Children with congenital proximal radioulnar synostosis often present in early childhood. The type of synostosis has been divided into various forms. A Type IV synostosis has a short bony segment with an anteriorly dislocated mushroom shaped radial head. The authors report a small cohort of 3 patients that presented with an acute elbow flexion contracture. The range of age was from 6-13 years. The authors also found previous case reports of a similar phenomenon.
Two of the three children underwent surgical intervention. At the time of surgery, a thickened annular ligament was noted to be distal to the mushroom shaped radial head. This ligament was entrapped about the neck of radius which prevented full extension. Excising the annular tissue with or without radial head excision resulted in resolution of the elbow contracture.
In children less than 5 years of age, the annular ligament is poorly adherent, as the radial head is not much larger than the radial neck. When a young child’s elbow is pulled into extension and pronation, the radial head may slip distally beneath the angular ligament. This entraps the ligament in the joint causing the typical pain and impairment of a “nursemaid elbow.” In these cases, however, the enlarged and thickening ligament traveled distally and encircled the radial neck. Division of this ligament resolved the problem and resulted in improved elbow extension.
Although this is an uncommon event in children with congenital proximal radial ulnar synostosis, it can cause considerable impairment to an already impaired upper extremity. Knowing that this entity can occur can facilitate the care of children with congenital proximal radioulnar synostosis.