NZ Skeptics Articles

The Throckmorton Sign

Mark Honeychurch - 2 September 2024

A couple of weeks ago I was browsing Reddit images (I guess it’s my old-school version of Tik Tok), when I came across a post extolling the virtues of the Throckmorton Sign as a diagnostic tool. This tool is named after Thomas Bentley Throckmorton, an early 20th century American neurologist.

The post that I was reading explained that it is used by radiologists to diagnose pelvic or hip fractures. Sometimes the pain of a fracture doesn’t feel localised, so a patient is unable to explain which side a fracture has occurred. In some occasions the damage is also not clearly visible in an X-ray, and in this case the Throckmorton Sign in the X-ray is said to help point in the direction of the issue.

The sign’s other popular name, the John Thomas Sign, might help you to figure out what this tool involves, as is the fact that this is predominantly useful as a diagnosis tool for men. If you’ve still not figured it out, here’s an X-ray that should make it even clearer - see if you can figure out what in this image is “pointing” in a certain direction:

Yep, the Throckmorton Sign is basically the direction the penis is pointing. The social media post I was reading explained that, for some reason or other, a man’s penis will usually point towards the side of the body that has been damaged. It seems like this is mostly a fun in-joke for radiologists, but some swear that it’s clinically useful - and certainly the author of the post I was reading seemed to think it was a real thing. If we also take this idea seriously for a second, it’s not too hard to think a scenario where it might make some kind of sense:

(Now, I’m going to use a man as an example here, but I understand that not all men have a penis, and not all people with a penis are men. I hope that this disclaimer is enough to excuse any places in the rest of this article where I might fail to consistently include trans women and others in my language)

Imagine a man who has fractured one side of their pelvis, and has not been able to ascertain on which side they are feeling pain. They are waiting for an X-ray to see if this will shed some light on the problem, lying on a gurney in a hospital gown. They are in serious pain, and lying on their back doesn’t help. Lying on one side is also painful, but on the other side there is a small amount of pain relief. When lying on their side, their penis would tend to gravitate downwards, and as they’re wheeled into the X-ray room, their penis is now pointing in a direction that has been dictated by the site of the injury, without them consciously being aware of it.

Granted, in this scenario it seems most likely that the damaged side of the pelvis would likely be the side that the patient isn’t lying on, and so the penis would tend to point in the opposite direction to the injury - a negative Throckmorton. I could also imagine that in some cases a patient might be required to lie on a certain side to align with the X-ray equipment, regardless of their pain. The patient could also be fitted with a catheter, which would have a bearing on which direction the penis points. Finally, there’s a chance that a patient could be wearing tight enough fitting underwear under their hospital gown (or instead of a hospital gown) that shifting from side to side wouldn’t have an effect on the direction they “dress”.

Yes, for those not in the know, men (and other penis owners) tend to have a side they “dress” (or “hang”) to - the side on which their penis naturally sits. This is true at least in countries where the adopted fashion includes tight clothing such as briefs, boxer shorts, trousers (or pants, if you’re that way inclined), etc. My understanding is that the side a man chooses involves a combination of comfort, ease of access through the fly, handedness, clothing design, genetics, and more. If you trust Real Men Real Style (and why wouldn’t you), 75% of men dress to the left, 17% to the right and 8% straight down - although, for the life of me, I couldn’t find where they sourced this statistic from. Maybe they asked around the office? (For the record, as well as being in the 10% minority of left-handed people, I’m one of the 17% who dress to the right - I wonder how tightly these might be correlated)

There have been several papers, letters, etc published in the last 20 years or so about the Throckmorton sign. We can see more names for this idea in the papers below, such as the “Oram’s Sign” and “Pelvic Shadowing”. The earliest of these academic writings (John Thomas sign: common distraction or useful pointer?) is even from New Zealand:

A response to the New Zealand letter (Yorkshire men straight to the point, or not? Validation of the John Thomas Sign) contains some puns that must have been fun to squeeze in:

“The ‘John Thomas Sign’ has been thrust, from the intellectual banter of trauma Meetings”

“We investigated whether the John Thomas (JT) sign was upstanding to scrutiny or a mere flop”

“The authors do not wish to go ‘head to head’ with the New Zealand group”

What’s great about the fact that so many academics have taken the time to take this idea seriously is that there’s now enough research that a team has been able to use the papers to create an academic summary:

For those not well-versed in these terms, a systematic review and meta-analysis are different ways of summarising previous research, and are usually considered to be the gold-standard for clinical research. A systematic review looks at all the previous research on a topic, deciding on minimum criteria for inclusion. These criteria can include pretty much anything to do with the methodology used in the study design, including blinding, availability of raw data, cohort size (number of subjects tested) and more. Any studies that fail to meet the criteria are excluded from the systematic review, and the remaining papers are summarised and a conclusion is reached about whether there’s a real effect being witnessed, and with medical papers whether that effect is clinically useful. A meta-analysis is similar to a systematic review, but it attempts to take the raw data from original studies (again, selected against a set of strict criteria) and merge them together using the magic of maths to create a resultant data set that is more “powerful” when combined than the original data sets. This new data might be able to detect a smaller effect size, or increase the confidence level that an effect is real rather than the result of random chance.

The results and conclusion of the systematic review and meta-analysis into the John Thomas Sign tell us exactly what we’d expect from this fun little idea:

Results: In total, nine articles were isolated and assessed. A total of 1942 participants were included. The mean sample size amongst these included studies was 243 participants with a median of 198 participants. Since the necessary data needed for the Meta-analysis was only present in the 6/9 studies assessed, these 6 were analyzed further. The JTS was positive in 1089 out of 1439 patients with a pooled sensitivity of 75.7% (95%CI, 73.4%-77.9%). There was a large variation in the sensitivity and specificity amongst studies, accounting for a non-significant summary Odds Ratio effect of -0.03.

Conclusions: Based on this review, there is insufficient statistical evidence to support the reliability of the JTS to predict the laterality in the case of a hip fracture on the standard AP pelvis x-ray.

So, basically, the results are a bit all over the place, with a conclusion that this should most definitely not be relied upon as a diagnostic tool - it’s much better to just look for the damage directly on the X-ray. As Chris Nickson and Mike Cadogan from the Life in the Fast Lane medical blog put it:

“the astute emergency physicians among us will wisely elect to actually look for pathology on the radiograph rather than rely solely on the JT sign”

p.s. I find it a little funny that Dr Throckmorton, having dedicated his life to both his profession and “fundamental Christian values”, is best known by radiologists around the world because of their jokes about penises being visible on X-rays.