The John Thomas sign (JT sign) is also known as Throckmorton sign is observed radiographically in male patients. A patient has a positive JT sign if his penis points towards the side of pathology on a radiograph of the pelvis.

The sign tends to be commented on by middle-aged male radiologists and orthopedists suffering from Peter Pan syndrome. Some may even suspect an occult fracture purely based on the observed radiographic penile orientation. While this can clearly be very amusing (in the same way that some people can’t help but laugh when they hear the word “Uranus”) the question remains – is the sign actually of any use?

Throckmorton sign John Thomas sign
Throckmorton sign: Penis Points to Pathology

A few studies have tried to answer this question.

1998 – The first was published by a few of my countrymen in the Medical Journal of Australia. They found that the the sensitivity (70%; 95%CI 62-78%) and specificity (67%; 95%CI 60-75%) for the JT sign were low.

2007Ya’ish and Baloch found that JT sign had sensitivity of 30.0% (95% CI 21.2-40.0%) and specificity of 86.0% (95%CI 77.6 – 92.1%).

2010Saeed Solooki and Amir Reza Vosoughi reviewed the usefulness of the John Thomas sign in determination of lower limb fractures. They evaluated 500 plain pelvic radiographs of male patients with single fracture in the lower limb. Positive sign was defined as direction of the penis shadow to the fractured limb. They found the sign to be positive in 87.8% of cases. Strongest positive correlation in patients with hip fractures.

Solooki et al 2010 John Thomas or Throckmorton sign evaluation

Number (Percentage) of positive and negative JT sign in each fracture group. Solooki et al 2010

2014Murphy et al evaluated the accuracy of the JT sign in the context of a consecutive series of male patients with hip fractures and tried to determine a relationship between side/size of penile lie and the side of fracture. They observed 200 male AP pelvis radiographs; 100 with hip fracture and 100 as control. The patient age as well as side, length and angle of penile lie were measured. They found the JT sign was positive in 46 cases, neutral in 11 and negative in 43 cases and found no link between side of fracture and penile attitude. 

2019Gerber et al assessed the clinical validity and accuracy of the JT sign (JTS) by performing a systematic review and meta-analysis. Nine articles were isolated and assessed and 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. They concluded that the penile shadow on an AP pelvic X ray is not a reliable “pointer” in determining the laterality of a pelvic or hip fracture. 

Gerber et al. Journal of Clinical Orthopaedics and Trauma 2017 John Thomas sign

Fig. 3. Illustration of the Positive and Negative JTS (John Thomas Sign). Gerber et al 2019
3a. Negative JT sign, penile shadow points away from left acetabular fracture
3b. Positive JT sign, penile shadow points towards the left acetabular fracture.
3c. Negative JT sign, penile shadow (arrows) is neutral or points away from the side of the fracture (left neck of femur fracture).
3d. Positive JT sign, penile shadow (arrows) points towards the side of the fracture (left neck of femur fracture) 

Clearly there are significant disparities in the findings of these studies, and a larger study is urgently needed. A future study must control for confounders such as patient handedness, whether boxers or briefs are worn, and which way things usually like to hang.

At this stage, although JT sign compares reasonably well with Homans sign (a useless test some misguided souls might still use to diagnose deep vein thrombosis), I think 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.

Conclusion: more studies needed.


References


Cite this article as: Chris Nickson and Mike Cadogan, "John Thomas sign," In: LITFL - Life in the FastLane, Accessed on May 19, 2022, https://litfl.com/john-thomas-sign/.

eponymictionary

the names behind the name

Chris is an Intensivist and ECMO specialist at the Alfred ICU in Melbourne. He is also a Clinical Adjunct Associate Professor at Monash University. He is a co-founder of the Australia and New Zealand Clinician Educator Network (ANZCEN) and is the Lead for the ANZCEN Clinician Educator Incubator programme. He is on the Board of Directors for the Intensive Care Foundation and is a First Part Examiner for the College of Intensive Care Medicine. He is an internationally recognised Clinician Educator with a passion for helping clinicians learn and for improving the clinical performance of individuals and collectives.

After finishing his medical degree at the University of Auckland, he continued post-graduate training in New Zealand as well as Australia’s Northern Territory, Perth and Melbourne. He has completed fellowship training in both intensive care medicine and emergency medicine, as well as post-graduate training in biochemistry, clinical toxicology, clinical epidemiology, and health professional education.

He is actively involved in in using translational simulation to improve patient care and the design of processes and systems at Alfred Health. He coordinates the Alfred ICU’s education and simulation programmes and runs the unit’s education website, INTENSIVE.  He created the ‘Critically Ill Airway’ course and teaches on numerous courses around the world. He is one of the founders of the FOAM movement (Free Open-Access Medical education) and is co-creator of litfl.com, the RAGE podcast, the Resuscitology course, and the SMACC conference.

His one great achievement is being the father of three amazing children.

On Twitter, he is @precordialthump.

| INTENSIVE | RAGE | Resuscitology | SMACC

Emergency physician MA (Oxon) MBChB (Edin) FACEM FFSEM with a passion for rugby; medical history; medical education; and asynchronous learning #FOAMed evangelist. Co-founder and CTO of Life in the Fast lane | Eponyms | Books | Twitter |

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