Radial Head Dislocations

The topic repeatedly warns against reducing a congenital dislocation — here is the entity, its natural history, and the reasoning behind benign neglect.

• A different lesion from birth. Congenital dislocation is a primary developmental anomaly (present at birth, frequently bilateral, often syndromic — Nail-Patella, Klippel-Feil, Ehlers-Danlos, Cornelia de Lange). Because the radiocapitellar joint never formed normally, the head becomes dome-shaped/convex, the capitellum hypoplastic, and the ulna short (negative variance) — the radiographic signature that separates it from an acquired dislocation.
• It is usually functional and painless. Most children adapt well with a near-normal, painless range of movement into early adulthood; it is frequently an incidental finding or noticed only as a lateral prominence or a modest loss of rotation.
• Why reduction fails. The joint surfaces have remodelled to incongruent shapes (a convex head against a deficient capitellum), so attempted reduction cannot restore a congruent joint — it produces pain and stiffness and re-dislocates. This is exactly why the correct answer is do not reduce; observe.
• When to intervene. Surgery is reserved for the symptomatic adult, where radial head excision can relieve pain (accepting some loss of strength and unpredictable results); reduction or reconstruction is not indicated for the established congenital head.

The radiocapitellar line is the single most important sign in this topic — it is how the missed Monteggia is caught — but it only works if drawn and interpreted correctly.

• Draw it through the neck, not the shaft. Take the line through the long axis of the radial neck/proximal radius, not the whole shaft; because the radial head sits slightly anterior to the shaft axis, a line taken off the shaft can falsely seem to miss (or hit) the capitellum. Drawn through the neck it should pass through the capitellum in every view and every degree of forearm rotation.
• It needs a true lateral (and all views). A malrotated or oblique film can make a normal line look displaced or hide a real dislocation, so confirm on a true AP and lateral (add an oblique if in doubt); the line holding on one view does not exclude a dislocation on another.
• The very young elbow is a trap. The capitellum does not ossify until about 1 year of age, so before then there is no bony capitellum to aim at — judge the cartilaginous position with ultrasound or against the contralateral elbow; mild normal variability also exists, so a line that just clips the capitellar edge with a straight ulna is usually normal.
• Pair it with the ulna. A disrupted radiocapitellar line should send you straight to the ulna — look for a fracture or the plastic ulnar bow sign (a Monteggia lesion) rather than accepting an "isolated" dislocation.

• PIN Palsy:
  • Common in Type I and III.
  • Usually resolves after reduction.
  • Iatrogenic risk during Kaplan approach.
• Recurrent Dislocation:
  • Failure to anatomically reduce the ulna.
  • Failure to recognize plastic deformation.
• Stiffness:
  • Loss of Pronation/Supination.
  • Common after open reduction.
• Radio-Ulnar Synostosis:
  • Risk with single incision or extensive dissection.

• Nursemaid's: Excellent. 100% recovery. High recurrence rate until age 5.
• Acute Monteggia:
  • Type I (Kids): Excellent if reduced. 90% good/excellent outcomes.
  • Type II (Adults): Variable. High risk of stiffness and heterotopic ossification. MEPS (Mayo Elbow Performance Score) averages 85.
• Chronic Missed:
  • Poor prognosis without surgery (progressive Valgus, PIN palsy).
  • Surgery (Osteotomy) has 70% success rate but high complication rate (stiffness, nerve injury).
• Congenital:
  • Generally functional adaptation.
  • Often pain-free until adulthood.
  • Excision in adulthood gives unpredictable pain relief.

Global epidemiology:

• Pulled elbow (nursemaid's) is among the most common upper-limb presentations in children under 5 worldwide, peaking at 1-4 years with a female and left-arm predominance; recurrence is frequent until ligamentous maturity around age 5.
• Monteggia lesions are uncommon (about 1-2% of forearm fractures); Bado type I predominates in children and type II in adults.
• Missed/chronic Monteggia is a recognised global source of avoidable disability and medicolegal claims, driven by failure to apply the radiocapitellar line on every paediatric elbow/forearm film.

Side-by-side guidance (where emphasis differs):

• Is truly isolated radial head dislocation real? Lincoln and Mubarak found a definable ulnar injury in every "isolated" case, yet rare genuinely isolated traumatic dislocations are reported. Practically, treat every paediatric "isolated" dislocation as a plastic Monteggia and scrutinise the ulna.
• Acute vs delayed osteotomy in missed Monteggia: No consensus on the upper time limit for attempting reduction. Many achieve good results up to 1-3 years from injury, challenging older teaching that reconstruction beyond a few months is futile. Outcome depends more on chronicity and ulnar remodelling than a fixed cut-off age.
• Annular ligament reconstruction — necessary or not? Some series (e.g. single-incision techniques) report stable reductions from ulnar osteotomy alone without formal annular reconstruction, questioning routine Bell-Tawse-type reconstruction and its stiffness/synostosis risk.
• Imaging before reduction of pulled elbow: Routine radiographs are not required in a classic presentation; films are reserved for atypical history or failed reduction, where occult fracture prevalence remains low.
• Stable Monteggia radial head — fix, replace or leave: In adult Bado II with comminuted radial head, the threshold for replacement vs excision vs fixation after restoring ulnar length is debated; excision is avoided where longitudinal/DRUJ instability coexists.
• PIN palsy — when to explore: Most resolve with observation after reduction, but persistent palsy beyond 3 months with nerve entrapment in the radiocapitellar joint may warrant exploration; the exact timing for surgery is not standardised.