Chapter 13: Forearm

The radius and the ulna lie parallel to each other and are invested at their proximal ends with a relatively large muscle mass. Because of their close proximity, injury forces typically disrupt both bones and their ligamentous attachments. They can be thought of conceptually as two cones lying next to each other pointing in opposite directions (Fig. 13–1).

The bones of the forearm are bound by several essential ligamentous structures (Fig. 13–2). On either end, the joint capsules of the elbow and wrist hold the radius and ulna together. Anterior and posterior radioulnar ligaments further strengthen these attachments proximally. The distal radioulnar joint contains a fibrocartilaginous articular disk that acts as an energy absorber with compressive forces. The third important ligamentous attachment is the interosseous membrane which provides longitudinal stability as well as load transference between the two bones.¹

Muscle attachments to the forearm bones are important because of their penchant for displacing fracture fragments. Simply speaking, the shafts of the radius and the ulna are surrounded by four primary muscle groups whose pull frequently results in fracture displacement or nullification of an adequate reduction (Fig. 13–3). These groups are as following:

1. Proximal: The biceps and the supinator insert on the proximal radius and exert a supinating force.

2. Midshaft: The pronator teres inserts on the radial shaft and exerts a pronating force.

3. Distal: Two groups of muscles insert on the distal radius. The pronator quadratus exerts a pronating force. The brachioradialis and abductor pollicis also produce deforming forces, depending on the location of the fracture. Of these, the brachioradialis exerts the predominant displacing force.

Consider that the ulna is a fixed straight bone around which the radius rotates. The radius, in contradistinction, has a lateral bow that must be preserved to allow full pronation and supination after healing (Fig. 13–4).² Forearms play an important part in the activities of daily living and the best patient outcomes often result from careful attention to maintenance of their length and alignment.

Classification

In this chapter, fractures of the radius and ulnar shaft will be considered. The shafts of the radius and ulna are defined as the diaphyses of the long bones not encompassed by joint capsules or ligaments. The reader is referred to Chapter 12 for a discussion of distal radius fractures, and Chapter 14 for a discussion of fractures of proximal structures such as the radial head, olecranon, and coronoid process. The classification system used in this chapter for radial and ulnar shaft fractures is based on anatomic as well as therapeutic considerations.

Fractures can occur anywhere along the shaft of the radius or ulna. These fractures are divided into three groups: (1) radial shaft fractures, (2) ulnar shaft fractures, and (3) combined radius and ulna fractures. The Monteggia (ulna fracture with radial head dislocation) and Galeazzi (radius fracture with distal radioulnar dislocation) fractures are classified under their respective single bone fractures but are paid special attention.

Radial Shaft Fractures

Radial shaft fractures can be divided into proximal, midshaft, and distal fractures (Fig. 13–5). Isolated fractures of the proximal two-thirds of the shaft of the radius are uncommon in adults because this area is well protected by the forearm musculature. A force powerful enough to break the radius is usually sufficient to also break the ulna.

Galeazzi fracture dislocation includes a fracture of the distal radius (usually between 5 and 7.5 cm from the distal articulation) which is obvious both clinically and radiologically.³ Coupled with the radius fracture is a dislocation of the distal radioulnar joint (DRUJ) which is more subtle. These are somewhat frequent injuries of the forearm with up to 3% of children and up to 7% of adult forearm fractures being Galeazzi fractures.⁴

Mechanism of Injury

The usual mechanism is a direct blow to the radial shaft, most commonly, at the junction of the middle and distal portions of the bone. It is at this point that the radius is least enshrouded by muscle and therefore more exposed to direct trauma.

Galeazzi fracture dislocation commonly is caused by axial loading (falls) and direct blows (especially motor vehicle accidents).

Examination

Tenderness is present at the fracture site and can be elicited with direct palpation or longitudinal compression of the injured bone.

