FIGURE 14-1 Bado classification. A: Type I (anterior dislocation): The radial head is dislocated anteriorly and the ulna has a short oblique or greenstick fracture in the diaphyseal or proximal metaphyseal area. B: Type II (posterior dislocation): The radial head is posteriorly or posterolaterally dislocated; the ulna is usually fractured in the metaphysis in children. C: Type III (lateral dislocation): There is lateral dislocation of the radial head with a greenstick metaphyseal fracture of the ulna. D: Type IV (anterior dislocation with radial shaft fracture): The pattern of injury is the same as with a type I injury, with the inclusion of a radial shaft fracture distal to the level of the ulnar fracture.

Bado Type I

A Bado type I lesion is an anterior dislocation of the radial head associated with an apex anterior ulnar diaphyseal fracture at any level. This is the most common Monteggia lesion in children and represents approximately 70% to 75% of all injuries.^{38,53,81,119,156}

Bado Type II

A Bado type II lesion is a posterior or posterolateral dislocation of the radial head associated with an apex posterior ulnar diaphyseal or metaphyseal fracture. This pattern is the most common Monteggia lesion in adults, but is relatively rare in children.^105,106,119 Type II lesions account for 6% of Monteggia lesions in children,⁷⁷ and are usually found in older patients¹⁰⁵ who have sustained significant trauma.^41,116,117

Bado Type III

A Bado type III lesion is a lateral dislocation of the radial head associated with a varus (apex lateral) fracture of the proximal ulna. This is the second most common pediatric Monteggia lesion.^{13,48,98,103,160} When an injury is characterized by an olecranon fracture and a lateral or anterolateral radiocapitellar dislocation but no radioulnar dissociation, the injury is not a true Monteggia lesion.^63,118,146

Bado Type IV

A Bado type IV lesion is an anterior dislocation of the radial head associated with fractures of both the ulna and the radius. The original description was of a radial fracture at the same level or distal to the ulna fracture. Type IV lesions are relatively rare in children.

Expansion of the Bado Classification: Monteggia Equivalent Lesions

Bado^8,10 classified certain injuries as equivalents to true Monteggia lesions because of their similar mechanisms of injury, radiographic appearance, or treatment methods. Since his original publication, the list of equivalent lesions has expanded case report by case report.

Type I Equivalents

Bado type I equivalents (Fig. 14-2) include isolated anterior dislocations of the radial head without ulnar fracture. This subclassification includes a “pulled elbow” or “nursemaid’s elbow” because the mechanism of longitudinal traction, pronation, and hyperextension is similar to a true type I lesion. In nursemaid’s elbow cases, the radiographs are normal. In type I equivalent lesions, the radial head is malaligned in its relationship to the capitellum and proximal ulna. However, the ulnar bow sign (Fig. 14-3) is normal as opposed to subtle plastic deformation of the ulna which will have a concave ulnar bow and can be misdiagnosed as a type I equivalent when the injury is really a Bado I lesion. This distinction can be critical in terms of operative decision making in that the type I equivalent lesion requires only open repair of the displaced ligament while the Bado type I lesion with plastic deformation requires correction of the ulnar deformity. Other type I equivalents (Fig. 14-2) include anterior dislocation of the radial head with ulnar metaphyseal or diaphyseal fracture and radial neck fracture; anterior dislocation of the radial head with radial diaphyseal fracture more proximal to ulnar diaphyseal fracture; anterior radial head dislocation with ulnotrochlear dislocation (Fig. 14-4)¹¹⁹; and anterior dislocation of the radial head with segmental ulna fracture.^{2,53,63,110,123,146} More case reports will probably expand this subclassification over time. The type I equivalents have been shown to have poorer outcomes and require more frequent operative intervention than true Monteggia lesions.^53,98 Poor outcomes may relate to intra-articular injury, coronoid fracture, comminution of the ulna fracture, and comminution of the radial head fracture.¹²⁶

Type II Equivalents

Bado^8,10 described type II equivalents to include posterior radial head dislocations associated with fractures of the proximal radial epiphysis or radial neck.

