You can have spikes added to your armor, which allow you to deal extra piercing damage on a successful grapple attack. The spikes count as a martial weapon. If you are not proficient with them, you take a -4 penalty on grapple checks when you try to use them. You can also make a regular melee attack (or off-hand attack) with the spikes, and they count as a light weapon in this case. (You can’t also make
an attack with armor spikes if you have already made an attack with another off-hand weapon, and vice versa.)
An enhancement bonus to a suit of armor does not improve the spikes’ effectiveness, but the spikes can be made into magic weapons in their own right.
Arcane Spell Failure Chance
Speed (20 ft.)
Melee Weapons (Martial)
Source: Core Rulebook