Fraktur Antebrachii

01Pathophysiology

The forearm is a mechanical unit formed by the radius and ulna linked at three points: the proximal radioulnar joint (PRUJ) at the elbow, the interosseous membrane (IOM) running between the two bones, and the distal radioulnar joint (DRUJ) at the wrist. This ring-like construct means that a fracture of one bone with significant shortening or angulation almost always disrupts the adjacent joint of the other bone. This principle is central to understanding why Monteggia and Galeazzi fracture-dislocations exist as predictable injury patterns rather than random occurrences.

When a patient falls on an outstretched hand, the force is transmitted axially through the wrist. If the wrist is in dorsiflexion, the distal radius fails on its dorsal cortex and the fragment displaces dorsally, producing a Colles fracture. If the wrist is in palmar flexion at impact, the fragment displaces volarly, producing a Smith fracture. The direction of displacement directly explains the resulting deformity on examination: dorsal angulation causes the "dinner fork" silhouette, while volar angulation causes the "garden spade" appearance.

In Monteggia fractures, the mechanism involves a direct blow or a fall with forced pronation. The proximal ulna fractures, and the energy propagates through the IOM to dislocate the radial head at the PRUJ. The radiocapitellar line, a line drawn through the long axis of the radius that should bisect the capitellum in every view, becomes disrupted. This finding is the radiographic hallmark.

In Galeazzi fractures, a fall or direct force fractures the radial shaft at the junction of the middle and distal thirds. The resulting shortening of the radius pulls the DRUJ apart through the IOM. The ulnar head becomes abnormally prominent at the wrist. This is sometimes called a "fracture of necessity" because it almost always requires surgical fixation in adults; closed treatment has an unacceptably high failure rate due to the deforming muscular forces (pronator quadratus, brachioradialis).

The nightstick fracture, an isolated ulnar shaft fracture from a direct blow (historically from blocking a strike with the forearm), is unique because it does not disrupt the ring construct if there is no significant displacement. This is why it is the one forearm shaft fracture that can often be treated nonoperatively.

In children, the periosteum is thick and the bone is more porous, leading to incomplete fracture patterns. A torus (buckle) fracture compresses one cortex without disrupting the other. A greenstick fracture breaks the tension-side cortex while bending the compression side. These heal rapidly and are treated with immobilization rather than surgery.

02Classification and Clinical Manifestation

Monteggia Classification (Bado)

03Diagnostic Workup

The best initial test for any suspected forearm fracture is plain radiography of the entire forearm, and the single most important principle is that films must include both the joint above and the joint below the injury. The most commonly tested error on exams is obtaining only a wrist film for a distal radius fracture without imaging the elbow, thereby missing a concomitant dislocation (Essex-Lopresti) or the reverse pattern.

When you see a proximal ulna fracture on film, your next step must be to carefully evaluate the lateral elbow radiograph for the radiocapitellar line. Draw a line along the axis of the proximal radius; it must pass through the center of the capitellum on every projection (AP, lateral, oblique). Disruption of this line is the radiographic confirmation of a Monteggia fracture-dislocation. This is a favorite exam image because students focus on the obvious ulna fracture and fail to recognize the subtle radial head dislocation.

For a radius shaft fracture, the next step is evaluating the DRUJ on the wrist film. Widening of the DRUJ, a fracture of the ulnar styloid process, or dorsal subluxation of the distal ulna all suggest a Galeazzi pattern. If clinical suspicion remains high but plain films are equivocal, a CT of the wrist can better define the articular surface and DRUJ congruity.

CT scanning is reserved for intra-articular fractures (Barton fracture, comminuted distal radius fractures) to guide surgical planning. It is the most accurate test for defining the number, size, and displacement of articular fragments.

A thorough neurovascular examination is not optional. The anterior interosseous nerve (AIN), a motor branch of the median nerve, is at risk in Monteggia fractures and proximal forearm injuries. Test AIN function by asking the patient to make an "OK" sign (pinch with the thumb IP joint and index DIP joint flexed). The posterior interosseous nerve (PIN) is at risk in Monteggia type II fractures and proximal radius fractures; test by asking for finger extension at the MCP joints. Median nerve compression (especially acute carpal tunnel syndrome) can complicate displaced distal radius fractures and constitutes an emergency requiring urgent reduction or surgical release.

