Radial Head Dislocation is uncommon. It most commonly presents as a partial dislocation or subluxation, also known as nursemaid’s elbow, seen in children. Complete radial head dislocation, although rare, is most commonly associated with high force injuries of the arm, and therefore are often associated with a forearm fracture or dislocation. A thorough history, physical exam, along with imaging, can aid in the appropriate evaluation and decrease the chances of complications by missed diagnosis. Although the reduction procedure is generally a straightforward process for radial head subluxation, a missed or neglected radial head dislocation will need surgical repair due to their association with ulnar fractures and other complications.[rx][rx][rx][rx][rx]
Complete radial head dislocation results from a high force injury, such as a significant motor vehicle accident or a fall onto an outstretched arm. It is extremely rare for the radial head to become dislocated without other associated injuries. Injuries associated with a radial head dislocation, include:
Terrible triad injury of the elbow: (fracture of the radial head, fracture of the ulnar coronoid process, and dislocation of the elbow)
The head of the radius may present as congenitally dislocated in association with other congenital abnormalities such as:
Causes of Radial Head Dislocation
The annular ligament stabilizes the radial head. In the case of subluxation in children, an axial force on an extended, pronated forearm causes the annular ligament to slip over the radial head. On the other hand, complete radial head dislocation can occur in children and adults. Such injury is most commonly from a high force injury causing a tear in the annular ligament. Less often, the annular ligament remains intact, connected to the lateral collateral ligament and the ulna, causing the radial head to slip under the annular ligament.
Symptoms of Radial Head Dislocation
- Swelling and tenderness
- Brushing and color change
- The child stops using the arm, which is held in extension (or slightly bent) and palm down.[rx]
- Minimal swelling.
- All movements are permitted except supination.
- Pain on the outer part of the elbow (lateral epicondyle)
- Point tenderness over the lateral epicondyle—a prominent part of the bone on the outside of the elbow
- Pain from gripping and movements of the wrist, especially wrist extension (e.g. turning a screwdriver) and lifting movements[rx]
- Sudden intense pain at the back of the elbow will be felt at the time of injury.
- The patient will in most cases be unable to straighten the elbow.
- Rapid swelling and bruising may start to appear. Trying to move the elbow will be painful and the back of the elbow will be very tender to touch.
Diagnosis of Radial Head Dislocation
History and Physical
A thorough history and description of events, whether traumatic or nontraumatic, should be obtained. The practitioner should also investigate the mechanism of injury and whether the injury involved pulling, pronation, supination, or rotational components. Any history of a congenital syndrome will play an important role. The way the patient holds the injured elbow can be helpful.
On physical exam; the child with a partial displacement of the annular ligament will protectively hold their arm, commonly in an extended and pronated fashion. This type of injury causes discomfort and pain over the radial head, and the child will refuse to use their arm by holding it close to their body. There will not be any swelling, ecchymosis, or deformities other than the unwillingness of the child to use their affected arm. The patient will resist any forearm range of motion testing.
In the setting of radial head dislocation due to traumatic injury, the practitioner should pay attention to deformities, swelling, neurovascular compromise, and length discrepancies when compared to the other limb. The examiner should have a high level of suspicion when there is restriction of movement of a joint. Range of motion testing demonstrates restriction, particularly during flexion of the elbow with an anterior radial head dislocation. The protuberant radial head may be visible and palpable, and this abnormality is what prompts the parents to seek medical advice.
Patients with congenital dislocation are generally asymptomatic until their adolescent years when they present with elbow locking or restriction of motion without any history of trauma.
Evaluation should include a thorough inspection, palpation, and range of motion testing of the entire affected arm. Imaging is imperative for traumatic injuries of the affected joint and the joints above and below. X-ray is useful and quick for an acute injury. The use of ultrasound may be helpful. However, CT and MRI can be adjuncts in multiple injuries.[rx][rx][rx][rx][rx][rx]
Monteggia injury is a radial head dislocation combined with an ulnar shaft fracture. The joint will demonstrate pain and swelling, with loss of range of motion at the elbow due to radial head dislocation. Loss of extensor muscle mobility can be due to posterior interosseous nerve injury, entrapment, or stretching. Bado classification is used to distinguish four types of Monteggia fracture based on the displacement of the radial head:
Type I: (70% of cases) Fracture of the proximal or middle third of the ulna accompanied by anterior dislocation of the radial head (most common in children/young adults)
Type II: (15% of cases) Fracture of the proximal or middle third of the ulna with accompanying posterior dislocation of the radial head (70 to 80% of adult Monteggia fractures)
Type III: (20% of cases) Fracture of the ulnar metaphysis (distal to coronoid process) with lateral dislocation of the radial head
Type IV: (5% of cases) Fracture of the proximal or middle third of the ulna and radius accompanied by dislocation of the radial head in any direction
Lateral view of the elbow and drawing of the radio-capitellar line described by Storen must be done to prevent missing a radial head dislocation. The axis of the radial neck drawn on the lateral view will run through the capitellar ossification center, which signifies no radial head dislocation. (Figure 1, Storen line)
Another helpful radiological tool, best viewed on the lateral view of the forearm, is the “ulnar bow sign.” Children with isolated radial head dislocation persistently had a slight curvature in the ulna on the lateral view. The posterior ulna cortex is linear, and any deviation from this line indicates a plastic fracture of the ulna. (Figure 2, ulnar bow sign)
The lateral humeral line (LHL) is often used to diagnose lateral radial head dislocation on the anterior-posterior X-ray. The LHL is a line drawn along the lateral edge of the most lateral condyle parallel to the axis of the distal shaft of the humerus. It typically intersects the lateral cortex of the radial neck. (Figure 3, lateral humeral line)
Congenital dislocations of the radial head are asymptomatic. Most commonly they will have radial head prominence and limited extension and supination of the elbow. Congenital dislocation is diagnosable on the radiological criteria described by McFarland:
Treatment of Radial Head Dislocation
The most common radial head dislocation is anterior but based on the force, and the mechanism of injury, lateral and posterior dislocation can occur as well. The annular ligament is the chief stabilizer of the radial head and prevents radial head dislocation. Other ligaments of the proximal radioulnar joint, such as quadrate and interosseous ligament help further stabilize this joint.
The treatment in the emergency setting for acute ulnar fracture with radial head dislocation up to 3 weeks after the initial injury is with sedation and closed anatomic reduction of the ulna by external maneuvers. This procedure is usually enough to reduce the radial head. Radial head stability should undergo testing with fluoroscopy after a successful reduction. Afterward, The elbow must undergo immobilization with a long arm cast with a 90-degree angle for 6 weeks. The position of the forearm during the immobilization will depend on the position associated with the greatest stability of the radius and ulna.
Children will have good outcomes with closed reduction. If there is any doubt about the stability of the reduced ulna fracture, then internal fixation is necessary. Children with irreducible and neglected/ missed anterior dislocation of the radial head will also need surgical correction. In adults, however, open surgical repair is almost always necessary.
There are several surgical procedures available to address chronic radial head dislocation, but most commonly used is open reduction with plate and screw fixation or intramedullary nail of the ulna and annular ligament reconstruction.
Congenital radial head dislocation will rarely require any intervention, until adulthood when significant pain and decreased range of motion becomes a concern. Radial head excision is an effective intervention in selected patients with significant elbow pain.
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