Shaken Baby Syndrome : Searching for the Scientific Evidence

Shaken baby syndrome, SBS, was first hypothesised in the 1970s and was originally termed "whiplash shaken infant syndrome." The diagnosis of SBS was based on a triad of symptoms: subdural haemorrhage (Fig. 1), retinal haemorrhage, and brain swelling. For decades, this diagnosis has been a cornerstone in prosecuting cases of alleged child abuse. However, the scientific basis for SBS has come under scrutiny, challenging its reliability and highlighting a potential avenue for wrongful convictions.

The Louise Woodward Case: A Landmark in SBS Legal History

The case of Louise Woodward, a British au pair charged with the involuntary manslaughter of eight-month-old Matthew Eappen in Newton, Massachusetts, is a landmark in the legal history of SBS. Woodward was initially found guilty of second-degree murder, with the conviction later reduced to involuntary manslaughter. The baby's death was attributed to a fractured skull and subdural hematoma, conditions often associated with SBS. However, during the trial, there was intense debate over the nature of the injuries and whether they were indeed indicative of SBS. The defence contested the prosecution's claims, arguing the absence of neck injuries and suggesting that the injuries could have predated Woodward's tenure as a caretaker​

Woodward's case played a pivotal role in raising awareness and skepticism about SBS. Woodward's conviction was based on assumptions now considered outdated. Dr. Patrick Barnes, an expert witness in the case, later stated that with current knowledge, he would not testify the same way, acknowledging the evolution in the scientific understanding of paediatric head injuries. This case exemplifies how medical evidence, once considered irrefutable, can be subject to reinterpretation with advancing scientific insight.

Figure 1. A subdural hematoma occurs when there is a rupture in a blood vessel, typically a vein, leading to blood leakage into the area beneath the dura mater, a membrane layer surrounding the brain. This area is referred to as the subdural space, named for its location beneath the dura. The accumulation of blood in this space due to the vessel tear is what constitutes a subdural haemorrhage.

History of Scientific Evidence on SBS

The concept that later came to be known as Shaken Baby Syndrome (SBS) originated in the mid-20th century, with the work of American paediatrician John Caffey. In 1946, Caffey described infants presenting with fractures in the long bones and subdural haemorrhage. At this stage, he hypothesized these might be due to unnoticed or concealed accidents, without realizing that he might be observing a pattern potentially related to abuse. However, the certainty around these initial observations would later become a subject of significant debate.

The broader understanding of child abuse in the medical community was influenced significantly by Henry Kempe's 1962 work on the "battered child syndrome." While this was a pivotal moment in bringing attention to the patterns of injury in abused children, it also marked the beginning of a narrative that would eventually lead to the controversial concept of SBS, a narrative that some argue was built on uncertain foundations.

The hypothesis of a whiplash-like mechanism causing internal head injuries in infants, proposed by British neurosurgeon Norman Guthkelch in 1971, further complicated the understanding of such injuries. Guthkelch observed infants with subdural haemorrhages but no external signs of injury, positing an acceleration-deceleration mechanism. This idea would later be crucial to the formation of the SBS hypothesis but also contributed to the growing complexities and uncertainties surrounding the diagnosis.

John Caffey’s 1972 study is often cited as the first to directly associate the act of shaking with a specific set of injuries, including subdural and retinal haemorrhages and long bone fractures. Caffey's work was instrumental in the medical recognition of SBS. However, in retrospect, this link between shaking and these specific injuries has become one of the most contentious issues in paediatric medicine, with increasing skepticism about the validity of SBS as a distinct syndrome.

Alternative Explanations: Expanding the Scientific Evidence

While widely accepted by prosecutors, child protection agencies, and much of the medical community, the SBS hypothesis has faced skepticism, particularly from the bioengineering and forensic scientific community. This skepticism primarily revolves around the biomechanics and antecedents of injuries attributed to SBS.

Shaken Baby Syndrome has been theorized to result from the impact of non-impact acceleration-deceleration forces. This hypothesis proposes that the simple back-and-forth motion of an infant's head could lead to the tearing of bridging veins, resulting in subdural hematomas and, in some cases, death. Contributing factors to the vulnerability of infants to such injuries include the relative largeness of an infant's head, underdeveloped neck muscles, the pliability of the skull, a sizeable subarachnoid space, and the brain's high water content.

