This is a clinical sign found specifically in males. For obvious reasons! It is usually referred to in cases of patients with orthopedic issues of the hip or upper femoral areas: one that is caught on an X-Ray. In a Throckmorton Positive patient, we would find the offending pathology on the side to which, err… to which the penis points.
Confused? Well, I can hardly blame you, because few are not taken aback when they first come across the details of this sign. To elucidate the sign and make comprehension easier, here is a classic example from Wikipedia of a Throckmorton Sign positive patient:
The penis is pointing to the left, where there is a pertrochanteric fracture. So, this patient is Throckmorton Sign positive on the left side.
In case you have not been able to catch on to it yet, this sign is a typical example of medical humor and not to be taken seriously. However, some people decided to take a scholarly look at the sign and assess how good (or bad) it was in ascertaining the correct side of the pathology.
In one of the studies (1) that I could dig up about the Throckmorton Sign, the investigators, very seriously, state:
In groups 1 [radiologically proven hip/femur fractures, n=100] and 2 [control group with no fractures but who got the hip/femur X rays done for suspected fractures, n=100] the penile shadow pointed to the left in 29, 20 and to the right in 16, 4 patients respectively. It pointed to the suspected side in 30 patients in group1 and 14 in group 2. JT sign had sensitivity of 30.0% (95% confidence interval 21.2% to 40.0%) and specificity of 86.0% (77.6 – 92.1%). Positive and negative predictive values were 68.2% (52.4 – 81.4%) and 55.1% (47.0 – 63.0%) respectively. The number of patients whose penis pointed to either side (right or left) rather than the midline, irrespective to the painful side, was significantly higher in those who had fractures (p=0.002, Fisher’s exact test), and in younger patients (p<0.0001, Mann Whitney U test).
Throckmorton sign has several known confounders. Apparently, handedness has a relationship with hanged-ness. Also, it seems, that, anatomically speaking,the male member is rarely the one to stay in an equivocal position (aka midline): it has a propensity to point more often to the left, though the study quite above (1) has shown that pathology or pain had a deviating effect.
This sign owes its names to an American Neurologist who practiced in the late 1800s and early 1900s. Tom Bentley Throckmorton, a graduate of the Jefferson Medical College in Philadelphia, received his doctorate in 1909. He practiced eventually in Iowa. He went on to be the Governor of the Iowa chapter of the American College of Physicians (according to Wikipedia)! He was the Governor of the Iowa chapter from 1927 to 1936. Throckmorton also published widely (as evidenced by his Google Scholar search results). Throckmorton passed away in 1961.
He has, to his name, another sign, the Throckmorton Reflex, which, for a change, is a real thing! It is a variant of Babinski’s reflex. There is extension of the big toe and flexion of other toes on percussion over the metatarso-phalangeal joint medial to the extensor hallucis longus muscle. He described this sign in a 1911 paper (3) in the Journal of the Americal Medical Association. This sign is positive in lesions affecting the pyramidal tract.
Unfortunately, the century-old JAMA paper seems to be locked behind a pay wall and I am not about to raise #icanhazpdf hell to access the paper for a mere blog post.
The sign is also known as the John Thomas sign. Who, pray, is John Thomas? Well, let Urban Dictionary clear it up for you:
1. F Ya’ish, & K Baloch (2008). John Thomas Sign: Truth or Myth? The Internet Journal of Orthopedic Surgery, 8 (2) DOI: 10.5580/854
2. Thomas MC, Lyons BD, Walker RJ. John Thomas sign: common distraction or useful pointer? Med J Aust 1998; 169 (11):670.
3. Throckmorton TB. A new method for eliciting extensor toe reflex. JAMA. 1911;LVI(18):1311-1312. doi:10.1001/jama.1911.02560180005003.