Type III and Type IV Equivalents

Bado^8,10 did not have equivalent lesions for the true type III and type IV lesions. Because mechanism of injury allows for this subclassification, case reports have emerged over time to include fractures of the distal humerus (supracondylar, lateral condylar) in association with proximal forearm fractures (Fig. 14-5).^{5,16,17,36,46,51,53,54,86,95,110,115,120,123,129}

Letts Classification

Letts et al.⁸¹ have described an alternate classification schedule for pediatric Monteggia fracture-dislocations based both on direction of radial head dislocation and the type of ulnar fracture (Fig. 14-6). Letts types A, B, and C are analogous to Bado type I lesions and are characterized by anterior dislocation of the radial head with an associated ulnar fracture. In a type A lesion there is plastic deformation of the ulna; in a type B lesion there is an incomplete or greenstick ulnar fracture, and in a type C lesion there is a complete ulnar fracture. Letts type D lesions are equivalent to Bado type II injuries and are characterized by posterior radial head dislocation. Letts type E lesions are equivalent to Bado type III injuries and are characterized by lateral radial head dislocation.

AUTHOR’S PREFERRED CLASSIFICATION

Mechanisms of Injury for Monteggia-Fracture Dislocations

Type I Mechanism of Injury

Three separate mechanisms of type I lesions have been described: direct trauma,^{10,22,27,42,96,113,116,131,151} hyperpronation, and hyperextension.^22,116

Direct Blow Theory

The first theory proposed in English literature was the direct blow mechanism described by Speed and Boyd¹³¹ and endorsed by Smith (Fig. 14-7).¹²⁷ This theory was actually proposed by Monteggia,⁹¹ who noted that the fracture occurs when a direct blow on the posterior aspect of the forearm first produces a fracture through the ulna. Then, either by continued deformation or direct pressure, the radial head is forced anteriorly with respect to the capitellum, causing the radial head to dislocate. Monteggia⁹¹ explained that these injuries sometimes resulted from a blow by a staff or cudgel on the forearm raised to protect the head.

The parry fracture, another term for the Monteggia fracture-dislocation, has been mentioned in the literature. During the American Civil War, Monteggia fractures were frequent because of direct blows on the forearm received while attempting to parry the butt of a rifle during hand-to-hand combat. The major argument against this theory as the mechanism is that in the usual clinical situation, there rarely is evidence of a direct blow to the posterior aspect of the forearm, such as a contusion or laceration.^42,151

Hyperpronation Theory

In 1949, Evans⁴² published his observations regarding anterior Monteggia fracture-dislocations. Previous investigators had based their direct blow theory on hypothesis and clinical observation, but Evans used cadaveric investigation to support his hyperpronation theory. He demonstrated that hyperpronation of the forearm produced a fracture of the ulna with a subsequent dislocation of the radial head. He postulated that during a fall, the outstretched hand, initially in pronation, is forced into further pronation as the body twists above the planted hand and forearm (Fig. 14-8). This hyperpronation forcibly rotates the radius over the middle of the ulna, resulting in either anterior dislocation of the radial head or fracture of the proximal third of the radius, along with fracture of the ulna. In actual patients reported on by Evans, the ulnar fractures demonstrated a pattern consistent with anterior tension and shear or longitudinal compression. His cadaveric investigation, however, showed the ulnar fracture pattern to be consistent with a spiral or rotational force. The hyperpronation theory was also supported by Bado.⁹

Two arguments have been used to dispute the hyperpronation mechanism.¹⁵¹ First, the ulnar fracture rarely presents clinically in a spiral pattern; it is often oblique, indicating an initial force in tension with propagation in shear rather than rotational. Second, the Evans experiments, which were performed on totally dissected forearms,⁴² did not take into consideration the dynamic muscle forces at play during a fall on an outstretched hand.

