In 1946, Dr. John Caffey, a pediatric radiologist, was the first to describe an association between long-bone fractures and intracranial hemorrhages without external signs of injury in children [6]. He concluded in his report that the same traumatic mechanism caused both injuries. In 1971, A.N. Guthkelch looked at “infantile subdural hematomas and its relationship to whiplash injuries” [15]. He concluded that subdural hematomas were the result of “acceleration-deceleration” forces seen with shaking rather than “direct violence” from impact to the infant’s head. Caffey later coined the term “whiplash shaken baby syndrome” to describe the combination of intracranial hemorrhage, long-bone fractures, and retinal hemorrhages with minimal or absent signs of external trauma [7]. Availability of computed tomography (CT) in the 1970s and magnetic resonance imaging (MRI) by the mid-1980s assisted exponentially with diagnoses of non-accidental head trauma which previously had been hard to radiographically define. These new technologies have helped to better understand the timing and evolution of intracranial hemorrhages after an injury. In 1987, Duhaime et al. reported that while shaking may be involved in causing an infant’s injuries, in some cases, especially in those that present in the more severe form, blunt impact may also come into play. These injuries involve the impact that results in focal injury and acceleration-deceleration forces that occur as the head is moving forward and then stopped at the point of impact, causing shearing forces on the bridging blood vessels and brain parenchyma [11].

The importance of impact has been a controversial issue and efforts to better understand the precise mechanism continues. The term shaken baby syndrome alone does not accurately represent those infants who demonstrate not only acceleration-deceleration injuries but also impact injuries. Because the specific mechanism of injury is rarely known with certainty, the terms abusive head trauma or non–accidental head trauma have been adopted as more broad and inclusive. These terms allow for the possibility of different mechanisms to explain a child’s clinical and radiographic findings and do not narrowly define an injury as a single occurrence or event. Understanding the biomechanical and biochemical events behind each individual finding has been paramount toward improving the diagnosis and treatment of these injuries, as well as the development of prevention programs to educate the public about this devastating type of physical child abuse.

Head trauma is the most common cause of child abuse fatalities. Incidence and prevalence are difficult to measure due to varied definitions and criteria for diagnosing intentional head trauma, unrecognized abuse, and a degree of physician reluctance to report certain injuries as abuse. The incidence during the first 2 years of life has been estimated to be between 16 and 30 cases per 100,000 infants per year. Children under 1 year of age are at the highest risk, with lower risk between 1 and 2 years, and the rate decreases thereafter [2, 19, 29]. Mortality has been found to be higher in children with inflicted injury (16.8 %) compared to those with accidental injury (10.7 %) [29].

Several studies have looked at the relationship between the infant and the perpetrators of abusive head trauma. Most studies show that males are identified as the perpetrator more often than females [20, 31, 32]. Debra Esernio-Jenssens et al. found when examining the effect of perpetrator gender on victim presentation and clinical outcomes that male perpetrators were younger and more likely to confess and be convicted. They also found that victims of male perpetrators had more serious acute presentations and suffered worse outcomes [13].

When looking at socioeconomic factors, households with young parents, single parents, lower socioeconomic status, presence of extended family or unrelated adults in the home, and/or previous child abuse are at higher risk for abusive head trauma [30, 31]. Infant prematurity, illness, and disability also put an infant at risk. Episodic crying in the newborn period where an infant is inconsolable may a trigger an inexperienced or frustrated caretaker to engage in a shaking event .

Due to the varied ways children can present as a result of abusive head trauma with often a lack of history given by the caretaker, intentional head trauma can be missed by physicians. When examined in isolation, each finding can result from inflicted trauma, accidental trauma, or other nontraumatic causes. This is most common in cases where a child presents with more nonspecific, less severe symptoms that are common to infancy, such as fussiness, crying, vomiting, lethargy, and loss of appetite. Abusive head trauma is also missed when there are no apparent external signs of trauma, such as scalp swelling or bruising. Carole Jenny et al. studied 173 children with abusive head injuries and found that 32.2 % (54 cases) were missed [18]. When these missed cases were compared to recognized cases, several differences were found regarding age, race, family composition, and severity of symptoms at the initial visit. Infants less than 6 months of age, of minority race, and with parents living apart were found to be more likely missed at the initial visit. Children who presented with irritability or vomiting were less likely identified as opposed to children presenting with respiratory distress, seizures, or facial bruising. This study demonstrates the difficulty in making a correct diagnosis in cases of abusive head trauma, especially when the caretaker gives an inaccurate history. For this reason, abusive head trauma should be considered in the differential diagnosis in cases of an infant with nonspecific symptoms.

