Dislocations of the Child’s Elbow

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CHAPTER 20 Dislocations of the Child’s Elbow

INTRODUCTION

Dislocation of the elbow in children is the most common childhood dislocation, constituting about 6% to 8% of elbow injuries.72,118 In general, however, because the attachments of ligaments and muscles are stronger than the adjacent growth plate, forces exerted about most joints tend to result in epiphyseal injury rather than simple dislocation of the adjacent joint. The elbow is unique in children because type I and II fractures through the distal humeral epiphysis are uncommon; hence, the finding for dislocation.

The purpose of this chapter is to discuss the practical aspects of the cause, recognition, and the management of dislocations about the elbow joint in children. Because the elbow is the most common joint injured in childhood, the chapter on imaging (see Chapter 12) and chapters dealing with images of other conditions (see Chapters 14 to 18 and Chapter 21) should be carefully studied.

ANATOMIC FACTORS PREDISPOSING TO ELBOW DISLOCATION IN CHILDREN

Although the anatomy of the elbow joint was thoroughly discussed in Chapter 2, it is important to emphasize some of the anatomic differences that are unique to the pediatric elbow joint.

GROWTH PLATES, APOPHYSIS, AND SECONDARY CENTERS OF OSSIFICATION

To a casual observer, the radiograph of a child’s elbow is an enigma—no two ever seem alike. The reason for this, of course, is that because the child is constantly growing, ossification centers are appearing and fusing, and cartilage is calcifying progressively until skeletal maturity is attained.

It is important to emphasize that there is usually a normal contralateral control that can be radiographed and compared with the radiograph of the injured elbow. This is not recommended as a routine practice, but sometimes it is necessary and useful, especially for those who treat elbow injuries in children only occasionally.

In general, the younger the child at the time of injury, the more difficult it is to assess the elbow, owing to the larger percentage of cartilage that is present about the elbow joint. Fortunately, new imaging modalities allow more accurate assessment.7,8 Yet, in the newborn or infant, it may be very difficult to diagnose an elbow injury or to determine whether it is a transcondylar fracture or a dislocation of the elbow (the former being much more common at this age). The ossific nuclei about the elbow joint are helpful in radiologic interpretation of elbow dislocation (see Chapter 12). The capitellum, whose center of ossification should be present by 6 months of age, facilitates the interpretation of radial head alignment, because a line drawn through the radial head should always intersect the capitellum no matter what view is taken (Fig. 20-1). This interpretation is improved even further with the appearance of the radial head secondary center of ossification, at around 5 years of age. The secondary center of ossification of the olecranon, which appears at about 9 years of age, allows a more accurate assessment of the position of the proximal ulna in relation to the distal humerus, an important consideration in the management of dislocations of the elbow in young children.

Both the medial and the lateral apophyses of the distal humerus may be injured in dislocations of the elbow in a child. Although many mnemonics have been devised by residents trying to remember the timing of ossification of the various centers about the elbow, the most important center to remember from a practical standpoint is the medial epicondylar apophysis of the distal humerus. This center is usually present by the age of 5 to 6 years, and because it is frequently entrapped within the joint following a dislocation of the elbow, it should always be searched for and identified after this age. Hence, if the center cannot be identified, it should be assumed that it is within the joint itself. In children younger than the age of 5 years, the diagnosis of entrapment must be clinical or by arthrography, because the apophysis is entirely cartilaginous.

The lateral epicondylar apophysis is injured less frequently. In posteromedial dislocations, it may suffer avulsion, owing to a severe varus strain on the elbow and may need to be repaired or fixed surgically.5

RADIAL HEAD AND NECK

The radial head and neck in children are cartilaginous but have the same relative diameters as the radial head and neck in adults. Dislocation of the radial head, either as an isolated event or in association with a Monteggia fracture, or with dislocation of the elbow joint itself, is facilitated by the resiliency of the cartilaginous component. Children’s bones have plasticity and can be bent like the proverbial greenstick without fracturing. In the type A Monteggia lesion, for instance, it is conceivable that the ulna bends to the point of fracture, whereas the radius only bends to the point at which the radial head slips under the annular ligament and dislocates anteriorly (Fig. 20-2).

