The symphysis pubis is a joint located at the front of the pelvis, connecting the two halves of the pubic bone. It forms a crucial link in the pelvic girdle, providing stability and aiding in the transmission of forces. This joint allows for slight movement.
Location and Structure
The symphysis pubis is located at the anterior aspect of the pelvis, where the left and right pubic bones meet. This connection is a secondary cartilaginous joint.
The joint consists of a fibrocartilaginous disc, known as the interpubic disc, nestled between the pubic bones. These bone surfaces are covered with hyaline cartilage, connecting to the disc. Four ligaments—the superior, inferior (arcuate), anterior, and posterior pubic ligaments—surround and reinforce the disc, contributing to the joint’s stability and flexibility.
Key Functions
The symphysis pubis primarily provides stability to the entire pelvic structure. It works with other pelvic joints to create a stable ring that supports the upper body and transfers weight to the lower limbs, essential for upright posture.
Beyond stability, the symphysis pubis also contributes to shock absorption during physical activities. Its design allows for small movements, typically around 2 millimeters of shift and 1 degree of rotation. This slight flexibility cushions impact during everyday movements like walking, running, and standing.
Significance in Pregnancy and Beyond
During pregnancy, hormonal shifts, particularly relaxin, soften and loosen the symphysis pubis’s ligaments and muscles. This process can begin as early as 10 weeks, preparing the pelvis for childbirth.
The increased laxity and mobility allow the pelvis to widen, which is crucial for facilitating the baby’s passage through the birth canal. While typically 4 to 5 millimeters wide in non-pregnant individuals, the gap can increase significantly during pregnancy, up to 9 millimeters or more.
These changes can sometimes lead to discomfort, known as Pubic Symphysis Dysfunction (PSD) or Pelvic Girdle Pain (PGP). Symptoms include pain in the front of the pubic bone, lower back, perineum, or upper thighs, sometimes with clicking or grinding sensations. Activities like walking, climbing stairs, or turning in bed can worsen this discomfort. In some instances, separation can exceed 10 millimeters, a condition called diastasis of the symphysis pubis. Though most commonly associated with pregnancy, symphysis pubis issues can also arise from injuries, infections, or conditions like osteoarthritis.