The iliofemoral ligament (Y ligament of Bigelow) is the strongest ligament in the body, with an inverted Y configuration from the AIIS diverging to both limbs of the intertrochanteric line. It is the primary restraint against hip hyperextension and external rotation. Standing erect in hyperextension actually tightens the Y ligament to passively support the body weight without muscle activation — the reason humans can stand for long periods without fatigue.
| Origin | Anterior inferior iliac spine (AIIS) |
|---|---|
| Insertion | Intertrochanteric line of the femur (both medial and lateral limbs diverging into a Y) |
| Actions | Prevents hip hyperextension — the strongest ligament in the body by tensile strength |
|---|
The Y ligament prevents anterior hip dislocation (which is rare compared to posterior dislocation from the posterior capsule weakness). Its extreme strength means that it rarely tears in isolation — anterior hip dislocations require combined obturator, pubic, or inferomedial escape routes. The Y ligament is released in hip arthroscopy to access the peripheral compartment.
Y ligament failure in extreme hyperextension-abduction producing anterior dislocation requiring urgent closed reduction under adequate analgesia and muscle relaxation.
