Read through the application form carefully.
http://www.caa.co.uk/docs/49/Medical...n%20MED160.pdf
There only seems to be one section (126) which applies to your situation.
I have a scar on my lower right leg from bone protrusion resulting from a compound fracture of tibia and fibula plus minor facial and head scars, all of which resulted from a road traffic accident. All I wrote was something like
"Serial 126 - RTA - date - #R Tib & Fib, minor head injuries, no complications" - the AME asked me what happened, I told him, we had a laugh about it and that was the end of it. Since then I write
"Serial 126 - RTA - No change".
Answer the questions truthfully but only what is asked for - do not embellish things with information that is not asked for. I think if everyone declared the reason for every single scar on their bodies the examination would need to be a lot longer (and the price would go up. DO NOT say that too loud at Gatwick. They'll form a committee to justify increasing charges and twenty meetings later the price will sky-rocket
).
Good luck - you shouldn't have any problems.