Geoff
I've got a feeling that the UK docs call the perinium (front of your bum) 12 o clock - so spine is 6.
I say this because my Doc confirms that I have a fissure at the front (less common in guys) which is slightly off the centre line - he calls it 11 o clock. This counts as within the usual areas (at or around 6 or 12 o clock). Mine came from a dose of Guardiosa (bacteria from fecal matter in water) after I swam in a pond! It took them months to diagnose and the end result was a tenderised bottom!
Good luck - I'm off to the hospital next week - having tried Rectogesic, Diltiazem and non-intervention I'm thinking off requesting a 'cut' - life's too short to have a pain in the arse all day (pardon my profanity)