A symphysis is a joint where two bones are connected by a thick pad of tough, flexible cartilage. Unlike the freely moving joints in your knees or shoulders, a symphysis allows only a small amount of movement. That limited motion is the whole point: these joints absorb shock, bear weight, and hold structures together while still giving your body just enough flexibility to function.
How a Symphysis Joint Works
The cartilage in a symphysis is fibrocartilage, the same dense, rubbery material found in knee menisci. It sits between two bone surfaces and acts like a built-in shock absorber. When you walk, run, or jump, the fibrocartilage compresses slightly to cushion the impact, then returns to its original shape. Different fiber arrangements within the cartilage handle different types of force: oblique fibers resist shearing, horizontal fibers resist pulling, and the cartilage tissue itself resists compression.
This design makes symphysis joints ideal for parts of the body that need stability under heavy loads but can’t be completely rigid. They’re classified as “slightly movable” joints, sitting between fully immovable joints (like the fused plates of your skull) and freely movable joints (like your hip or elbow).
Where Symphysis Joints Are in Your Body
There are three main symphysis joints, and they fall into two categories based on size.
Narrow symphyses include the pubic symphysis, which connects the left and right halves of your pelvis at the front, and the manubriosternal joint, where the upper and middle portions of your breastbone meet. These joints have a relatively thin cartilage disc and allow very little movement.
Wide symphyses are the intervertebral discs between each pair of vertebrae in your spine. These are the largest symphysis joints in the body, with thick fibrocartilage pads that cushion your vertebrae during high-impact activities. You have 23 of them stacked along your spinal column, and together they account for roughly a quarter of your spine’s total length.
There’s also the mandibular symphysis, the joint at the center of your chin where the two halves of the jawbone meet. In humans, this joint fuses into solid bone during infancy, so adults no longer have a functional symphysis there. During fetal development, the symphysis stays vertically oriented, and after birth it gradually tilts backward as the chin becomes more prominent.
The Pubic Symphysis in Detail
The pubic symphysis is the one most people encounter by name, especially during pregnancy. In healthy adults, this joint measures roughly 2.5 to 5 mm wide. It sits right at the front center of the pelvis and plays a critical role in stabilizing the pelvic ring while you stand and move.
The forces on this joint change depending on what you’re doing. When you stand on both legs, the pubic symphysis experiences pulling (tensile) forces as your body weight spreads evenly through the pelvis. When you stand on one leg, the forces shift to compression and shearing. The joint’s broad contact surfaces distribute these forces evenly, which helps protect the cartilage from damage during everyday activities like walking and climbing stairs.
Changes During Pregnancy
During pregnancy, a hormone called relaxin loosens the ligaments around the pelvis, including those supporting the pubic symphysis. Relaxin works by breaking down the fibers that keep connective tissue firm. This softening allows the joint to widen gradually, from about 4 mm at 8 weeks of pregnancy to roughly 7 mm by the time the baby is due. That extra flexibility helps the pelvis expand during childbirth.
In some cases, the joint widens too much. A gap greater than 10 mm, combined with symptoms like pain and difficulty walking, typically leads to a diagnosis of pubic symphysis diastasis. One documented case involved a separation of over 4 cm, though symptoms resolved after about 8 weeks of pelvic stabilization with a support band.
Symphysis Pubis Dysfunction
Symphysis pubis dysfunction (SPD) is pain centered at the pubic symphysis, most commonly during pregnancy. The discomfort ranges from mild aching to sharp pain that makes it difficult to walk, climb stairs, or get in and out of a car. Pain during sex is also common.
The severity depends on how weight and pressure distribute across your pelvis. Some people feel it only with certain movements, while others have constant discomfort. Diagnosis usually involves a physical exam checking for tenderness and swelling at the joint, along with a review of your medical history. Outside of pregnancy, infections and inflammatory conditions like osteitis pubis can also cause pain at the pubic symphysis, particularly in athletes who place repetitive stress on the pelvic area.
Intervertebral Discs as Symphyses
Your spinal discs are symphysis joints, even though most people think of them simply as “discs.” Each one consists of a tough fibrocartilage ring surrounding a gel-like center. This structure lets adjacent vertebrae tilt and rotate slightly relative to each other, which is what allows your spine to bend and twist. At the same time, the thick cartilage pad absorbs the compressive forces that travel down your spine every time you take a step or land from a jump.
Because these are the widest symphyses in the body, they handle significantly more motion than the pubic symphysis or the manubriosternal joint. That greater range of movement, combined with the constant loading they endure, is also why intervertebral discs are more prone to wear and injury over time. Disc herniation, bulging, and degeneration are all problems that arise in these particular symphysis joints.