Galeazzi fracture dislocations demonstrate tenderness over the obvious fracture of the radius as well as in the DRUJ. Displacement of the ulnar head either dorsally or ventrally is commonly felt.^5–7

Imaging

Routine anteroposterior (AP) and lateral views of the forearm are obtained. Radial shaft fractures are frequently associated with serious but often missed elbow and wrist injuries, so both joints should be seen on radiographs. Isolated, angulated, or displaced radius fractures of the distal shaft suggest that a DRUJ subluxation or dislocation is present.

There are four reliable radiographic signs of injury to the DRUJ (Figs. 13–6 and 13–7).

1. Fracture of the base of the ulnar styloid

2. AP view: Widening of the distal radial ulnar joint space

3. Lateral view: Dislocation of the distal radius relative to the ulna

4. Shortening of the radius by more than 5 mm⁸

Associated Injuries

A distal radial shaft fracture is frequently associated with a distal radioulnar dislocation (Galeazzi fracture dislocation). High-energy mechanisms with extensive soft-tissue injury may be associated with acute compartment syndrome.⁸

Treatment

Radius—Proximal One-Third

Emergency department (ED) management should include the application of AP splints (Appendix A–10). The elbow should be in 90 degrees of flexion with the forearm in supination. Supination of the forearm is required to prevent the supinating forces of the supinator and biceps muscles that insert on the proximal portion of the radius from causing displacement.² Follow-up radiographs to detect displacement are essential. These fractures are rare and urgent orthopedic referral is appropriate.

ED management should include immobilization in a long-arm posterior splint (Appendix A–9) with the forearm in supination and the elbow in 90 degrees of flexion. Discussion with an orthopedist may be prudent as the treatment of choice usually includes open reduction and internal fixation.

If the radius fracture involves the proximal one-fifth of the bone, treatment is controversial. Because of the small size of the proximal fragment, internal fixation is difficult. Most patients are treated with a manipulative reduction and immobilization in AP splints (Appendix A–10). The elbow should be in 90 degrees of flexion and the forearm in supination.

Radius—Midshaft

Referral is indicated after immobilization in AP splints (Appendix A–10). The elbow should be in 90 degrees of flexion and the forearm in moderate supination. Follow-up radiographs are strongly encouraged.

Discussion with an orthopedist may be prudent as the treatment of choice usually includes open reduction and internal fixation. Initially, immobilize with 90 degrees of elbow flexion and moderate forearm supination (Appendix A–10).

Radius—Distal One-Third

Referral is indicated after immobilization in AP splints (Appendix A–10). The elbow should be in 90 degrees of flexion and the forearm in pronation. An angulated, nondisplaced fracture may be associated with subluxation of the DRUJ.

The treatment of Galeazzi fracture dislocation varies with age. Adults invariably have poor outcomes if they are treated with reduction and casting. Thus, Galeazzi injury was termed “the fracture of necessity” by authors who felt only surgical intervention would allow good patient outcomes.⁶ Operative reduction and internal fixation remains the treatment of choice.

Children, as is so often the case in orthopedics, have very good results with conservative treatment. They are frequently treated with reduction and long-arm casting.⁴

Regardless of the patient’s age it seems prudent to involve the orthopedic surgeon early in treatment decisions involving displacement of the distal radial diaphysis.

Complications

Radial shaft fractures are associated with several complicating factors.

1. Nondisplaced fractures may undergo delayed displacement due to muscular traction with subsequent poor functional outcomes. Follow-up radiographs to ensure proper positioning are essential.

2. Malunion or nonunion may be secondary to inadequate reduction or immobilization.

3. Rotational deformities must be detected and treated early.

4. DRUJ subluxation or dislocation (Galeazzi fracture) may be unrecognized and the patient end up with a poor functional outcome.

5. Neurovascular injuries can occur, but are uncommon.

Ulnar Shaft Fractures

Ulnar shaft fractures can be classified into three groups: (1) nondisplaced, (2) displaced (>5 mm), and (3) Monteggia fracture dislocations (Fig. 13–8). The midshaft of the ulna is the most frequent location of a fracture (Fig. 13–9).

