A surgical instrument includes a mount body, an arm, a joint, and a tool; the mount body configured to mount to a retractor, a bottom surface of the mount body facing the retractor when mounted, a front edge of the mount body running at an angle to the bottom surface; the arm pivotally connected on a proximal end of the arm via the joint to or along the front edge of the mount body; the tool connected to a distal end of the arm; the arm configured to be movable between a plurality of positions relative to the mount body and to be temporarily lockable in these positions; and the joint configured such that a proximal portion of the arm extending from and adjacent the mount body is pivotable to and temporarily lockable in a position substantially perpendicular to the mount body along portions of the front edge.