A study published a couple years ago on a cranial growth has recently gotten new life as the media discovered it and has pitched it as "horns" or "bone spurs" created by cellphone use. Anthropologists and other scientists, however, have been thoroughly debunking the study this week and calling journalists out on their lack of research into the topic.
A BBC in depth story published on June 13 discussed a number of changes to the human skeleton that anatomists, doctors, and biological anthropologists have seen over time. As one of the examples, the BBC report refers to a 2018 article in Nature: Scientific Reports by David Shahar and Mark Sayers, both biomechanics experts in the School of Health and Sport Sciences at the University of the Sunshine Coast in Australia. Their 2018 paper follows up and expands on a similar study they published in the Journal of Anatomy in 2016.
Shahar and Sayers examined x-rays of 1,200 individuals aged 18 to 86 years old, who were all radiographed at the same chiropractic clinic; many of the people were therefore symptomatic for cervical spine (neck) pain. Using the x-rays, the researchers measured the external occipital protuberance (EOP), a bony projection in the back of the human skull that anchors the top of the nuchal ligament, which terminates at the spine of the last cervical vertebra. The areas where muscles, tendons, and ligaments attach to bone are called entheses, and researchers often see bone growth or reduction at these sites depending on growth or trauma.
In order to understand the presence and form of the enlarged EOP in their sample population, Shahar and Sayers did logistic regression analysis. They note in the results section of their 2018 paper that "sex was the primary predictor [of enlarged EOP presence], with males being 5.48 times more likely to have EEOP than females (P < 0.001)." The same conclusion was reached in their 2016 study, where they write, based on a much smaller sample of 218 people, that the enlarged EOP "was significantly more common in males (67.4%) than in females (20.3%)."
Shahar and Sayers's finding makes complete sense to bioarchaeologists and palaeoanthropologists, scientists who work with ancient human bones, because a larger and rougher area on the back of the skull has been known for centuries to be associated more with males than with females, due to differences in overall average musculature. A robust posterior skull and projecting EOP are in fact one of the five major ways that forensic anthropologists and archaeologists can estimate the sex of an unknown skull with a reasonable degree of certainty.
The "enlarged EOP" studies have gotten new life this past week particularly because of Shahar and Sayers's interpretations of their data. In concluding their 2018 paper, they write, "We hypothesise that the use of modern technologies and hand-held devices may be primarily responsible for these postures and subsequent development of adaptive robust cranial features in our sample. An important question is what the future holds for the young adult populations in our study, when development of a degenerative process is evident in such an early stage of their lives?"
This interpretation, of course, has wildly spun out of control and landed in the form of headlines like this one from today's Washington Post: "Horns are growing on young people's skulls. Phone use is to blame, research suggests." And anthropologists are not happy. Here's why:
1. The study ignores anthropological research over many decades.
John Hawks, a palaeoanthropologist at the University of Wisconsin, took to Twitter this morning in a thread about the Washington Post's piece. He notes that the finding would be interesting if true, "but there are many warning flags with this study. The external occipital protuberance is a well-studied trait in anthropology, and we know a lot about its frequency in different populations. This paper cites none of that."
To get a feel for the anthropological research on entheseal changes, I talked to two bioarchaeologists whose research focuses on identifying patterns in past populations and attempting to understand repetitive movements those people were engaged in.
"I've seen plenty of enlarged EOPs in the early Medieval skulls I've studied -- male ones, mostly," Nivien Speith of the University of Derby tells me. "It could be genetic, or even just a simple bony outgrowth that has unknown etiology. Often, they can occur through trauma to the area as well."
Sara Becker of the University of California Riverside said that she is "not surprised by this study. My own research supports the idea that constantly performing a movement that is unusual - in this case staring downward for long periods of time - would affect and stress the muscles." These unusual movements, Becker notes, can cause underlying skeletal changes in kids, but cautions that Shahar and Sayers "study adults, which is where things get murky."
As Becker writes in a forthcoming article in the International Journal of Paleopathology, variation in entheseal changes, such as the enlarged EOP, often correlate with age, particularly advancing age, rather than providing information on muscle stress. While Shahar and Sayers note that they saw a surprisingly high number of enlarged EOPs in their younger age cohort, Becker also says that a variety of factors go into these changes.
