A surgical instrument for implanting a spinal fixation rod, comprising: an engagement assembly including a motion inhibitor configured to releasably engage the spinal fixation rod, the engagement assembly includes a first engagement wall and a second engagement wall so as to define a rod receiving gap that is defined between the first and second engagement walls (73, 119), the rod receiving gap configured and sized to receive a portion of a spinal fixation rod and to permit the spinal fixation rod to pivot therein; a transfer assembly comprising a shaft operably coupled to the motion inhibitor; and an actuator operably coupled to the shaft so as to translate the shaft upon actuation of the actuator; and wherein movement of the shaft causes at least one of the first and second engagement walls (73, 119) to move toward the other of the first and second engagement walls (119, 73) between a first position in which the rod receiving gap has a first size and a second position in which the rod receiving gap has a second size, the second size being less than the first size, wherein the surgical instrument extends along a longitudinal axis, a lateral axis that extends substantially perpendicular to the longitudinal axis, and a transverse axis that extends substantially perpendicular to the longitudinal axis and the lateral axis, characterized in that the engagement assembly includes first and second retaining walls, a lower surface, and a lip that form an engagement pocket, and a bottom surface of the retaining walls and the lower surface separated and define a retention gap therebetween, the retention gap being shaped to receive a corresponding surface of the spinal fixation rod such that the engagement pocket is contoured and sized to allow removal of the spinal fixation rod therefrom only when the spinal fixation rod is oriented substantially perpendicular to the longitudinal and lateral axes (L, A) and substantially parallel to the transverse axis, or substantially parallel to the longitudinal axis, or at an angle relative to the transverse axis. an engagement assembly including a motion inhibitor configured to releasably engage the spinal fixation rod, the engagement assembly includes a first engagement wall and a second engagement wall so as to define a rod receiving gap that is defined between the first and second engagement walls (73, 119), the rod receiving gap configured and sized to receive a portion of a spinal fixation rod and to permit the spinal fixation rod to pivot therein; a transfer assembly comprising a shaft operably coupled to the motion inhibitor; and an actuator operably coupled to the shaft so as to translate the shaft upon actuation of the actuator; and wherein movement of the shaft causes at least one of the first and second engagement walls (73, 119) to move toward the other of the first and second engagement walls (119, 73) between a first position in which the rod receiving gap has a first size and a second position in which the rod receiving gap has a second size, the second size being less than the first size, wherein the surgical instrument extends along a longitudinal axis, a lateral axis that extends substantially perpendicular to the longitudinal axis, and a transverse axis that extends substantially perpendicular to the longitudinal axis and the lateral axis, characterized in that the engagement assembly includes first and second retaining walls, a lower surface, and a lip that form an engagement pocket, and a bottom surface of the retaining walls and the lower surface separated and define a retention gap therebetween, the retention gap being shaped to receive a corresponding surface of the spinal fixation rod such that the engagement pocket is contoured and sized to allow removal of the spinal fixation rod therefrom only when the spinal fixation rod is oriented substantially perpendicular to the longitudinal and lateral axes (L, A) and substantially parallel to the transverse axis, or substantially parallel to the longitudinal axis, or at an angle relative to the transverse axis.