Hyperextension Theory

In 1971, Tompkins¹⁵¹ analyzed both theories and presented good clinical evidence that type I Monteggia fracture-dislocations were caused by a combination of dynamic and static forces. His study postulated three steps in the fracture mechanism: Hyperextension, radial head dislocation, and ulnar fracture (Fig. 14-9). The patient falls on an outstretched arm with forward momentum, forcing the elbow joint into hyperextension. The radius is first dislocated anteriorly by the violent reflexive contracture of the biceps, forcing the radius away from the capitellum. Once the proximal radius dislocates, the weight of the body is transferred to the ulna. Because the radius is usually the main load-bearing bone in the forearm, the ulna cannot handle the transmitted longitudinal force and, subsequently, fails in tension. This tension force produces an oblique fracture line or a greenstick fracture in the ulnar diaphysis or at the diaphyseal–metaphyseal junction. In addition to the momentum of the injury, the anterior angulation of the ulna results from the pull of the intact interosseous membrane on the distal fragment, causing it to follow the radius. The brachialis muscle causes the proximal ulnar fragment to flex.

Summary of Type I Mechanism of Injury

The type I lesion can probably be caused by any of the three proposed mechanisms, but the most common mechanism is a fall on an outstretched hand that forces the elbow into complete extension, locking the olecranon into the humerus. The forearm is in a rotational position of neutral to midpronation. As the proximal ulna locks into the distal humerus, the bending force stresses the proximal radioulnar joint. Because of the relatively pronated position of the joint, the ligamentous restraints are lax, providing only tenuous stability for the radial head. The anterior bending force, combined with a reflexive contraction of the biceps, violently dislocates the radial head anteriorly. The radioulnar joint and its ligamentous complex are at risk because of the ligamentous laxity and the decreased contact area between the proximal radius and ulna created by the rotation of the forearm. At midrotation, the short axis of the elliptical radial head is perpendicular to the ulna, causing the annular ligament and the dense anterior portion of the quadrate ligament to be relaxed. The contact area of the proximal radioulnar joint, because of the shape of the radial head, is also decreased, further reducing the stability of the joint. The ulna, now the main weight-bearing structure of the forearm, is loaded by a continued bending moment, causing tension on the anterior cortex and producing failure. The force at the site of failure is propagated in shear at approximately 45 degrees to the long axis of the ulna. This mechanism may produce plastic deformation with an anterior bow, a greenstick fracture, or an oblique fracture pattern, all of which are observed clinically. As the anterior bending movement continues, the vector of the biceps changes and acts as a tether and resists any further advance of the proximal radius. The distal fragment of the ulna continues to advance, acting as a fulcrum against the radial shaft. The anteriorly directed force of the distal ulnar fragment, combined with the retrograde resistance of the biceps, may create a fracture of the radius, or a type IV lesion.

Type II Mechanism of Injury for Monteggia-Fracture Dislocations

The cause of the type II Monteggia lesion is subject to debate. Bado¹⁰ thought the lesion was caused by direct force and sudden supination. Penrose¹⁰⁸ analyzed seven fractures in adults and noted that a proximal ulnar fracture was the typical pattern. He postulated that the injury occurred by longitudinal loading rather than by direct trauma.¹³¹ Olney and Menelaus⁹⁸ reported four type II lesions in their series of pediatric Monteggia fractures. Three of these patients had proximal ulnar fractures and one had an oblique midshaft fracture, suggesting two different mechanisms of injury.

The mechanism proposed and experimentally demonstrated by Penrose¹⁰⁸ was that type II lesions occur when the forearm is suddenly loaded in a longitudinal direction with the elbow in approximately 60 degrees of flexion. This investigation demonstrated that a type II lesion occurred consistently if the ulna fractured; otherwise, a posterior elbow dislocation was produced (Fig. 14-10). The difference in bone strength of the ulna may explain the reason for the high incidence of type II Monteggia lesions in older adults and their rarity in children. Penrose¹⁰⁸ further noted that the rotational position of the forearm did not seem to affect the type of fracture produced.

Haddad et al.⁵⁸ described type II injuries caused by low-velocity injuries in six adults, five of whom were on long-term corticosteroid therapy. They suggested that this supports the theory that the type II Monteggia injury is a variant of posterior elbow dislocation, in that it occurs when the ulna is weaker than the ligaments surrounding the elbow joint, resulting in an ulnar fracture before the ligament disruption required for dislocation.

