Upper Extremity Injuries in Children

Prevalence, Epidemiology, and Definitions

Patterns of injury in children are different from those of adults, partly because of the unique structure of the pediatric skeleton. Injuries of the upper extremity account for 65% of all fractures and dislocations in children and often are the result of a fall on an outstretched hand. The distal radius, the supracondylar elbow, and the clavicle are among the most common sites of upper extremity injury. In this chapter, the most common patterns of injury in the upper extremity are discussed.

Anatomy

During development, the skeleton changes in length, width, shape, alignment, and rotation. Enchondral ossification is the process of continuous replacement of cartilaginous tissue by osseous tissue and represents the primary mechanism of longitudinal growth. This process is centered at the growth plates interposed between the metaphysis and epiphysis. There is a separate spherical growth plate in the epiphysis surrounding the secondary ossification center. With maturation, the secondary ossification center assumes a more hemispheric shape and, in time, directly apposes the physis. Radial growth of the diaphysis and portions of the metaphysis occurs by intramembranous ossification . This process involves direct formation of cortical bone by osteoblasts.

The physis is divided into zones based on cell histology and function. The germinal zone is the area adjacent to the epiphysis and consists of poorly organized chondrocytes that serve as the stem cells for the growing physis. The proliferative zone contains flattened chondrocytes that are rapidly dividing. The chondrocytes enlarge, vacuolate, and undergo apoptosis in the hypertrophic zone. The zone of provisional calcification is the portion of the hypertrophic zone that is adjacent to the metaphysis and is the site of transition between cartilage and bone. The shape of the physis changes during development so that fracture patterns differ with age. For example, the initial discoid shape of the physis of the proximal femur and humerus becomes highly contoured. Fractures that propagate directly through the physis without a metaphyseal component become less common as children mature.

The physis has a dual blood supply. The epiphysis, germinal matrix, and upper proliferative zones are supplied by the epiphyseal artery. The metaphysis receives blood supply from the nutrient artery centrally and the metaphyseal arteries peripherally. The metaphyseal blood supply extends into the lowermost portions of the hypertrophic chondrocytes, which are responsible for synthesizing bone matrix. The perichondrium and peripheral physis also receive contributions from the perichondrial artery. The central portion of the physis remains relatively avascular and is particularly prone to ischemic injury. There are connections between the epiphyseal and metaphyseal vessels that involute within the first year of life. After this stage, transphyseal vascular communication occurs physiologically at the time of physeal closure only.

The periosteum plays a unique role in osseous injury. It is thicker than that in adults and is less often disrupted in trauma, contributing to more stable fractures in children. Subperiosteal collections are common in children because the periosteum is loosely adherent to the bone throughout most of its length. However, at the physis, the periosteum is continuous with the perichondrium, which is a firm point of attachment. The perichondrium attachment is a barrier to the spread of subperiosteal disease. The periosteum also plays an important role in new bone formation, contributing to the rapid healing of children's fractures.

Joint development in the upper limb involves a predictable pattern of appearance and fusion of the secondary ossification centers. Ossification centers usually appear and fuse with the metaphysis earlier in girls than in boys.

The clavicle is the first bone in the body to ossify, with intramembranous ossification occurring at two sites in the central portion of the bone at around 5 weeks' gestation. Most of the longitudinal growth of the clavicle during childhood and adolescence occurs at the medial physis. Ossification of the medial epiphysis usually occurs between 12 and 19 years of age, and fusion usually takes place by the mid-twenties or later. The lateral ossification center is often not observed because it ossifies and subsequently fuses in a relatively short period at the end of the second decade of life.

At the medial end of the clavicle, the diarthrodial articulation with the sternum allows a wide range of motion, including elevation, anterior and posterior translation, and rotation. There is osseous incongruity with limited contact between the medial clavicle and superior sternum while there is strong ligamentous support from the costoclavicular, interclavicular, and capsular ligaments. The anterior and posterior capsular ligaments attach primarily to the medial epiphysis, in part, explaining why medial physeal injuries are more common than true sternoclavicular separations in children. The acromioclavicular joint is also a diarthrodial joint. It allows several degrees of movement in anteroposterior and superoinferior planes and allows synchronous clavicular-scapular rotation. As in adults, the strong acromioclavicular and coracoclavicular ligaments provide joint stability. The coracoclavicular ligamentous attachment at the distal clavicle is stronger than the periosteum, predisposing children and adolescents to distal clavicular physeal injuries as opposed to true acromioclavicular separation.

