
lol..not at all anna :D
(when Im training I tell my students "the stupidest question is the one that
wasnt asked!" *wry smile* )
Marrow bone (cortical tubular bone) does contain fat.
Knuckle bones are softer honeycomb tissue (cancellous bone)
You do get some fat,connective muscle tissue etc on the Knuckles but I would say not enough to make any major nutritional impact, thats why they're favoured as 'recreational' bones.
I would say it very much depends on your dog (size/breed/propensity to over eat or put on weight), type of diet and excercise levels as to how closely you should take into account 'any' added fat from recreational bones, the ones that really do make a difference for the worst (IMO) are the deep fried variety of bones you see in petshops/PAH etc.
RMB's are a different kettle of fish and of course should be taken into account with feeding levels (if for example your a half and halfer barfer ;) )
HTH? :D