Type III Mechanism of Injury for Monteggia-Fracture Dislocations

Wright¹⁶³ studied fractures of the proximal ulna with lateral and anterolateral dislocations of the radial head and concluded that the mechanism of injury was varus stress at the level of the elbow, in combination with an outstretched hand planted firmly against a fixed surface (Fig. 14-11). This usually produces a greenstick ulnar fracture with tension failure radially and compression medially. The radial head dislocates laterally, rupturing the annular ligament. Hume⁶³ suggested that type III lesions may be the result of hyperextension of the elbow combined with pronation of the forearm. Other authors confirmed the mechanism of varus force at the elbow as the cause of type III injuries.^{10,38,93,106,146} The direction of the radial head dislocation is probably determined by the rotational and angular force applied simultaneously to the varus moment at the elbow.⁹³

Type IV Mechanism of Injury for Monteggia-Fracture Dislocations

Bado⁸ proposed that a type IV lesion is caused by hyperpronation. Of the case reports discussing the mechanism of injury, both hyperpronation⁴⁸ and a direct blow¹²⁰ have been postulated. Olney and Menelaus⁹⁸ reported a single type IV lesion in their series but did not discuss the mechanism. Type IV lesions appear to be caused by the mechanism described for type I lesions.

Associated Injuries with Monteggia Fracture-Dislocations

Monteggia lesions have been associated with fractures of the wrist and the distal forearm,¹⁰ including distal radial and ulnar metaphyseal and diaphyseal fractures.^10,64,66,120 Galeazzi fractures may also occur with Monteggia lesions.^10,27,28,80 Radial head and neck fractures are commonly associated with type II fractures^10,77 but may occur with other types.^1,45,49,141 With a type II lesion, the radial head fracture is usually at the anterior rim.^41,105 Strong et al.¹⁴⁰ reported two type I equivalent lesions consisting of a fractured radial neck and midshaft ulnar fracture. This injury pattern is notable because of significant medial displacement of the distal radial fragment. Obtaining and maintaining reduction of the radius proved difficult with a closed technique.

Fractures of the distal humerus lateral condyle have also been associated with Monteggia fractures.^31,106 Ravessoud¹¹⁵ reported an ipsilateral ulnar shaft lesion and a lateral condylar fracture without loss of the radiocapitellar relation, suggesting a type II equivalent (Fig. 14-5). Kloen et al.⁷² reported a bilateral Monteggia fracture-dislocation and described the operative technique for its treatment. Despite surgical and rehabilitative challenges, excellent results were obtained in both elbows. In essence, any fracture about the elbow and forearm should be inspected for an associated Monteggia lesion.

Signs and Symptoms of Monteggia Fracture-Dislocations

Type I Clinical Findings

Bado,^8,10 in his original description, provided an accurate clinical picture of Monteggia fracture-dislocations. In general, there is fusiform swelling about the elbow. The child has significant pain and has limitations in elbow flexion and extension as well as forearm pronation and supination. Usually, an angular change in the forearm itself is evident, with the apex shifted anteriorly and mild valgus apparent. There may be tenting of the skin or an area of ecchymosis on the volar aspect of the forearm. It is imperative to check for an open fracture wound. The child may not be able to extend the fingers at the metacarpophalangeal joints or retropulse the thumb secondary to a posterior interosseous nerve palsy. Later, as the swelling subsides, anterior fullness may remain in the cubital fossa for the typical type I lesion. However, this finding may be subtle because children will usually have an elbow flexion posture following injury. If the injury is seen late, there will be a loss of full flexion at the elbow and a palpable anterior dislocation of the radial head. The radial head–distal humerus impingement that occurs may be a source of pain with activities. There is usually loss of forearm rotation with late presentation. Progressive valgus may occur if the anterior radial head dislocation worsens.

