Pelvic Ligaments: Structure, Function, and Clinical Importance

What are the ligaments between the pelvic bones?

The pelvic bones, comprising the two hip bones (ilium, ischium, pubis) and the sacrum and coccyx, are interconnected by a complex network of exceptionally strong ligaments that provide crucial stability, facilitate weight transfer, and allow for limited, yet vital, movement.

Understanding the Pelvic Girdle

The human pelvis forms a robust bony ring that serves as the foundation for the axial skeleton, transferring weight from the spine to the lower limbs. It also protects vital pelvic organs and provides attachment points for numerous muscles. The primary joints within this girdle, where ligaments play a pivotal role, are:

• Sacroiliac (SI) Joints: These are the two large, strong joints connecting the sacrum (the triangular bone at the base of the spine) to the ilium (the largest part of each hip bone).
• Pubic Symphysis: This is the cartilaginous joint located at the front of the pelvis, connecting the left and right pubic bones.

The integrity and function of these joints are overwhelmingly dependent on the intricate network of ligaments that bind the pelvic bones together.

Key Ligaments of the Pelvis

The ligaments of the pelvis can be broadly categorized based on the joints they stabilize or the bones they connect.

Ligaments of the Sacroiliac Joints (SIJs)

These are among the strongest ligaments in the body, reflecting their critical role in weight bearing and stability.

• Anterior Sacroiliac Ligaments:
  • Location: Thin and broad bands of fibers that connect the anterior (front) surface of the sacrum to the ilium.
  • Function: Provide limited support to the anterior aspect of the SI joint, preventing excessive anterior translation of the sacrum. They are relatively weaker compared to their posterior counterparts.
• Posterior Sacroiliac Ligaments:
  • Location: Consist of multiple strong, interwoven fibers on the posterior (back) aspect of the SI joint. They are often divided into superficial and deep layers.
  • Function: These are exceptionally strong, providing significant stability to the SI joint, resisting anterior and inferior displacement of the sacrum. They limit sacral nutation (forward tilting) and counternutation (backward tilting).
• Interosseous Sacroiliac Ligaments:
  • Location: Deepest and strongest of the SI ligaments, situated in the roughened area between the sacrum and the ilium.
  • Function: Act as the primary bond between the sacrum and ilium, preventing separation and providing immense stability. They are crucial for resisting shearing forces and maintaining joint integrity.

Ligaments of the Pubic Symphysis

The pubic symphysis is a fibrocartilaginous joint that allows for minimal movement, primarily stabilized by its surrounding ligaments.

• Superior Pubic Ligament:
  • Location: Connects the superior (upper) aspects of the two pubic bones, running transversely across the top of the pubic symphysis.
  • Function: Provides superior stability, preventing upward separation of the pubic bones.
• Inferior (Arcuate) Pubic Ligament:
  • Location: A strong, thick arch of fibers that connects the inferior (lower) aspects of the two pubic bones, forming the superior boundary of the subpubic angle.
  • Function: Provides robust inferior stability to the pubic symphysis, resisting downward separation and supporting the arch of the pelvis.

Extrinsic Ligaments of the Pelvis (Sacro-Ischial Ligaments)

These ligaments connect the sacrum to parts of the ischium (a component of the hip bone), further reinforcing the pelvic ring and forming important foramina.

• Sacrotuberous Ligament:
  • Location: A broad, flat band extending from the lateral (side) border of the sacrum and coccyx to the ischial tuberosity (the bony prominence you sit on).
  • Function: Crucial for resisting sacral nutation (forward tilt) and preventing upward rotation of the sacrum. It converts the greater sciatic notch into the greater sciatic foramen and helps form the lesser sciatic foramen.
• Sacrospinous Ligament:
  • Location: A thinner, triangular ligament extending from the lateral border of the sacrum and coccyx to the ischial spine (a pointed projection on the ischium).
  • Function: Divides the greater sciatic foramen from the lesser sciatic foramen. It works in conjunction with the sacrotuberous ligament to stabilize the sacrum and resist its rotation.

Functional Significance and Biomechanics

The collective action of these pelvic ligaments is paramount for:

• Weight Transmission: They are fundamental in transferring the body's weight from the vertebral column, through the sacrum, to the hip bones and ultimately to the lower limbs during standing, walking, and running.
• Pelvic Stability: They create a rigid yet slightly flexible ring, capable of withstanding significant compressive and shearing forces. This stability is vital for efficient locomotion and preventing injury.
• Force Absorption: The slight elasticity of some ligaments, combined with the fibrocartilage of the symphysis, allows for minor shock absorption during movement.
• Movement Limitation: While allowing for crucial limited movement (e.g., during childbirth), these ligaments primarily restrict excessive motion at the SI joints and pubic symphysis, preventing instability and potential damage.

Clinical Considerations

Understanding these ligaments is critical for health and fitness professionals:

• Sacroiliac Joint Dysfunction: Pain and altered movement patterns in the lower back and buttock region are often attributed to issues with the SI joints, which can involve ligamentous laxity or stiffness.
• Pubic Symphysis Dysfunction (SPD): Common during pregnancy due to hormonal changes (relaxin) that increase ligamentous laxity, leading to pain and instability in the pubic region.
• Trauma: High-impact forces can lead to sprains or ruptures of these strong ligaments, resulting in severe pain and pelvic instability requiring significant rehabilitation.
• Rehabilitation: Physical therapy often targets the muscles surrounding the pelvis to provide dynamic stability, compensating for any underlying ligamentous laxity or dysfunction.

Conclusion

The ligaments between the pelvic bones form an indispensable structural and functional unit. From the robust sacroiliac ligaments that anchor the spine to the lower body, to the reinforcing sacrotuberous and sacrospinous ligaments, and the stabilizing ligaments of the pubic symphysis, each plays a vital role in maintaining the integrity, stability, and biomechanical efficiency of the pelvic girdle. A comprehensive understanding of these structures is essential for anyone seeking to optimize human movement and address musculoskeletal health.