Posterior
Posterolateral
Anterolateral
Anterior
Figure 3-1. Regions of a rib. The rib typically is divided into four regions. The posterior region is the area from the medial tip of the rib head to the lateral margin of the rib tubercle. The pos- terolateral region is the area from the lateral margin of the rib tubercle to the most lateral point of the rib. The anterior and anterolateral regions of the rib span from the most lateral point of the rib to the sternal end. The interface of the anterior and anterolateral regions is the midpoint.
Of the four regions of the rib, fractures located in the posterior region are regarded as the strongest indicator of nonaccidental injury [2, 3, 7, 8, 15, 16, 18]. Posterior rib fractures are often multiple, arranged in a serial pattern, and bilateral [16]. Kleinman et al. [7] found that of 84 rib fractures identified in 31 infant victims of nonaccidental injury, 53 fractures (63%) were located in the posterior region of the rib. Bulloch et al. [2] conducted a retro- spective study of infants treated at two children’s hospi- tals over a 3-year period and identified 39 cases with rib fractures; 32 (82%) of the cases were classified as child abuse. The authors found posterior rib fractures were more common than anterior ones but found no
significant difference in location of the fracture between nonaccidental and accidental injury.
Mechanisms postulated to cause posterior rib frac- tures include avulsive forces applied to the rib head and posterior levering of the rib over the transverse pro- cess of the thoracic vertebra [2, 8, 15, 19]. The develop- ing rib head is primarily hyaline cartilage and is analogous to the metaphysis of a long bone at the chondro- osseous interface. The structure is held in place with strong ligamentous attachments. When excessive force is applied to the costovertebral articu- lation, an osseous fragment is avulsed from the rib head (Figs. 3.2–3.9) [8].
Figure 3-2. Rib head fractures in situ. Rib head fractures (arrows) are shown in situ in a 2-month-old male. Note the absence of hemorrhage at the fracture sites. The cause of death was clas- sified as blunt trauma of the head with skull fractures and sub- dural hemorrhage, the manner as homicide.
Figure 3-3. Avulsion fracture of the rib head. An avulsion fracture of a rib head is shown after processing; the view is of the articu- lating surface (same individual as shown in Fig. 3.2). Note the exposed trabecular bone of the articulating surface of the rib head. The fracture is similar in structure to a partial classic meta- physeal lesion (see Chap. 5).
F 3-5. Avulsion fracture of the rib head in situ. An avulsion
Figure 3-6. Partial avulsion rib head fracture. This partial avulsion fracture of the rib head was observed in a 2-month-old male;
the view is of the pleural surface. The cause and manner of death were classified as undetermined.
Figure 3-7. Healing rib head fractures in a 2-month-old male. Note the thickened cortical bone (arrows) and the lipping of the bone callus over the articulation surface of the rib head. The cause and manner of death were classified as undetermined.
Figure 3-8. Healing rib head fracture. This healing rib head frac- ture (arrow) was observed in an 11-week-old female with mini- mal fracture callus formation. A healing fracture of the rib neck (arrowhead) also is present. The cause of death was classified as blunt force head trauma, the manner as homicide.
Figure 3-9. Rib head fractures in a 4-month-old male who under- went a median sternotomy during organ recovery. Several healing rib fractures and an acute cranial fracture were noted in the decedent. The rib head fractures were the only acute rib fractures observed. Because of the surgical history, organ recovery could not be excluded as a possible cause of the fractures. The cause of death was classified as blunt force trauma to the head, the manner as homicide.
Kleinman et al. [7, 8, 16] found that when the chest is forced posteriorly, a classic level 1 lever is formed at or near the costovertebral articulation point (the rib tuber- cle and vertebral transverse process). The costoverte- bral ligaments are stronger than the bone, and excessive forces result in the failure of the rib in the region of the rib neck and tubercle (Figs. 3.10–3.15). Based on animal experimentation and assailant testimony, Kleinman [16]
suggested that posterior rib fractures result when an infant is held by the chest while the thorax is squeezed in
the anteroposterior plane. The infant is held facing the adult with the adult’s palms on the infant’s sides, fingers on the back, and thumbs near the midline of the chest.
Kleinman [16] also postulated that similar forces occur when the chest is forced onto a broad surface while the back is unsupported. Kleinman and Schlesinger [8]
reported that posterior rib fractures do not occur when the anterior chest is compressed and the back is sup- ported on a broad surface (such as with the administra- tion of cardiopulmonary resuscitation [CPR]).
Figure 3-10. Posterior rib fractures. These acute posterior rib frac- tures (arrows) were found in a 2-month-old female. The cause of death was classified as acute bacterial bronchopneumonia associated with bronchopulmonary dysplasia due to prematurity, the manner as natural. Decreased bone quality has been doc- umented as associated with prematurity in the neonatal period (see Chap. 7). The decedent was born at 27 weeks’ gestation.
Figure 3-11. Posterior fracture of the rib head (same individual as shown in Fig. 3.10). Note the porotic cortical bone of the rib head (arrow). The hyperporosity reduced the bone’s ability to withstand low-level forces.
Figure 3-12. Acute incomplete fracture of the rib neck in a