Monteggia fracture dislocations are displaced fractures of the proximal one-third of the ulnar shaft combined with a radial head dislocation. Radial head dislocations can occur only if there is complete rupture of the annular ligament. Monteggia fracture dislocations account for 1% to 2% of all forearm fractures.⁹ Bado’s four type classification system is frequently used and is shown below with the frequency of the type of injury shown in parentheses.¹⁰

1. Ulnar shaft fracture with anterior dislocation of the radial head (60%). This is the most frequent type in children and young adults.

2. Ulnar shaft fracture with posterior or posterolateral dislocation of the radial head (15%). In some studies this is the most common presentation in adults.^9,11,12

3. Ulnar metaphyseal fractures with lateral or anterolateral dislocation of the radial head (20%). This is a common childhood fracture resulting from a direct blow to the inner elbow.

4. Ulnar and radial shaft fracture (proximal one-third) and anterior dislocation of the radial head (5%).¹³

Mechanism of Injury

A direct blow to the ulna is the most common mechanism, and the resulting fracture is often referred to as a “nightstick fracture,” as if the individual was holding up the arm to protect the face from the downward strike of a police nightstick. With the arm up in this manner, the ulna is exposed and not well protected by soft tissues. This mechanism is common in automobile accidents or fights. Excessive pronation or supination can also result in ulnar shaft fractures.

Monteggia fracture dislocation has a number of mechanisms of injury postulated as would be expected by the varying directions of radial head dislocation. Falls on the outstretched hand, falls on the elbow, and direct blows to the ulna are among the suggested mechanisms of injury.⁹ Posterior dislocations (Bado, type 2) are frequently associated with fractures of the radial head or coronoid process and are most frequent in middle-aged or elderly patients. These patients are felt to have the same mechanism as patients who have dislocated their elbow but osteoporosis allowed a fracture instead.

Examination

Swelling and tenderness with palpation are evident over the fracture site. Palpation of the ulna will elicit pain localized to the fracture site.

Monteggia fracture dislocations are characterized by shortening of the forearm due to angulation. The radial head may be palpable in the antecubital fossa following anterior dislocations. Pain and tenderness will be present over the proximal ulna and are exacerbated by any motion. Crepitus is often felt in the joint if motion is allowed.

Monteggia fracture dislocations characteristically have more pain with pronation and supination than isolated ulnar shaft fractures.

Imaging

AP and lateral views will generally demonstrate the injury (Figs. 13–10 and 13–11). If there is significant displacement, elbow and wrist views should be added to exclude articular injury, subluxation, or dislocation. In any fracture of the ulna, especially proximal fractures, the emergency physician should evaluate the radiocapitellar line on the lateral radiograph. A line drawn down the center of the neck and head of the radius should intersect the middle of the capitellum. If this intersection does not occur, the proximal radioulnar joint is disrupted. See Chapter 6 for further details.

Associated Injuries

Although fractures of the distal two-thirds of the ulnar shaft are rarely accompanied by associated injuries, a fracture to the proximal one-third of the ulna should be evaluated for radial head dislocation.²

Infrequently, paralysis of the deep branch of the radial nerve can occur; however, function usually returns without treatment.¹¹ High-energy mechanisms with extensive soft-tissue injuries may be associated with acute compartment syndrome.

Treatment

Nondisplaced or minimally displaced (<5 mm) fractures of the ulnar shaft can typically be treated with a long-arm splint (Appendix A–9). Orthopedic referral is recommended.¹⁴

Cadaver studies have confirmed that displacement of the ulna by 50% of its width causes significant disruption of the interosseous membrane.¹⁵ Proximal one-third fractures of the ulna that are displaced are more likely to have associated injury to the ligamentous structures of the radial head.

