Radioulnar synostosis is a rare condition where there is an abnormal connection ( synostosis) between the

radius In classical geometry, a radius (: radii or radiuses) of a circle or sphere is any of the line segments from its Centre (geometry), center to its perimeter, and in more modern usage, it is also their length. The radius of a regular polygon is th ...

and

ulna The ulna or ulnar bone (: ulnae or ulnas) is a long bone in the forearm stretching from the elbow to the wrist. It is on the same side of the forearm as the little finger, running parallel to the Radius (bone), radius, the forearm's other long ...

bones of the

forearm The forearm is the region of the upper limb between the elbow and the wrist. The term forearm is used in anatomy to distinguish it from the arm, a word which is used to describe the entire appendage of the upper limb, but which in anatomy, techn ...

. This can be present at birth (

congenital A birth defect is an abnormal condition that is present at childbirth, birth, regardless of its cause. Birth defects may result in disability, disabilities that may be physical disability, physical, intellectual disability, intellectual, or dev ...

), when it is a result of a failure of the bones to form separately, or following an injury (post-traumatic). It typically causes restricted movement of the forearm, in particular rotation (

pronation Motion, the process of movement, is described using specific anatomical terminology, anatomical terms. Motion includes movement of Organ (anatomy), organs, joints, Limb (anatomy), limbs, and specific sections of the body. The terminology used de ...

and

supination Motion, the process of movement, is described using specific anatomical terms. Motion includes movement of organs, joints, limbs, and specific sections of the body. The terminology used describes this motion according to its direction relativ ...

), though is usually not painful unless it causes

subluxation A subluxation is an incomplete or partial dislocation of a joint or organ. According to the World Health Organization, a subluxation is a "significant structural displacement" and is therefore visible on static imaging studies, such as X-rays. ...

of the radial head. It can be associated with

dislocation In materials science, a dislocation or Taylor's dislocation is a linear crystallographic defect or irregularity within a crystal structure that contains an abrupt change in the arrangement of atoms. The movement of dislocations allow atoms to sli ...

of the radial head which leads to limited elbow extension.

Types

Congenital

Congenital radioulnar synostosis is rare, with approximately 350 cases reported in journals. It typically affects both sides (bilateral) and can be associated with other skeletal problems such as hip and knee abnormalities, finger abnormalities ( syndactyly or clinodactyly), or Madelung's deformity. It is sometimes part of known genetic syndromes such as

Klinefelter syndrome Klinefelter syndrome (KS), also known as 47,XXY, is a chromosome anomaly where a male has an extra X chromosome. These complications commonly include infertility and small, poorly functioning testicles (if present). These symptoms are often n ...

(48,XXXY variant), Apert, Williams, Cornelia de Lange, or Holt–Oram. It has been reported to run in families typically following an

autosomal dominant In genetics, dominance is the phenomenon of one variant (allele) of a gene on a chromosome masking or overriding the Phenotype, effect of a different variant of the same gene on Homologous chromosome, the other copy of the chromosome. The firs ...

inheritance pattern, which means that children of an affected parent have a 50% chance of having the condition. When associated with amegakaryocytic thrombocytopenia, this inheritance has been found to be caused by mutations to the '' HOXA11'' gene. It is also one of the known manifestations of the

fetal alcohol spectrum disorder Fetal alcohol spectrum disorders (FASDs) are a group of conditions that can occur in a person who is exposed to alcohol during gestation. FASD affects 1 in 20 Americans, but is highly misdiagnosed and underdiagnosed. The several forms of the ...

, which results from prenatal exposure to alcohol.

Acquired

Post-traumatic cases are most likely to develop following surgery for a forearm

fracture Fracture is the appearance of a crack or complete separation of an object or material into two or more pieces under the action of stress (mechanics), stress. The fracture of a solid usually occurs due to the development of certain displacemen ...

; this is more common with high-energy injuries where the bones are broken into many pieces ( comminuted). It can also develop following soft tissue injury to the forearm where there is haematoma formation.

Diagnosis

Diagnosis at birthday is best done using ultrasound technology. In younger children and adults, diagnosis is done with x-ray machine at the radioulnar bones.

Treatment

It is sometimes possible to correct the problem with surgery, though this has high failure rates for treatment of post-traumatic radioulnar synostosis. Indication for the surgical treatment of congenital radioulnar synostosis include severe disability due to bilateral disorder or hyperpronation ≥ 90°.

References

External links

* {{Medical resources , ICD10 = {{ICD10, Q74.0 , ICD9 = {{ICD9, 755.53 , ICDO = , OMIM = 179300 , DiseasesDB = , MedlinePlus = , eMedicineSubj = , eMedicineTopic = , MeSH = , GeneReviewsNBK = , GeneReviewsName = , Orphanet = 3269 Orthopedic problems Congenital disorders