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Just to remind you, for those of you who don’t remember exactly what the spinal column looks like. You have lordosis in two areas; in the cervical area here and in the lumbar area here. Now there are  more complicated in the cervical area but in the lumbar area, as you can see this curve, the apex is usually (it’s not in this diagram) but the apex is usually at L4 and L5 so that the forces tend to push in different directions. One is the anterior shear and the posterior shear on this apex. And usually when you have problems in the lower back, it is usually at L4 and at L5.