Pelvic Ligaments: Sacroiliac, Accessory, and Pubic Symphysis

What are the important ligaments of the pelvis?

The pelvis, a foundational structure connecting the axial skeleton to the lower limbs, relies on a complex network of strong ligaments to maintain stability, facilitate load transfer, and enable controlled movement. These critical connective tissues primarily stabilize the sacroiliac joints and the pubic symphysis, ensuring the integrity and functional efficiency of the pelvic girdle.

Introduction to Pelvic Ligaments

The pelvic girdle is formed by the two hip bones (innominate bones), the sacrum, and the coccyx. Its primary functions include transmitting forces from the trunk to the lower limbs, providing attachment points for muscles, and protecting visceral organs. Given the immense forces it must withstand, the pelvis is inherently stable, largely due to its robust ligamentous apparatus. These ligaments, composed primarily of dense regular connective tissue, are crucial for limiting excessive motion at the sacroiliac (SI) joints and the pubic symphysis, thereby preventing injury and supporting efficient biomechanics.

Key Ligaments of the Sacroiliac Joint (SIJ)

The sacroiliac joints, connecting the sacrum to the ilium of each hip bone, are synovial joints with limited mobility, designed more for stability than movement. Their integrity is paramount for effective load transfer between the spine and lower extremities.

• Anterior Sacroiliac Ligaments: These are thin, broad bands covering the anterior aspect of the SI joint. While less robust than their posterior counterparts, they contribute to anterior joint stability and resist excessive anterior translation of the sacrum.
• Posterior Sacroiliac Ligaments:
  • Short Posterior Sacroiliac Ligaments: Located superiorly, these strong, short fibers run obliquely from the sacrum to the ilium. They are crucial for resisting anterior and inferior displacement of the sacrum.
  • Long Posterior Sacroiliac Ligaments: Extending more inferiorly, these ligaments run vertically from the posterior superior iliac spine (PSIS) to the third and fourth sacral segments. They are particularly important in resisting counter-nutation (posterior tilting) of the sacrum and are often implicated in SI joint pain.
• Interosseous Sacroiliac Ligament: Considered the strongest of the SIJ ligaments, this deep, short, and very strong ligament fills the irregular space between the sacrum and ilium posteriorly. It firmly binds the sacrum to the ilium, effectively preventing separation of the joint surfaces and resisting all forms of movement. Its primary role is to restrict anterior and inferior movement of the sacrum.

Accessory Ligaments of the Pelvis

Beyond the direct SIJ ligaments, several strong accessory ligaments play a vital role in pelvic stability by connecting the sacrum to the ischium, further reinforcing the pelvic ring.

• Sacrotuberous Ligament: This large, strong ligament originates from the posterior superior and inferior iliac spines, the sacrum, and the coccyx, and inserts onto the ischial tuberosity. It is critical for preventing upward tilting (nutation) of the sacrum and resisting posterior rotation of the ilium relative to the sacrum. It also forms part of the boundaries of the greater and lesser sciatic foramina.
• Sacrospinous Ligament: Deeper and triangular, this ligament extends from the lateral border of the sacrum and coccyx to the ischial spine. It works in conjunction with the sacrotuberous ligament to stabilize the sacrum, resisting nutation and excessive anterior rotation of the sacrum. It also divides the greater and lesser sciatic notches into their respective foramina.

Ligaments of the Pubic Symphysis

The pubic symphysis is a cartilaginous joint (symphysis) connecting the two pubic bones anteriorly. While less mobile than the SI joints, its stability is maintained by strong ligaments.

• Superior Pubic Ligament: This ligament runs across the superior aspect of the pubic bones, connecting them. It reinforces the joint superiorly and limits superior separation.
• Inferior Pubic Ligament (Arcuate Pubic Ligament): A thick, strong arch of fibers connecting the inferior rami of the pubic bones. It forms the superior boundary of the pubic arch and is crucial for resisting inferior separation and providing support to the joint.

The Role of Pelvic Ligaments in Stability and Function

The collective action of these ligaments is indispensable for optimal pelvic function:

• Load Transfer: They facilitate the efficient transfer of weight and forces from the upper body through the sacrum to the lower extremities, and vice versa.
• Limiting Motion: By restricting excessive movement at the SI joints and pubic symphysis, they prevent hypermobility and potential injury to the pelvic ring.
• Energy Absorption: Their viscoelastic properties allow them to absorb and dissipate forces, protecting the spine and lower limbs from shock.
• Proprioception: Ligaments contain mechanoreceptors that provide sensory feedback to the central nervous system, contributing to balance, posture, and motor control.

Clinical Significance and Common Issues

Understanding these ligaments is crucial for clinicians and fitness professionals alike, as they are frequently involved in pelvic pain and dysfunction.

• Ligament Laxity: Conditions such as pregnancy (due to hormonal changes like relaxin) can lead to increased ligamentous laxity throughout the pelvis, potentially causing SI joint or pubic symphysis pain and instability.
• Trauma: Direct trauma, falls, or high-impact activities can strain or tear pelvic ligaments, leading to acute pain and instability.
• Chronic Overload/Repetitive Stress: Sustained asymmetrical loading or repetitive movements can lead to chronic inflammation or micro-tears in the ligaments.
• Pain Referral: Injury or dysfunction of these ligaments can refer pain to the lower back, buttock, groin, or even down the leg, mimicking other conditions.
• Rehabilitation: Targeted exercises focusing on core stability, gluteal strength, and proper movement patterns are essential for supporting the ligamentous structures and restoring pelvic stability after injury or during periods of laxity.

Conclusion

The ligaments of the pelvis form a vital, interconnected system that underpins the structural integrity and functional efficiency of the entire body. From the robust interosseous ligament securing the SI joint to the strong sacrotuberous ligament providing accessory stability, each plays a specific role in load transfer, limiting motion, and preventing injury. A comprehensive understanding of these anatomical structures is fundamental for anyone involved in human movement, ensuring effective assessment, training, and rehabilitation strategies for pelvic health.