The Hip Joint

Key points

• • It is a multiaxial ball-and-socket joint; the deep acetabulum, deepened further by the fibrocartilaginous labrum, makes it far more stable than the shoulder.
• • The iliofemoral ligament is one of the strongest ligaments in the body and resists extension; the pubofemoral and ischiofemoral ligaments complete the capsule.
• • The head is supplied mainly by the medial and lateral circumflex femoral arteries through retinacular vessels; the artery within the ligament of the head matters in children but is minor in adults.
• • Because those retinacular vessels run along the neck, a fracture of the femoral neck can cut off the supply and cause avascular necrosis of the head.
• • The capsule encloses the whole neck in front but only the proximal two-thirds behind, so the back of the neck is partly outside the capsule.
• • By Hilton's law the nerve supply is femoral, obturator, superior gluteal and the nerve to quadratus femoris; because the hip and knee share innervation (notably the femoral and obturator nerves), hip disease may present as referred knee pain.