Misunderstanding and Misuse of Basic Clinical Decision Principles among Child Abuse Pediatricians

The previous post about Dr. Cox, ensnared in a CPT (Child Protection Team) witch hunt in Wisconsin, has led me to evaluate several more research reports on child abuse, including SBS (shaken baby syndrome), AHT (abusive head trauma), and sentinel injuries.  These reports are rife with critical assumptions, severe limitations, and gross errors which greatly limit the resulting conclusions in most studies I have reviewed.  However, one study that was pointed out to me today  takes the cake.  I don't know what the prevalence of this degree of misunderstanding is, but CPTs and child abuse pediatricians need make sure they have a proper understanding of sensitivity, specificity, positive and negative predictive value, base rates, etc.  And they should not be testifying about the probability of child abuse at all if they don't have this stuff down cold. And I think this means that some proportion of them needs to go back to school or stop testifying.

The article and associated correspondence at issue is entitled The Positive Predictive Value of Rib Fractures as an Indicator of Nonaccidental Trauma in Children published in 2004.  The authors looked at a series of rib fractures in children at a single Trauma Center in Colorado during a six year period and identified all patients with a rib fracture.  They then restricted their analysis to children less than 3 years of age.  There were 316 rib fractures among just 62 children in the series; the average number of rib fractures per child is ~5.  The proper unit of analysis for a study looking at positive predictive value is children, sorted into those with and without abuse, and with and without rib fracture(s) as seen in the 2x2 tables below.

Bad Science + Zealotry = The Wisconsin Witch Hunts. The Case of John Cox, MD

John Cox, MD

I stumbled upon a very disturbing report on NBC News today of a physician couple in Wisconsin accused of abusing their adopted infant daughter.  It is surreal and horrifying and worth a read - not because these physicians abused their daughter, but because they almost assuredly did not.  One driving force behind the case appears to be a well-meaning and perfervid, if misguided and perfidious, pediatrician at University of Wisconsin who, with her group, coined the term "sentinel injuries" (SI) to describe small injuries such as bruises and oral injuries that they posit portend future larger scale abuse.  It was the finding of SI on the adopted infant in the story that in part led to charges of abuse against the father, Dr. Cox, got his child put in protective services, got him arrested, and threatens his career.  Interested readers can reference the link above for sordid and sundry details of the case.

Before delving into the 2013 study in Pediatrics upon which many contentions about SI rest, we should start with the fundamentals.  First, is it plausible that the thesis is correct, that before serious abuse, minor abuse is detectable by small bruises or oral injuries?  Of course it is, and it sounds like a good narrative.  But being a good plausible narrative does not make it true and it is likewise possible that bruises seen in kids who are and are not abused reflect nothing more than accidental injuries from rolling off a support, something falling or dropping on them, somebody dropping them, a sibling jabbing at them with a toy, and a number of things.  To my knowledge, the authors offer no direct evidence that the SIs they or others report have been directly traced to abuse.  They are doing nothing more than inferring that facial bruising is a precursor to Abusive Head Trauma (AHT), and based on their bibliography they have gone out of their way to promote this notion.