Letter John Thomas sign: common distraction or useful pointer?
MJA 1998; 169: 670
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To the Editor: Anthropomorphic studies of the penis have largely
centred on comparisons of length and girth and have not always grasped
the substance of a more important companion feature, namely
direction. The "John Thomas" (JT) sign refers to the position of the
penis in relation to unilateral disease on routine x-ray, with a
positive sign being implied when inclined to the side of the disorder
(eg, a fractured hip). Although readily recognised, it has attracted
little scholarly attention, being confined to darkroom banter or to
impressing humourless medical students. While some degree of
prudishness may have been responsible for curbing potential
applications of the JT sign in the past, we believe that the position of
the penis now needs to be set straight.
We identified 65 consecutive male patients with a fractured right hip and 65 with a fractured left hip. The penile position was graded as positive (illustrated in the Figure), negative or equivocal (part of the glans below the symphysis). The penile bent was similarly defined in a further 65 patients in whom fracture was suspected but not identified.
The JT sign was positive (ie, the penis inclined toward the fracture) in 70% of patients with hip fracture (91/130), negative in 11% (14/130) and equivocal in 19% (25/130). Consequently, the sensitivity (70%; 95% CI, 62%-78%) and specificity (67%; 95% CI, 60%-75%) for the JT sign are low. The genital disposition did not correlate with length of stay (r = 0.14). Demonstration of the JT sign before x-ray may be as useful as demonstrating leg shortening and external rotation -- synonymous but in no way diagnostic. And, if all patients with suspected hip fractures are routinely x-rayed, the prognostic significance of the pointer is minimised. Nonetheless, while the clinical utility of the JT sign may be limited, it appears to be real and reproducible. Thirty-one per cent of patients (20/65) presenting with a hip injury without fracture inclined to the injured side. If at least half of x-rays for hip fracture confirm the diagnosis, the predictive value of a positive JT sign is over 69%. Similar eponymous signs, such as Homan's, are widely flaunted. By comparison, the JT has been underexposed. Genital asymmetry is common and varies with handedness,1 although most incline leftward. That equal proportions of right (46/65) and left (45/65) hip fractures had positive signs in our study would reinforce the belief that somatic sensations can override higher cerebral control. Recent data suggest that genital inclination may be related to, among other things, different patterns of cognitive function and certain malignancies.2 The findings in our study, like those of the recent United States Starr Report,3 point to at least one more discriminating relationship.
Merlin C Thomas Brett D Lyons Robert J Walker Dunedin Department of Medicine, Dunedin Clinical School
of Medicine
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