Fractures of Both Forearm Bones, Monteggia & Galeazzi Fracture-Dislocations

Both-bone Forearm Fractures — WHY Reduction Must Be Anatomical

The radius and ulna function as a parallelogram that allows pronation and supination; the radius rotates around the fixed ulna about the radial bow. It follows that a forearm-shaft fracture is a joint injury in disguise — if length, angulation and above all rotation and the radial bow are not accurately restored, forearm rotation is permanently lost. This is why, unlike many diaphyseal fractures, both-bone forearm fractures in the adult require anatomical reduction and rigid internal fixation — typically open reduction and plating (compression plates) of both bones. In children, whose remodelling potential is large, most are managed by closed reduction and an above-elbow cast, accepting minor angulation but never malrotation.

Clinical and Radiological Assessment

There is pain, deformity and loss of forearm rotation. The cardinal rule of forearm and elbow trauma applies: a fracture of one forearm bone with shortening or angulation is almost always accompanied by a fracture or a dislocation of the other, because the two bones are bound together by the interosseous membrane and the two radio-ulnar joints. Therefore the X-ray must include both the elbow and the wrist — an isolated 'ulna fracture' that also shows a dislocated radial head is a Monteggia injury, and missing it is a classic and costly error.

Monteggia and Galeazzi Fracture-dislocations

These two named injuries embody that rule — a fracture of one bone with dislocation of the radio-ulnar joint at the other end of the forearm. The monteggia fracture-dislocation is a fracture of the proximal ulna with dislocation of the radial head (classified by Bado on the direction of the radial-head dislocation). The galeazzi fracture-dislocation is a fracture of the distal radius with dislocation of the distal radio-ulnar joint. They are compared below.

Management of the Fracture-dislocations

In the adult both are treated operatively. In a Monteggia injury, anatomical fixation of the ulna (plating) usually allows the radial head to reduce spontaneously; the radial head is checked and, if it does not reduce, the annular ligament or an interposed structure is dealt with. In a Galeazzi injury, the radius is plated and the DRUJ is then assessed and stabilised (the Galeazzi is sometimes called the 'fracture of necessity' because non-operative treatment in the adult reliably fails). In children, both are often amenable to closed reduction. The pin (posterior interosseous nerve) must be examined in every Monteggia injury.

Complications

Early: the forearm is a common site of compartment syndrome — a high-energy both-bone fracture, a tight cast or a crush injury must raise this suspicion, and pain on passive finger extension is the key early sign. Nerve injury (the pin in Monteggia) may occur. Late: malunion with loss of the radial bow → permanent loss of pronation/supination (the functional penalty this whole injury is about); non-union (favoured by the tenuous blood supply of the mid-forearm and by soft-tissue stripping at surgery); and radio-ulnar cross-union (synostosis) — a bony bridge between the two bones that abolishes rotation, seen especially after high-energy injuries, when both fractures are at the same level, or after excessive surgical dissection.

Always image the joint above and below a forearm fracture.

• The forearm is a rotating parallelogram — restoring length, angulation, rotation and the radial bow is essential, or pronation/supination is lost.
• Adult both-bone forearm fractures need anatomical reduction + rigid plating of both bones; children are usually managed by closed reduction and an above-elbow cast.
• Always X-ray the elbow and the wrist — a fracture of one forearm bone is commonly accompanied by dislocation of the other radio-ulnar joint.
• Monteggia (MUGR) = proximal ulna fracture + radial head dislocation; risk to the posterior interosseous nerve. Treat by ORIF of the ulna; the radial head usually reduces.
• Galeazzi (GRUM) = distal radius fracture + DRUJ dislocation; the adult 'fracture of necessity' → ORIF of the radius + DRUJ stabilisation.