The scapula begins as a cartilaginous anlage during the fifth week of gestation, originating at the mid-cervical level. It descends to the upper thoracic levels during subsequent development of the shoulder joint, with failure of appropriate descent resulting in a Sprengel deformity. The scapula begins to ossify by the eighth week of gestation. The primary ossific nucleus is completely ossified at birth. Additional ossification centers are later evident at the coracoid, glenoid, acromion, and inferior margin of the scapula and should not be mistaken for avulsion injuries. Acromial ossification centers appear at puberty and usually fuse by ages 22 to 25 years. Failure of fusion results in an os acromiale.

Development of the glenohumeral joint is complete at approximately 40 weeks' gestation. Mahasen and Sadek demonstrated that the 40-week fetus and adult share comparable glenohumeral joint structure and morphology.

The primary ossification for the humerus appears at approximately the sixth week of fetal life. The ossified humeral diaphysis and proximal and distal metaphyses are present at birth. An ossified proximal humeral epiphysis is seen in approximately 20% of full-term newborns ( eFig. 38-1 ) and is normally present in the remainder by 6 months. A greater tuberosity ossification is usually evident between 7 months and 3 years of age. The lesser tuberosity ossification is usually evident approximately 2 years after appearance of the greater tuberosity. Between 5 and 7 years of age, the humeral head, lesser tuberosity, and greater tuberosity merge. The proximal humeral physis accounts for nearly 80% of the growth of the humerus. The proximal humeral physis remains open until ages 14 to 17 years in girls and ages 16 to 18 years in boys. The normal proximal humeral physis should not be mistaken for a fracture.

The elbow is a hinge joint. Surrounding soft tissues provide primary stability. The ligamentous structures around the elbow in children have sufficient laxity so that dislocation, spontaneous reduction, and reduction by manipulation are relatively easy. The annular ligament is primarily responsible for stability of the proximal radioulnar joint.

None of the secondary ossification centers of the elbow is present at birth ( eFig. 38-2 ). The age at appearance of the ossification centers is highly variable; however, the chronologic order is relatively constant. The capitellum is the first to appear, at between 6 months and 2 years of age. The radial head appears at between ages 2 and 4 years. The medial epicondyle appears at between 4 and 6 years of age, the trochlea at 9 or 10 years of age, the olecranon between 9 and 11 years of age, and the lateral epicondyle between and years of age ( eFig. 38-3 ). The trochlea usually develops from multiple sites of ossification ( eFig. 38-4 ). This should not be mistaken for a disease. The distal humeral ossification centers, except the medial epicondyle, fuse with one another and then with the distal humeral metaphysis between ages 14 and 16 years. The medial epicondyle may not fuse until age 18 or 19 years ( eFig 38-5 ).

The wrist joint is surrounded by dense ligamentous and capsular attachments. The triangular fibrocartilage complex (TFCC) consists of the triangular fibrocartilage and the ulnocarpal ligaments. The TFCC firmly attaches to the distal radius, distal ulna, and the volar carpus. This provides a flexible mechanism for stable rotational movements of the distal radius and ulna and maintains congruity of the radioulnar joint. It also provides a cushion for forces transmitted through the ulnar-carpal axis.

The secondary ossification center of the distal radius appears between 6 and 12 months of age. The center in the distal ulna appears at approximately age 6 years. There may be a separate ossification center at the tip of the ulnar styloid. The distal radial physis fuses at approximately age 17 years in girls and between ages 18 and 19 years in boys. The distal ulna fuses between ages 16 and 17 years in girls and between ages 17 and 18 years in boys. The physes of the distal radius and ulna contribute 75% to 80% of the total growth of the forearm.

