Hip Joint

The hip joint is a ball-and-socket joint that represents the articulation of the bones of the lower limb and the axial skeleton (spine and pelvis). The rounded femoral head sits within the cup-shaped acetabulum.

The acetabulum is united by the three bones of the pelvis (the ischium, ilium and pubis). Between them is a Y-shaped cartilaginous growth plate.

The acetabulum covers nearly half of the femoral head. The articulation is deepened by the labrum, a fibrocartilaginous lip that extends around the acetabulum an crosses the equator of the femoral head.

Motion

* Flexion: ilipsoas, rectus femoris
* Extension: hamstrings
* Abduction: gluteus minimus and medius
* Adduction: adductors muscles
* External rotation: obturator internus, gemelli, piriformis and gluteus maximus
* Internal rotation: gluteus minimus and medius

**Acetabulum**

* Acetabular fossa: Central cartilage devoid region
* Acetabular notch: Osseous opening inferior margin with no cartilage.
	+ Covered by synovium: Extra-articular
* Anterior & posterior rims: Osseous margins of acetabulum

**Labrum**

* Fibrocartilage
* Resides on acetabular rim
* Vascular supply: Branches obturator, superior & inferior gluteal arteries
* Function
	+ Protect cartilage: Distributes forces by maintaining synovial fluid layer between articular surface
	+ Prevents lateral translation femoral head

**Femoral Head**

* 2/3 of sphere
* Covered by articular cartilage
	+ Except central fovea capitis
	+ Cartilage thickest superiorly
* Fovea capitis: Central cartilage devoid depression on head. Attachment site for ligamentum teres

Relations

* anteriorly: iliopsoas and femoral vessels
* posteriorly: sciatic nerve and obturator internus with gemelli muscles
* superiorly: gluteus minimus and medius
* inferiorly: pectineus and obturator externus

Joint Capsule

* 2 layers: Internal synovial; external fibrous
	+ External forms capsular ligaments
* Attachments
	+ Acetabulum - circumferential around the labrum
	+ Femur
		- Anterior: Intertrochanteric line
		- Posterior: mid way femoral neck
		- Anterior attachment more lateral than posterior attachment
		- Fibres reflect back as retinacular fibres that blends with the periosteum.
* External layer: Ligaments of joint capsule
	+ Iliofemoral (Bigelow ligament)
		- Anterior, superior longitudinal spiral
		- Inverted Y-shape
		- Prevents hyperextension
		- Strongest ligament in body
		- Medial attachment anterior inferior iliac spine
	+ Pubofemoral: Anterior, inferior, longitudinal spiral
		- Prevents hyperabduction
		- Medial attachment obturator crest pubis
	+ Ischiofemoral: Posterior, longitudinal spiral
		- Weakest
* Synovial layer
	+ lines all the capsules and the articular surfaces including the fovea and the circumference of the labrum
* Ligamentum Teres
	+ Attachments: Fovea capitis & transverse ligament
	+ Lined by synovium: Intracapsular, extra-articular
	+ Artery of ligamentum teres which is essentially negligible.
* Transverse Ligament
	+ Spans acetabular notch
		- Completes socket of acetabulum
	+ Blends with labra at margins of notch
		- Labroligamentous sulci at junction

Arterial supply

* Trochanteric anastomoses receiving supply from multiple branches, but mainly the medial circumflex artery. These run along the neck beneath the retincular fibres.
* Femoral head mainly receives fro medial and lateral circumflex femoral and artery of ligamentum teres (branch of posterior division of obturator artery)
* Superior and inferior gluteal arteries offer descending branches to the trochanteric anastomoses.

Venous drainage

* follows arterial supply

Innervation

* Branches from nerve to rectus femoris (femoral), nerve to quadratus femoris (sciatic), anterior division obturator nerve, accessory obturator nerve, superior gluteal nerve.

Variant:

* Perilabral sulci
* Sublabral recess
* Enostosis (bone island)
* Allen's fossa (small cervical depression by NOF)
* Os acetabuli (ossicle in the upper rim of the acetabulum)