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

radius In classical geometry, a radius ( : radii) of a circle or sphere is any of the line segments from its center to its perimeter, and in more modern usage, it is also their length. The name comes from the latin ''radius'', meaning ray but also the ...

and

ulna The ulna (''pl''. ulnae or ulnas) is a long bone found in the forearm that stretches from the elbow to the smallest finger, and when in anatomical position, is found on the medial side of the forearm. That is, the ulna is on the same side of t ...

bones of the forearm. This can be present at birth (congenital), 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 terms. Motion includes movement of organs, joints, limbs, and specific sections of the body. The terminology used describes this motion according to its direction relative ...

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 relative ...

), though is not usually painful unless it causes

subluxation A subluxation is an incomplete or partial dislocation of a joint or organ. According to the World Health Organization (WHO), a subluxation is a "significant structural displacement", and is therefore always visible on static imaging studies, suc ...

of the

radial head The head of the radius has a cylindrical form, and on its upper surface is a shallow cup or fovea for articulation with the capitulum of the humerus. The circumference of the head is smooth; it is broad medially where it articulates with the rad ...

. 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 sl ...

of the radial head which leads to limited elbow extension.

Types

Congenital

Congenital radioulnar synostosis is rare, with approximately 350 cases reported in journals, and it typically affects both sides (bilateral) and can be associated with other skeletal problems such as hip and knee abnormalities, finger abnormalities (

syndactyly Syndactyly is a condition wherein two or more digits are fused together. It occurs normally in some mammals, such as the siamang and diprotodontia, but is an unusual condition in humans. The term is from Greek σύν, ''syn'' 'together' and δά� ...

clinodactyly Clinodactyly is a medical term describing the curvature of a digit (a finger or toe) in the plane of the palm, most commonly the fifth finger (the "little finger") towards the adjacent fourth finger (the "ring finger"). It is a fairly common iso ...

), or

Madelung's deformity Madelung's deformity is usually characterized by malformed wrists and wrist bones and is often associated with Léri-Weill dyschondrosteosis. It can be bilateral (in both wrists) or just in the one wrist. It has only been recognized within the pa ...

. It is sometimes part of known genetic syndromes such as

Klinefelter syndrome Klinefelter syndrome (KS), also known as 47,XXY, is an aneuploid genetic condition where a male has an additional copy of the X chromosome. The primary features are infertility and small, poorly functioning testicles. Usually, symptoms are su ...

(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 effect of a different variant of the same gene on the other copy of the chromosome. The first variant is termed dominant and t ...

inheritance pattern which means 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 Homeobox protein Hox-A11 is a protein that in humans is encoded by the ''HOXA11'' gene. Function In vertebrates, the genes encoding the class of transcription factors called homeobox genes are found in clusters named A, B, C, and D on four se ...

'' gene.

Acquired

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

fracture Fracture is the separation of an object or material into two or more pieces under the action of stress. The fracture of a solid usually occurs due to the development of certain displacement discontinuity surfaces within the solid. If a displa ...

, 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.

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 ≥9

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