Development of the carpus and hand occurs in an orderly fashion and is commonly used as a means of assessing overall skeletal maturation. The capitate is the only carpal bone that may be ossified at birth. The hamate is the next carpal bone to ossify, beginning by 3 months of age. The other carpal bones are not radiographically apparent until around 30 months. The pisiform is the last to ossify at around 10 years. The scaphoid bone ossifies in a distal to proximal direction.

The epiphyses of the metacarpals, except for the first, are distal. The phalangeal epiphyses are proximal. The epiphyses of the metacarpals and proximal phalanges begin to ossify around 1 year of age, followed by the middle and distal phalanges. Fusion of the phalangeal physes begins distally, between ages 13 and 14 years in girls and ages 15 and 16 years in boys. The proximal phalanges are next. The growth plates of the middle phalanges and the metacarpals fuse last, at approximately age 15 years in girls and age 17 years in boys.

The collateral ligaments and dorsal and volar capsules provide significant stability to the metacarpophalangeal and interphalangeal joints. In the interphalangeal joints and the first metacarpophalangeal joint, the collateral ligaments originate from the head of the more proximal phalanx or metacarpal and insert on the metaphysis of the phalanx. This provides protection for the physis and may account for the low incidence of Salter-Harris, type III injuries in these joints. In the second through fifth metacarpophalangeal joints, the collateral ligaments arise from the metacarpal epiphysis and insert on the epiphyses of the proximal phalanges. Salter-Harris, type III injuries are relatively more common in these joints.

Biomechanics

Skeletal development is influenced by growth and activity in childhood. Under normal conditions, three types of stress occur: tension, compression, and shear. If these exceed the strength of cartilage or bone, a fracture may result. The bones in children are more porous than those in adults. This prevents the propagation of fracture lines and is probably the reason that children's bones tend to fail in compression. Children's bones can also fail in tension, which is the mechanism that almost always occurs in adults. With bending, bones almost always fail first on the tension side. If the fracture line does not propagate, an incomplete greenstick type of fracture results. Pediatric bone, compared with adult bone, is also less likely to return to its original shape after a force has been removed; it is less elastic . Therefore, bowing deformity may occur in the absence of an overt fracture.

The tensile strength of children's bones is less than that of ligaments; therefore, mechanisms that might cause ligament injury in an adult are more likely to cause bone injury in children. The physeal cartilage is the weakest site of the growing skeleton. It is weaker than cortical bone, which is, in turn, weaker than ligaments.

Pathology

Pediatric fractures can be classified into five types: plastic deformation, buckle fracture, greenstick fracture, complete fracture, and physeal injury ( eFig. 38-6 ).

Plastic deformation is a manifestation of the ability of children's bone to absorb more energy prior to fracture than adult bone. This injury is most common in children younger than the age of 5 years. Radiographs reveal a smoothly bowed appearance of the bone without a discrete cortical break ( eFig. 38-7 ). Although this is a common injury of the forearm, it can often be overlooked.

Buckle fractures represent compression failure of bone that usually occurs at the junction of the metaphysis and diaphysis ( eFig. 38-8 ). The porous bone of the metaphysis is buckled by the denser bone of the diaphysis. The distal radius is the most common site of buckle fracture in the upper extremity.

Greenstick fractures are incomplete fractures typically in the diaphysis of a long bone. These injuries result from a failure of the convex side of a bending bone. The fracture line does not propagate through the concave side ( eFig. 38-9 ).

Complete fractures propagate entirely through the bone and may be transverse, oblique, or spiral. Spiral fractures usually result from a rotational force and may be associated with child abuse. Spiral and transverse fractures are relatively stable and easier to reduce because of the remaining intact periosteum. Oblique fractures are unstable because of their tendency to cause more periosteal disruption.

