Violent Infant Surrogate Shaking: Continuous High-Magnitude Centripetal Force and Abrupt Shift in Tangential Acceleration May Explain High Risk of Subdural Hemorrhage

Abstract

Violent shaking is believed to be a common mechanism of injury in pediatric abusive head trauma. Typical intracranial injuries include subdural and retinal hemorrhages. Using a laboratory surrogate model we conducted experiments evaluating the head motion patterns that may occur in violent shaking. An anthropomorphic test device (ATD; Q0 dummy) matching an infant of 3.5 kg was assembled. The head interior was equipped with accelerometers enabling assessment of three-axial accelerations. Fifteen volunteers were asked to shake the surrogate vigorously holding a firm grip around the torso. We observed the volunteers performing manual shaking of the surrogate at a median duration of 15.5 sec (range 5-54 sec). Typical acceleration/deceleration patterns were produced after 2-3 shakes with a steady-state shaking motion at a pace of 4-6 cycles (back and forth) per second. Mean peak sagittal tangential accelerations at the vertex were 45.7g (range 14.2-105.1g). The acceleration component in the orthogonal direction, the radial acceleration, fluctuated around a negative mean of more than 4g showing that the surrogate head was continuously subjected to centripetal forces caused by rotations. This surrogate experiment showed that violent shaking may induce high peak tangential accelerations and concomitantly a continuous high-magnitude centripetal force. We hypothesize that the latter component may cause increased pressure in the subdural compartment in the cranial roof and may cause constant compression of the brain and possibly increased stretching or shearing of the bridging veins. This may contribute to the mechanism accountable for subdural hematoma in abusive head trauma.

Keywords: abusive head trauma; biomechanical model; infant; injury; shaken baby.

FIG. 1.

The instrumented Q0 dummy used for the shaking experiments. (A) Dummy in the hands of a participant. (B) Sensor module inside the head containing two accelerometers on each (x, y, z) axis. Positive (x, y, z) axes are indicated with arrows. (C) Schematic drawing of neck, dummy head.

FIG. 2.

Accelerations measured by the vertex, x, y, and z sensors during the entire shaking session of Volunteer 2.

FIG. 3.

Detail view of seconds 5.0 to 5.5 from Figure 2, the accelerations measured for Volunteer 2. Shaded bars A to E and the photos on top of these bars illustrate which accelerations were measured during which phase in the shaking cycle. The dashed arrows in A to E indicate the motion directions of the dummy head. Shaded circles AX, AZ, CV, DZ, and EX are regions of interest that are further discussed in the text.