1. An expandable spinal fixation system comprising:an expandable barrel assembly having:
an upper barrel half having a distal end and a proximal end, wherein the proximal end of the upper barrel comprises a slot formed therein;
a lower barrel half having a distal end and a proximal end, wherein the proximal end of the lower barrel comprises a projection portion configured to be received in the slot; and
a securing assembly having a plate adapted to bias the projection against the upper barrel proximal end and a securing member adapted to releasably bias the plate against the projection, and wherein, when the securing member biases the plate against the projection, the lower barrel half is fixed relative to the upper barrel half; and
a fixed barrel assembly having a body sized to fit between the upper barrel half and the lower barrel half, wherein the body extends along a longitudinal axis,
wherein the upper barrel half is capable of moving with respect to the lower barrel half.