Overview

TypeBall-and-socket synovial (multiaxial)

Strongest ligamentIliofemoral (Y ligament of Bigelow)

Close-packed positionExtension + medial rotation + abduction

The femoral head (≈2/3 of a sphere) fits deeply into the acetabulum, which is further deepened by the fibrocartilaginous acetabular labrum and completed inferiorly by the transverse acetabular ligament bridging the acetabular notch. Only the horseshoe-shaped lunate surface is articular; the central acetabular fossa contains a fat pad and the ligament of the head of the femur (ligamentum teres), which carries a small branch of the obturator artery.

The strong capsule attaches to the acetabular rim and transverse ligament and, on the femur, to the intertrochanteric line anteriorly but only halfway along the neck posteriorly (so the posterior neck is partly extracapsular). Its deep circular fibres form the zona orbicularis. Three spiral capsular ligaments reinforce it, all tightening in extension ("screwing" the head into the socket): the Y-shaped iliofemoral ligament (of Bigelow) — from the AIIS to the intertrochanteric line, the strongest ligament in the body, preventing hyperextension and allowing standing with little muscular effort; the pubofemoral ligament (limits abduction); and the ischiofemoral ligament (posterior, the weakest; limits medial rotation).

Movements: flexion (≈120° with knee flexed), extension (≈10–20°), abduction (≈45°), adduction (≈30°), medial and lateral rotation (≈40–45°) and circumduction. The close-packed position is extension with medial rotation and abduction.

Location: Groin/hip region, deep to the femoral triangle anteriorly and the gluteal muscles posteriorly.

Parts & subdivisions

Acetabulum and labrum
Deep socket deepened by the fibrocartilaginous labrum.
Femoral head
≈2/3 of a sphere; fovea for the ligament of the head.
Iliofemoral ligament
Y-shaped; strongest ligament; prevents hyperextension.
Pubofemoral ligament
Limits abduction and extension.
Ischiofemoral ligament
Posterior; limits medial rotation.
Ligament of the head of the femur
Intracapsular; carries the artery of the ligament of the head (obturator) — minor in adults.
Transverse acetabular ligament
Bridges the acetabular notch; vessels pass beneath it.

Anatomy

Innervation: Femoral nerve (via nerves to rectus femoris), obturator nerve, nerve to quadratus femoris and superior gluteal nerve (Hilton’s law) — hip pain is often referred to the knee via the obturator and femoral nerves.
Arterial supply: Medial and lateral circumflex femoral arteries (retinacular branches — medial circumflex is dominant), artery of the ligament of the head (obturator), superior and inferior gluteal arteries.
Articulations: Head of the femur ↔ lunate surface of the acetabulum.
Ligaments: Iliofemoral, pubofemoral, ischiofemoral, zona orbicularis, ligament of the head of the femur, transverse acetabular ligament, acetabular labrum.

Function

Supports the weight of the head, upper limbs and trunk in standing and gait
Flexion, extension, abduction, adduction, rotation and circumduction of the thigh

Clinical significance

Posterior hip dislocation

The commonest type (≈90%) — a knee striking the dashboard drives the flexed, adducted femur backward. The limb is shortened, flexed, adducted and internally rotated; the sciatic nerve (especially its fibular division) and the femoral head blood supply are at risk (AVN). Requires urgent reduction. Anterior dislocation leaves the limb abducted and externally rotated.

Developmental dysplasia of the hip (DDH)

Shallow acetabulum with instability or dislocation; risk factors: female, breech, first-born, family history, oligohydramnios. Screened by Barlow (dislocates a reduced hip) and Ortolani (reduces a dislocated hip — "clunk") tests and ultrasound; treated with a Pavlik harness.

Osteoarthritis and hip replacement

Groin pain, stiffness and loss of internal rotation first; total hip arthroplasty is one of the most successful operations in medicine.

Trendelenburg sign

Weakness of the hip abductors (gluteus medius/minimus; superior gluteal nerve) causes the pelvis to drop on the unsupported side when standing on the affected leg.

Compiled from standard anatomy and physiology references — see the Skeletal System sources. For education only; not medical advice.