Iliofemoral, pubofemoral and ischiofemoral ligaments
Mnemonic
“Y, Z, and a spiral”, three capsular ligaments named for their attachments:
- Iliofemoral (Y ligament of Bigelow) - the strongest ligament in the body, anterior, preventing hyperextension and allowing standing with minimal muscle work
- Pubofemoral - anteroinferior, limiting abduction and extension
- Ischiofemoral - posterior, the weakest, limiting internal rotation
“The posterior capsule is the weakest, which is why dislocation is posterior.” Around 90 per cent of hip dislocations are posterior, typically a dashboard injury with the hip flexed and adducted, giving a shortened, adducted, internally rotated limb and risking the sciatic nerve.
Anterior dislocation gives the opposite posture: abducted and externally rotated.
The ligamentum teres carries the artery to the head of femur, which is significant in children but contributes little in adults, where the head depends on the retinacular branches of the medial circumflex femoral artery. That is why an intracapsular neck of femur fracture risks avascular necrosis and is treated with replacement rather than fixation.
Expansion
- Iliofemoral ligament - anterior, Y-shaped, the strongest; resists hyperextension
- Pubofemoral ligament - anteroinferior; resists excess abduction and extension
- Ischiofemoral ligament - posterior and weakest; resists medial rotation
The intracapsular ligament of the head of the femur carries a small artery to the femoral head, important in children.