It is of interest to note that in most cases requiring open reduction of the radial head, the annular ligament is actually intact. A similar situation may be found with the traumatic isolated dislocation of the radial head that occurs in very young children in which the radius bends just enough for the head and neck to slip under the annular ligament (called nursemaid’s elbow). When trauma is less severe, as in a pulled elbow, the head of the radius has simply slipped into the annular ligament, and there is no actual dislocation. A supination maneuver “screws” the radial head out of the annular ligament, usually with no actual damage to the ligament itself.

This combination of generalized laxity, the large cartilaginous component, the lack of osseous stability, and the presence of osseous plasticity as well as numerous secondary centers of ossification and apophyses all contribute to the anachronism of a greater tendency of dislocation of the pediatric elbow joint than seen with other joints.

TYPES OF DISLOCATION OF THE RADIAL HEAD

CONGENITAL DISLOCATION

Congenital dislocation of the radial head is a controversial lesion, because some maintain this lesion does not exist at all and all such appearances are simply traumatic or developmental dislocations. This subject is discussed in more detail in Chapter 13. Here, I reserve the diagnosis of congenital dislocation for that entity in which congenital malformation of the extremity is obvious (Fig. 20-3). When isolated dislocation of the radial head is not accompanied by other congenital lesions, the congenital basis for the lesion cannot be substantiated. The long-standing nature of the dislocation can be inferred from the marked convexity of the radial head associated with elongation of the radial neck (Fig. 20-4).27,28 Congenital dislocation of the radial head may be associated with radioulnar synostosis, the synostosis almost always occurring between the proximal radius and the ulna.3236

Hypoplasia of the capitellum associated with dislocation of the radial head strongly suggests that the dislocation is congenital. The radiologic appearance of congenital dislocations of the radial head has been emphasized by Miura.37 In congenital dislocations, the posterior border of the ulna is usually concave rather than slightly convex, with the radial head being dome-shaped with no central depression (see Fig. 20-3). Posterior congenital dislocation, which constitutes about 40% of congenital dislocations of the radial head, is associated with an accentuation of the normal convexity of the posterior border of the ulna. In fact, because we have not been able to diagnose this pathology, at best, we consider this a developmental problem.28

DEVELOPMENTAL DISLOCATION

Many instances of developmental or secondary dislocation of the radial head are misinterpreted as being congenital in origin.28 Developmental dislocation is defined as any dislocation of the radial head that results from maldevelopment of the forearm. There are many inherited and acquired disease processes affecting the growth plate of the forearm bones that result in asymmetric growth between the radius and the ulna and subsequent dislocation of the radial head. These include the nail patella syndrome, Silver syndrome, arthrogryposis, Cornelia de Lange syndrome, and cleidocranial dysostosis. Asymmetric growth also occurs in multiple exostoses or diaphyseal aclasis. The ulna is most frequently affected at the distal ulnar growth plate; the radius then overgrows relative to the ulna (Fig. 20-5). Paralysis of the muscles innervated by the C5-6 nerve root, as in a nerve root palsy, also predisposes to a gradual dislocation of the radial head that occurs over a number of years of growth or occasionally in infancy.17 Cerebral palsy also may produce isolated dislocation of the radial head through marked spasticity of the muscles attached to the radius (Fig. 20-6).21 Trauma to the radius or the ulna, resulting in asymmetric growth, may also produce dislocation of the radial head. Fracture of the neck of the radius that has not been corrected adequately may result in the proximal radial epiphysis growing laterally instead of toward the capitellum (Fig. 20-7).2026

A detailed developmental posterior study at the Mayo Clinic describes several grades, or types, of radial head dislocation with characteristic radiographic appearance (Fig. 20-8). Types II and III are complete dislocations and are more obvious cosmetically but have relatively little functional loss except forearm rotation.28 Type I dislocations commonly are associated with late degenerative arthrosis and consist more of a subluxation than a frank dislocation. However, consistent with the definition of forearm maldevelopment, all types have a previous proximal ulnar bow.

There are few indications for operative treatment of developmental dislocation of the radial head. For example, a malunion of the radius and the ulna that is obviously directing the head of the radius laterally, posteriorly, or anteriorly should be corrected with an osteotomy to redirect the proximal radius or the deformed ulna19; otherwise, excision of the radial head can be effective to improve motion, lessen pain, or to improve cosmesis.