Type II Clinical Findings

Similar to type I lesions, the elbow region is swollen but exhibits posterior angulation of the proximal forearm and a marked prominence in the area posterolateral to the normal location of the radial head. The entire upper extremity should be examined because of the frequency of associated injuries.^74,105

Type III Clinical Findings

Lateral swelling, varus deformity of the elbow, and significant limitation of motion (especially supination) are the hallmarks of type III Monteggia fracture-dislocations. Again, these signs can be subtle and missed by harried clinicians. Injuries to the radial nerve, particularly the posterior interosseous branch, occur more frequently with type III lesions than other Monteggia fracture-dislocations.^13,119,134

Type IV Clinical Findings

The appearance of the limb with a type IV lesion is similar to that of a type I lesion. However, more swelling and pain can be present because of the magnitude of force required to create this complex injury. Particular attention should be given to the neurovascular status of the limb, anticipating the possible increased risk for a compartment syndrome.

Clinical Findings in Monteggia Equivalents and Associated Injuries

In a Monteggia equivalent injury, clinical findings are similar to those for the corresponding Bado lesion, with the common triad of pain, swelling, and deformity. Given the frequency of associated skeletal injuries, a careful examination of the entire upper extremity should be performed. This involves careful inspection of the skin and palpation of the distal humerus lateral condyle, the distal radius, and the distal radioulnar joint. Given the high frequency of radial nerve injuries with Monteggia fracture-dislocations,^{13,14,63,96,119,127,134} a careful examination of neurologic examination should be performed. Because the posterior interosseous branch is most commonly injured, the clinician should routinely examine motor function of the extensor digitorum comminus and the extensor pollicis longus. Failure to extend the fingers at the metacarpophalangeal joints or retropulse the thumb are concerning for a posterior interosseous nerve palsy.

Imaging and Other Diagnostic Studies for Monteggia-Fracture Dislocations

The standard evaluation of a Monteggia fracture-dislocation includes anteroposterior (AP) and lateral radiographs of the forearm and elbow. Any disruption of the ulna, including subtle changes in ulnar bowing, should alert the clinician to look for disruption of the proximal radioulnar joint.^{30,32,68,70,83} Unfortunately, the dislocated radial head is all too often missed in the acute setting. It must be stressed that every forearm and elbow injury requires close scrutiny of the radial head–capitellar relationship. In cases where plain radiographs are concerning but equivocal, fluoroscopic imaging or cross-sectional imaging such as magnetic resonance imaging (MRI) or ultrasound scan should be strongly considered. The goal for every radiologist, orthopedist, and emergency department physician should be to never miss a Monteggia lesion in the acute setting.

Type I Radiographic Evaluation

The radiographic alignment of the radial head and capitellum is particularly important and is best defined by a true lateral view of the elbow. In a type I Monteggia fracture-dislocation, the radiocapitellar relationship may appear normal on an AP radiograph despite obvious disruption on the lateral view (Fig. 14-12). If there is any doubt regarding the radiocapitellar alignment, further radiographic evaluation must be obtained. Smith¹²⁷ and later Storen¹³⁸ noted that a line drawn through the center of the radial neck and head should extend directly through the center of the capitellum. This alignment should remain intact regardless of the degree of flexion or extension of the elbow (Fig. 14-13). In some instances, there is disruption of the radiocapitellar line in a normal elbow. Miles and Finlay⁹⁰ pointed out that the radiocapitellar line passes through the center of the capitellum only on a true lateral projection. They reported five patients in whom the elbow was clinically normal but the radiocapitellar line appeared disrupted. In analyzing the radiographs, they found that the radiographic projection of the elbow was usually an oblique view or that the forearm was pronated in the radiograph. If this disruption appears on radiographs in a child with an acute injury, however, it is the treating surgeon’s responsibility to ensure that it is an insignificant finding.

As John Hall often said, “Monteggia lesions are not like throwing horse shoes; being close does not count.” It is still too frequent an occurrence that a highly qualified, distraught, orthopedic surgeon will call for referral of a chronic Monteggia lesion that was missed acutely. With late presentation of a chronic Monteggia injury, an MRI scan may be useful to determine the congruency of the radial head and capitellum. If the radial head is no longer centrally concave or the capitellum is no longer symmetrically convex, surgical reduction may fail to improve pain or restore motion.

