A surgical instrument for correcting spinal deformities, the surgical instrument comprising a tubular body having a proximal end, a distal end opposite the proximal end, and a midsection extending between the proximal end and the distal end, the tubular body defining a longitudinal axis and a longitudinal passage extending along the longitudinal axis from the proximal end to the distal end, the longitudinal passage adapted to receive a second instrument through the tubular body, the tubular body further defining a first longitudinal slot and a second longitudinal slot opposite the first longitudinal slot, the first longitudinal slot and the second longitudinal slot terminating at the distal end of the tubular body and forming a transverse passage through the tubular body, the transverse passage adapted to receive a longitudinal fixation element through the tubular body, the tubular body further comprising a first extension and a second extension opposite the first extension, the first extension separated from the second extension by the first longitudinal slot and the second longitudinal slot, the first extension comprising a first pivot arm for detachably connecting the surgical instrument to a first connector on the vertebral anchor and a second pivot arm for detachably connecting the surgical instrument to a second connector on the vertebral anchor, the first pivot arm having a first activation end and a first attachment end opposite the first activation end, and the second pivot arm having a second activation end and a second attachment end opposite the second activation end, the first pivot arm defining a first anti-splaying slot, and the second pivot arm defining a second anti-splaying slot, characterized in that the first anti-splaying slot extends from the first activation end to the first attachment end, the first anti-splaying slot is open to the longitudinal passage, the first anti-splaying slot is adapted to receive a first anti-splaying element (250; 260) on the second instrument, the second anti-splaying slot extends from the second activation end to the second attachment end, the second anti-splaying slot is open to the longitudinal passage, and the second anti-splaying slot is adapted to receive a second anti-splaying element (250, 260) on the second instrument. the tubular body further defining a first longitudinal slot and a second longitudinal slot opposite the first longitudinal slot, the first longitudinal slot and the second longitudinal slot terminating at the distal end of the tubular body and forming a transverse passage through the tubular body, the transverse passage adapted to receive a longitudinal fixation element through the tubular body, the tubular body further comprising a first extension and a second extension opposite the first extension, the first extension separated from the second extension by the first longitudinal slot and the second longitudinal slot, the first extension comprising a first pivot arm for detachably connecting the surgical instrument to a first connector on the vertebral anchor and a second pivot arm for detachably connecting the surgical instrument to a second connector on the vertebral anchor, the first pivot arm having a first activation end and a first attachment end opposite the first activation end, and the second pivot arm having a second activation end and a second attachment end opposite the second activation end, the first pivot arm defining a first anti-splaying slot, and the second pivot arm defining a second anti-splaying slot, characterized in that the first anti-splaying slot extends from the first activation end to the first attachment end, the first anti-splaying slot is open to the longitudinal passage, the first anti-splaying slot is adapted to receive a first anti-splaying element (250; 260) on the second instrument, the second anti-splaying slot extends from the second activation end to the second attachment end, the second anti-splaying slot is open to the longitudinal passage, and the second anti-splaying slot is adapted to receive a second anti-splaying element (250, 260) on the second instrument.