Radial Head Dislocations

Definitions:

• Dislocation: Complete loss of articular contact.
• Subluxation: Partial loss (e.g., Nursemaid's).
• Congenital: Developmental anomaly, present at birth.
• Traumatic: Acquired, usually high energy.

Epidemiology:

• Children: Common. Peak age 4-10 (Monteggia) or 1-4 (Nursemaid's).
• Adults: Rare as isolated injury. Usually associated with complex fracture-dislocations (Terrible Triad, Monteggia).
• Mechanism:
  • Nursemaid's: Axial traction on pronated forearm.
  • Monteggia: Fall on outstretched hand (FOOSH) with pronation (Type 1) or flexion (Type 2).

Bony Anatomy:

• Radial Head: Concave, articulates with convex capitellum. It is not perfectly circular (more oval).
  • Safe Zone: The "Safe Zone" for hardware is the 90 degree arc that does not articulate with the ulna (Non-articular surface). This corresponds to the tripod position (lateral).
• Radial Notch: Indentation on proximal ulna for radial head.
• Relation: The radius moves with the ulna during flexion/extension but rotates around it during pronation/supination.
• Capitellum: The center of rotation for the radiocapitellar joint.
• Proximal Radio-Ulnar Joint (PRUJ): A trochoid (pivot) joint.

Stabilizers (Primary & Secondary):

• Primary:
  • Ulnohumeral Joint: The coronoid is the primary stabilizer against posterior subluxation.
  • MCL (Anterior Bundle): Primary stabilizer against Valgus.
  • LCL (LUCL): Primary stabilizer against Varus and Posterolateral Rotatory Instability (PLRI).
• Secondary:
  • Radial Head: An important secondary stabilizer against Valgus (if MCL is cut).
  • Capsule: Anterior capsule resists extension.
• Annular Ligament: Primary stabilizer of the PRUJ. It arises from the anterior and posterior margins of the sigmoid notch. It is tighter around the neck than the head (funnel shape), preventing distal migration (Nursemaid's).

Nerves:

• PIN: Winds around the radial neck within the supinator muscle. Highly susceptible to injury in Anterior (Type 1) or Lateral (Type 3) dislocations.
  • Safe Zone: The PIN is safe if the forearm is Pronated during lateral dissection. Supination brings the nerve closer to the surgical field in the Kaplan approach.
• Median Nerve: Can be entrapped in the joint in rare medial dislocations.
• Ulnar Nerve: Risk in Type 4 Monteggia or during medial approach for coronoid.

Vascular:

• Recurrent Radial Artery: The "Leash of Henry". Must be ligated to mobilize the supinator.
• Radial Artery: Anterior to the bicipital tuberosity.
• Blood Supply to Radial Head: Extra-osseous supply from the radial recurrent artery enter the neck. Intra-osseous supply is poor. "Watershed" area in the lateral portion of the head (Safe Zone).

Biomechanics:

• Load Transmission: The Radial Head transmits 60% of axial load at the elbow.
• Longitudinal Stability: The Radial Head prevents proximal migration of the radius (with IOM). Excision leads to proximal migration (Ulnar Variance becomes positive) leading to DRUJ pain.

History:

• Child (1-4y): "Pulled up by arm", crying, arm held by side.
• Trauma: FOOSH.
• Chronic: Loss of ROM, prominence on lateral elbow (radial head).

Physical Exam:

• Nursemaid's: Arm held in extension + pronation. Resists supination. No swelling (if acute).
• Fracture: Swelling, bruising, deformity of ulna.
• Palpation: Palpate the radial head. Is it in the joint? Does it rotate?
• PIN: Check thumb extension.

Differential Diagnosis:

X-rays:

• Elbow AP/Lat: Mandatory.
  • Check: Radiocapitellar Line.
  • Check: Ulnar bowing (Plastic deformation).
  • Check: Capitellum shape (Round vs Flat).
• Forearm: Exclude shaft fractures.
• Wrist: Exclude Galeazzi.

CT Scan:

• Indicated for chronic cases to assess articular congruity and ulnar deformity planning.
• Adult Type II Monteggia (Check for coronoid fracture).
• 3D Reconstruction: Essential for understanding the "shotgun" deformity of the proximal ulna in comminuted Monteggia fractures.

Radiographic Parameters (Detailed):

Associated Injuries (The Checklist):

• Coronoid Fracture: 10-15% of radial head dislocations. Pathognomonic for Terrible Triad.
• LCL Rupture: Always present in dislocation. Usually avulses from the Lateral Epicondyle.
• MCL Rupture: Present in valgus instability or high energy trauma.
• DRUJ Injury: Present in Type 4 Monteggia or Essex-Lopresti (Longitudinal instability). Always examine the wrist!
• Capitellar Shear Fracture: The radial head can shear off the capitellum/trochlea as it dislocates.

MRI:

• Rarely indicated in acute setting.
• Useful in chronic "painful clicking" to assess for loose bodies or plica.
• Can assess integrity of the PIN in non-recovering nerves.

• 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.

Complications Detail:

• Stiffness: The most common complication. Extension loss of 10-15 degrees is common and functional. Flexion loss is poorly tolerated. Pronation/Supination loss is common if IOM injured.
• Heterotopic Ossification (HO): Common in adults with head injury or prolonged intubation. Indomethacin prophylaxis indicated for high risk.
• Synostosis: Cross-union between radius and ulna. Risk factors: Single incision for both bones, delayed fixation, head injury. Treatment: Excision after bone scan is "cold" (12-18 months).
• Implant Removal: Plates on the proximal ulna are prominent and often require removal. 40% removal rate.

Mayo Elbow Performance Score (MEPS):

• Pain (45 points): None = 45, Moderate = 30, Severe = 0.
• Motion (20 points): Greater than 100 deg arc = 20, 50-100 = 15, Less than 50 = 5.
• Stability (10 points): Stable = 10, Unstable = 0.
• Function (25 points): Combing hair, Feeding, etc.
• Greater than 90 = Excellent, 75-89 = Good.

• 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.

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):

Registry / outcome notes: There is no dedicated radial head dislocation registry; radial head arthroplasty data are captured indirectly within elbow arthroplasty and implant series rather than national joint registries (NJR, AOANJRR, AJRR), which focus on hip/knee/shoulder. Most evidence is therefore Level IV case series.

High- vs limited-resource practice:

• Well-resourced: CT/3D planning for comminuted proximal ulna, modular radial head implants, hinged external fixators, and intra-operative imaging are routinely available.
• Limited-resource: Reliance on plain radiographs and the radiocapitellar line, plate or even K-wire/ex-fix ulnar fixation, and biological annular reconstruction (triceps/forearm fascia) rather than implants. Early recognition of the plastic Monteggia is the single highest-yield, low-cost intervention.