I had to look this up to find out what it was. It's more often called the
John Thomas sign and seems to have been named after a physician named
Thomas Bentley Throckmorton who was born in 1885 and died in 1961. It is exceedingly unlikely that the screenwriters or film audiences in 1938 would have known about this -- I doubt if there are hardly any screenwriters or members of a film audience who have no training in a medical profession who've heard of it today. So I think the problem with "Throckmorton" has to do with its sound and length, not an association with this discredited medical sign.
https://radiopaedia.org/articles/throckmorton-sign-pelvis?lang=us