Congenital radioulnar synostosis presenting in adulthood - a case report

Congenital radioulnar synostosis is a rare developmental skeletal malformation of the upper limb, characterized by the fusion of the proximal ends of the radius and ulna from birth. The failure of prenatal longitudinal segmentation of the adjacent radius and ulna results in a fibrous bony bridge between the radius and ulna. We present a 23-year-old female who presented with pain and restricted mobility of the left elbow joint for 7 years. A plain X-ray was performed for the patient, revealing a diagnosis of congenital radio-ulnar synostosis. Careful evaluation of the anatomical relations and spatial orientation of bony structures is required for the diagnosis and treatment of such cases.


Introduction
Congenital radioulnar synostosis (CRUS) is an uncommon developmental skeletal malformation of the upper limb, characterized by a fusion of the proximal ends of the radius and ulna from birth [1].
In fact, the failure of prenatal longitudinal segmentation of the adjacent radius and ulna results in a fibrous bony bridge between radius and ulna [2]. Therefore, CRUS is thought to be caused by some in-utero insult. CRUS may result in severe disability especially when it is bilateral or there is considerable hyperpronation (i.e. ≥ 90) as adaptations are significantly poorer in such conditions [3]. Although the exact cause and pattern of inheritance of CRUS is still unknown, some studies have reported that it is inherited in an autosomal dominant manner [4]. Most often, congenital malformations are associated with chromosome X aberrations [5]. In 60% of cases, CRUS is bilateral and may be associated with other conditions such as hip dislocation, clubfeet, polydactyly or syndactyly and cardiac or urinary tract abnormalities [6].
Clinical features of CRUS include restricted movements of the forearm, especially rotation i.e. supination and pronation [7]. However, the condition is not usually painful until the subluxation of the radial head occurs [7]; hence the diagnosis of CRUS is usually delayed.
Radiological examination reveals fusion or synostosis at the proximal ends of the radius and ulna [6]. Posterior dislocation of the radial head and proximal radioulnar fusion are other features of CRUS, which may coexist, in the same patient, as well as, it might present as separate entities [8]. The authors classify congenital radio-ulnar synostosis according to the degree of ossification, length of the synostosis and the involvement of the radial head [3]. Surgical management of CRUS is controversial and is based on individual functional limitations [7].
Mild deformity, minimal functional deficit and developed adjustments to activities are contraindications to surgical procedures [7]. Surgery is indicated in those who have bilateral CRUS or in those with severe rotational limitations [1]. Usually, surgery is recommended before the child starts schooling. The excision of the radial head at maturity is performed for symptomatic subluxation of the radial head [7].
Pronation of 15-60 degrees and over 60 degrees is relative and absolute indications for surgery, respectively [1]. To date, no case report has been published on CRUS from Saudi Arabia. Therefore, this case report is a valuable addition to the literature where we are presenting a 23-year old Saudi female with CRUS.  Figure   3) corroborated these findings and the patient was diagnosed with a type 2; visible bony synostosis with a normal and reduced radial head.

Discussion
At five weeks of gestation, the humours, radius and ulna are continuous with each other and joined together by a common perichondrium [9]. Then at the sixth week, tissues condensate to Page number not for citation purposes 3 separate the cartilaginous anlage of the three bones. Congenital radioulnar synostosis results from the failure of the longitudinal separation and persistence of the cartilaginous anlage of the forearm during the 7 th week of gestation that results in a persistent bridge of tissue [4].
The persistent tissue bridge commonly ossifies into an osseous synostosis, but might also remain unossified as a fibrous synostosis [9]. It has also been reported to be associated with other congenital malformations such as hip dislocation, polydactyly and talipes equinovarus [5]. This patient was managed with non-steroidal anti-inflammatory drugs (NSAIDs), occupational therapy and activity modification. Like most other patients with congenital radio-ulnar synostosis, she was a poor candidate for surgery -it rarely succeeds in adult patients [6]. However, if diagnosed during childhood when it most frequently presents [1], derotational osteotomy is a viable surgical therapeutic strategy. Careful planning after a thorough evaluation of the anatomical relations and spatial orientation of bony structures is required [7].

Conclusion
Careful thorough examination of upper limb at birth may offer some surgical correction of congenital radioulnar synostosis such as derotational osteotomy.