04Management and Treatment

Acute Stabilization

The immediate priorities are analgesia, assessment for neurovascular compromise, and splinting in a position of comfort. For displaced distal radius fractures, perform closed reduction using a hematoma block (inject 5-10 mL of 1% lidocaine without epinephrine directly into the fracture hematoma) or procedural sedation. Apply longitudinal traction, disimpact the fragment, and correct the deformity. After reduction, apply a well-padded sugar-tong splint to prevent pronation and supination while allowing for swelling. The splint extends from the dorsal MCP joints, around the elbow at 90 degrees of flexion, to the volar MCP joints.

For all shaft fractures (Monteggia, Galeazzi, both-bone), initial management is a long arm splint with the elbow at 90 degrees and the forearm in neutral or the position of stability, followed by urgent orthopedic referral.

Compartment syndrome of the forearm is a surgical emergency that can complicate any forearm fracture. The hallmark is pain out of proportion to the injury, especially pain with passive extension of the fingers. If compartment syndrome is suspected, all circumferential dressings must be removed immediately and the compartment pressure measured. Pressures within 30 mmHg of the diastolic blood pressure (delta pressure less than or equal to 30 mmHg) or absolute pressures above 30 mmHg are indications for emergent fasciotomy. Do not wait for the "classic" signs of pallor and pulselessness; these are late and indicate irreversible damage.

Definitive (Long-Term) Management

For Colles fractures, if the reduction is stable and the fracture meets alignment criteria, transition from splint to a short arm cast at 1-2 weeks when swelling subsides, and immobilize for a total of 4-6 weeks. If instability is present (comminution, loss of reduction on follow-up films, intra-articular extension), proceed to ORIF with a volar locking plate.

Galeazzi fractures in adults always require ORIF of the radius. After fixation, the DRUJ is tested intraoperatively. If stable, the arm is immobilized in supination. If unstable, the DRUJ is pinned with K-wires or repaired.

Monteggia fractures in adults require ORIF of the ulna. Anatomic reduction of the ulna length and alignment will usually reduce the radial head indirectly. A post-fixation radiograph must confirm restoration of the radiocapitellar line.

Contraindications and Cautions: In the elderly osteoporotic patient with a distal radius fracture, hardware fixation into severely osteoporotic bone has higher complication rates (screw cutout, plate failure). Fragment-specific fixation, external fixation, or augmentation with bone cement may be preferred. In open fractures, administer IV antibiotics (typically a first-generation cephalosporin such as cefazolin 2 g IV; add an aminoglycoside for grossly contaminated wounds), administer tetanus prophylaxis if indicated, and perform urgent irrigation and debridement in the operating room before definitive fixation.

05Differential Diagnosis and Distractors

06Traps and High-Yield Pearls

The single most common way students lose points on forearm fracture questions is by failing to recognize the associated joint injury. A vignette will show you a clear ulnar shaft fracture and ask for the next step or the diagnosis. The trap answer is "isolated ulnar shaft fracture" or "nightstick fracture." The correct answer is to recognize it as a Monteggia fracture by noting clues like loss of elbow extension, a disrupted radiocapitellar line, or an instruction in the stem saying the elbow films are abnormal. The same logic applies to Galeazzi: if you see a radius shaft fracture, you must check the DRUJ. The tested principle is that the forearm is a ring structure, and a displaced fracture of one bone must disrupt the ring somewhere else.

A second frequent trap involves compartment syndrome. The question will describe a patient with a forearm fracture who, hours later, has worsening pain despite adequate analgesia and pain with passive finger extension. The distractor answer is to order more imaging or increase pain medication. The correct answer is always to measure compartment pressures and proceed to fasciotomy.

For pediatric questions, remember that children remodel bone far better than adults. The tested concept is that most pediatric forearm fractures, including Monteggia and Galeazzi patterns, can be managed with closed reduction and casting, while the same fractures in adults almost universally require ORIF. A torus fracture requires only a removable splint, not a circumferential cast, and does not need repeat radiographs.

Finally, do not confuse the names: Monteggia is proximal ulna plus radial head dislocation (think "MU" for Monteggia-Ulna); Galeazzi is radius shaft plus DRUJ dislocation (think "GR" for Galeazzi-Radius). Reversing these is one of the most common errors on timed exams.