The effect of postern-lateral spinal fusion was studied on the fixed intervertebral space and other lumbar intervertebral spaces in 15 patients who obtained solid union at L5/S1 level, and was compared with P-L fusion of L4/5 level. With regard to radiological approach, we have measured the angle displacement, horizontal displacement and disc space height using Dupuis' method. It was recognized that there was evenly increased motion angle for other lumbar intervertebral spaces. It was called “distribution effect”. In comparison with P-L fusion of L4/5 level, motion angle in L5/S1 level decreased slightly. Nevertheless, there was no difference as to “distribution effect” between L4/5 level and L4/5 level.
