Ligaments of the hip joint

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Ligaments of the Hip Joint

The hip joint (a ball-and-socket synovial joint) is stabilized by a strong fibrous capsule reinforced by four main external ligaments and one intracapsular ligament. The capsule itself attaches proximally to the acetabular rim and distally to the intertrochanteric line anteriorly and femoral neck posteriorly.

Fig. 6.33 - Fibrous membrane and ligaments of the hip joint. (A) Fibrous membrane. (B) Iliofemoral and pubofemoral ligaments - anterior view. (C) Ischiofemoral ligament - posterior view. (Gray's Anatomy for Students)

1. Iliofemoral Ligament (Ligament of Bigelow)

Position: Anterior to the hip joint
Shape: Inverted Y (triangular); the strongest ligament in the body
Proximal attachment: Apex at the anterior inferior iliac spine (AIIS) and margin of the acetabulum
Distal attachment: Along the entire intertrochanteric line; thicker bands attach above and below the line, giving it the classic Y shape
Two bands:
- Superior (lateral-horizontal) band - taut in external rotation, lax in internal rotation; attaches to the upper intertrochanteric line and anterior base of greater trochanter
- Inferior (medial-vertical) band - taut in extension, lax in flexion; attaches to the distal-medial intertrochanteric line
Function: Limits anterior hip translation during extension and external rotation; most important ligament for standing stability
Clinical note: Also called the ligament of Bigelow; the strongest single ligament in the human body

2. Pubofemoral Ligament

Position: Anteroinferior to the hip joint
Shape: Triangular, relatively weak
Proximal attachment: Base attached to the iliopubic eminence, obturator crest, superior pubic ramus, and obturator membrane
Distal attachment: Blends with the fibrous membrane and the deep surface of the iliofemoral ligament; inserts medially near the lesser trochanter
Function: Reinforces the inferior capsule; resists hyperextension and hyperabduction
Tension: Taut with internal rotation and lax with external rotation

3. Ischiofemoral Ligament

Position: Posterior to the hip joint; reinforces the posterior capsule
Proximal attachment: Ischium, just posteroinferior to the acetabulum (ischial portion of the acetabular rim)
Distal attachment: Greater trochanter, deep to the iliofemoral ligament
Two bands:
- Superior band - spirals laterally and upward; inserts at the posterior base of the greater trochanter
- Inferior band - courses laterally and downward; inserts on the posteroinferior aspect of the femoral neck base
Function: Limits posterior translation with internal rotation; prevents hyperextension
Tension: Taut and appears longer with internal rotation; lax with external rotation

4. Zona Orbicularis

Structure: A deeper layer of circular, transversely oriented fibers encircling the femoral neck - not a true separate ligament but a thickening of the deep capsule
Attachments: No direct bony attachment; merges with and is reinforced by the three main capsular ligaments
Function: Encircles the femoral neck like a collar; forms the narrowest portion of the articular cavity; resists inferior distraction of the femoral head
Imaging: Best seen on MR arthrography as a natural tightening of the joint capsule around the mid femoral neck

5. Ligament of the Head of the Femur (Ligamentum Teres / Round Ligament)

Position: Intracapsular but extrasynovial (synovium forms a sleeve around it)
Proximal attachment: Fovea capitis on the femoral head
Distal attachment: Acetabular fossa, transverse acetabular ligament, and margins of the acetabular notch
Function: Plays a role in hip stabilization; resists subluxation forces; most taut when the hip is flexed, adducted, and externally rotated
Key clinical point: Carries the artery of ligamentum teres (a branch of the obturator artery), which contributes to blood supply to the femoral head (important in children; less significant in adults)
Tears: Prevalence at hip arthroscopy is 4-15%; third most common cause of hip pain in athletes; strongly associated with labral tears and cartilage lesions

Transverse acetabular ligament (A) and Ligament of the head of femur with its blood supply (B)

Fig. 6.31 - (A) Transverse acetabular ligament. (B) Ligament of the head of femur with the acetabular branch of the obturator artery. (Gray's Anatomy for Students)

6. Transverse Acetabular Ligament

A band of fibrocartilage that bridges the acetabular notch inferiorly, converting it into a foramen
Serves as a partial distal attachment for the ligamentum teres
Deepens the acetabulum and contributes to joint stability

Functional Summary Table

Ligament	Position	Prevents	Taut With
Iliofemoral (Bigelow)	Anterior	Extension, external rotation	Extension
Pubofemoral	Anteroinferior	Hyperextension, hyperabduction	Internal rotation
Ischiofemoral	Posterior	Hyperextension, internal rotation	Internal rotation
Zona orbicularis	Circumferential (deep)	Inferior distraction	-
Ligamentum teres	Intracapsular	Subluxation	Flexion + adduction + ER

Key Functional Principle

All three capsular ligaments (iliofemoral, pubofemoral, ischiofemoral) are oriented in a spiral/helical fashion around the joint. In extension, they wind upon themselves, tightening and drawing the femoral head firmly into the acetabulum - stabilizing the standing posture with minimal muscle energy. In flexion, they unwind and become lax, permitting greater mobility. This is why the hip is most stable (and dislocations less common) in extension, and most vulnerable in flexion.

Sources:

[Gray's Anatomy for Students](Gray's Anatomy for Students, pp. 662-663)
[Imaging Anatomy: Bones, Joints, Vessels and Nerves, Vol. 3](Imaging Anatomy Vol. 3, pp. 737-740)
[Thieme Atlas of Anatomy: General Anatomy and Musculoskeletal System](Thieme Atlas, p. 6723)

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