Can shaking alone cause fatal brain injury? A biomechanical assessment of the Duhaime shaken baby syndrome model

A biomechanical model of a one-month old baby was designed and tested by Duhaime and co-workers in 1987 in an attempt to assess the biomechanics of the shaken baby syndrome (SBS). The study implied that pure shaking alone cannot cause fatal head injuries, a factor which has been applied in criminal courts. In an attempt to test the validity of the model a preliminary study was undertaken in which a replica was constructed and tested. The broad description of the design and construction of the Duhaime model allowed for variations and therefore uncertainties in its reproduction. It was postulated therefore that differences in certain parameters may increase angular head accelerations. To further investigate this observation, an adjustable replica model was developed and tested. The results indicated that certain parameter changes in the model did in fact lead to an increase in angular head acceleration. When these parameter changes were combined and an injurious shake pattern was employed, using maximum physical effort, the angular head acceleration results exceeded the original Duhaime et al. (1987) results and spanned two scaled tolerance limits for concussion. Additionally, literature suggests that the tolerance limits used to assess the shaking simulation results in the original study may not be reliable. Results from our study were closer to the internal head injury, subdural haematoma, tolerance limits. A series of end point impacts were identified in the shake cycles, therefore, an impact-based head injury measure (Head Injury Criterion - HIC) was utilized to assess their severity. Seven out of ten tests conducted resulted in HIC values exceeding the tolerance limits (critical load value, Sturtz, 1980) suggested for children. At this present stage the authors conclude that it cannot be categorically stated, from a biomechanical perspective, that pure shaking cannot cause fatal head injuries in an infant. Parameters identified in this study require further investigation to assess the accuracy of simulation and increase the biofidelity of the models before further conclusions can be drawn. There must now be sufficient doubt in the reliability of the Duhaime et al. (1987) biomechanical study to warrant the exclusion of such testimony in cases of suspected shaken baby syndrome.