Introduction: The main objective of all the sagittal compensating mechanisms is to allow a subject to stand and keep an erect position.
Materials and methods: The cascade of compensating mechanisms appears progressively with the increasing amount of imbalance of the spine until compensation is no longer possible. The loss of lumbar lordosis can be considered as the initiating event of sagittal imbalance. This loss of the normal lordosis pushes the C7 plumb line forward.
Results: The assessment of sagittal balance has to include to be complete: a parameter measuring the global balance of the trunk, either C7 plumb line and sacral plateau, the position of the pelvis rotation by the pelvic tilt, and a description of the position of the lower limbs. Those three parameters have been taken into account by the newly described method called full balance integrated (FBI). This evaluation is easily done on a sagittal full spine standing X-ray from C2 to the pelvis, including the first 10 cm of the femur.
Conclusion: Three questions to answer: What is the value of the pelvis incidence? Is the patient balanced? Are there compensatory mechanisms?