functional abilities of the affected child and the range of movements in the elbow.

• The surgical treatment option is only indicated in bilateral cases with extreme functional disabilities. However, it has the highest rate of recurrence.

• Various surgical techniques, such as modified osteotomy or distraction osteogenesis.

• The operative procedure involves surgical reconstruction of the elbow to a functional position.

Conclusion

Humero-Radial Synostosis is an uncommon genetic condition causing developmental defects of the upper limb. This condition is characterized by the abnormal fusion of the radius bone to the humerus bone at the elbow level. The etiology of this condition remains unclear. They occur either as an isolated disorder or in association with other syndromes. The affected child has difficulty performing day-to-day activities like feeding and toileting. In most cases of the condition, the elbow is located in a functional position. The bilateral presence of defects is often indicated for surgical intervention.