Referral after immobilization with a long-arm splint (Appendix A–9) is indicated. A 2012 Cochrane Review was unable to distinguish whether better patient outcomes were associated with surgery.¹⁶ Thus, management remains the surgeon’s dilemma. Most orthopedic surgeons prefer open reduction with internal fixation in the management of these fractures, especially if the injury has a high-energy mechanism. Low-energy mechanisms in the elderly might be treated with functional bracing.²

In adults, the extremity should be immobilized in a long-arm posterior splint (Appendix A–9). Surgical reduction and repair is the most common treatment.

In children, emergency management includes immobilization in a posterior long-arm splint (Appendix A–9). Closed reduction of the injury is typically carried out under general anesthesia.

Regardless of the patient’s age, it seems prudent to involve the orthopedic surgeon early in treatment decisions.

Complications

1. Paralysis of the deep branch of the radial nerve, which is usually secondary to a contusion and typically heals without treatment.

2. Nonunion due to an inadequate reduction or immobilization.

3. Delayed discovery leading to poorer patient outcomes.

Combined Radius and Ulna Fractures

Fracture of the radius and ulna, also known as both bone forearm fractures, are most common in children, and account for 45% of all fractures in childhood.¹⁷ Combined forearm fractures also occur in adults, although the management is very different. In adults, nondisplaced fracture of both forearm bones is rare, because a force with enough energy to break both bones typically causes displacement.

The classification of combined radius and ulna fractures is based on displacement and angulation (Fig. 13–12). Plastic deformation and greenstick fractures, incomplete fractures that do not involve both cortices of the bone, are also considered. For further discussion of these fractures in children, the reader is referred to Chapter 6.

Mechanism of Injury

Two mechanisms result in fractures of the forearm shaft. A direct blow, as during a vehicular collision, is the most common mechanism encountered. In children, the most common mechanism is a fall on an outstretched arm.

Examination

Pain, swelling, and loss of function of the hand and forearm are usually encountered. Examination of the elbow and wrist is important to detect possible injury to the proximal or distal ligamentous structures. Deformity of the forearm may be quite obvious (Fig. 13–13). Deficits of the radial, median, and ulnar nerves are uncommonly seen, but must be excluded.

Imaging

AP and lateral views are adequate for defining the fracture fragments (Figs. 13–14 and 13–15). Wrist and elbow views should also be obtained and evaluated for fracture, dislocation, or subluxation. Subtle subluxation of the DRUJ may only be evident on computed tomography (CT). A line drawn through the radial neck and head should pass through the center of the capitellum (radiocapitellar line). If it does not, injury to the proximal radioulnar joint should be suspected.

Associated Injury

Fracture of the radial and ulnar shaft may be associated with injury to the proximal and DRUJs. Neurovascular involvement is uncommon in closed injuries to the forearm. High-energy mechanisms with extensive soft-tissue injuries may be associated with acute compartment syndrome.

Treatment

This is an uncommon injury because a force great enough to break both forearm bones usually causes displacement. Nonetheless, if neither bone is displaced nor angulated, the patient can be treated with AP splints, with the elbow in 90 degrees of flexion and the forearm neutral (Appendix A–10). Definitive management includes a well-molded long-arm cast. Caution: Repeat radiographs are required as delayed displacement is common. Urgent orthopedic follow-up is indicated in all cases.

In adults, closed reduction generally fails to achieve and maintain proper alignment and poor patient outcomes ensue. ED management includes long-arm immobilization and a discussion with the orthopedic surgeon about operative reduction and internal fixation (Fig. 13–16). Open fractures require immediate operative intervention as outlined in Chapter 1.

In children, displaced both bones forearm fractures are usually treated with closed reduction and immobilization. Good results occur in 85% of these patients.¹⁷ The orthopedic surgeon often carries out the reduction and immobilization as there are quite a few nuances of these proceedings. Sedation of the child is common either in the operating room or as procedural sedation in the ED. A method of closed reduction is described in Figure 13–17.

These fractures are a variation of the Monteggia fracture (discussed previously—Bado type 4) and require open reduction and internal fixation.

