The pelvic ring, also known as the pelvic girdle, is a ring of bones shaped like a basin that connects the torso to the legs. It supports the weight of the upper body and transfers some of the weight to the lower limbs when standing. It provides protection to vulnerable organs and supports posture.
The primary function of the pelvic ring is to support the weight of the upper body while standing and sitting. When standing and walking, the pelvic girdle transfers the weight from the axial skeleton, which consists of the 80 bones of the head and trunk of the body, to the lower limbs. It is very strong and sturdy with limited mobility, maintaining strong bonds with the powerful muscles of the legs.
The two hip bones connect and make up the pelvic ring. It is formed where the hip bones meet at the pubic symphysis and connect with the sacrum at the sacroiliac joints. The pubic symphysis is the cartilaginous joint where the left and right pubic bone meet. The sacrum is a large triangular bone, attached to the last lumbar vertebra and the tailbone, which is wedged between the two hip bones. This is connected to the hip bones by the sacroiliac joints.
The pelvic ring contains five joints. It has two sacroiliac joints, where the hip bones meet the sacrum. There are two hip joints, where the hip bones connect to the femurs, or leg bones. Lastly, there is the symphysis pubis, which connects the left and right pubic bones.
Each of these joints have limited mobility, with the exception of the hip joints, as the pelvis is responsible for carrying the weight of the upper body. When weight is placed on the ring, as when sitting or standing, it transforms from a loose structure to a load-bearing stable one. This transformation is triggered when pressure travels down through the spine and causes the sacroiliac ligaments to tighten.
The pelvic ring also provides and home and protective shelter for internal organs. It protects internal reproductive organs, such as the uterus and ovaries, as well as inferior parts of the urinary tracts. These bones also protect and are attached to muscles and membranes of the external reproductive organs.
Posture is also affected by the pelvis ring. These bones are held in a delicate balance that determines the curve of the spine. If the pelvic girdle is abnormally tilted, it will cause poor posture, which can lead to serious injury and discomfort.