A minimally invasive spinal fixation system comprises first and second bone screws each including a threaded shaft for respective engagement with a vertebra and a yoke articulatingly attached to the shaft, each yoke including a pair of upstanding opposed arms defining a slot therebetween. A connecting element has opposite ends and a longitudinal axis extending therebetween, the connecting element including a tab adjacent each end projecting from the connecting element transversely to the longitudinal axis. Bone screw extensions are provided for guiding the placement of the connecting element into the yoke slots, each extension having a pair of opposing slots that are sized to pass the tabs through the extensions when oriented in a first position and to prevent passage when the tabs are oriented in a second different position.
