Pulled Elbow (Nursemaid's Elbow / Radial Head Subluxation)

Definition & Epidemiology

• Peak age: 2-3 years (range: 6 months to ~6 years)
• Sex: Girls slightly more affected than boys
• Side: Left arm more commonly than right
• By age 5, the annular ligament thickens and strengthens, making the injury much less common

Anatomy

1. Radiocapitellar joint - between the radial head and the capitellum of the humerus (this is the joint involved in pulled elbow)
2. Proximal radioulnar joint - the radial head sits within the radial notch of the ulna
3. Humeroulnar joint

Mechanism & Pathology

1. Sudden longitudinal traction is applied with the elbow extended and wrist pronated
2. The radial head moves distally, away from the capitellum
3. The annular ligament tears at its periosteal attachment to the radial neck
4. When traction is released, the detached flap of annular ligament slips proximally and becomes trapped between the radial head and the capitellum
5. The arm snaps back but with the ligament now interposed in the radiocapitellar joint

Clinical Features

X-Ray Findings

X-rays are typically NORMAL in pulled elbow.

• Swelling or deformity is present
• Uncharacteristic history / concern for non-accidental trauma
• Tenderness over the humerus, distal radius, or wrist (not just the elbow)
• Child does not regain arm use after reduction

• Proximal displacement of the annular ligament
• Diffuse thickening of the annular ligament at the radiocapitellar joint
• Pericapsular edema

Reduction Technique

• Support elbow; grip distal forearm
• Firmly hyperponate the forearm with moderate pressure over radial head
• A palpable/audible "click" confirms reduction

• Supinate the forearm while applying thumb pressure over radial head
• Then flex the elbow in one continuous motion
• Click felt as radial head reduces

Summary Table

Complications of Pulled Elbow

1. Recurrence (Most Common Complication)

• Rate: ~20% overall; up to one-third of children experience at least one recurrence
• Recurrence is especially common in the weeks immediately following the first episode
• Risk is highest in children under 5; declines sharply after age 5 as the annular ligament matures and thickens
• Recurrence usually resolves spontaneously around age 5 when the ligamentous structures about the elbow mature
• Parents should be counselled to avoid axial traction on the child's arm - no lifting by the wrist/hand, no swinging by the arms
• After multiple recurrences, parents may be taught to perform the reduction maneuver at home

2. Reduction Failure / Delayed Reduction

• A click is not always felt during reduction; up to 30% of patients require two or more attempts before a successful click is produced
• If no click is detected and the child does not use the arm within 30 minutes, repeat reduction attempts are recommended
• Children seen several hours after the injury may be more difficult to reduce due to soft tissue swelling and muscle spasm around the joint; oral/nasal midazolam can be a useful adjunct in this scenario
• 6 out of 10 patients released without confirmed arm use will have spontaneous restoration of function; the other 4 require further remanipulation

3. Missed or Delayed Diagnosis

• An older child often points to the dorsal distal forearm as the site of pain, misleading the clinician toward a distal radial buckle fracture
• The classic traction history is present in only ~50% of cases; 22% present after a fall
• Infants under 6 months typically sustain the injury by rolling over in bed - this can incorrectly trigger a child abuse investigation
• Conditions mimicking pulled elbow that must be excluded:
  • Supracondylar fracture
  • Lateral condyle fracture
  • Radial head/neck fracture
  • Radial bowing fracture
  • Septic arthritis / osteomyelitis
  • Tumour
• Ultrasound can help - the "hook sign" (hyperechoic J-shaped supinator muscle above the radial head) has been reported as 100% sensitive for radial head subluxation and can confirm diagnosis without radiation

4. Persistent / Delayed Return of Function

• Most children (90%) regain arm use within 30 minutes of successful reduction
• A minority take longer, especially:
  • Children seen late after the injury
  • Anxious or distressed children who will not use even a successfully reduced limb
  • When no click was perceived during reduction
• If function has not returned after 24 hours, re-evaluation and radiographs are indicated
• Delayed return of function beyond 24 hours raises concern for an alternative diagnosis (fracture, infection)

5. Osteochondritis Dissecans of the Radial Head (Rare, Long-Term)

• Pathomechanically, repetitive or unrecognised radial head subluxation has been linked to the development of osteochondritis dissecans (OCD) of the radial head
• Proposed mechanism: repeated micro-trauma at the radiocapitellar joint disrupts the blood supply to the radial head cartilage
• This is rare and primarily a concern in cases of chronic or recurrent subluxation that goes untreated

6. Unnecessary Radiation Exposure

• Because the X-ray is almost always normal, ordering radiographs routinely exposes the child to unnecessary radiation
• More importantly, positioning the arm for the lateral view (forearm in supination) can spontaneously reduce the subluxation during the X-ray - meaning the study is normal on the post-reduction film and the clinician may incorrectly conclude there was never a subluxation
• The main role of X-ray is to exclude fracture, not to diagnose pulled elbow

7. Non-Accidental Trauma Concern

• Pulled elbow in infants under 6 months from rolling over in bed does not automatically warrant a child abuse investigation - this is an important distinction to avoid unnecessary social/legal consequences for the family
• However, if external signs of trauma (bruising, abrasions, swelling) are present or the history is inconsistent, safeguarding evaluation is appropriate

Summary Table

X-Ray Findings in Pulled Elbow (Radial Head Subluxation)

The Core Principle

X-rays are almost always NORMAL in pulled elbow.

When to X-Ray

• Swelling, bruising, or deformity is present
• History is atypical or uncharacteristic
• Tenderness over the humerus, distal radius, wrist, or clavicle (not just the elbow)
• Child does not regain arm use within 24 hours of reduction
• Concern for non-accidental trauma
• Reduction attempts have failed

Possible X-Ray Findings (When Present)

1. Normal Radiograph (Most Common)

2. The Radiocapitellar Line (Most Important Sign)

• Draw a line along the long axis of the radial shaft/neck
• In a normal elbow, this line should bisect (pass through) the middle of the capitellum on every view - AP, lateral, and oblique

• The radiocapitellar line may be displaced by >3 mm from the capitellum
• The line drawn along the radial axis courses superior to (above) the capitellum instead of intersecting it
• This indicates the radial head has shifted out of normal alignment with the capitellum

Important caveat: In young children, the radiocapitellar line may not reliably bisect the capitellum even in normal patients, so an abnormal RCL is suggestive of, but not pathognomonic for, injury. - Rosen's Emergency Medicine

3. Increased Radio-Coronoid Distance (Lateral View)

• On the lateral X-ray, there may be a subtle increase in the radio-coronoid distance - the space between the radial head and the coronoid process of the ulna
• This reflects the slight distal displacement of the radial head relative to its normal articulation
• This is a subtle and inconsistently present sign

4. Fat Pad Signs (If Present - Indicates Effusion)

• A posterior fat pad on the lateral view is always pathological - it indicates a joint effusion (haemarthrosis)
• In pulled elbow, fat pad signs are usually absent (no haemarthrosis, since there is no bony injury)
• If a posterior fat pad IS present, think of an occult fracture (most commonly radial head/neck fracture in adults, supracondylar fracture in children) rather than pulled elbow

5. No Fracture (Role of X-Ray = Exclusion)

Anatomy Diagram - Normal vs. Pulled Elbow

Ultrasound Findings (Alternative to X-Ray)

• Uses an anterior longitudinal view across the radiocapitellar joint
• The "hook sign": the hyperechoic J-shaped supinator muscle above the radial head - reported as 100% sensitive for radial head subluxation
• Can also exclude a posterior fat pad (which would suggest a supracondylar fracture)
• Useful for confirming reduction

Summary Table