The pubis is a key component of the pelvic girdle, connecting the spine to the lower limbs. It is one of three bones that form each half of the pelvis, also known as the innominate bone.
What is the Pubis?
The pubis is the most anterior and inferior of the three bones (ilium and ischium) that compose the hip bone. These bones fuse into a single hip bone by adulthood. Positioned at the front of the pelvic girdle where its two halves connect, the pubis forms the anterior portion of the obturator foramen, a large opening enclosed by a membrane for nerves and blood vessels.
Anatomy of the Pubis
The pubis has three main parts: the body and two rami (superior and inferior). The body is the central, flattened portion, connecting with the opposite pubic bone. The superior ramus projects upwards and laterally, forming part of the acetabulum (hip joint socket). The inferior ramus extends downwards and laterally, joining the ischium to complete the obturator foramen. Landmarks include the pubic crest (a thickened upper border), the pubic tubercle (a rounded projection at the lateral end of the crest), and the pectineal line (a ridge on the superior ramus forming part of the pelvic brim).
The Pubis and its Functions
The pubis contributes to stability and movement. Its most notable role is forming the pubic symphysis, a cartilaginous joint where the two pubic bones meet. This joint, composed of fibrocartilage and reinforced by ligaments, allows slight movement, particularly during walking, running, and childbirth. It also supports upper body weight and protects pelvic organs like the bladder and reproductive organs. The pubis serves as an attachment site for muscles and ligaments, including those of the abdomen, thigh, and pelvic floor (e.g., rectus abdominis, adductor muscles, levator ani). These facilitate movement, posture, and continence.
Sex-Specific Differences in the Pubis
While fundamental structure is shared, morphological differences exist between sexes, linked to childbirth in females. The prominent difference is the subpubic angle, formed by the inferior rami of the pubis and ischium. In females, this angle is wider and U-shaped (74.0°-106.5°, around 90 degrees), facilitating a larger pelvic outlet for childbirth. Conversely, the male angle is narrower and V-shaped (50.8°-84.6°, around 70 degrees). Male pelvic bones are generally thicker and denser than female bones. These distinctions are significant in fields like forensic anthropology for skeletal identification.