Arthrodesis of long segments of the spine to a sacrum may be necessary for a variety of pathologic conditions and indications. The surgery may be necessary for patients who have had prior surgery, had failure of fusion, or had degeneration above the area of prior fusion. Revision of prior surgeries, in which distraction instrumentation was used and resulted in flat-back deformity, remains a problem. A better understanding of the biomechanical stresses placed on the fixation devices and the bone-implant interface have resulted in development of improved techniques of fixation in the lower lumbar spine and the sacrum. This fixation always requires multiple levels of segmental spinal purchase. The type of purchase obtained is dependent on the design of the fixation, whether it is wire, hook, or screw, and the bone into which it is placed. The surgeon needs to understand the limitations of both the instrumentation and bone prior to proceeding with this demanding surgery. When so much emphasis is placed on instrumentation, a tendency exists to not pay enough attention to the most important part of the operation. This surgery is always an arthrodesis and an attempt to place the spine in a stable and balanced position. Meticulous surgical techniques for arthrodesis are required, or failure is likely to occur. If the spine is placed in an unbalanced situation and the fusion area is placed under tension, failure of fusion and, subsequently, of the instrumentation will occur. The understanding of these concepts and principles is more critical to the success of this type of surgery than the specific instrumentation used. Instrumentation will continue to change using different metallurgy and designs, but these principles and the goal of obtaining a solid arthrodesis and a balanced spine will never change.