hmm……楼上的理论支持在20080630版的FAQ53页
If you attack only with your armor spikes during your turn
(or use the armor spikes to make an attack of opportunity), you
use them just like a regular weapon. If you use the full attack
action, you can use armor spikes as either a primary light
weapon or as an off-hand light weapon, even if you’re using a
shield or using a two-handed weapon. In these latter two cases,
you’re assumed to be kicking or kneeing your foe with your
armor spikes.