As research in experimental angular acceleration injury has evolved, it's become apparent that the duration of acceleration is a crucial biomechanical factor influencing the type of injury. Specifically, large angular accelerations over shorter time periods tend to cause subdural hematoma, whereas injuries occurring over longer periods are more likely to result in diffuse axonal injury. In support of this finding, in the 1980s, Thibault and Gennarelli developed a tolerance scale for non-human primates, correlating these factors to specific types of injury, such as concussion, subdural hematoma, or diffuse axonal injury. When this scale is adjusted for an infant's brain mass, the angular acceleration and velocity typically associated with shaking fall well below the injury threshold. This suggests that the act of shaking a baby is insufficient to recapitulate the triad proposed in SBS. However, values for impacts due to falls are within the range that can cause concussion, subdural, and diffuse axonal injuries. This is consistent regardless of neck conditions, with or without skulls, and a padded surface only slightly modifies these outcomes.

In their study titled "The Shaken Baby Syndrome: A Clinical, Pathological, and Biomechanical Study," Duhaime et al., investigated the biomechanics of injuries associated with SBS. They concluded that the forces generated by shaking are "well below the injury range" necessary to cause the types of brain injuries typically ascribed to SBS. This finding raised critical questions about the traditional understanding of how these injuries occur.

Another significant study by Prange et al., titled "Anthropomorphic Simulations of Falls, Shakes, and Inflicted Impacts in Infants," further challenged the SBS hypothesis. Published in the Journal of Neurosurgery, the study found no evidence that the force experienced during shaking is sufficient to cause subdural haemorrhages (SDHs) or primary traumatic axonal injuries (TAIs) in infants. This lack of correlation between the shaking force and the injuries typically associated with SBS suggests that other factors might be responsible for such injuries.

How Common is Subdural Hematoma in Infancy?

Advancements in radiological imaging provide some clues as to the reliability of shaking baby syndrome. Rooks et al., revealed that around 46% of asymptomatic infants exhibit signs of subdural haemorrhages following normal births. This prevalence might be even higher among infants displaying symptoms, those who have experienced difficult births, or in cases examined post-mortem. Although most subdural haemorrhages related to birth tend to resolve without any apparent symptoms, there are instances where these haemorrhages indicate more severe underlying issues or evolve into chronic conditions. In such cases, these haemorrhages can develop membranes that are prone to rebleeding.

In his assessment of the reliability of retino-dural haemorrhage, as a result of SBS, the grandfather of the condition, Dr Norman Guthkelch expressed concern that the true prevalence of SDH may be underestimated, thereby throwing doubt on its true concordance with SBS. Dr Guthkelch explained that the focus in cases of symptomatic infants should not be solely on assigning blame or identifying a “culprit” – often the last person in care of the baby. Instead, he proposed there was a crucial need to concentrate on the early detection of infants with pre-existing conditions that may predispose them to such complications. Moreover, he pressed the need to emphasize the development of appropriate treatment options for these conditions, rather than defaulting to a search for blame in the event of symptomatic manifestations of these haemorrhages.

Gender Differences

A particular finding in the identification of SBS, is the increased incidence of males as victims. Indeed, in the Duhaime et al study, they described the cases they reviewed as fifty-seven patients with suspected shake injury, ranging in age from 1 month to 2 years (mean 7.85 months), where 65% of the patients were male. A more recent study demonstrated that in comparison with the expected 51.4% male frequency in newborns, there is a notable overrepresentation of males presenting with subdural hematoma (SDH). In four separate groups that studied SDH in infancy, the incidence of males was 65.3%, 62.2%, 62.6%, and 68.8%. This trend is believed to be linked to the larger head size of male infants compared to females, which has several implications (Miller and Miller, 2010).

Miller and Miller found that the greater head circumference in male newborns may make them more susceptible to acquiring a small subdural hemorrhage (SDH) during the minor traumas typical of the birthing process. Such initially small SDHs might later re-bleed and become symptomatic, potentially leading to misdiagnosis as Shaken Baby Syndrome (SBS) and child abuse. Secondly, due to their larger head size, male infants may be more likely than female infants to sustain a SDH from short falls. These injuries might not present symptoms immediately but could become apparent hours to weeks later, leading to cases of unexplained SDH.

Finally, infants with macrocephaly, particularly those associated with increased extra-axial fluid spaces (IEAFS), could be at a heightened risk of developing SDH. The larger head size and the greater tension of the bridging vessels in the extra-axial fluid spaces may contribute to this increased risk. These findings suggest that many infants diagnosed with SBS may have been incorrectly labeled as victims of child abuse. Instead, their SDHs might result from small haemorrhages incurred during birth, which enlarge during early infancy, from short falls, or from macrocephaly with IEAFS.

