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Ulna shaft fracture

Introduction

Forearm fractures more commonly occur in men than women, owing to a higher incidence in men of participation in contact sports, altercations, falls from height, and motor vehicle collisions. Ulna shaft fractures may occur from direct trauma along its subcutaneous border, classically described as a "nightstick fracture" as a victim attempts to protect the head from assault.

Anatomy

The ulna is a relatively straight bone that serves as an axis around which the laterally bowed radius rotates in pronation and supination. Since the ulna and radius form a ring connected by the interosseous membrane and ligaments, a fracture that shortens the ulna may result in a fracture or a dislocation of the radius at the proximal or distal radioulnar joint.

Classification

Fractures of the ulna shaft may be described as nightstick fractures, Monteggia fractures, or stress fractures. A Monteggia fracture denotes a proximal ulna fracture associated with dislocation of the radial head. Monteggia fractures can be described according to the Bado classification:

Type I: Anterior dislocation of the radial head with associated anteriorly angulated fracture of the ulnar shaft. Typically occurs from forced pronation
Type II: Posterior/posterolateral dislocation of the radial head with associated posteriorly angulated fracture of the ulnar shaft. Typically occurs from axial loading of the forearm with a flexed elbow
Type III: Lateral/anterolateral dislocation of the radial head with fracture of ulnar metaphysis. Typically occurs from forced abduction of the elbow
Type IV: Anterior dislocation of the radial head with fractures of both the radius and ulna within proximal third at the same level. Typically occurs from a mechanism similar to Type I, but the radius also fails.

Presentation

Patients with a nightstick fracture typically present with pain, swelling, focal tenderness, and abrasions overlying the site of trauma. Patients with Monteggia fractures present with elbow swelling, deformity, crepitus, and painful elbow range of motion, especially pronation and supination. Since radial or posterior interosseous nerve injury is relatively common, especially with type II Bado fractures, a careful neurovascular examination is paramount.

Diagnosis

Standard AP, lateral, and oblique radiographs of the elbow and forearm should be obtained. It is important for the forearm views to also include the wrist. When assessing these views, normal radiographic lines should be evaluated to rule out injury. For example, on a supinated lateral view, lines drawn tangential to the radial head anteriorly and posteriorly should enclose the capitellum, and a line drawn through the radial head and shaft should always line up with the capitellum regardless of the view.

Treatment

For nondisplaced or minimally displaced nightstick fractures, defined as < 10 degrees of angulation in any plane or <50% displacement of the shaft, initial treatment consists of placement of a sugar-tong splint for 7-10 days. This can be followed by functional bracing for 8 weeks with active range of motion exercises for the elbow, wrist, and hand, or simple immobilization in a sling with a compression wrap, depending on the patient's symptoms. Displaced nightstick fractures should be treated with open reduction and internal fixation using a 3.5mm dynamic compression plate.

As opposed to Monteggia fractures in the pediatric population, which can be treated with closed reduction and casting, Monteggia fractures in adults require operative treatment. The radial head should be closed reduced with the patient under anesthesia, followed by open reduction and internal fixation of the ulna shaft with a 3.5mm dynamic compression plate. Fixation of the ulna usually renders the radial head stable in >90% of cases. If the radial head cannot reduce despite ulna reduction and stabilization, the annular ligament, or rarely the radial nerve, may be interposed. Associated radial head fractures may require open reduction and fixation; and if so, the annular ligament should be repaired. Post-operatively, the patient is placed in a posterior elbow splint for 5-7 days followed by physical therapy with active elbow and forearm range of motion. However, if the ulnar fixation or radial head stability is questionable, a long arm cast with serial radiographic evaluation can be done instead. Once radiographs demonstrate healing, a supervised physical therapy regimen can be initiated.

Complications

Although uncommon, persistent radial head instability can occur following anatomic reduction of the ulna. If the radial head redislocates in the first 6 weeks post-operatively, the quality of ulna reduction must be critiqued. If the reduction is nonanatomic, repeat reduction and fixation with an open reduction of the radial head may be done. Dislocation of the radial head beyond 6 weeks postoperatively is best managed by radial head excision. Nerve injury is also common with ulnar shaft fractures. They are most commonly seen with Bado Type II and III injuries, and the radial, median, posterior interosseous, or anterior interosseous nerve can be involved. Nerve injury may also occur from excessively forceful reduction maneuvers or during open reduction from errant retractor placement. If the nerve palsy persists after 3 months of observation, surgical exploration is indicated.

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