ILIOFEMORAL LIGAMENT (Y-Ligament of Bigelow)

10-Mark Orthopaedic PG Answer

1. Introduction

2. Anatomy

Position

• Located anterior to the hip (ball-and-socket) joint
• Intimately blends with the anterior fibrous capsule

Attachments

Shape

3. Relations

4. Microstructure

• Composed of dense, parallel collagen bundles arranged in a spiral/helical pattern around the femoral neck
• This spiral arrangement means fibers tighten (coil) in extension and relax in flexion
• The ligament undergoes tensile stresses of up to 350 N before rupture

5. Functions

1. Prevents hyperextension of the hip - the most important function; tightens during hip extension
2. Maintains erect posture - in the anatomical standing position, body weight tends to extend the hip; the iliofemoral ligament resists this passively, reducing the need for active muscle contraction
3. Limits external rotation - especially the lateral (superior) arm
4. Limits abduction - especially the medial (inferior) arm
5. Position of maximum stability: Hip in extension + internal rotation (ligament fully taut)
6. Position of maximum laxity/maximum joint volume: Hip in slight flexion + external rotation (clinically, patients hold the hip in this position during effusion/haemarthrosis for pain relief)

6. Flowchart: Functional Biomechanics

HIP MOVEMENT
      │
      ├─── EXTENSION
      │         │
      │    Iliofemoral ligament TIGHTENS (coils)
      │         │
      │    ┌────┴────┐
      │    │         │
      │  Superior   Inferior
      │  band        band
      │  limits      limits
      │  Ext.Rot     Abduction
      │    │         │
      │    └────┬────┘
      │         │
      │   Maximum Stability
      │   (Hip extended + internally rotated)
      │
      └─── FLEXION
                │
         Iliofemoral ligament RELAXES
                │
         Reduced anterior stability
                │
         ┌──────┴──────┐
         │             │
      Posterior    Anterior
      dislocation  dislocation
      more common  less common
      (flexed hip) (extended hip)

7. Clinical Significance

A. Hip Dislocation

• Posterior dislocation (most common ~90%): Occurs when hip is flexed (e.g., dashboard injury) - ligament is relaxed, femoral head dislocates between the iliofemoral and ischiofemoral ligaments superoposteriorly
• Anterior dislocation: Occurs with hip in extension - the ligament must tear for this to occur; hence anterior dislocations are rarer
• Posterior dislocations are commoner precisely because the iliofemoral ligament is slack in flexion
• After dislocation, the iliofemoral ligament tear does not reliably heal, risking persistent anterior instability

B. Hip Fractures

• Increased tension in the iliofemoral ligament contributes to femoral neck fractures and posterior comminution of the neck in high-energy injuries (Rockwood & Green, 2025)
• The capsule (with the ligament anteriorly) is taut in extension and internal rotation - relevant to positioning during closed reduction of fractures

C. Hip Arthroplasty (THA)

• Anterolateral and anterior approaches to THA require division of the iliofemoral ligament
• Posterior approach preserves it - hence the anterior approach has inherently less posterior stability whereas posterior approach preserves the anterior restraint
• Surgeons performing anterior/anterolateral approaches must repair the capsule/iliofemoral ligament to reduce dislocation risk

D. Hip Arthroscopy / Capsular Plication

• Awareness of the ligament anatomy is needed to avoid iatrogenic damage during portals and arthroscopic procedures
• Capsular plication of the iliofemoral ligament is used to treat hip microinstability

E. Congenital Hip Dysplasia (DDH)

• A lax/underdeveloped iliofemoral ligament contributes to hip instability in DDH

F. Positioning During Examination / Anaesthesia

• Effusion causes the hip to adopt flexion + external rotation (position of maximum volume, ligament relaxed)
• Painful hip conditions are clinically assessed with FABER/FADIR tests - these involve loading the iliofemoral ligament

8. Comparison with Other Hip Ligaments

9. Important Exam Points (High-Yield)

• Strongest ligament in the body - 350 N tensile strength
• Called Y-ligament of Bigelow or iliofemoral ligament
• Apex at AIIS, base at intertrochanteric line
• Taut in extension, relaxed in flexion - spiral/helical fiber arrangement
• Limits hyperextension of hip - critical for bipedal erect posture
• Posterior hip dislocation is common because the hip is flexed (ligament is relaxed) during the mechanism of injury
• Maximum joint volume / least pain = slight flexion + external rotation (ligament lax)
• Position of maximum stability = extension + internal rotation (ligament taut)
• Iliopsoas bursa may communicate with hip joint through the gap between iliofemoral and pubofemoral ligaments

10. Summary Flowchart

ILIOFEMORAL LIGAMENT (Y-Ligament of Bigelow)
            │
    ┌───────┼───────┐
    │       │       │
Anatomy  Function  Clinical
    │       │       │
Y-shaped  Anti-    Dislocation
Apex:AIIS extension  (posterior
Base:     + Erect    > anterior)
ITL       posture       │
    │       │       THA surgery
Two bands: Spiral   (anterior
Superior   fibres   approach)
Inferior   tighten      │
    │     in extn   Hip instability
    │       │       arthroscopy
    └───────┴───────┘
           │
    Strongest ligament
    in the human body

• Gray's Anatomy for Students (p. 663) - iliofemoral ligament anatomy and attachments
• Rockwood & Green's Fractures in Adults, 10th Ed. 2025 - role in femoral neck fractures
• Rheumatology, 2-Volume Set (Elsevier 2022) - hip joint capsule and Y-ligament of Bigelow
• Systematic review on iliofemoral ligament as hip stabilizer (PMC8335960) - confirms primary role in anterior hip stability; tear does not heal after dislocation