From the RuneScape Wiki, the wiki for all things RuneScape
A Broken axe (mithril) was a mithril axe that was broken by an ent random event. Broken mithril axes could be fixed at Bob's Brilliant Axes in south Lumbridge for 18 coins.
The broken axe was removed with the removing of the ent random event on 25 February 2009. This item no longer exists, as all broken axes were automatically repaired in the update.