While society's outrage at the assault on its most vulnerable members is understandable, there have been cases where both medical science and legal systems may have overreached in hypothesizing and criminalizing alleged acts of violence. These cases often rely solely on the presence of the classic triad, or even just parts of it, without sufficient investigation into natural causes. However, the presence of retino-dural haemorrhage in infants should not automatically lead to an inference of shaking or other forms of abuse. As Tuerkheimer has warned, there is a danger in presuming criminal intent based solely on the classic triad of retino-dural haemorrhage and encephalopathy, especially when no other explanation is apparent.

Shaken Baby Syndrome gets a New Name

Prior to 2009, the American Academy of Pediatrics had identified the shaken baby hypothesis as a distinctly defined form of child abuse. However, since then, they had moved to recognize it as a subject of controversy, hence the avoidance of the specific term "shaken baby syndrome" and the adoption of the term "abusive head trauma" instead of "shaken baby syndrome." This same change in nomenclature was adopted in the UK by the Crown Prosecution Service. However, despite apparent evidence that shaken baby syndrome is not a scientifically valid diagnosis, the exact same criteria is used to define the new term non-accidental head injury (NAHI). The CPS describes NAHI as follows:

"Generally, cases where NAHI is alleged depend on a trilogy of findings of intracranial injuries (the triad) consisting of:

• Encephalopathy (defined as any disease of the brain affecting the brain's function)

• Subdural haemorrhages (bleeding in the subdural space); and

• Retinal haemorrhages (bleeding within the retina)."

The term non-accidental head injury (NAHI), continues to be used interchangeably with "shaken baby syndrome" (SBS), and essentially describes a similar set of conditions but under a different label. This renaming, however, does not address the core issues surrounding the diagnosis of SBS, particularly the concerns about the sufficiency of shaking alone to cause the characteristic triad of symptoms. Perhaps of greater concern is the guidance provided by the CPS on NAHI, which places undue importance on the role of shaking as a cause of the triad of symptoms:

"Whilst not entirely understood, the mechanism for these injuries is thought to be the shaking of the infant, with or without impact on a solid surface. This moves the brain within the skull, damaging the brain and shearing the bridging veins between the dura and the arachnoid and sometimes causing retinal haemorrhages. Nevertheless, despite medical uncertainty surrounding the mechanism, the triad of injuries is a strong medical pointer to the infliction of NAHI." Crown Prosecution Service - Legal Guidance, Domestic abuse , Violent crime

The guidance from the CPS is deeply troubling, owing to recent medical research that suggests that the symptoms described in NAHI/SBS can arise from a variety of causes not necessarily related to abuse, such as birth trauma, accidental injuries, medical conditions, or even natural causes. The assumption that shaking alone can lead to these three symptoms has been increasingly questioned. More recently an Appeals Court in the U.S. State of New Jersey rejected the use of NAHI/SBS in a criminal case of child abuse.

“The very basis of the theory has never been proven..., The State has not demonstrated general acceptance of the SBS/AHT hypothesis to justify its admission in a criminal trial.” Judge Greta Gooden Brown

The reliance on the triad for diagnosing SBS/NAHI has significant legal implications, potentially leading to wrongful convictions in cases where caregivers or parents are accused of abuse based on these medical findings. The lack of specific and reliable criteria for distinguishing between accidental and non-accidental injuries poses a challenge for both medical and legal professionals.

A Case In Point

The case of Robert Roberson, a Texas inmate sentenced to death based on a conviction for causing his daughter's death through "shaken baby syndrome," highlights the detrimental consequences of the lack of scientific rigour and consistency in the criminal justice system. Despite significant scientific critique SBS/NAHI as a valid cause of harm, the US Supreme Court recently declined Roberson's appeal for reconsideration. This was Roberson's only remaining opportunity to appeal his conviction, and prevent the State of Texas from executing him.

Roberson was convicted in 2003 for the death of his two-year-old daughter Nikki, who passed away in hospital after showing symptoms like brain swelling, then interpreted as definitive signs of child abuse. His conviction was heavily reliant on this interpretation, as it is one of the three elements observed in the diagnostic triad attributed to SBS/NAHI. In Nikki's case, several alternative explanations, such as high fever, undiagnosed pneumonia, and unsafe medication, were later identified as potential causes of her medical decompensation. These findings challenge the initial diagnosis and raise questions about Roberson's guilt.

