COMPUTER-ASSISTED SPINE SURGERY

When inserting screws into a vertebral pedicle, the surgeon usually ex poses the back part of the vertebra and uses his or her anatomic knowl edge to align the drill in the proper direction, A slight error in dir ection may result in an important error in the position of the tip of the screw This is done with no direct visibility of crucial structures (spinal cord, pleura, vessels), Statistical analysis of a series of s urgical procedures has shown that 10% to 40% of the screws are not ins talled correctly, To reduce the risk of complication, a computer assis ted method is proposed that enables the surgeon to place a screw at a position preoperatively defined in 3 dimensions using computed tomogra phy images, This allows the surgeon to align a standard surgical drill with the optimal position and direction. The depth of the pilot hole during drilling also is monitored by the system to prevent penetration of the anterior cortex of the vertebral body, Using this procedure, i n vitro tests were performed and showed that an accuracy of less than 1 mm can be obtained, Clinical trials were done in 10 patients who suf fered severe scoliosis or spondylolisthesis, The trajectory of the hol es drilled in L2, L3, L4, and L5 vertebrae were checked for all clinic al tests, Postoperative radiographs and computed tomography scans show ed that the screws were well inserted in each plane for each pedicle, This technique also can be used to perform osteosynthesis at the thora cic and cervical levels.