Subluxation of the radial head is one of the most common pediatric orthopedic injuries. This can occur in children whose age ranges from less than 6 months to the preteens. The majority of radial head subluxations occur between 1 and 3 years of age.1 It is a rare injury before 1 year of age and after 8 years of age.
Historically, the classic mechanism involves axial or longitudinal traction on an extended elbow with the forearm pronated. This often occurs while someone is holding onto the child by the hand or wrist. While being held, the child is then pulled or the child falls and is suspended by the arm. The subluxation is seen more often in the left arm than the right. This is due to more people being right-handed and holding the child's left hand or wrist while walking. It is not uncommon, however, for the child to present with a history of a fall or rolling over in bed.1
This orthopedic injury involves the region of the elbow (Figure 83-1). The annular ligament is a thick band that wraps around the upper radial neck and radial head (Figure 83-1A). It guides the radial head as the forearm moves through pronation and supination. The injury causes the radial head to become partially dislocated from its articulation with the ulna and the capitellum of the humerus while the forearm is in a pronated state. The annular ligament then slips proximally and its lateral end becomes entrapped between the radial head and the capitellum (Figure 83-1B). The forearm becomes locked in pronation due to the entrapped annular ligament. This condition is painless as long as the forearm is held in pronation. Supination of the forearm causes pain, so the child holds the extremity in pronation. The act of supination would also spontaneously return the annular ligament to its anatomic position and reduce the subluxation.
Anatomy of the elbow region. A. Normal anatomy. B. A radial head subluxation. Note the entrapped annular ligament.
Children will present in no apparent distress.2 They are usually resting comfortably and have some reservation in using the affected extremity. The arm will be held with slight flexion of the elbow and pronation of the forearm (Figure 83-2A). The child may point to an area of pain, but this is not often the case. A child may be much more comfortable with the parent examining and questioning areas of tenderness as opposed to the unknown and sometimes intimidating Emergency Physician.