Here's a hint as to what the Throckmorton Sign is. It's also known as the John Thomas Sign, and it's going to make the x-ray in this entry ever so slightly not safe for work.
Doctors have all kinds of medical slang, much of which they keep from the public for obvious reasons. Here's a relatively innocent one that slipped through into public knowledge. It's called the Throckmorton Sign, and it shows up in x-rays of male patients. In case the "male" didn't tip you off, it is also called the John Thomas Sign.
It's the slight "shadow" of the penis that shows up on medical x-rays of the male pelvis. For the most part, it's just a funny thing that doctors notice and that they point out, or that they have to explain to relatively new interns. One doctor, though, suggested that the sign indicated something interesting. After reviewing x-rays, the doctor noticed that, for patients with hip fractures, the Throckmorton Sign always pointed towards the fracture. The doctor wrote a letter to a medical journal about the anomaly.
Others wrote back, noting that patients with hip fractures angled their hips slightly to avoid discomfort, which is why the Throckmorton Sign always faced toward the broken hip. It was a side effect of posture, not an actual medical symptom. And it's great slang. Can any doctors comment on why it's called "throckmorton"?
Image: Attribution: © Nevit Dilmen.