Monteggia Fracture-Dislocation

Monteggia fracture dislocation is a fracture of the proximal ulna with dislocation of the radial head from the capitellum and the proximal radioulnar joint. It accounts for 1 to 2% of forearm fractures, with a paediatric peak at 4 to 10 years.

The Bado classification describes the direction of radial head dislocation. Type I is anterior with an ulnar fracture angulated forward, and is the most common in children. Type II is posterior, with a posterior ulnar angulation, and is more frequent in older adults. Type III is lateral with a metaphyseal ulnar fracture. Type IV is a radial head dislocation with fractures of both forearm bones.

The mechanism is a fall on the hand with forced forearm pronation or hyperextension, or a direct blow to the posterior forearm. In plastic deformation of the ulna the radial head can dislocate with no visible ulnar fracture.

The dislocated radial head is missed on first assessment in a notable minority. Complications are posterior interosseous nerve palsy (about 10 to 20%, usually a neurapraxia recovering in 3 to 6 months), compartment syndrome, redislocation, malunion, ulnar nonunion, radioulnar synostosis, and a late chronic radial head dislocation.

Pathophysiology.

The ulna angulates or fractures, shortening the forearm, and the annular ligament tears or is stripped so the radial head leaves the joint. Soft tissue (annular ligament, capsule) can lie in the joint and block reduction.

The injury is unstable in children when the ulna fractures obliquely or comminuted, and in adults it is nearly always unstable and needs fixation.

Elbow pain and swelling, an ulnar angulated forearm, a prominent radial head palpable in the antecubital fossa (anterior type), and limited pronation and supination. Elbow flexion may be restricted by the block.

Test the posterior interosseous nerve (weak finger and thumb extension, with preserved wrist extension that deviates radially). Check the radial pulse and capillary refill, and examine the forearm compartments for tense swelling and pain on passive stretch. Check for open wounds.

• Radiographs of the whole forearm including the elbow and wrist, anteroposterior and lateral. The radiocapitellar line, drawn through the centre of the radial shaft and neck, must cross the capitellum on every view. Any ulnar fracture or plastic bowing needs this check.
• Compare with the other elbow in children. Ultrasound can show the radial head position in young children.
• CT or MRI for subtle dislocation, and for chronic cases.
• Always examine the wrist for an associated distal radioulnar injury.

Differential diagnosis.

• Isolated ulnar fracture or plastic deformation with a normal radial head.
• Radial head subluxation and congenital radial head dislocation.
• Galeazzi fracture dislocation and both bone forearm fracture.
• Elbow dislocation and Essex-Lopresti injury.

Children.

• Closed reduction under sedation or anaesthesia: restore ulnar length and alignment, and the radial head usually reduces. Check stability with imaging through full rotation.
• Immobilise in the position that holds the radial head reduced on imaging: usually 100 to 110 degrees of flexion with supination for anterior injuries, and about 60 to 70 degrees of flexion for posterior injuries. Long arm cast for 4 to 6 weeks.
• Unstable or oblique ulnar fractures: fix the ulna with an elastic intramedullary nail (2.0 to 3.0 mm) or a plate. If the radial head stays out, open reduction removes the interposed annular ligament, which is then repaired.
• Chronic (over 4 to 6 weeks) dislocations need reconstruction by ulnar osteotomy with annular ligament reconstruction, a specialist procedure.

Adults. Open reduction and fixation of the ulna with a 3.5 mm compression plate restores length and alignment, and the radial head then reduces. If it does not, open reduction and annular ligament repair follow. Radial head fractures in Bado II injuries are fixed or replaced. Immobilise for 1 to 2 weeks, then move early.

Open injury.

• Give intravenous co-amoxiclav 1.2 g every 8 hours (or cefazolin 2 g every 8 hours) within 1 hour of injury.
• Continue until 24 hours after wound closure for types I and II. For type III, continue until 72 hours or 24 hours after soft tissue cover, whichever is earlier.
• Co-amoxiclav maximum is 3.6 g daily. Give every 12 hours at creatinine clearance 10 to 30 mL/min. Check liver tests in courses over 7 days.

For heavy contamination or soft tissue loss add gentamicin 5 mg/kg intravenously once daily for up to 72 hours. Check creatinine daily and a level before the second dose. Avoid it, or extend the interval, at eGFR under 60 mL/min/1.73 m2.

With severe penicillin allergy use clindamycin 600 mg intravenously every 8 hours (maximum 2.7 g daily) with gentamicin.

Children: co-amoxiclav 30 mg/kg intravenously every 8 hours (maximum 1.2 g a dose) and gentamicin 7 mg/kg once daily (5 mg/kg from 12 years).

Give a tetanus booster 0.5 mL intramuscularly if the last dose was over 10 years ago. Add tetanus immunoglobulin 250 units intramuscularly (500 units if over 24 hours since injury or heavily contaminated) when immunisation is incomplete or unknown. Debride and stabilise within 24 hours (within 12 hours for gross contamination).

Analgesia.

• Adults: paracetamol 1 g orally every 6 hours for up to 5 to 7 days (maximum 4 g daily; 3 g daily when weight is under 50 kg or in hepatic impairment).
• Adults: ibuprofen 400 mg orally every 8 hours with food for up to 5 days (maximum 1200 mg daily; avoid with eGFR under 30 mL/min/1.73 m2, peptic ulcer or anticoagulant use).
• Adults: oral morphine 5 to 10 mg every 4 hours as needed for up to 3 days. Start 2.5 to 5 mg with age over 75 or eGFR under 30. Avoid exceeding 60 mg in 24 hours without senior review. Monitor sedation and respiration, and give a laxative.
• Children: paracetamol 15 mg/kg orally every 4 to 6 hours (maximum 75 mg/kg daily and not exceeding 4 g daily) and ibuprofen 10 mg/kg orally every 6 to 8 hours with food (maximum 40 mg/kg daily and not exceeding 2400 mg daily), for up to 5 days.
• Children: ketamine 1 to 2 mg/kg intravenously for reduction under sedation, with airway skilled staff and continuous oximetry and capnography.

Monitoring. Radiographs at 1 week, 2 weeks and 6 weeks to detect redislocation. Posterior interosseous nerve function at each visit. Forearm compartments in the first 48 hours. Rotation and elbow range at 6 weeks and 3 months.

Referral and escalation. Refer every Monteggia injury to orthopaedics the same day. Emergency for compartment syndrome (pain on passive stretch, tense forearm), open fracture, neurovascular compromise, or an irreducible radial head.

Special groups.

• Children: unrecognised injuries in a child with an ulnar fracture are common, so check the radial head in every forearm fracture.
• Older adults: osteoporotic bone favours plate fixation with locking screws.
• Kidney impairment: avoid ibuprofen, reduce morphine and extend gentamicin intervals.
• Region specific: delayed presentation after traditional bone setting leads to chronic dislocation.