In patients with cerebral palsy, if the bicipital tendon appears to be subluxating the radial head anteriorly, lengthening the biceps may prevent future dislocation. Once the dislocation is well established, attempts to relocate the radial head probably should not be made, and the dislocation should be accepted. Future resection of the radial head at skeletal maturity can be performed if the head is cosmetically or functionally a problem. The gradual nature of the dislocation and adjacent changes in the surrounding tissues and bone make this type of relocation of the radial head much more difficult than the acute traumatic injury.26

Relocation of the radial head by shortening the radius and reconstitution of the annular ligament is ineffective.

TREATMENT OF ACUTE ANTERIOR DISLOCATION

OPEN REDUCTION

Triceps Fascial Reconstruction

The technique of open reduction of an anterior dislocation of the radial head in children described by Lloyd-Roberts and Bucknill20 is one I have used with success. This consists of using the lateral portion of the tendon of the triceps for reconstruction of the annular ligament (Fig. 20-9A).

A posterolateral incision is preferred rather than a posterior incision, which may disorient the surgeon to the position of the radial head. The triceps tendon is identified, and a long (10-cm) strip is removed from the lateral margin, ensuring attachment at the distal ulnar insertion. The tendon is increased in length by continuing the dissection through the periosteum to a point opposite the neck of the radius, where it is then passed around the neck and sutured to itself and the ulnar periosteum with enough tension to hold the radial head in place. A Kirschner wire is then passed through the ulna into the radius to ensure solid fixation until the tendon has healed (see Fig. 20-9B).18

The extremity is kept immobilized in an above-elbow plaster cast for 6 weeks; gradual mobilization is begun at 6 weeks after the Kirschner wire has been removed. If there is any difficulty in reducing the radial head, careful inspection of the joint capsule may reveal some infolding or tissue interposition, which may have to be excised.

Specific care must be exercised when exposing the neck of the radius in a child. Unlike the adult, the radial nerve may be only a fingerbreadth below the head of the radius rather than the classic two fingerbreadths that is often referenced.

PEDIATRIC MONTEGGIA FRACTURE DISLOCATION

The Monteggia injury is uncommon in children but by no means rare. In the 5-year period from 1978 to 1982 at the Winnipeg Children’s Hospital, 33 children were treated for a variety of Monteggia lesions. The true incidence of this fracture-dislocation is unknown, but it is more common than is generally appreciated. Olney and Menelaus53 reported 102 children with acute Monteggia lesions over a 25-year period.

ETIOLOGY

The most common cause of dislocation of the radial head associated with an ulnar fracture in childhood is a hyperextension injury,44,62 followed by a hyperpronation injury.45 In hyperpronation, Bado39 pointed out that the bicipital tuberosity is posterior, thus predisposing the proximal radius to the greatest force during violent contraction of the bicipital tendon. In young children, the force generated by the biceps is less than that in the adult, and this mechanism probably is significant only in older children.

A direct blow over the posterior proximal ulna will produce a Monteggia lesion with anterior dislocation of the radial head, but this is an uncommon mechanism in children.

In our experience, this lesion is most frequently produced by a hyperextension injury. Further support for this theory is the observation that, in open type C injuries, the proximal ulnar fragment pierces the skin on the volar ulnar aspect of the forearm. This would not be possible if the arm were in full pronation because of imposition of the radius.

Because of the plasticity of the forearm bones, the radial head and neck may slip under the annular ligament and dislocate as the shaft of the radius bends. Indeed, many of the isolated traumatic dislocations of the radial head are undoubtedly variations of the Monteggia4648 (Monteggia equivalent), in which the ulna has simply bent but not fractured. The radial shaft is bent to the extent that the head and neck are slipped from within the annular ligament, resulting in an apparent isolated dislocation of the radial head.30,43

CLASSIFICATIONS

Classifications of the Monteggia lesion are based largely on the injury in adults39 (see Chapter 27). Because of differences in the configuration of the injury in childhood, the following pediatric classification is suggested to include dislocation of the radial head associated with the plasticity of the forearm bones in childhood (Fig. 20-10).