Skull fractures, intracranial bleeding, retinal hemorrhage, and skeletal findings can be found in cases of non-accidental head trauma. The biomechanical conditions that cause these injuries have been studied to help understand how these injuries occur and help in prevention, diagnosis, and treatment approaches. Shaking is a commonly reported mechanism of injury reported by perpetrators who admitted to abuse. Starling and her colleagues [32] found that, in 81 cases where the perpetrator admitted to injuring the baby, 61 % reported shaking. Impact trauma, either alone or combined with shaking has also been described and can result in significant head injury. In severe cases, cervical spine injury has also been found.

The mechanism of injury that leads to injuries seen in abusive head trauma, such as subdural hematomas, retinal hemorrhage, diffuse axonal injury, and skeletal findings, has been greatly discussed in the literature. One large debate has been whether shaking alone can cause the severe injuries seen in infants. This is the reason the terminology has changed from shaken baby syndrome to abusive head trauma. This term does not limit the mechanism to shaking alone but includes other possible mechanisms that may be involved. Due to the lack of physical models , many biomechanical questions remain unanswered.

The forces acting on the head in non-accidental trauma include contact and inertial (acceleration and/or deceleration) forces. Contact forces occur when the head is struck by an object or comes in contact with a hard surface, as in a fall. Upon impact, there is deformation at the point of impact and forces are distributed. This is why visible signs of impact may not always be seen. Inertial forces occur as the brain and its structures are placed in motion. This includes the acceleration-deceleration motion that occurs when these structures are in motion and suddenly stopped. Inertial forces can be either translational, in which structures move in a straight line, or rotational, in which they move around an axis or center of rotation. The center of rotation is usually the cervical spine in the case of shaking. These forces can cause shearing of parasagittal bridging veins which leads to subdural hematomas and diffuse axonal injury. This also explains some contrecoup injury at the point opposite to impact where the brain is stopped in its motion. The acceleration-deceleration forces not only have an impact on the bridging vessels of the brain but also can cause diffuse axonal injury, injury to the vessels and nerves of the eye, and spinal cord injury.

In addition to the type of force that is involved, the amount of force is equally important in predicting and assessing intracranial injuries. Impact forces depend on the amount of force applied to the head by an object or the height of a fall. The higher the fall, the greater the impact on the head. The magnitude of rotational forces are influenced by the velocity of the acceleration and deceleration. The greater the velocity, the greater the forces of acceleration and deceleration. Generally, the greater the forces, the greater the severity of injury and the deeper it extends into the brain [28].

Medical terminology should reflect the medical diagnosis. For this reason, the term “shaken baby syndrome” should not be used in infants with impact alone or with multiple mechanisms of head and brain injury. In the 2009 policy statement by The American Academy of Pediatrics, they recommended the adoption of the term “abusive head trauma” as the diagnosis. This term more accurately describes the “constellation of cerebral, spinal, and cranial injuries that result from inflicted head injury to infants and young children” [8].

The presentation of a child who has suffered abusive head trauma can vary greatly depending on the mechanism and severity of the injury. The presentation of accidental trauma and abusive head trauma can also overlap and look very similar, making a diagnosis of intentional trauma difficult. However, most low-impact injuries and short-distance falls are well tolerated and severe injuries are less likely to result. Since much of the research and analysis of abusive head trauma is focusing on the mechanism of injury and acute and delayed distributed injuries, the classification had been divided into primary and secondary traumatic brain injury much the way accidental head trauma research has divided the acute and delayed effects of severe TBI.