Obtaining an arthrodesis of the lumbar spine has always been a problem, especially in the presence of severe disease. The understanding of the segmental character of the lesions and the application of sound orthopedic principles toward low-back spine pathology has led the way to improving arthrodesis with rigid internal fixation. For about eight years, segmental spinal instrumentation has been used in 352 cases to "stabilize" the spine. Many modifications have taken place and knowledge of the biomechanics of abnormal spine has increased through designs of new methods for different disorders. Fixation of low back, when indicated, should be rigid. The rectangular or rhomboid-shaped rod, bent to conform to the lamina cephalad and caudad, and fixed segmentally, proves to be the most rigid. It is contoured to maintain lordosis, sometimes in distraction, sometimes in compression. Fixation is not a substitute for correction of bony deformity or a good surgical arthrodesis. The objective is to maintain correction and promote prompt bony fusion.