Shatterbone Strike is a 3rd-level barbarian encounter attack power.[PH2:53]
Shatterbone Strike
Barbarian Attack 3
The fury of your assault knocks your foe off balance, leaving a hole in its defenses.
Encounter ✦ primal, weapon
Melee weapon
Target: One creature
Attack: Strength vs. AC
Hit: 2[W] + Strength modifier damage, and the target takes a –2 penalty to AC until the end of your next turn.
Thaneborn Triumph: The penalty to AC equals your Charisma modifier.