The AO internal fixation system(the Fixateur Interne) is effective in reducing and stablizing a variety of unstable thoracolumbar fracture patterns. It is relatively effective in decompressing the canal of retropulsed bony fragments associated with burst fracture. Sixty-Two patients with unstable thoracolumbar spine fractures were treated with the AO internal fixator. They were followed for an average of 21 months(range 15-29 months). A compartive radiographic analysis of kyphosis and vertebral height was made using pre-operative, post-operative and follow-up radiogram. Changes in neural canal compromise were measured in 18 cases of burst fractures. Failure of instrumentation occured in 9 cases which were carefully analyzed. Recently, we've constructed the system of which the Schanz screws would be directed divergently in sagittal plane in the hope that the load to the screws might be reduced, thus the failure rate.