Type II Radiographic Evaluation

Standard AP and lateral radiographs of the forearm demonstrate the pertinent features for classifying type II Monteggia fracture-dislocations. The typical findings include a proximal metaphyseal fracture of the ulna, with possible extension into the olecranon (Fig. 14-14).^41,98,147 Oblique diaphyseal ulnar fractures can also result in a type II Monteggia lesion.^8,41,98 The radial head is dislocated posteriorly or posterolaterally¹⁰ and should be carefully examined for other injuries. Accompanying fractures of the anterior margin of the radial head have been noted.^41,105 Initially, these rim fractures are subtle in children but can lead to progressive subluxation and make late reconstruction difficult. Cross-sectional imaging, such as an MRI or ultrasound scan, should be obtained if further characterization of the injury pattern is deemed warranted.

Type III Radiographic Evaluation

In type III lesions, the radial head is displaced laterally or anterolaterally,^104,106 which is best visualized on the AP radiograph (Fig. 14-15). The ulnar fracture often is in the metaphyseal region,^{10,13,63,69,92,119,163} but it can also occur more distally.^10,11,47,162 Varus deformity is common to all ulna fractures, regardless of the level. Radiographs of the entire forearm should be obtained because of the association of distal radial and ulnar fractures with this complex elbow injury.¹⁴⁷ As with all Monteggia injuries, the acute lesion can be missed if proper radiographs are not obtained and careful evaluation of the studies is not performed.

Type IV Radiographic Evaluation

In a type IV Monteggia fracture-dislocation, the anterior radial head dislocation is similar to that in a type I lesion (Fig. 14-16). The radial and ulnar fractures generally are in the middle third of the shaft,³⁹ with the radial fracture typically distal to the ulnar fracture. The fractures may be incomplete or complete. Although this injury pattern is uncommon in adults and rare in children, the radiocapitellar joint should be examined in all midshaft forearm fractures to avoid missing the proximal radioulnar joint disruption (Fig. 14-17). Failure to recognize the radial head dislocation is the major complication of this fracture.¹²

Radiographic Evaluation of Monteggia Equivalents

As with the true Bado types, careful radiographic study should be made with at least two orthogonal views of the elbow in addition to standard views of the forearm. Special views such as obliques should be obtained to clearly delineate the associated injuries (e.g., radial head or neck fracture, distal humerus lateral condyle fracture) and allow adequate pretreatment planning. Cross-sectional imaging, such as an MRI or ultrasound scan, should be obtained as needed if further characterization of the injury is required.

Traumatic Versus Congenital Dislocation

Distinguishing between traumatic and congenital radial head dislocations can be challenging. When radiocapitellar alignment is disrupted radiographically, evaluation of the shape of the radial head and capitellum can help determine the cause of the disruption, especially if there is no history of trauma or the significance of the trauma is questioned. The presence of a hypoplastic capitellum and a convex deformed radial head suggests a congenital etiology (Fig. 14-18).⁸⁷ True congenital radial head dislocations are usually (but not always) posterior, may be bilateral, and can be associated with various syndromes such as Ehlers–Danlos and nail–patella.^3,84 To avoid missing the diagnosis of an acute Monteggia fracture-dislocation, all anterior radial head dislocations should be at least suspected of having a traumatic origin.^3,26,84

Outcome Measures for Monteggia-Fracture Dislocations

To assess recovery and patient outcome following closed or open treatment of Monteggia lesions, the clinician should carefully measure union rate, time to union, pain, patient satisfaction, elbow flexion and extension, and forearm rotation. Common treatment complications must be accurately recorded, especially because acute Monteggia injuries continue to be missed or inadequately treated, resulting in the development of chronic Monteggia lesions. An improved understanding of return to sports and functional outcomes is critical. The disabilities of the arm, shoulder, and hand (DASH) score can be used to measure the disability following Monteggia fracture-dislocations, but has not been validated in children. Joint-specific outcome measures have been developed for the elbow, but many of these measures would benefit from further research into their validity, reliability, and applicability in children.¹²⁸ For pediatric patients, the pediatric outcomes data collection instrument (PODCI) offers a validated tool, but its upper limb disability measurement is broad and not joint or disease specific. The development and validation of pediatric upper limb outcome measures is needed.

