Monthly Archives: July 2009

Beware the Spinal Trap

Today, numerous blogs and magazines from all around the world will publish Simon Singh’s article on chiropractic from April 2008, with the libellous part removed. The Guardian withdrew the article after the British Chiropractic Association sued for libel (please repost).

BEWARE THE SPINAL TRAP

Some practitioners claim it is a cure-all, but the research suggests chiropractic therapy has mixed results – and can even be lethal, says Simon Singh.

You might be surprised to know that the founder of chiropractic therapy, Daniel David Palmer, wrote that “99% of all diseases are caused by displaced vertebrae”. In the 1860s, Palmer began to develop his theory that the spine was involved in almost every illness because the spinal cord connects the brain to the rest of the body. Therefore any misalignment could cause a problem in distant parts of the body.

In fact, Palmer’s first chiropractic intervention supposedly cured a man who had been profoundly deaf for 17 years. His second treatment was equally strange, because he claimed that he treated a patient with heart trouble by correcting a displaced vertebra.

You might think that modern chiropractors restrict themselves to treating back problems, but in fact some still possess quite wacky ideas. The fundamentalists argue that they can cure anything, including helping treat children with colic, sleeping and feeding problems, frequent ear infections, asthma and prolonged crying – even though there is not a jot of evidence.

I can confidently label these assertions as utter nonsense because I have co-authored a book about alternative medicine with the world’s first professor of complementary medicine, Edzard Ernst. He learned chiropractic techniques himself and used them as a doctor. This is when he began to see the need for some critical evaluation. Among other projects, he examined the evidence from 70 trials exploring the benefits of chiropractic therapy in conditions unrelated to the back. He found no evidence to suggest that chiropractors could treat any such conditions.

But what about chiropractic in the context of treating back problems? Manipulating the spine can cure some problems, but results are mixed. To be fair, conventional approaches, such as physiotherapy, also struggle to treat back problems with any consistency. Nevertheless, conventional therapy is still preferable because of the serious dangers associated with chiropractic.

In 2001, a systematic review of five studies revealed that roughly half of all chiropractic patients experience temporary adverse effects, such as pain, numbness, stiffness, dizziness and headaches. These are relatively minor effects, but the frequency is very high, and this has to be weighed against the limited benefit offered by chiropractors.

More worryingly, the hallmark technique of the chiropractor, known as high-velocity, low-amplitude thrust, carries much more significant risks. This involves pushing joints beyond their natural range of motion by applying a short, sharp force. Although this is a safe procedure for most patients, others can suffer dislocations and fractures.

Worse still, manipulation of the neck can damage the vertebral arteries, which supply blood to the brain. So-called vertebral dissection can ultimately cut off the blood supply, which in turn can lead to a stroke and even death. Because there is usually a delay between the vertebral dissection and the blockage of blood to the brain, the link between chiropractic and strokes went unnoticed for many years. Recently, however, it has been possible to identify cases where spinal manipulation has certainly been the cause of vertebral dissection.

Laurie Mathiason was a 20-year-old Canadian waitress who visited a chiropractor 21 times between 1997 and 1998 to relieve her low-back pain. On her penultimate visit she complained of stiffness in her neck. That evening she began dropping plates at the restaurant, so she returned to the chiropractor. As the chiropractor manipulated her neck, Mathiason began to cry, her eyes started to roll, she foamed at the mouth and her body began to convulse. She was rushed to hospital, slipped into a coma and died three days later. At the inquest, the coroner declared: “Laurie died of a ruptured vertebral artery, which occurred in association with a chiropractic manipulation of the neck.”

This case is not unique. In Canada alone there have been several other women who have died after receiving chiropractic therapy, and Edzard Ernst has identified about 700 cases of serious complications among the medical literature. This should be a major concern for health officials, particularly as under-reporting will mean that the actual number of cases is much higher.

If spinal manipulation were a drug with such serious adverse effects and so little demonstrable benefit, then it would almost certainly have been taken off the market.

Simon Singh is a science writer in London and the co-author, with Edzard Ernst, of Trick or Treatment? Alternative Medicine on Trial.

You can find this article and information about Simon Singh’s case at the Sense About Science website, as well as a petition to keep libel laws out of science.

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Above photo by jharkn under creative commons license.

