A posterior spinal fusion system may include a plurality of cannulas (142, 262, 272) that mate with connecting elements (140) having cages (152) polyaxially coupled to pedicle screws (150, 260, 270). The cannulas (142, 262, 272) maintain access to the pedicle screws (150, 260, 270) to facilitate percutaneous insertion of a fusion rod (316) into engagement with the cages (152). Each cannula (142, 262, 272) has a pair of blades (194, 196) that may be held together by an abutment member (144, 264, 274). Each abutment member (144, 264, 274) is configured to abut the skin to define a variable subcutaneous length of the corresponding cannula (142, 262, 272). Each abutment member (144, 264, 274) is also lockably removable from the corresponding blades (194, 196) to enable the blades to pivot with respect to the connecting element (140) to a position in which they can be withdrawn from the connecting element. The blades (194, 196) of each cannula are spaced apart to provide first and second slots (220) of each cannula, through which the fusion rod (316) can be percutaneously inserted.