PATHOANATOMY AND APPLIED ANATOMY RELATING TO MONTEGGIA FRACTURE-DISLOCATIONS

Understanding the anatomy of the proximal radioulnar joint, radiocapitellar joint, and proximal forearm is critical to understanding the treatment of acute and chronic Monteggia lesions. The bony architecture, joint contour, and periarticular ligaments provide stability to the proximal forearm and elbow. The muscle insertions and origins affect stability and determine surgical exposure along with the neighboring neurovascular structures.

Ligaments

Annular Ligament

The annular (or orbicular) ligament (Fig. 14-19) is one of the prime stabilizers of the proximal radioulnar joint during forearm rotation. The annular ligament encircles the radial neck from its origin and insertion on the proximal ulna. Because of the shape of the radial head, the annular ligament tightens in supination. The annular ligament is confluent with the remainder of the lateral collateral ligamentous complex which provides stability to the radiocapitellar and proximal radioulnar joints and resists varus stress. Displacement of the annular ligament occurs in a Monteggia lesion.¹⁴⁴

Quadrate Ligament

The quadrate ligament^35,67,153 is just distal to the annular ligament and connects the proximal radius and ulna (Fig. 14-19). It has a dense anterior portion, thinner posterior portion, and even thinner central portion. The quadrate ligament also provides stability to the proximal radioulnar joint during forearm rotation. The anterior and posterior borders become taut at the extremes of supination and pronation, respectively.

Oblique Cord

The oblique cord (Fig. 14-20), also known as the Weitbrecht ligament, extends at a 45-degree angle from the ulna proximally to the radius distally and is present in approximately 53% of forearms.¹⁵² The oblique cord originates just distal to the radial notch of the ulna and inserts just distal to the bicipital tuberosity of the radius. With supination, the oblique cord tightens and may provide a marginal increase in stability to the proximal radioulnar joint. The clinical relevance of this structure is uncertain.

Interosseous Ligament

The interosseous ligament (Fig. 14-20) is distal to the oblique ligament with its primary fibers running in the opposite direction (from radius proximally to ulna distally) to the oblique cord. However, similar to the oblique cord, it tightens in supination and provides further stability to the proximal radioulnar joint. The central band of the interosseous ligament is the stiffest stabilizing structure of the forearm.¹⁵⁹

Bony Architecture

The bony architecture of the elbow creates a relatively constrained hinge. The concave surface of the radial head matches the convex surface of the capitellum and provides stability to the radiocapitellar joint. In contrast, the bony geometry of the proximal radioulnar joint provides minimal inherent stability.

Radius

The shape of the radial head is generally elliptical in cross section (Fig. 14-21).²⁵ In supination, the long axis of the ellipse is perpendicular to the proximal ulna, causing the annular ligament and the anterior portion of the quadrate ligament to tighten and stabilize the proximal radioulnar joint. In addition, the contact area between the radius and the radial notch of the ulna increases in supination because of the broadened surface of the elliptical radial head proximal to distal in that position. This may provide some additional stability.

The radius “radiates” around the ulna. For this reason, the radius must have an anatomic bow to achieve full forearm rotation while maintaining stability at the proximal and distal radioulnar joints (Fig. 14-21). With the radius in supination, the bow tightens the oblique cord and interosseous ligament, thereby increasing stability of the proximal radioulnar joint.

Musculature

Biceps Brachii

The biceps brachii inserts into the bicipital tuberosity of the radius and acts as both flexor of the elbow and supinator of the forearm. The biceps acts as a deforming force in anterior Monteggia fracture-dislocations, pulling the radius anteriorly as the elbow is forcibly extended (Fig. 14-9).¹⁵¹ During treatment of type I and type IV lesions, care is taken to maintain the elbow in flexion to prevent recurrent anterior subluxation of the radial head while the soft tissues heal.

Anconeus

The anconeus may act as a dynamic stabilizer of the elbow joint by providing a valgus moment at the joint during extension and pronation.^11,151 It may also act as a deforming force, along with the forearm flexors, on complete fractures of the ulna in a Monteggia lesion. Surgical exposure of the proximal radioulnar and radiocapitellar joints is usually performed through the anconeus–extensor carpi ulnaris interval.

