There is damage to the articular surface cartilage which can occur either from an acute injury or more commonly after repetative injury and/or wear and tear. If the the bones at the joint in questions are not aligned properly then this mechanically adds to the wear the the joint receives with activity and increases the propensity of this occuring. Pictured below is linear damage to the articular surface of the 2nd metatarsal head.
The following pictures are debridement of damaged cartilage of the second metatarsal head that is abnormal in appearance and/or loose. This is removed completely to expose the subchondral (underneath cartilage) bone plate.
Drills holes are then placed through the bone plate to allow bleeding in the area which will aide in healing of the cartilage surface with fibrocartilage which is a kind of scarring of cartilage.