Symphysis Pubis: Structural & Functional Classification, Anatomy, and Clinical Relevance

What is the classification of symphysis pubis?

The symphysis pubis is classified structurally as a cartilaginous joint, specifically a symphysis, and functionally as an amphiarthrosis, meaning it is a slightly movable joint.

Understanding Joint Classification

To properly classify the symphysis pubis, it's essential to understand the two primary systems used in anatomy to categorize joints (articulations):

• Structural Classification: This system categorizes joints based on the material that connects the bones and whether a joint cavity is present. The three main structural types are fibrous, cartilaginous, and synovial joints.
• Functional Classification: This system categorizes joints based on the degree of movement they permit. The three main functional types are synarthroses (immovable), amphiarthroses (slightly movable), and diarthroses (freely movable).

Structural Classification of the Symphysis Pubis

The symphysis pubis falls under the cartilaginous joint category. More specifically, it is a type of cartilaginous joint known as a symphysis.

• Cartilaginous Joints: In these joints, the bones are united by cartilage. There is no joint cavity.
• Symphysis: This particular type of cartilaginous joint features a pad or disc of fibrocartilage between the articulating bones. Fibrocartilage is a tough, resilient tissue that can withstand significant compression and tension. Other examples of symphyses in the body include the intervertebral discs between vertebrae.

In the case of the symphysis pubis, the two pubic bones (left and right) are joined anteriorly by a thick, flattened disc of fibrocartilage.

Functional Classification of the Symphysis Pubis

Functionally, the symphysis pubis is classified as an amphiarthrosis.

• Amphiarthrosis: This term describes a joint that permits only a slight degree of movement. While not as rigid as a completely immovable (synarthrotic) joint, it does not allow the wide range of motion seen in freely movable (diarthrotic) joints like the knee or shoulder.

The slight movement permitted by the symphysis pubis is crucial for various physiological functions, particularly during gait (walking) and childbirth.

Anatomical Structure of the Symphysis Pubis

The symphysis pubis is a critical component of the pelvic girdle, located anteriorly where the two halves of the pelvis meet.

• Articulating Bones: The superior rami of the left and right pubic bones. Each pubic bone contributes an oval-shaped articular surface.
• Intervening Material: A dense, fibrocartilaginous disc, often thicker in women than in men, sits between the two pubic bones. This disc acts as a shock absorber and allows for minimal movement.
• Ligamentous Support: The joint is reinforced by several strong ligaments that contribute to its stability:
  • Superior Pubic Ligament: Connects the superior aspects of the pubic bones.
  • Inferior Pubic (Arcuate) Ligament: Forms a strong arch inferiorly, connecting the inferior rami of the pubic bones.
  • Anterior and Posterior Pubic Ligaments: Provide additional reinforcement.

Role and Importance in Movement and Stability

Despite its limited mobility, the symphysis pubis plays a vital role in the biomechanics of the pelvis and lower body:

• Pelvic Stability: It helps to unite the two halves of the pelvis, providing stability to the pelvic ring, which is crucial for transmitting forces from the axial skeleton to the lower limbs and vice versa.
• Weight Bearing: It assists in distributing weight and absorbing shock during activities like walking, running, and jumping.
• Subtle Movements: The slight movement it allows is important for:
  • Gait: Permitting small shifts and rotations of the pelvis during walking to optimize energy efficiency.
  • Childbirth: Its slight flexibility, particularly under the influence of hormones like relaxin during pregnancy, allows for a small degree of widening of the pelvic outlet, which is essential for the passage of the fetal head.

Clinical Relevance and Considerations

Understanding the classification and function of the symphysis pubis is important in clinical contexts:

• Symphysis Pubis Dysfunction (SPD): Also known as Pelvic Girdle Pain (PGP), this common condition, particularly in pregnancy, involves excessive laxity or misalignment of the symphysis pubis, leading to pain and instability.
• Trauma: The joint can be injured through high-impact trauma, leading to sprains, dislocations, or fractures of the adjacent pubic bones.
• Inflammation: Conditions like osteitis pubis, an inflammation of the pubic symphysis, are common in athletes due to repetitive stress.

Conclusion

In summary, the symphysis pubis is a fascinating example of a joint that perfectly balances stability with a necessary degree of flexibility. Structurally, it is a cartilaginous joint of the symphysis type, characterized by its fibrocartilaginous disc. Functionally, it is classified as an amphiarthrosis, signifying its capacity for slight, yet critical, movements. This unique classification underpins its vital role in pelvic integrity, weight distribution, and the biomechanics of human locomotion and parturition.