Let’s consider two positions of the calcaneus acting at the subtalar joint.
The image on the left demonstrates the calcaneus medially under the tibia creating a ‘longer leg’ by supinating the foot and lifting the tibia vertically. The subtalar joint is stiff with this foot type and does not wiggle side to side and twist very well, but it could loosen up with the right stimulus.
The image on the right demonstrates the calcaneus laterally under the tibia creating a ‘shorter leg’ by allowing the tibia to drop down and in. The subtalar joint is usually not the problem with this foot type and often times the calcaneus is able to wiggle side to side and twist very well.
From the foot types above we now have 1. a longer leg, and 2. a shorter leg. This leg length discrepancy creates compensations from the ground up causing SI dysfunction on the ‘shorter side’. I like this idea but not as much as the future post that will pose another hypothesis.
A link to a video I watched on youtube provided me with the idea of subtalar joint dysfunction, leading to leg length, leading to SI dysfunction.