Approximately 15% of all children's fractures involve the physis. The distal radius is the most frequent site of injury. Physeal fractures are usually classified according to the Salter-Harris system ( eFig. 38-10 ). A type I injury is a fracture through the physis that causes widening of the physeal space. Type II fractures extend through the physis and metaphysis. Growth disturbance is an infrequent result of type I and type II injuries. Type III fractures involve the physis and epiphysis, interrupting the articular surface. Type IV injuries involve the metaphysis, physis, and epiphysis. Type V injuries are compression or crushing injuries to the physis. Ogden and Rang have made additions to the original classification. A type VI lesion involves an injury to the perichondrium at the periphery of the physis. A type VII fracture is an injury to the epiphysis that does not involve the physis. A type VIII lesion involves an injury to the metaphyseal vasculature and impairs enchondral ossification. A type IX injury involves the periosteum and interferes with membranous bone formation.

In the original article by Drs. Robert Salter and William Harris, the principal line of fracture was stated to be confined to the hypertrophic zone of the growth plate.

Experimental studies have since shown that the line of fracture may involve any portion of the growth plate. Although most of these injuries heal without complication, damage to the growing physis can cause limb shortening, deformity, and growth arrest. Shapiro has provided a pathophysiologic classification for physeal fractures. In type A fractures, the avascular physeal cartilage remains as a barrier between the metaphyseal and epiphyseal vessels. Normal growth continues after cartilage repair. In type B fractures, transphyseal vascular communication occurs secondary to either gross displacement of a type IV Salter-Harris fracture or in the setting of physeal crushing or fissuring (which can occur in Salter-Harris, types I to V fractures). Type C fractures disrupt the epiphyseal vascularity, causing loss of the physeal chondrocytes.

MRI may provide important information regarding the potential for growth disturbance in physeal injuries. Fracture lines that traverse the juxtaepiphyseal region are more likely to result in growth disturbance. Studies have demonstrated that the course of a physeal fracture line can be traced with MRI. MRI can also show the early changes of ischemia in the setting of physeal injuries. The role of MRI in diagnosis of physeal injuries has not been fully defined; however, it may be important in identifying a subset of patients for whom early intervention may be indicated.

Manifestations of the Disease

Injuries of the Clavicle

The clavicle is the most commonly fractured bone at birth, with a reported incidence of less than 2% after vaginal delivery. Many (>30%) of these fractures are first identified at follow-up appointments. Risk factors include prolonged labor, high birth weight, shoulder dystocia, and instrumented deliveries. The mechanism of injury is believed to be axial compression in the birth canal. Affected infants will often demonstrate decreased movement of the ipsilateral arm (pseudoparalysis). There is an association between birth-related clavicle fractures and Erb's palsy, which is not surprising in light of the shared risk factors. On examination, there is often a palpable abnormality.

Birth-related clavicle fractures are typically undisplaced or minimally displaced, usually occurring at the junction of the middle and lateral thirds of the clavicle ( Fig. 38-1 ). Incomplete fractures require no treatment. Complete fractures are often immobilized by pinning the arm sleeve to the shirt. Uneventful, complete recovery is the norm. Identification of callus formation around a clavicle fracture is useful in determining the age and probable nature of the injury. Birth injuries typically demonstrate dense callus by 6 weeks with complete remodeling by 6 months (see Fig. 38-1 ). Fractures demonstrating absence or a lesser degree of healing are not likely to be the result of birth trauma.

After the newborn period, the clavicle is one of the most frequently fractured bones in children and the most commonly fractured bone around the shoulder, usually involving the midshaft ( Fig. 38-2 ). In a large review of clavicle fractures in children ages 2 to 16 years, approximately half were related to a fall and approximately a fourth were related to other sports injury. Typically, fractures result either from a fall onto the point of the shoulder, a fall on an outstretched hand, a direct blow to the clavicle, or a lateral compression injury. Stress injuries of the distal clavicle are rare in adolescents but can be seen in adolescent weightlifters. Radiographically, this may appear as decreased mineralization and resorption of the distal tip.

