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Monteggia Fractures – Causes, Symptoms, Treatment

Monteggia fractures most commonly result from a direct blow to the forearm with the elbow extended and forearm in hyperpronation. The energy from the ulnar fracture gets transmitted along the interosseous membrane leading to rupture of the proximal quadrate and annular ligaments, disrupting the radiocapitellar joint. In conjunction with the bimodal distribution, diaphyseal forearm fractures in young males are commonly due to high-energy trauma, for example, falls from height, sports injuries, motor vehicle accidents, and fractures in elderly females are due to low-energy trauma such as a ground-level fall.[rx][rx][rx]

Classification System of Monteggia Fractures

In 1967, Dr. Jose Luis Babo classified Monteggia fractures into four types. These types depend on the direction of the radial head dislocation.[rx]

Type I

The proximal ulna is fractured and radial head dislocation directed anteriorly.
Most common type in children accounting for 70% of cases, 15% of cases in adults.
Mechanism of Injury: (1) direct blow to posterior elbow, (2) hyper-pronated force on an outstretched arm, (3) contracted biceps resists forearm extension causing dislocation and followed by impact leading to ulna fracture.

Type II

Both the ulnar shaft fracture and radial head dislocation are directed posteriorly
Mechanism of Injury: Axial load directed up the forearm with a slightly flexed elbow.
Most common type in adults accounting for approximately 80% of cases.
Associated with an instability of the ulnohumeral joint and high rates of radial head fracture and posterior interosseous nerve injury.

Type III

Ulnar fracture with a radial head dislocation directed laterally.
Mechanism of Injury: Varus force on an extended elbow leads to a greenstick fracture of the ulna.
More frequently seen in children.

Type IV

Fractures of the ulnar and radial shafts with an anterior radial head dislocation
Rarest type and poorly understood mechanism.

Causes of Monteggia Fractures

Mechanisms include:

Fall on an outstretched hand with the forearm in excessive pronation (hyper-pronation injury). The ulna fractures in the proximal one-third of the shaft due to extreme dislocation. Depending on the impact and forces applied in each direction, degree of energy absorption determines pattern, the involvement of the radial head, and whether or not open soft tissue occurs.
Direct blow on the back of the upper forearm would be a very uncommon cause. In this context, isolated ulnar shaft fractures are most commonly seen in defense against blunt trauma (e.g. nightstick injury). Such an isolated ulnar shaft fracture is not a Monteggia fracture. It is called a ‘nightstick fracture’.

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Diagnosis of Monteggia Fractures

Exam:
– r/o tear of the annular ligament
– associated nerve injury:
– paralysis of deep branch of the radial nerve is most common;
– the posterior interosseous nerve may be wrapped around the neck of radius, preventing reduction;
– note: that patients whose operative treatment is delayed may be found to have a progressive PIN palsy from
constant pressure exerted by the dislocated radial head;
– spontaneous recovery is usual & exploration is not indicated;

– Radiographs:
– dislocation of radial head may be missed, even though frx of the ulna is obvious (need AP, lateral and oblique X-rays of the elbow)
– a line is drawn thru radial shaft and radial head should align w/ capitalism in any position if the radial head is in normal position
– this is esp true on the lateral projection;
– the apex of angular deformity of ulna usually indicates the direction of radial head dislocation;

– Reduction:
– immobilize forearm in neutral rotation w/ slight supination, w/ cast carefully molded over the lateral side of the ulna at the level of fracture;
– keep elbow flexed ( > 90 deg), to relax biceps so that full supination can be avoided w/o losing reduction;

– Non-Operative Treatment:
– realize that even w/ successful closed reduction of the ulna (and accompanying reduction of the radial head) that subsequently
there may be slow and progressive shortening and angulation;
– hence, these patients will require close follow up;

Treatment of Monteggia Fractures

Nonoperative
- closed reduction
  - indications
    - more common and successful in children
    - must ensure stabilty and anatomic alignment of ulna fracture
  - technique
    - cast in supination for Bado I and III
Operative
- ORIF of ulna shaft fracture
  - indications
    - acute fractures which are open or unstable (long oblique)
    - comminuted fractures
    - most Monteggia fractures in adults are treated surgically
- ORIF of ulna shaft fracture, open reduction of radial head
  - indications
    - failure to reduce radial head with ORIF of ulnar shaft only
      - ensure ulnar reduction is correct
    - complex injury pattern
- IM Nailing of ulna
  - indications
    - transverse or short oblique fracture

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Delayed Dx:
– when dx is delayed < 3 months, ORIF is indicated;
– when > 3 months has elapsed, consider non-op treatment because bony ankylosis of the elbow may occur following surgery;
– bony ankylosis may be more disabling than the joint instability
– in a child, a dislocated radial head should never be resected, since it will cause cubitus valgus, prominence of the distal end of ulna,
and radial deviation of the head

Pearls and Pitfalls of Technique

Missing pediatric – Monteggia leads to poor results. All “isolated ulna fractures” must be scrutinized for radio capitellar subluxation. Careful weekly radiographic follow-up, for the first 3 weeks after reduction is important to ensure the maintenance of reduction throughout treatment.
Radiographic reading – Radiocapitellar line: The radial neck line should bisect the capitellar ossific nucleus.
Ulnar bow sign: subtle bowing in the direction of the radial head dislocation. The posterior ulnar border should be straight.
Most pediatric Monteggia fractures can be treated via closed means. Comminution, long oblique and very proximal ulna fractures have a higher risk of needing operative fixation.
Residual radiocapitellar instability is almost always a result of residual ulnar deformity.
Adult fractures often involve collateral ligament injury and radial head and coronoid fractures.
The surgeon should be prepared to perform appropriate repairs and replacements.
Osteoporosis must be taken into account when treating adult fractures.The threshold should be low for use of locking plate technology and for replacement instead of repair of the radial head.