Summary

A Monteggia fracture-dislocation is a fracture of the Proximial Third of the Ulna with an associated dislocation of the Radial Head (Proximal Radioulnar Joint - PRUJ). It is a notorious trap for the unwary clinician: the ulna fracture is obvious, but the radial head dislocation is frequently missed (30-50% cases), leading to disastrous chronic limitation of elbow flexion and rotation. The Radiocapitellar Line determines diagnosis: a line drawn through the radial shaft MUST bisect the capitellum on all views. Treatment in adults is surgical (ORIF Ulna) to restore length, which usually reduces the radial head. In children, closed reduction is often successful. [1,2,3]

Key Facts

• Mnemonic: MUGR. (Monteggia Ulna, Galeazzi Radius).
• Radiocapitellar Line: If the line misses the capitellum, the radial head is dislocated.
• Nerve at Risk: Posterior Interosseous Nerve (PIN). It wraps around the radial neck and can be stretched or tethered.

Clinical Pearls

"Every Ulna Fracture is a Monteggia until proven otherwise": If you see an isolated ulna shaft fracture ("Nightstick fracture"), look at the elbow. If the PRUJ is tender or the X-ray is imperfect, assume the head is out.

"The Ulna Rules the Radius": The radius is tethered to the ulna by the interosseous membrane. If the ulna shortens/angulates, the radius MUST dislocate to accommodate the length mismatch. Restoring ulna length anatomically pulls the radius back into place.

"Bado I is Commonest": Anterior dislocation of the radial head with anterior angulation of the ulna (Extension type). Common in children.

                 MONTEGGIA FRACTURE
                        ↓
             ADULT OR CHILD?
             ┌──────────┴──────────┐
           CHILD                 ADULT
             ↓                     ↓
        CLOSED REDUCTION      OPEN REDUCTION (ORIF)
       (MUA + Long Arm Cast)    (Plate the Ulna)
             ↓                         ↓
      CHECK REDUCTION          DID HEAD REDUCE?
      (Radiocapitellar)         ┌──────┴──────┐
      ┌──────┴──────┐         YES            NO
    YES            NO          ↓              ↓
   CAST           ORIF      REHAB           OPEN
                                         REDUCTION
                                       (Annular Lig repair)

1. Surgical Fixation (Adults)

• Mandatory.
• Technique: Compression Plating (3.5mm LCP/DCP) of the Ulna.
• Goal: Anatomical length and alignment.
• The "Pop": Often, as the plate reduces the ulna, the radial head clunks back in.
• Irreducible Head?: If head stays out, the Annular Ligament may be interposed. Requires open reduction (Kaplan or Kocher approach) to fish out the ligament.

2. Paediatric Management

• Type I (Anterior): Closed reduction. Flex elbow to 110 degrees (relax biceps) and Supinate. Cast.
• Type II (Posterior): Reduce in Extension.
• Type III (Lateral): Reduce with Valgus stress.

3. Chronic Missed Monteggia

• Problem: Radial head overgrows. Ulna heals short.
• Treatment: Ulnar Osteotomy (break ulna, lengthen it with graft/fixator) to pull radial head back in. Or Radial Head Excision (Adults).

Ring et al (1998)

• Landmark paper on Adult Monteggia fractures.
• Associated with Excellent results IF:
  1. Ulna is rigidly fixed (Plate).
  2. Radial head reduction is confirmed.
  3. Early motion is started.

Konrad et al (2007)

• Long term follow up. Even with good reduction, 50% have some radiographic arthritis, but functional scores remain high.

What is a Monteggia fracture?

You broke one of the two bones in your forearm (Ulna), and the force popped the other bone (Radius) out of the elbow joint. It's a "double whammy".

Why do I need surgery?

In adults, we cannot hold the broken bone straight in a cast. If the Ulna heals crooked or short, the elbow joint will never fit back together, and your arm will be permanently stiff.

The Nerve (PIN)

(If applicable) You can't lift your thumb because the nerve that runs around the elbow bone was stretched when it dislocated. It usually wakes up, but it takes months. We will watch it.

Q1: Define the Radiocapitellar Line. A: A line drawn down the longitudinal axis of the radial shaft should bisect the capitellum of the humerus in all radiographic views (AP and Lateral), regardless of the degree of flexion/extension. Failure to do so implies radial head subluxation/dislocation.

Q2: Which Bado type has the highest risk of nerve injury? A: Bado Type II (Posterior). Up to 20% incidence of PIN palsy. Also associated with Coronoid fractures ("Terrible Triad" variant).

Q3: How do you treat a chronic missed Monteggia in a child (4 months post injury)? A: The ulna has healed in a malunited (short/angulated) position. The radial head is overgrown. Treatment involves an Ulnar Lengthening Osteotomy (Callus distraction or plate with graft) and Open Reduction of the Radial Head + Annular Ligament Reconstruction (Bell-Tawse procedure).

(End of Topic)