Pubic symphysis

At a glance

English

Pubic symphysis

Latin (TA2)

Symphysis pubica

System

Cartilage

Region

Abdomen

Side

Single, on the midline

About the pubic symphysis

The pubic symphysis is the joint where the two halves of the pelvis meet in front. The oval medial surfaces of the right and left pubic bones face each other across the midline, and the joint lies anterior and inferior to the urinary bladder behind the lower abdominal wall. It is a secondary cartilaginous joint, or symphysis: there is no synovial lining, and only very small movements take place, of the order of a couple of millimetres of glide and about a degree of rotation in most adults.

Each bony face is coated with a thin film of hyaline cartilage, and the two coated faces are bound together by a thick fibrocartilaginous interpubic disc. A small non-synovial cleft often forms in it. The gap is a few millimetres wider in front than behind. Its centre is avascular, which suits the steady compression it carries. In the newborn the joint is relatively broad, with thick cartilage end-plates; it reaches adult proportions by mid-adolescence, after which the end-plates thin, and the joint wears steadily with age.

Ligaments blend so closely with the disc that their fibres merge with it. The superior ligament runs across the top of the joint as far as each pubic tubercle and is strengthened by the tendons of rectus abdominis, the external oblique and gracilis. The inferior, or arcuate, pubic ligament is a thick triangular band that rounds off the top of the pubic arch and is attached on each side to the inferior pubic rami; these two give most of the joint's strength. Thinner bands cover the front and back.

Mechanically the joint is a tie beam. The weight of the trunk passes from the sacrum through the sacroiliac joints along two bony arches to the hips, and the symphysis holds the front ends of those arches together while absorbing shock during walking. Wide leg splits open it slightly, and repeated strain of this kind can jam it out of line, needing reduction by a clinician. Osteitis pubis, an inflammatory cause of groin pain in sport, settles with rest and anti-inflammatory drugs; ankylosing spondylitis can fuse the joint and ochronosis leaves calcium in it. Its surfaces wear at a steady rate, so forensic anthropologists use them to age a skeleton.

Attachments and function

Attaches from

The symphyseal surface of the body of the right pubic bone, covered by hyaline cartilage.

Attaches to

The matching symphyseal surface of the left pubic bone, the two joined by the fibrocartilaginous interpubic disc.

Function

Holds the front of the pelvic ring together, transmits and absorbs load between the two halves of the pelvis, and allows slight gliding, separation and rotation.

Nerve supply

Branches of the iliohypogastric, ilio-inguinal and pudendal nerves supply the joint and its ligaments.

Blood supply

Pubic branches of the obturator and inferior epigastric arteries; the central part of the disc is avascular.