The pubis, or pubic bone, is a fundamental part of the human pelvic girdle, forming a protective bony ring that connects the trunk to the lower limbs. It is the smallest of the three bones that fuse to create the large, irregular hip bone on each side of the body. The pubis provides stability, supports the body’s weight, and protects the urinary and internal reproductive organs housed within the pelvic cavity.
Precise Anatomical Location
The pubis is located at the very front, or anterior, portion of the pelvis, making it the most forward-facing of the three hip bones. It sits below the lower abdominal muscles and is positioned just above the external genitalia. This placement forms the forward curve of the bony pelvis, creating a protective shield for the organs behind it.
The hip bone, also known as the coxal bone, is formed from the fusion of three separate bones: the ilium, the ischium, and the pubis. The pubis is continuous with the ischium toward the back and bottom, and with the ilium toward the top and back. In adults, the pubis maintains its identity as the front-most segment of this large structure. The pubis acts as a junction, providing a stable platform for the attachment of various ligaments and tendons from the abdomen and thigh muscles.
Key Components of the Pubic Bone
Each single pubic bone consists of three main parts that extend out from a central region. The largest and flattest part is the pubic body, which forms the strong, middle portion of the bone.
Extending from the body are two bony projections called rami. The superior pubic ramus extends upward and outward, connecting the pubic body to the ilium and ischium. This ramus helps to form part of the socket for the hip joint, known as the acetabulum.
The inferior pubic ramus extends downward and laterally from the pubic body. This lower branch travels to meet and fuse with the ramus of the ischium. The superior and inferior rami, along with the ischium, define the obturator foramen, which is the large opening in the hip bone that allows for the passage of nerves and vessels.
The Central Joint: The Pubic Symphysis
The human pelvis is made up of two mirror-image hip bones, meaning there is a pubic bone on the left side and a matching one on the right side. The pubic symphysis is the specialized joint that connects the bodies of these two separate pubic bones at the front midline. This joint is classified as a secondary cartilaginous joint, meaning it is made up of both hyaline cartilage and a thick disc of fibrocartilage.
The fibrocartilage disc provides a strong yet slightly flexible connection between the two bony surfaces. While the pubic symphysis holds the pelvic bones firmly in place, it allows for minimal movement, up to about two millimeters. This slight flexibility is reinforced by four strong ligaments surrounding the joint, which help to absorb shock during movement. For people who become pregnant, the ligaments in the symphysis loosen, allowing the pelvis to widen slightly to accommodate childbirth.