A medical device for grinding substance inside a body lumen includes a rotatable tubular drive shaft, a treatment member connected to the drive shaft, and a tubular member possessing an axially extending lumen that extends throughout the tubular member. The tubular member is mounted on the treatment member and surrounds a portion of the treatment member so that the treatment member is rotatable relative to the tubular member. The treatment member includes a shearing portion, and the tubular member includes a protrusion that projects toward the lumen of the tubular member. The protrusion is located axially in front of the shearing portion and interacts with the shearing portion during relative rotation between the treatment member and the tubular member to shear debris resulting from the grinding of the substance.