Step 1 topics → Musculoskeletal, Skin, and Connective Tissue → Radial Head Subluxation (Nursemaid's Elbow)

Radial Head Subluxation (Nursemaid's Elbow)

USMLE Step 1 trap: Confuses the traction mechanism of nursemaid's elbow with a FOOSH injury. Nursemaid's elbow results from sudden axial traction on a pronated, extended forearm (e.g., pulling a child by the hand), causing the annular ligament to slip over the radial head.

Radial head subluxation, or nursemaid's elbow, is a pediatric injury where the annular ligament slips over the radial head after sudden longitudinal traction on the forearm — and on USMLE Step 1, the classic misconception is confusing this traction mechanism with a FOOSH injury, which causes fractures, not subluxation. It's one of the most common elbow injuries in young children, typically under age 5, because the annular ligament is lax and the radial head is not yet fully developed. Step 1 tests this as a straightforward presentation question — you need to recognize the mechanism and age group, and know which reduction maneuver to use.

The exam will give you a toddler holding the arm slightly flexed and pronated, refusing to use it, with no obvious deformity or swelling. The parent history usually involves lifting or swinging the child by the arm. Step 1 wants you to identify the mechanism (traction, not a fall), name the displaced structure (the annular ligament over the radial head), and select the correct management. Imaging is typically normal or unnecessary — the diagnosis is clinical.

What trips students up is conflating this injury with a FOOSH (fall on outstretched hand) mechanism, which causes fractures, not subluxation. The other common error is thinking supination alone reduces it — in reality, you need supination plus elbow flexion, or alternatively hyperpronation, which actually has a higher first-attempt success rate on clinical data. USMLE Step 1 questions on this topic are low-yield but straightforward if you lock in the mechanism and the two-step reduction.

From real student decks
16%have cards covering this topic
0%have mature cards

A gap in most decks — fewer than half of students in our cohort have cards covering this topic.

Common misconceptions

Common mistake
Wrong: Nursemaid's elbow results from a fall on an outstretched hand.
Right: Nursemaid's elbow results from sudden axial traction on a pronated, extended forearm (e.g., pulling a child by the hand), causing the annular ligament to slip over the radial head.
A FOOSH injury transmits compressive force through the wrist and elbow, causing fractures like a distal radius fracture or radial head fracture — it does not pull the annular ligament over the radial head. Nursemaid's elbow requires a pulling or traction mechanism, typically when an adult yanks a child's hand or swings them by the arms. The key anatomical point is that the annular ligament is loose in young children and can displace proximally over the radial head when the forearm is pulled while pronated and extended.
Common mistake
Wrong: Supination alone is sufficient to reduce radial head subluxation.
Right: Reduction requires either supination with elbow flexion or hyperpronation; hyperpronation has a higher first-attempt success rate.
Supination alone does not reliably reduce the subluxation because the annular ligament remains caught unless the elbow is simultaneously flexed to allow the ligament to slide back into place — so the correct maneuver is supination-flexion as a combined movement. Hyperpronation works by rotating the radial head in the opposite direction, which mechanically dislodges the trapped ligament, and multiple clinical studies show it succeeds on the first attempt more often than supination-flexion. Knowing both maneuvers and the relative superiority of hyperpronation is exactly what a Step 1 question will test.
Free Deck audit

See if your Anki deck covers this topic.

Upload your deck →
Guided session

Stuck on this? An AI tutor that probes your understanding.

Start a session →

What the exam tests

  1. Recognize the classic presentation: a child under 5 years old who suddenly refuses to move one arm after being pulled or lifted by the hand, holding the arm pronated and slightly flexed with no swelling or deformity.
  2. Identify the correct mechanism — axial traction on a pronated, extended forearm causes the annular ligament to slip over the radial head, which is distinct from a fall on an outstretched hand.
  3. Select the appropriate reduction maneuver: supination combined with elbow flexion, or hyperpronation — and know that hyperpronation has a higher first-attempt success rate.

Can you avoid these mistakes?

A 3-year-old is brought in after her father pulled her arm to stop her from running into the street. She is now holding her right arm slightly flexed and pronated and refuses to use it. X-ray is unremarkable. What is the diagnosis, and what structure is displaced?
You attempt to reduce a nursemaid's elbow by supinating the forearm alone and it fails. What should you do next, and why does this alternative maneuver work mechanically?
A parent says their toddler tripped and fell onto an outstretched hand and now won't move the arm. Why should nursemaid's elbow be lower on your differential compared to a child who was pulled by the hand?
Which reduction technique for radial head subluxation has the higher first-attempt success rate in clinical studies — supination-flexion or hyperpronation — and what is the expected sign that reduction has occurred?

Related topics

Bone Cells and Matrix Endochondral vs Membranous Ossification Fracture Healing Stages Compartment Syndrome

See how your Anki deck covers this topic.

Upload your deck for a free audit →