Roberson, who came close to execution in 2016, has now exhausted his appeals and relies on the clemency of Texas Governor Greg Abbott. Calls for reevaluation of the case have come from various quarters, including retired judges, forensic scientists, paediatric doctors, and even the lead police detective on the case, Brian Wharton, who has expressed regret over the Supreme Court's refusal to review the case. Wharton lamented the failure of the justice system to uphold its ideals in Roberson's case, criticizing the system for resisting justice.

Figure 2. Women are disproportionately convicted of crimes where children are the victims. The recent exonerations in the US reveal that women are also more likely to be convicted of crimes where there was no actual crime.

Shaken Baby Syndrome and Exonerations

The 2022 report by the National Registry of Exonerations, provides a comprehensive analysis of exonerations for murder, sexual assault, and drug crimes since 1989. The registry has documented over 3,200 exonerations in 33 years. Within this framework, Shaken baby syndrome cases represent a unique subset, wherein the convictions are often solely based on medical evidence that is increasingly contested (Fig. 2).

The core of the SBS/NAHI controversy lies in the disconnect between medical science and legal standards. While paediatrics may generally accept SBS, experts in biomechanics and forensic sciences express significant doubts. This divergence is critical, as legal decisions heavily rely on medical testimonies, often treating them as definitive proof of guilt. The reliance on a potentially flawed diagnosis can, and has, led to wrongful convictions, as seen in cases like Michelle Heale's.

The experiences of individuals who were wrongfully convicted based on debatable SBS evidence, underscore the real-life impacts of this controversy. Each new exoneration in a SBS/NAHI case catalyzes a re-examination of SBS/NAHI in legal contexts, revealing a broader issue of outdated or unverified medical claims in the courtroom. The challenges presented by SBS/NAHI cases call for a reassessment of how medical science is used in courtrooms. It raises questions about the standards for admitting scientific evidence and the training of legal professionals in understanding and critically evaluating scientific claims.

The intersection of SBS/NAHI, wrongful convictions, and the judicial system's handling of scientific evidence reveals a critical gap in our legal framework. This gap not only undermines the credibility of forensic science but also poses a severe risk of injustice. As scientific understanding evolves, so must the legal standards for evidence admissibility to ensure fair and accurate judicial outcomes. The ongoing debate over SBS/NAHI is a clarion call for the legal system to realign with the principles of scientific rigor and integrity.

References

Caffey J. The whiplash shaken infant syndrome: manual shaking by the extremities with whiplash induced intracranial and intraocular bleeding, linked with permanent brain damage and mental retardation. Pediatrics 1974;54:396– 403

Duhaime AC, Gennarelli TA, Thibault LE, Bruce DA, Margulies SS, Wiser R. The shaken baby syndrome. A clinical, pathological, and biomechanical study. J Neurosurg. 1987 Mar;66(3):409-15. doi: 10.3171/jns.1987.66.3.0409. PMID: 3819836.

Gennarelli TA, Thibault LE. Biomechanics of acute subdural hematoma. J Trauma. 1982 Aug;22(8):680-6. doi: 10.1097/00005373-198208000-00005. PMID: 7108984.

Guthkelch AN. Infantile subdural haematoma and its relationship to whiplash injuries. Br Med J. 1971 May 22;2(5759):430-1. doi: 10.1136/bmj.2.5759.430. PMID: 5576003; PMCID: PMC1796151.

Miller R, Miller M. Overrepresentation of males in traumatic brain injury of infancy and in infants with macrocephaly: further evidence that questions the existence of shaken baby syndrome. Am J Forensic Med Pathol. 2010 Jun;31(2):165-73. doi: 10.1097/PAF.0b013e3181d96a8e. PMID: 20308871.

Prange MT, Coats B, Duhaime AC, Margulies SS. Anthropomorphic simulations of falls, shakes, and inflicted impacts in infants. J Neurosurg. 2003 Jul;99(1):143-50. doi: 10.3171/jns.2003.99.1.0143. PMID: 12854757.

Rooks VJ, Eaton JP, Ruess L, Petermann GW, Keck-Wherley J, Pedersen RC. Prevalence and evolution of intracranial hemorrhage in asymptomatic term infants. AJNR Am J Neuroradiol. 2008 Jun;29(6):1082-9. doi: 10.3174/ajnr.A1004. Epub 2008 Apr 3. PMID: 18388219; PMCID: PMC8118856.

Tuerkheimer, Science-Dependent Prosecution and the Problem of Epistemic Contingency: A Study of Shaken Baby Syndrome, 3 Ala. L. Rev. 523 (2011).

https://www.cps.gov.uk/legal-guidance/non-accidental-head-injury-cases-nahi-formerly-referred-shaken-baby-syndrome-sbs