The impact of cranial plasticity on the reconstruction of human population history

Palaeoanthropologists are interested in reconstructing the evolutionary history of our species from fossil remains. Like other taxonomists they are primarily interested in identifying shared derived traits, otherwise known as synapomorphies. A synapomorphic trait is shared by some members of a taxa and not by others, since the former inherited this trait from a common ancestor. For instance, the retention of a clavicle (collar bone) is one of the more cited synapomorphic traits common to all primates.

A homoplasy is a trait that is present in two or more taxa but that has not been derived through common ancestry but rather through convergence, parallelism, or reversal. The wings of insects, birds and bats are homoplasies, since they arose through convergent evolution. Thus, homoplasies and synapomorphies may be identical in appearance but are distinguished by whether or not they arose through common ancestry. As a result, it can often difficult to pry apart traits which are synapomorphies from those which are homoplasies. A subset of homoplasies are termed homoiologies. Lycett and Collard (2005) define homoiologies as:

“… phylogenetically misleading resemblances among a group of taxa that can be ascribed to phenotypic plasticity. That is, homoiologies are homoplasies that result from the expression by a genotype of different phenotypes in response to different environmental conditions.”

They arise primarily from nonheritable epigenetic responses to mechanical stimuli. The “homoiology hypothesis” (Lieberman 1995) was derived from the well known fact that bone shape and size can be modified by mechanical loading. As such, homoiologies are expected to have greater influence upon the more plastic regions of a phenotype.

The homoiology hypothesis makes two testable predictions:

1. Traits subject to biomechanical stress should exhibit higher within-taxon variability due to the increased plasticity.

2. These traits should be less reliable for reconstructing phylogeny.

Previous studies have examined the homoiology hypothesis in various primate species (Collard and Wood 2007, 2000). These studies found that the regions of the skull associated with mastication indeed exhibited higher within-taxon variability but they were as reliable in reconstructing phylogenetic relationships as other regions of cranium not directly associated with masticatory function. Since these studies looked at interspecific studies, it was suggested that maybe homoiology was a greater problem for intraspecific studies.

A paper (in press) in the Journal of Human Evolution by Noreen von Cramon-Taubadel tests the homoiology hypothesis in an intraspecific study of human populations. Areas of the skull related with mastication would be expected to be under greater biomechanical stress, and as such be more affected by homoiology. She divided the skull into zones thought to be related to mastication (zygotemporal and palatomaxilla regions) and zones relatively unaffected by mastication (the upper face, cranial vault and basicranium). She tested the predictions of the homoiology hypothesis by comparing craniometric data with matched molecular data for 12 modern human populations.

Like previous interspecific studies, regions of the skull related to mastication show great variability (as predicted by the homoiology hypothesis) but these regions were no less reliable at reconstructing phylogenies (at variance with the homoiology hypothesis). It is worth noting that if biomechanical stress affects all individuals in the same way then these characters will not confound the phylogenetic analysis.

These findings mean that the homoiology hypothesis is flawed in at least some of its premises. The results of this and previous studies suggest that within-taxon variability should not be used to assertion the usefulness of cranial traits for determining phylogenetic relationships. Moreover, it does not appear to hold that homoiologies are any more problematic in determining intraspecific evolutionary relationships as interspecific ones. Finally, even though regions of the skull related to mastication are more variable than non-masticatory regions, they do not seem to be any less reliable for the reconstruction of phylogenies.

References
Collard and Wood. Hominin homoiology: An assessment of the impact of phenotypic plasticity on phylogenetic analyses of humans and their fossil relatives. Journal of human evolution (2007) vol. 52 (5) pp. 573-584.

Collard and Wood. How reliable are human phylogenetic hypotheses?. Proc. Natl. Acad. Sci. U.S.A. (2000) vol. 97 (9) pp. 5003-6.

Cramon-Taubadel. Revisiting the homoiology hypothesis: the impact of phenotypic plasticity on the reconstruction of human population history from craniometric data. Journal of Human Evolution (2009) pp. 1-12.

Lieberman. Testing hypotheses about recent human evolution from skulls: integrating morphology, function, development, and phylogeny. Curr. Anthropol. (1995) 36, 159–197.

Lycett and Collard. Do homoiologies impede phylogenetic analyses of the fossil hominids? An assessment based on extant papionin craniodental morphology. Journal of human evolution (2005) vol. 49 (5) pp. 618-642.

Wood and Lieberman. Craniodental variation in Paranthropus boisei: a developmental and functional perspective. American Journal of Physical Anthropology (2001) vol. 116 (1) pp. 13-25.

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Above photo by wauter de tuinkabouter under creative commons license.