Acute Plastic Deformation Fracture

This relatively rare injury, usually of the forearm, most frequently occurs in young children because their bones are pliable. It occurs when a longitudinal deforming force begins to cause microfractures without completely breaking the bony cortex.^18,19 The microfractured bone remains permanently curved (bowed) after the deforming force has been removed.

Acute plastic deformation fracture (APDF) may include any combination of: overt fracture of the radius with APDF of the ulna, overt fracture of the ulna with APDF of the radius, or APDF of both bones simultaneously.

Classically, plastic deformation fracture occurs in a young child with a fall on the outstretched hand injury. There is tenderness over the deformity of the obvious fracture and more diffuse tenderness along the plastically deformed bone due to the extensive microfractures of the cortex. Pronation and supination are limited by the curvature.

Lack of a cortical defect and subtle curvature of the long bone makes discovery of this injury difficult. Nevertheless, as the axiom suggests, when there is a displaced fracture of one bone in the forearm one should be looking for its partner. APDF may be the “partner” to an otherwise obviously displaced fracture in the forearm.

Good AP and lateral x-rays help to discover this injury. If there is doubt about how the films should be interpreted, comparison views of the opposite extremity may be helpful (Fig. 13–18).

Complications of this injury are well known. Natural remodeling may not be adequate to correct the deformity in older children. Bowing of a forearm bone causes abnormalities of the interosseous space resulting in problems pronating and supinating the forearm and its consequent poorer patient outcomes. Reduction of the obvious fracture may not be possible without reducing the plastic deformation.

Treatment includes long-arm immobilization with the elbow in 90-degree flexion and forearm in supination as well as an urgent referral to orthopedics. Usually reduction under anesthesia is performed.^18,19

These represent the commonly occurring middle ground between complete bony fracture and plastic deformation of the bone. One cortex is overtly fractured but the other is plastically deformed (Fig. 13–15). Hence, greenstick fractures only occur in the supple bones of children.

They are initially treated with immobilization in a long-arm splint (Appendix A–9). Referral to an orthopedic surgeon is often appropriate. Reduction of a greenstick fracture may be necessary when angulation is more than 15 degrees.

Complications

Combined shaft fractures of the radius and the ulna are associated with numerous complications.

1. Nerve injury is uncommon in closed injuries, but is frequently seen with open fractures. There is an equal frequency of involvement between the radial, ulnar, and median nerves.

2. Vascular compromise is an uncommon complication because of the presence of arterial collaterals.

3. Nonunion or malunion may ensue.

4. Compartment syndromes can occur following combined shaft fractures. It is important to recognize that distal pulses will remain intact despite elevated compartment pressures and compromised capillary flow. The treatment is emergent referral for evaluation and possible fasciotomy.

5. Synostosis (bone fusion) of the radius and ulna may complicate the management of combined shaft fractures.

6. Pronation and supination may be permanently impaired.

Contusions

The tendons of the lower forearm are close to the skin, and traumatic tenosynovitis can occur after a direct blow. The treatment for this condition is simple immobilization. Nonsteroidal anti-inflammatory agents are useful for pain. Contusions of the upper forearm are treated the same as contusions elsewhere.

Strains

The muscles of the forearm are closely interconnected in the same sheath, and a strain of one muscle often causes discomfort with motion of other nearby muscles. This makes it difficult to isolate individual strains. The mechanism of injury is most often overuse. On examination, the patient will demonstrate swelling and inflammation of the tendon and muscle, which is painful to stress and tender to palpation. The treatment consists of ice compresses followed by local heat and immobilization. Nonsteroidal anti-inflammatory agents are also appropriate.

Forearm Compartment Syndromes

Acute compartment syndrome is a condition that results from increased fluid pressure within an enclosed fascial space. The increasing compartmental pressure inhibits blood flow through the venules and the capillary bed resulting in intracompartmental muscle and nerve ischemia. Time dependent (6–12 hours) necrosis may result in muscle dysfunction and contracture.²⁰ The forearm is the most common site for compartment syndrome to develop in the upper extremity.²¹ Because the misdiagnosis or even a delay in diagnosis of this condition may lead to permanent muscle dysfunction and contracture, it is of critical importance that emergency physicians be knowledgeable about this condition.

