Interpubic disc

At a glance

English

Interpubic disc

Latin (TA2)

Discus interpubicus

System

Cartilage

Region

Whole body

Side

Single, on the midline

About the interpubic disc

The interpubic disc is the main binding tissue of the pubic symphysis, the joint that closes the pelvic girdle in front. It lies in the midline between the oval symphyseal surfaces of the two pubic bones and holds them firmly together. The joint is a secondary cartilaginous joint with no synovial lining, and the disc is what makes it so: each bony face carries a thin coat of hyaline cartilage, and the fibrocartilage of the disc is fused to both coats.

The disc is thicker in front than behind, so the gap between the bones is a few millimetres wider anteriorly. Its fibres are mostly type I collagen, arranged in bundles that follow the lines of tension, with cartilage cells lying between them. A small, slit-like space often appears within it, usually towards the upper back part; it is not a true joint cavity because it has no synovial membrane. The middle of the disc has no blood vessels and is nourished by diffusion, a pattern that suits the compressive load it bears.

Ligaments around the joint are so closely bonded to the disc that their fibres interlace with it. The superior pubic ligament crosses its upper border to each pubic tubercle, and the thick arcuate (inferior) pubic ligament curves along its lower border to the inferior pubic rami, forming the rounded top of the pubic arch. Thinner anterior and posterior fibres cover its faces, and the front ones are strengthened by the tendons of the abdominal muscles and the adductors.

Acting with these ligaments, the disc resists the two halves of the pelvis being pulled apart or sheared on each other while allowing a slight give that absorbs shock during walking and running. It wears with age, and the changing surface of the symphysis on either side of it is used to estimate adult age from a skeleton. Inflammation at the joint, osteitis pubis, causes groin pain in athletes, and the disc can ossify in ankylosing spondylitis.

Attachments and function

Attaches from

Fused to the hyaline cartilage covering the symphyseal surface of the right pubic bone.

Attaches to

Fused to the hyaline cartilage covering the symphyseal surface of the left pubic bone, and blended at its margins with the pubic ligaments.

Function

Binds the two pubic bones together, resisting separation and shear while allowing slight movement and absorbing shock.

Nerve supply

The surrounding joint tissues are supplied by branches of the iliohypogastric, ilio-inguinal and pudendal nerves.

Blood supply

Its centre is avascular; the periphery receives twigs from the pubic branches of the obturator and inferior epigastric arteries.