Lateral Clavicular Physis and Acromioclavicular Joint

Whereas true acromioclavicular (AC) separations can be seen in older adolescents, AC separations in children are rare. A direct blow to the AC joint in a younger child will more often result in a lateral physeal injury with tearing of the periosteal sleeve away from the medial fracture fragment. The periosteal sleeve is firmly attached to the intact AC and coracoclavicular ligaments. The retained periosteal sleeve usually allows for adequate healing and remodeling ( Fig. 38-3 ). True AC separations in older adolescents are clinically and radiologically equivalent to adult AC joint injuries.

Medial Clavicular Physis and Sternoclavicular Joint

As with the lateral clavicle, medial clavicular physeal injuries (Salter-Harris I and II) in children and adolescents can mimic true sternoclavicular dislocations. These injuries usually occur as a result of a lateral compressive force. If the shoulder is rolled posteriorly during the compressive force, the adjacent first rib will act as a fulcrum, and the medial clavicle will be anteriorly displaced. If the shoulder is rolled anteriorly during the compressive force, the result will be posterior displacement of the medial clavicle. Posteriorly displaced fractures and dislocations, particularly those with pronounced posterior displacement, are often associated with significant neurovascular and upper mediastinal abnormalities. Consequently, contrast medium–enhanced CT is extremely useful for the diagnosis of regional osseous and extraosseous abnormalities.

Radiography

Standard radiographic views of the clavicle typically include straight and cephalad-angled anteroposterior projections. The cephalad-angled view minimizes superimposition of ribs and scapula. The sternoclavicular joint can be examined with frontal, oblique, and lateral views. The AC joint is commonly examined with anteroposterior views performed with 15 degrees of cephalad angulation to minimize acromial superimposition.

Magnetic Resonance Imaging

Magnetic resonance imaging and MR angiography may be useful in the diagnosis of soft tissue and vascular injuries associated with medial clavicle/sternoclavicular injuries.

Multidetector Computed Tomography

Computed tomography is the study of choice for sternoclavicular injuries. CT can be useful in discerning medial clavicle physeal injuries from true sternoclavicular separations ( Fig. 38-4 ). Contrast-enhanced CT with multiplanar and 3D reconstruction is extremely useful in the setting of fracture-dislocations involving the medial clavicle and sternoclavicular joints, particularly when there is posterior displacement. Aside from osseous and joint abnormality, CT permits examination of subjacent vascular and upper mediastinal structures. There is usually little need for CT in the setting of clavicle shaft fractures in the absence of more significant thoracic trauma.

Ultrasonography

Blab and colleagues demonstrated slightly greater accuracy of ultrasonography in diagnosing clavicle fractures in infants as compared with radiography, noting better visualization of greenstick-type fractures. These authors also demonstrated earlier identification of callus when using ultrasonography.

Scapular Fractures

Scapular fractures in infants should be viewed as highly specific for nonaccidental trauma ( eFig. 38-11 ). As in adults, scapular body fractures are typically the result of high-energy trauma to the thorax, usually with significant concomitant thoracic injuries, including chest wall and neurovascular injuries. These fractures may be easily missed on preliminary radiography, particularly when there are significant associated injuries. Avulsion fractures involving the coracoid and glenoid growth centers may also occur ( eFig. 38-12 ).

Radiography

Scapular body fractures may be evident on initial chest radiographs obtained in trauma patients. Dedicated radiographic views, including anteroposterior and particularly scapular Y-views, will aid in the detection of fractures and fragment separation. The axillary view is useful for the identification of extra-articular glenoid fractures. Coracoid fractures are often not evident on anteroposterior views. Anteroposterior views with cephalic angulation of at least 30 degrees and Stryker views have been reported to improve the detection of coracoid fractures.

Computed Tomography

Multidetector computed tomography (MDCT) with multiplanar and 3D reconstructions may be helpful in defining fracture morphology. Usually the scapula is included in CT examinations performed on patients with significant thoracic trauma.

Magnetic Resonance Imaging

MRI is typically not necessary for evaluation of the acute scapular trauma. However, it may be useful in evaluation of fractures of the coracoid or glenoid growth centers (see eFig. 38-12 ). Normal apophyses at these locations may be difficult to distinguish from pathologic fracture lines.