The forearm has three major compartments. The volar compartment is most commonly affected, but compartment syndrome may develop in the dorsal compartment or the lateral compartment, known as the “mobile wad.” The lateral mobile wad contains the brachioradialis and the extensor carpi radialis longus and brevis.

Forearm compartment syndrome occurs most commonly after fractures. Nevertheless, isolated soft-tissue injuries account for approximately 25% of occurrences.^20,22 Despite the historical association of supracondylar fractures with compartment syndrome (Volkmann contracture), distal radius fractures are consistently the most common cause of the problem in the forearm.^22,23 Other less common causes include iatrogenic events such as CT-contrast infiltration of an intravenous line, improper use of a pneumatic tourniquet, and as a complication of thrombolytics.²⁴

Clinical Presentation

The clinical presentation of compartment syndrome encompasses the following general sequence, and for further information the reader is referred to Chapter 4:

1. Severe pain is the first and most important symptom to occur. The pain is usually out of proportion to the severity of the injury.

2. As compartment pressure rises a palpably tense compartment is the most reliable physical finding.²⁰

3. Increased pain with passive stretch of the enclosed muscles. This is often difficult to distinguish from the underlying pain with movement of the injury.

4. Paresis and paresthesias develop later in the syndrome. By this time, some element of muscle necrosis may have begun.

5. Pulse may be reduced or absent. This is an ominous finding that occurs only after extensive, irreparable damage has been done. (Do not wait for this finding.)

Although the diagnosis of compartment syndrome is a clinical one, measurement of compartment pressures may assist in making the diagnosis. Compartment pressures should be measured in each compartment of the forearm using a Stryker device or the infusion technique.²¹ This technique, as well as a more detailed discussion of compartment syndrome, can be found in Chapter 4.

To measure the volar compartment, the needle is inserted 1.5 cm medial to a vertical line drawn through the middle of the forearm (Fig. 13–19).²⁵ Multiple measurements should be taken as the pressures at different sites within the same compartment may be significantly different. The dorsal compartment is measured 1.5 cm lateral to the posterior aspect of the ulna. The mobile wad is measured by inserting the needle within the muscles lateral to the radius. In each case, the needle is inserted to a depth of approximately 1.5 cm.²⁶

The normal compartment pressure is between 0 and 8 mm Hg. There is a great deal of literature devoted to what is the dangerous intracompartmental pressure. There is some consensus that the difference between the diastolic blood pressure and the compartment pressure is the most important measurement (ΔP) (This represents the capillary bed perfusion pressure).^20,27 Most authors agree that the diagnosis of acute compartment syndrome is made clinically with pressure measurements used to augment the decision making process when necessary. Pressure measurements may be most useful when the patient is unable to give a history, that is, the patient is: on a ventilator, in surgery, a young child, or a host of other possible scenarios. Some recent evidence suggests that continuous intracompartmental pressure monitoring is a tool that the orthopedic surgeons may employ to assist them in evaluating patients with possible or potential acute compartment syndrome.²⁸

Treatment

The extremities should not be elevated but rather placed at heart level to optimize arterial pressure and venous drainage. Patients presenting with compartment syndrome symptoms and wearing a cast may have the symptoms relieved by the simple maneuver of removing or splitting the cast and padding.²⁹ The removal of a constrictive cast and padding can reduce the compartment pressure by 85%.³⁰

If symptoms persist after the removal of constrictive casts or bandages, surgical intervention with fasciotomy is often indicated. Orthopedic consultation should be obtained as soon as this condition is strongly suspected. Timely intervention may prevent irreversible damage to the muscles and nerves of the affected compartment. This is one of the few orthopedic problems where emergency intervention is necessary. Fasciotomy is the intervention of choice.