Fig. 1.

Normal balance spine (left side), progressive loss of lordosis due to lumbar disc collapse leads to anterior moving of the C7 plumb line with a progressive retroversion of the pelvis to compensate (compensated balance) (central drawing), pelvis retroversion had a limit and the progression of the kyphosis imposed a flexion of the knees but it is not enough and C7 plumb line falled in the front of femoral heads (decompensated balance : imbalance) (right side)