Why these two positions come top of the list is to do with angle and 'vigour'. According to the study's authors:
We can speculate that when the man is in a dominant position and very excited, intercourse can become extremely vigorous, triggering greater impact at the time of trauma when the penis slips out of the vagina and hits against the perineum or pubic symphysis.
During missionary, with the woman on top, her position or shifting of position can also cause a breakage.
Other injuries on the list which were much rarer included:
Masturbation (17 per cent)
'Rolling over' (3 per cent)
'Blunt trauma' (2 per cent)
According to NHS England, 'reported cases of penile fracture are rare', but they also say this may be because men do not report injuries out of embarrassment.
Seeking medical attention is always better than giving in to social embarassment.
The positions which were most dangerous for women were not addressed in the study.