Pelvic Girdle Joints: Anatomy, Function, and Clinical Relevance

What are joints of the pelvic girdle?

The pelvic girdle is a robust bony ring that connects the axial skeleton (spine) to the lower limbs, and its structural integrity and functional capacity are largely defined by three critical joint complexes: the two sacroiliac joints and the pubic symphysis, complemented by the two hip joints.

Understanding the Pelvic Girdle and Its Articulations

The pelvic girdle, comprised of the two hip bones (ossa coxae or innominate bones) and the sacrum, serves as a crucial anatomical bridge. It supports the weight of the upper body, transmits forces to the lower limbs, provides attachment for powerful muscles, and protects pelvic organs. The stability and mobility required for these functions are facilitated by specialized joints, each contributing uniquely to the girdle's overall mechanics. For fitness professionals and enthusiasts, understanding these articulations is fundamental to comprehending movement, identifying potential dysfunctions, and designing effective training programs.

Key Joints of the Pelvic Girdle

The primary joints directly forming and articulating with the pelvic girdle are the sacroiliac joints, the pubic symphysis, and the hip joints.

Sacroiliac (SI) Joints

The sacroiliac joints are perhaps the most complex and often misunderstood joints of the pelvic girdle.

• Anatomy: These are a pair of synovial joints (though with limited movement) located on either side of the sacrum, where it articulates with the ilium (the largest part of the hip bone). The joint surfaces are irregular and interlock, contributing to their inherent stability.
• Function: The primary role of the SI joints is to transmit the weight of the upper body from the axial skeleton to the lower limbs, acting as shock absorbers. While classified as synovial, their movement is minimal, primarily consisting of slight gliding and rotation (nutation and counternutation). This limited motion is crucial for accommodating forces during gait and maintaining spinal stability.
• Ligaments: The SI joints are reinforced by an incredibly strong network of ligaments, making them among the most stable joints in the body. Key ligaments include:
  • Anterior Sacroiliac Ligaments: Thinner, but reinforce the anterior aspect.
  • Posterior Sacroiliac Ligaments: Extremely strong, connecting the sacrum to the ilium posteriorly.
  • Interosseous Sacroiliac Ligaments: The strongest, filling the space between the sacrum and ilium, providing significant stability.
  • Sacrotuberous and Sacrospinous Ligaments: Connect the sacrum to the ischial tuberosity and ischial spine, respectively, further stabilizing the sacrum relative to the pelvis.
• Clinical Relevance: Due to their role in weight transmission and limited movement, SI joints are a common source of lower back and buttock pain, often referred to as Sacroiliac Joint Dysfunction (SIJD). This can arise from excessive or insufficient movement, muscle imbalances, or trauma.

Pubic Symphysis

The pubic symphysis is a cartilaginous joint located at the very front of the pelvis.

• Anatomy: This joint connects the two pubic bones (rami) at the midline. It is a secondary cartilaginous joint (symphysis), meaning it is formed by a fibrocartilaginous disc sandwiched between the articular surfaces of the two pubic bones.
• Function: The pubic symphysis provides stability to the anterior pelvic ring and allows for a slight degree of movement, particularly important during childbirth when hormonal changes increase its laxity. It also helps to absorb forces transmitted through the pelvis.
• Ligaments: The fibrocartilaginous disc is reinforced by strong ligaments:
  • Superior Pubic Ligament: Runs across the top of the joint.
  • Inferior Pubic Ligament (Arcuate Ligament): Forms a strong arch beneath the joint.
  • Anterior and Posterior Pubic Ligaments: Provide additional reinforcement.
• Clinical Relevance: Pain at the pubic symphysis, often termed Pubic Symphysis Dysfunction (PSD) or Pelvic Girdle Pain (PGP), is common during pregnancy due to hormonal changes and increased mechanical stress. It can also occur in athletes due to repetitive stress or muscle imbalances.

Hip (Coxal) Joints

While not strictly part of the pelvic girdle's bony ring, the hip joints are integral to its function, forming the critical articulation between the pelvic girdle and the lower limbs.

• Anatomy: These are large, multi-axial ball-and-socket synovial joints. The spherical head of the femur articulates with the acetabulum, a deep socket formed by the fusion of the ilium, ischium, and pubis of the hip bone. The acetabulum is deepened by a fibrocartilaginous rim called the acetabular labrum.
• Function: The hip joints are designed for both significant mobility and robust stability, allowing for a wide range of movements (flexion, extension, abduction, adduction, internal and external rotation, circumduction) while bearing substantial body weight. They are crucial for locomotion, balance, and transferring forces between the trunk and lower extremities.
• Ligaments: The hip joint capsule is reinforced by some of the strongest ligaments in the body, limiting excessive movement and contributing to stability:
  • Iliofemoral Ligament (Y-ligament of Bigelow): The strongest ligament in the body, preventing hyperextension of the hip.
  • Pubofemoral Ligament: Prevents excessive abduction and hyperextension.
  • Ischiofemoral Ligament: Prevents excessive internal rotation and hyperextension.
  • Ligament of the Head of the Femur (Ligamentum Teres): Contains a small artery supplying the femoral head, with a minor role in stability.
• Clinical Relevance: The hip joints are susceptible to conditions such as osteoarthritis, labral tears, impingement syndromes (FAI), and various forms of tendinopathy, all of which can significantly impact mobility, stability, and overall functional capacity.

Functional Significance of Pelvic Girdle Joints

The coordinated function of these joints is paramount for human movement and stability:

• Weight Bearing and Force Transmission: The SI joints and hip joints are critical for absorbing and transmitting forces from the ground up and the trunk down, ensuring efficient load distribution during standing, walking, and running.
• Stability and Mobility Balance: The pelvic girdle masterfully balances stability (provided by the strong ligaments of the SI joints and pubic symphysis) with the necessary mobility for locomotion (primarily from the hip joints).
• Core Integration: The pelvic girdle serves as the foundation for the core musculature. Optimal function of its joints is essential for effective core stabilization, which in turn supports spinal health and athletic performance.
• Gait Mechanics: The subtle movements within the SI joints and pubic symphysis, combined with the extensive range of motion at the hip joints, are fundamental to the efficient and fluid mechanics of walking and running.

Clinical Considerations and Common Issues

Understanding the joints of the pelvic girdle is crucial for identifying and addressing common issues:

• Pelvic Girdle Pain (PGP): A broad term encompassing pain originating from the SI joints, pubic symphysis, or both. Often related to altered joint mechanics, muscle imbalances, or ligamentous laxity.
• Referred Pain: Dysfunction in the pelvic girdle joints can refer pain to the lower back, groin, buttocks, or even down the leg, mimicking other conditions.
• Impact of Muscle Imbalances: Weakness or tightness in surrounding muscles (e.g., glutes, deep hip rotators, core muscles, hip flexors) can significantly affect the biomechanics and stability of these joints, leading to pain or dysfunction.
• Rehabilitation and Training: Exercise interventions often focus on strengthening the stabilizing muscles around the pelvis and hips, improving joint mobility where restricted, and enhancing neuromuscular control to optimize force transmission and reduce stress on these critical articulations.

Conclusion

The joints of the pelvic girdle—the sacroiliac joints, the pubic symphysis, and the hip joints—are foundational to human movement, stability, and load bearing. Their intricate anatomy and biomechanics allow for a delicate balance between rigidity and flexibility, enabling everything from standing upright to complex athletic maneuvers. A comprehensive understanding of these joints empowers fitness professionals and individuals alike to appreciate the complexity of the human body, optimize movement patterns, and address potential sources of musculoskeletal pain effectively.