Ligament of the Head of the Femur: Origin, Function, and Clinical Significance

What is the Origin of the Ligament of the Head of the Femur?

The ligament of the head of the femur, also known as the ligamentum teres femoris or round ligament, originates from the acetabular notch and the transverse acetabular ligament within the acetabulum of the hip bone.

Introduction to the Ligament of the Head of the Femur

The hip joint is a critical ball-and-socket synovial joint, designed for extensive mobility while maintaining significant stability. Within the intricate architecture of this joint lies a unique intra-articular structure: the ligament of the head of the femur (LHF). Often referred to as the ligamentum teres femoris (Latin for "round ligament of the femur"), this structure plays a multifaceted role that extends beyond simple mechanical stabilization, particularly in terms of vascular supply to the femoral head. Understanding its precise origin is fundamental to appreciating its anatomical and functional significance.

Anatomical Origin

The ligament of the head of the femur arises from specific points within the acetabulum, the cup-shaped socket of the hip bone that articulates with the head of the femur.

• Acetabular Notch: The primary origin point is the acetabular notch, which is the inferior deficiency or gap in the rim of the acetabulum. This notch is not covered by articular cartilage.
• Transverse Acetabular Ligament: Extending across and bridging the acetabular notch is the transverse acetabular ligament. This strong, fibrous band effectively completes the acetabular rim, transforming the notch into a foramen (opening) through which blood vessels and nerves can pass. The ligament of the head of the femur takes a significant portion of its origin from this transverse ligament.

From these origins, the ligament projects superiorly and medially into the hip joint cavity, heading towards its insertion point on the femoral head.

Course and Insertion

Once originating from the acetabular notch and transverse acetabular ligament, the ligament of the head of the femur courses obliquely within the hip joint capsule. It passes through the joint's synovial fluid, covered by a synovial sheath, before attaching to the fovea capitis femoris.

• Fovea Capitis Femoris: This is a small, non-articular depression located on the medial aspect of the head of the femur. It is the specific site where the ligament firmly inserts.

This unique intra-articular but extrasynovial (covered by synovium but not within the synovial cavity itself) position allows it to traverse the joint without impeding articulation.

Functional Significance

While historically considered a vestigial structure, modern understanding attributes several important functions to the ligament of the head of the femur:

• Vascular Supply: Perhaps its most critical role, especially during early life, is to transmit the foveal artery (also known as the artery of the ligamentum teres or the acetabular branch of the obturator artery). This artery provides a vital blood supply to the head of the femur, particularly its epiphysis, during childhood. In adults, its contribution to the femoral head's blood supply diminishes as other arteries (medial and lateral circumflex femoral arteries) become dominant, but it can still provide collateral circulation.
• Mechanical Stability (Debated): Its direct contribution to the overall mechanical stability of the hip joint is debated. Some studies suggest it acts as a secondary stabilizer, becoming taut and resisting excessive adduction and external rotation, particularly when the hip is flexed. However, its primary role is generally not considered to be a major mechanical stabilizer.
• Proprioception: The ligament contains nerve endings that contribute to proprioception, providing the central nervous system with information about the position and movement of the hip joint.

Clinical Relevance

Understanding the origin and function of the ligament of the head of the femur is crucial for diagnosing and managing various hip pathologies:

• Injury and Tears: The LHF can be torn or damaged, often as a result of trauma, such as hip dislocations, or in conditions like femoroacetabular impingement (FAI) and hip dysplasia. A torn ligament can be a source of hip pain, instability, and mechanical symptoms (e.g., clicking, catching).
• Avascular Necrosis (AVN): Compromise or disruption of the foveal artery, particularly in childhood (e.g., due to hip dislocation or fracture), can lead to avascular necrosis of the femoral head, a severe condition where bone tissue dies due to lack of blood supply.
• Diagnostic Imaging: Injuries to the LHF are increasingly recognized and can be visualized using advanced imaging techniques such as Magnetic Resonance Imaging (MRI) or during hip arthroscopy.

Conclusion

The ligament of the head of the femur, originating from the acetabular notch and transverse acetabular ligament, is a small but significant structure within the hip joint. While its role in mechanical stability may be secondary, its primary function in providing a crucial vascular pathway to the femoral head, particularly during development, cannot be overstated. Its presence also contributes to hip proprioception. A comprehensive understanding of its anatomy and function is essential for clinicians and fitness professionals alike when addressing hip health and pathology.