Why is FA IR that is decreased bilaterally usually considered a patho-compensatory pattern?
Individuals who compensate by externally rotating their bilateral femurs in their anteriorly rotated and inwardly directive acetabulums have a tendency to overstretch their iliofemoral and pubofemoral ligaments by over-contracting their femoral acetabular external rotators. Their posterior capsules usually become restrictive and tight over time secondary to establishing a bilateral AF ER (acetabular femoral external rotation) osseous position. Because of the overstretched anterior soft tissue and restrictive posterior capsule and soft tissue, internal rotation is decreased or limited actively or passively. This is considered a pathologic event because of compensatory activity of the femoral acetabular external rotators to align the femurs on a pelvis that is orienting both femurs inwardly.
