Isolated ulnar hemimelia (ORPHA:93320)
A rare congenital limb malformation characterized by complete or partial absence of the ulna.
Epidemiology
Ulnar longitudinal deficiency incidence is estimated at 1/25,000-100,000 live births, with a male to female ratio of 3:2. The prevalence is unknown.
Clinical description
The disorder is reported to be unilateral in about 70% of cases, and is mostly right-sided and incomplete. The most common feature is the shortening of the entire upper limb and mainly the forearm, radial bowing and tendency of the hand to drift to the ulnar side of the wrist. Other skeletal upper limb anomalies such as humeroradial synostosis, congenital radial head dislocation, carpal or metacarpal coalition, and digital abnormalities such as syndactylies or thumb malformations are frequently seen. In total, 90% of cases have missing fingers. In rare cases (type 0), missing finger rays are the only clinical feature. The disorder is mostly non-syndromic and may be associated with scoliosis, fibular hemimelia, proximal focal femoral deficiency and phocomelia. The patients may be asymptomatic in the presence of isolated mild ulnar deficiency. Cases of prominent ulnar deficiency accompanied by complex upper limb abnormalities leading to severe disability may however also be observed. The disability caused by the disorder and associated anomalies may lead to severe functional limitations of daily life activities in childhood necessitating surgical correction early in life.
Etiology
The ulnar longitudinal deficiency is caused by an interruption of the sonic hedgehog (SHH) pathway, which is responsible for the development of ulnar-sided forearm structures during embryogenesis. The deformity is believed to develop between the 4th and 7th week of gestation.
Diagnostic methods
Diagnosis is based on clinical examination and X-rays. In utero, prenatal ultrasound may potentially detect this malformation and thus be a valuable imaging modality for early diagnosis.
Differential diagnosis
The differential diagnosis should include focal fibrocartilaginous dysplasia, dyschondrogenesis, congenital pseudarthrosis of the ulna, Nievergelt syndrome and embryofetopathy due to maternal diabetes mellitus.
Antenatal diagnosis
Prenatal diagnosis is possible using ultrasound, 3D-ultrasound or fetal magnetic resonance imaging.
Genetic counseling
Most of the reported cases are sporadic but a few familial cases have been described.
Management and treatment
Management should be highly individualized. The timing and procedure to be performed may be dictated by the age of the patient, bilaterality, and the extent of the hand malformations and forearm stability. Nonsurgical management approaches may rarely be sufficient. Different surgical approaches including syndactyly separation, thumb metacarpal rotation osteotomy, pollicization, ulnar anlage resection, one-bone forearm creation, and humeral derotational osteotomy are possible.
Prognosis
Patients with ulnar longitudinal deficiency may have limited motion, function and strength, but in general, the limb and hand will function as supportive limb. The severity of the disorder and the presence or absence of the accompanying skeletal anomalies determine the time of presentation and the clinical course.

                            Last update: 
                            August 2020


                            - Expert reviewer(s): 
                            Pr Sebastian FARR  - Pr Christof RADLER