Ligamentum Teres: Vascular Role, Stability, and Clinical Significance

What is the function of the ligamentum teres ligament of the head of the femur?

The ligamentum teres of the head of the femur primarily serves as a conduit for a crucial blood supply to the femoral head, particularly during childhood, and offers only minor mechanical stability to the hip joint.

Introduction to the Ligamentum Teres

The ligamentum teres femoris, also known as the round ligament of the femur or the ligament of the head of the femur, is a small, triangular, somewhat flattened ligament located within the hip joint capsule. It originates from the fovea capitis, a small depression on the head of the femur, and inserts into the acetabular notch and transverse acetabular ligament, deep within the acetabulum of the pelvis. Despite its designation as a "ligament," its mechanical role in hip joint stability is often misunderstood and significantly less prominent than its vascular function.

Primary Function: Vascular Supply

The most critical and universally acknowledged function of the ligamentum teres is its role as a conduit for blood vessels supplying the femoral head.

• Artery to the Ligament of the Head of the Femur: Within the ligamentum teres runs a branch of the obturator artery (or sometimes a branch of the medial circumflex femoral artery). This artery, often referred to as the artery to the ligament of the head of the femur, provides a vital blood supply to the epiphysis (the end part of the bone, which is initially separated from the main bone by cartilage but later fuses with it) and growth plate of the femoral head, especially during the formative years of childhood and adolescence.
• Protection Against Avascular Necrosis (AVN): While the primary blood supply to the adult femoral head comes from the retinacular arteries (branches of the medial and lateral circumflex femoral arteries), the artery within the ligamentum teres can become a crucial anastomotic (connecting) blood supply if these major retinacular arteries are compromised. This makes it a significant protective factor against avascular necrosis (AVN) of the femoral head, a condition where bone tissue dies due to a lack of blood supply. In young children, before the epiphyseal plates close and the main retinacular vessels fully mature their supply to the epiphysis, the artery within the ligamentum teres is particularly essential.

Secondary (Controversial and Minor) Functions

Beyond its primary vascular role, the mechanical and proprioceptive functions of the ligamentum teres are considered secondary and are subjects of ongoing research and debate.

• Minor Mechanical Stability:
  • Historically, it was thought to provide significant mechanical stability to the hip joint, especially in adduction and flexion. However, anatomical studies and biomechanical analyses have shown that it is a relatively weak structure and remains slack in most physiological positions of the hip.
  • It only becomes taut in extreme positions of flexion, adduction, and external rotation. Even then, its contribution to overall hip joint stability is minimal compared to the robust extra-capsular ligaments (iliofemoral, pubofemoral, and ischiofemoral ligaments) and the surrounding musculature. Its small size and relatively loose attachment do not lend it to being a primary stabilizer.
• Proprioception:
  • The ligamentum teres contains nerve endings, suggesting a potential role in proprioception – the body's sense of its position in space. These mechanoreceptors could provide feedback to the central nervous system regarding hip joint position and movement, contributing to neuromuscular control and coordination. However, the extent of this contribution compared to other joint mechanoreceptors is still under investigation.
• Synovial Fluid Distribution:
  • Some theories suggest it may play a minor role in distributing synovial fluid within the hip joint, aiding in lubrication and nutrient delivery to the articular cartilage. This function is largely speculative.

Clinical Significance and Pathologies

Injuries or pathologies involving the ligamentum teres, while less common than other hip conditions, can have notable clinical implications.

• Ligamentum Teres Tears:
  • These can occur due to acute trauma (e.g., hip dislocation, sports injuries involving forced hip movements) or repetitive microtrauma.
  • Symptoms often include groin pain, clicking, catching, or instability within the hip joint.
  • Diagnosis can be challenging and often requires MRI or diagnostic arthroscopy for definitive identification.
• Avascular Necrosis (AVN):
  • As mentioned, compromise to the artery within the ligamentum teres, particularly in children (e.g., in conditions like Legg-Calvé-Perthes disease or after hip trauma), can significantly increase the risk or severity of AVN of the femoral head.
• Impingement:
  • In some cases of femoroacetabular impingement (FAI) or other intra-articular hip pathologies, the ligamentum teres itself can become hypertrophied (enlarged) or impinged, contributing to pain and mechanical symptoms.

Conclusion

The ligamentum teres of the head of the femur, while often overlooked due to its small size, holds a critically important, though often underappreciated, function. Its primary role is to act as a vital vascular conduit, delivering essential blood supply to the femoral head, especially during early development, thereby protecting against avascular necrosis. Its contributions to mechanical stability are secondary and minimal, limited to extreme hip positions, though its potential role in proprioception is an area of continued scientific interest. Understanding its true function is crucial for clinicians and fitness professionals alike when considering hip pathologies and rehabilitation strategies.