The mechanical effectiveness of applying transverse forces by segmental spinal instrumentation to correct scoliosis is examined in this paper. Comparisons with traditional Harrington instrumentation are made on the basis of each method's potential to produce corrective bending moments and their ability to transfer this correction to the spine. Recognizing the scoliosis is a three-dimensional deformity, biomechanical evaluations are performed in each of the three anatomic planes, with special attention paid to maintaining normal sagittal plane contour and transverse plane derotation. Such an analysis indicates that segmental spinal instrumentation has a clear mechanical advantage over traditional Harrington instrumentation in providing and maintaining correction. Proposed improvements include the development of instrumentation which can be segmentally attached to the vertebra without invading the spinal canal.