Figure 4-13. Posterior view of bilateral scapular fractures. This pos- terior view of the right and left scapulae pictured in Fig. 4.12 shows the location and extent of the fractures on the posterior blade surfaces (arrows).
Although the clavicle is classified as a long bone, it does not contain a medullary cavity. The medial articular end is approximately triangular in shape, and the lateral articular end is relatively flat. The shaft and articular ends form a double curvature (S shape). The clavicle is located just under the skin at the root of the neck, leav- ing it relatively unprotected from impact. Because it is connected to the acromial and coracoid processes of the scapula by ligamentous attachment, the clavicle also may be injured by an impact to the glenohumeral joint. Falls, sports injuries, and motor vehicle crashes often result in clavicle fractures, which are reported as the most common pediatric fracture [9, 30].
The S shape of the clavicle is divided into thirds for mechanical classification of fractures by location [9, 31, 32]. Group I fractures are those of the middle one third, group II fractures are of the lateral third (Figs. 4.13–4.18), and group III fractures are of the medial third. The mid- clavicular shaft contains a weak spot, which is a prod- uct of the double-curvature shape, and this is the most frequent site of accidental clavicular fractures (group I fractures). Group I fractures typically result from direct impact to the lateral shoulder, as may occur in a fall.
Group II fractures and group III fractures are those of the lateral third and medial third, respectively. Neer [32]
further categorized group II fractures into five types based on the relationship of the fracture to the coraco- clavicular ligaments. Group II fractures in an infant or young child with no history of major accidental trauma are more suspicious for nonaccidental injury, because fracture of the lateral third of the clavicle typically is caused by a direct blow to the top of the shoulder [9, 10]. Impact to the top of the shoulder is unlikely to occur in a short fall. Group III fractures are categorized into five types based on the severity of the fracture (e.g., degree of displacement, involvement of the articular surface, epiphyseal separation, and comminution).
Group III fractures of the medial third are the least com- mon clavicular injury [33]. Medial clavicular fractures are caused by direct impact to the anterior chest, which may occur through several accidental mechanisms
[9, 30]. In the absence of an accidental cause, a medial clavicle fracture in an infant or young child, as is the case in sternal fracture, may increase suspicion of non- accidental injury.
Clavicle fractures also may result from birth trauma;
typically these injuries are group I fractures of the mid- shaft [34]. Current research shows that fractures during birth may not be clearly associated with a traumatic birth event or be the result of congenital skeletal pathol- ogy. Beall and Ross [35] conducted a retrospective study of all deliveries at a large urban teaching hospital from January 1996 to March 1999 to observe the inci- dence of birth-related clavicle fracture and to quantify the association of clavicle fracture with shoulder dysto- cia. Shoulder dystocia is the inability of the infant to pass through the birth canal in a timely manner because the shoulders are wedged within the pelvic girdle. Shoulder dystocia traditionally has been associated with clavicle fractures [35]. The researchers found 26 clavicle frac- ture cases among the 4,297 births (5%). In these cases, clavicle fracture was significantly associated with increased maternal age and birthweight greater than 4,000 g, but not with documented shoulder dystocia events.
As further supporting evidence, Groenendaal and Hukkelhoven [36] concluded from an extensive retro- spective study of neonate fractures in the Netherlands that clavicle fractures may be sustained during birth without a documented birth trauma event. The authors researched the incidence of unexplained clavicle frac- tures in full-term neonate admissions during the perina- tal period to ten neonatal intensive care units and 60%
of the level 2 hospitals in the Netherlands from 1997 to 2004. The study data were accessed from The Netherlands Perinatal Registry. Documented birth trauma and/or congenital bone disease cases were excluded. Of the 158,035 full-term births recorded, 1,174 had fractures and 227 of the fractures were unexplained by birth trauma. Clavicle fractures were noted in 212 of the 227 unexplained fracture cases; the additional 15 fractures were humeral (12) and femoral (3).
Figure 4-18. Clavicle injury associated with humeral fracture.
SPNBF is present on the lateral third of the left clavicle of a 3-year-old male (arrow). The injury is associated with a com- plete fracture of the left proximal humerus. The cause of death was classified as blunt trauma of the head, the manner as homicide.
Figure 4-14. Osteopenic left clavicle of a 1-month-old female with a complete oblique fracture of the lateral third of the shaft. SPNBF is present on the acromial end and on the shaft adjacent to the fracture. The fracture likely is a result of hyper- rotation of the clavicle during birth. The cause of death was classified as sudden infant death syndrome, the manner as
natural. Figure 4-15. Magnified view of a clavicular fracture. This view of
the oblique fracture described in Fig. 4.14 shows the fracture margins and SPNBF on the acromial end and shaft. Note the normal absence of a medullary cavity in the clavicular shaft.
Figure 4-17. Remodeled clavicular fracture. A remodeled frac- ture callus is present on the lateral third of the right clavicular shaft of a 12-month-old female (arrow). The cause of death was classified as multiple blunt force injuries and malnutrition, the manner as homicide.
Figure 4-16. Stereomicroscopic view of the inferior surface of the clavicular fracture described in Figs. 4.14 and 4.15. Note the rounded fracture margins and early soft callus formation (arrow).
Summary
Fractures of the neck, sternum, scapula, lateral or medial clavicle, and the thoracolumbar and sacral regions of the spine are uncommon in infants and young children. Without an explanatory history of acci- dental trauma, these fractures may raise suspicions of child abuse injury. Infants are at higher risk for C1–C2 fractures because of their immature neck structures, but the most common type and site of pediatric verte- bral fracture are vertebral body compression fractures in the thoracolumbar region. Fractures of the immature sternum are rare but may not be as specific to child
abuse injury, as previously thought. Scapular fracture is highly specific for nonaccidental injury and may be the result of abnormal forces generated during shaking or abnormal rotation or traction of the arm. Although frac- ture at the clavicle midshaft is a very common pediat- ric injury, fractures of the lateral or medial third of the clavicle are more suspicious for nonaccidental injury.
Birth trauma is a possible mechanism for clavicle injury and is a consideration when healing clavicle fractures are observed during the infant postmortem skeletal examination.
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Fractures occurring in the humerus, ulna, radius, femur, tibia, and fibula are collectively categorized as long bone fractures. Long bone fractures are further classified by type and location. Interpretation of the forces associated with the fracture depends on the location, type, and extent of the fracture. Common long bone fracture types include spiral, oblique, transverse, torus (or buckle), greenstick, and classic metaphyseal lesion (CML) [1]. A spiral fracture circles the shaft and typically results from a rotational force. An oblique fracture crosses the bone diagonal to the long axis, and a transverse fracture crosses the bone at a right angle to the long axis. A torus (or buckle) fracture, in which the cortical bone balloons out, is typically the result of a compression force loading through the long axis of the bone. A greenstick fracture is an incomplete fracture, most often an incomplete transverse fracture, and is commonly found in children as a result of the increased elasticity of the developing bone. CML is a fracture of the physeal plate of a long bone.
In terms of location, a developing long bone is conventionally divided into four regions:
the shaft (or diaphysis), metaphysis, physis, and epiphysis. The shaft, the tubular midsec- tion of the bone, is subdivided into three regions: the mid, distal, and proximal one third.
The metaphyses are the flared regions of the proximal and distal ends of the long bone.
At the transition between the shaft and the metaphysis, the cortical bone thins and the density of the trabecular bone increases. The physis is the proximal or distal surface (end plate) of the long bone at the chondro-osseous interface. The epiphysis is the cartilagi- nous end of the bone containing the secondary ossification site.