Speith points out that, among anthropologists who have been studying the evolution of the human skull for centuries, "there is no known or evidenced direct association between an EOP exostosis and prolonged, habitual activity." But this could be the result of poor definitions. "Currently, there is no definitive palaeopathological methodology for recording entheseal changes," Becker notes, and there have long been concerns within the field of anthropology about observer error in scoring. "Presently, the best general method to record any entheseal changes may be descriptive, noting any dry bone patterns" such as irregularity, erosion, cavitation, and other anomalous bone forms, Becker suggests.
Shahar and Sayers also call the enlarged EOP a "degenerative process," and the news media has reported it as a "bone spur." These are problematic terms, Becker asserts, because "in this case, they're referring to bone growths that could be due to bone building from increased musculature and movement, not degeneration."
Regardless of the definition, though, if Shahar and Sayers are correct, the enlarged EOP could indeed be a new adaptation, triggered by a new posture. But Hawks remains unconvinced.
2. The Nature article contains multiple errors.
In referencing the main conclusion of the 2018 article, that sex was the primary predictor of enlarged EOP, Shahar and Sayers offer a chart -- but one that "shows almost no difference between males and females (and young females [are] higher than males)," Hawks points out. "One of these is obviously wrong!"
Further, the paper has no table of results or much beyond the incorrect graph. "If the paper included any table with results, it would be easy to see where the error is," Hawks complains. "As it is, the results appear to be total nonsense."
Other researchers on Twitter also had issues with the study methodology. Nsikan Akpan, who holds a PhD in pathobiology, asked his followers to spot how Shahar and Sayers's methods don't match their conclusions. He then quote-tweeted a response from a user named Dhari who suggests he'd like to see quadratic age and that it "would've been helpful to see the actual logistical model. Given how extremely parsimonious the model is, it seems many possible confounders are absorbed in the error."
Hawks voices the concern that I have heard from many researchers over the last week of this news landing in our inboxes: "How did this get through even the most basic, cursory peer review?"
3. The interpretation of "phone bone" far over-reaches the study parameters.
Suggesting that large EOPs may be related to strong neck muscles is not an outlandish suggestion at all, and in fact has been known and proven time and time again. But attributing this change to looking at cellphones smacks of "kids these days" complaints.
Shahar and Sayers actually explain that they found only one published study on the topic of EOP changes, which may have led them to think that EOP changes are a new topic and therefore worth pathologizing. They cite this 2017 BMJ Case Report on an "occipital spur" that the study authors Eby Varghese and colleagues recognize is a normal variant but that was also symptomatic. In the report, a woman presented to a dentist with misaligned teeth and tenderness over her EOP. It was suggested she rest on soft pillows to resolve it. Varghese and colleagues importantly note that an exaggerated EOP "often presents in late adolescence due to the growth spurts, and as the protuberance grows in size, it causes subperiosteal stretching resulting in tenderness."
In order to figure out if adolescents and children are at greater risk of developing EOP, then, it would appear that Shahar and Sayers need to design a study that examines these age groups. Although more difficult in terms of ethics and permissions, this sort of study would reveal whether EOP expression is happening at younger ages. However, the study would also need to use individuals who were not otherwise symptomatic, if the goal were to understand the prevalence of enlarged EOP within a population. Shahar and Sayers took their sample from, presumably, chiropractic patients and therefore not a random sample. Because of this, they cannot fairly conclude that there is a direct connection between enlarged EOP and neck issues.
Becker suggests that what Shahar and Sayers have identified is indeed a growth process, but is not sure what it means. "I would be less worried about the 'horn' area," she concludes, "and more worried about vertebrae that are getting damaged and the risk for osteoarthritis from the unusual neck position."
Until further, better designed and better reported studies are done, Hawks doesn't think the panic over cellphone use is warranted. "I'm seeing people forwarding this link who are justifying their own belief that parents should limit screen time for kids," he tells me. "Same old stuff that drives stories about evil devices." Akpan as well concludes that "those statistical blips - plus the fact that they didn't actually measure cellphone usage—make the takeaways pretty suspect."
Will your kid's "evil" cellphone give him "horns"? No. But if your neck hurts after hours of looking down at it, you might want to lie down on a pillow for a bit.