Nerves

Posterior Interosseous Branch of the Radial Nerve

The radial nerve (Fig. 14-22) passes the distal humerus in the brachialis–brachioradialis interval. As the nerve descends into the forearm, it divides into the superficial radial sensory branch and the posterior interosseous motor branch. The posterior interosseous nerve passes under the Arcade of Frohse (Fig. 14-22) and between the two heads of the supinator, when present, or beneath the supinator when there is only one head. The nerve’s close proximity to the radial head and neck makes it susceptible to injury with Monteggia fracture-dislocations.⁷⁰ Injuries to the posterior interosseous nerve occur more frequently with type III lesions than other types of Monteggia fracture-dislocations.^13,119,134 In chronic Monteggia lesions, the posterior interosseous nerve can be adherent to the dislocated radial head or, less commonly, entrapped in the radiocapitellar joint.¹²¹ Care must be taken to avoid injury to the radial nerve in surgical reconstructions of the chronic anterior dislocation.

Ulnar Nerve

The ulnar nerve passes posterior to the medial intermuscular septum of the arm, through the cubital tunnel behind the medial epicondyle of the distal humerus, and then between both heads of the flexor carpi ulnaris into the forearm. The ulnar nerve is at risk for injury with type II Monteggia lesions because of the stretch associated with varus deformity and also with ulnar lengthening in chronic Monteggia reconstructions.

GENERAL TREATMENT PRINCIPLES FOR MONTEGGIA-FRACTURE DISLOCATIONS

Although most treatment algorithms for Monteggia fracture-dislocations are based on the Bado classification, Ring and Waters¹¹⁹ recommended that treatment choices be based on the type of ulnar fracture rather than on the Bado type. They recommended plastic deformation of the ulna be treated with closed reduction of the ulnar bow to obtain stable reduction of the radiocapitellar joint. Incomplete (greenstick or buckle) fractures of the ulna are similarly treated with closed reduction and casting. In children, most type I Monteggia injuries with plastic deformation of the ulna or incomplete ulnar fractures are stable when immobilized in 100 to 110 degrees of elbow flexion and full forearm supination.

However, any Monteggia lesion with a complete fracture of the ulna can be unstable after closed reduction. Therefore, with complete transverse or short oblique ulnar fractures or Monteggia lesions associated with a radial fracture (type IV lesions), intramedullary fixation is recommended. Long oblique or comminuted ulnar fractures, which can develop shortening and malalignment even with intramedullary fixation, are best stabilized with plate and screw fixation. Using this treatment protocol, Ring and Waters¹¹⁹ reported excellent results in all 28 patients treated within 24 hours of injury.

As noted, successful treatment is dependent on three goals: Anatomical correction of the ulnar deformity, achieving a stable congruent reduction of the radiocapitellar joint, and maintenance of ulnar length and fracture stability. For plastic deformation and incomplete fractures, these goals can usually be achieved with closed reduction and cast immobilization. For complete fractures, fracture instability after closed reduction may lead to loss of anatomic ulnar length and redislocation of the radial head. These injuries are generally treated with internal fixation.

TREATMENT OPTIONS FOR TYPE I MONTEGGIA-FRACTURE DISLOCATIONS

Nonoperative Treatment of Type I Monteggia Fracture-Dislocations

Indications/Contraindications

Closed reduction and cast immobilization is recommended as an initial treatment strategy for all type I Monteggia fracture-dislocations in which the ulna is plastically deformed or there is an incomplete fracture (greenstick or buckle). Operative intervention is recommended if there is a failure to obtain and maintain ulnar fracture reduction or a failure to obtain and maintain a congruent reduction of the radiocapitellar joint. In patients with complete transverse or oblique fractures of the ulna, closed reduction alone risks loss of reduction in a cast and development of a chronic Monteggia lesion. In these fractures, operative intervention is recommended to facilitate maintenance of ulnar alignment and the radiocapitellar reduction (Table 14-2).

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