Axespike

 
Prerequisite(s): Weapon Focus (Armor Spikes), Heavy Armor Proficiency, Weapon Proficiency (Armor Spikes and Greataxe)
 
Benefit: When you make a full attack with your greataxe, you can make an additional attack with your armor spikes at a -5 penalty. You can only add 1/2 your Strength modifier to the damage from this extra attack, as if it were an attack with an off-hand weapon.
 
Source: Races of Stone