science

John Thomas sign

John Thomas sign is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand John Thomas sign rather than just read about it. In short: The John Thomas sign, also known as the Throckmorton sign, is a slang or joke term used in the field of radiology. It refers to the position of a penis as it relates to pathology on an X-ray of a pelvis.

Key takeaways

John Thomas sign belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect John Thomas sign to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of John Thomas sign from memory before moving on to harder problems.

Reference excerpt

The John Thomas sign, also known as the Throckmorton sign, is a slang or joke term used in the field of radiology. It refers to the position of a penis as it relates to pathology on an X-ray of a pelvis. When the penis (visible on the X-ray as a shadow) points towards the same side as a unilateral medical condition such as a broken bone, this is considered a "positive John Thomas sign," and if the shadow points to the other side, it is a "negative John Thomas sign." Studies have shown that the "sign" is no better than chance at identifying the location of a hip fracture. In those cases where the John Thomas sign is positive, it has been proposed that a person with a displaced hip fracture may try to lie on the injured side to immobilize the fracture and reduce pain; the penis then inclines toward the downward (injured) side. Andy Murray, British professional tennis player, released a picture of his pelvic X-ray following his hip resurfacing surgery on January 29, 2019, clearly demonstrating an example of a negative John Thomas or Throckmorton sign where his penis pointed away from the site of injury. The release of the X-ray image with visible genitalia was discussed by Piers Morgan on Good Morning Britain, prompting Murray, who was watching at the time, to message the show, stating, "Please can you stop discussing my genitals on national TV, I was heavily medicated at the time of posting."

References

Illustrations

Worked examples

Example 1 — a first encounter with John Thomas sign

Start with the simplest possible case. Write down what John Thomas sign claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to John Thomas sign before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about John Thomas sign ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of John Thomas sign

In research: John Thomas sign appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses John Thomas sign in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: John Thomas sign is common in secondary-school and first-year university syllabi. It links to neighbouring topics Human penis, Medical slang, Penis, so understanding it makes those chapters shorter.
In everyday life: Look for John Thomas sign outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study John Thomas sign in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what John Thomas sign means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain John Thomas sign out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is John Thomas sign in simple terms?

Why does John Thomas sign matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study John Thomas sign?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on John Thomas sign.