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There is some evidence that the position and angle of the sacrum underneath the lumbar vertebra does make a difference in intervertebral shear forces. Evidently, the more horizontal the sacrum is, the less load and stress are placed on that area. This is a position called lumbar lordosis (swayback).
Body weight, muscle strength (and strain), and age do seem to have some bearing on the magnitude of shear forces placed on the sacrum. Peak load occurs at the L4-L5 level. A fusion at this segment is more likely to create stress and load compared with a L5S1 fusion.
Sometimes the surgeon artificially increases the lordosis by placing an implant to change the spinal orientation. The idea is to slow the degenerative processes that occur above the level of the fusion.
Maintaining segmental stability may reduce biomechanical stresses that lead to disc degeneration. A rectangular-shaped angulation cage may be the answer. More studies are needed to confirm this hypothesis.
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