04/09/2022
š WHAT'S UNDER THE SACRUM?
The sacrum is a large wedge shaped vertebra at the inferior end of the spine. It forms the solid base of the spinal column where it intersects with the hip bones to form the pelvis. The sacrum is a very strong bone that supports the weight of the upper body as it is spread across the pelvis and into the legs.
The female sacrum is shorter, wider, and curved more posteriorly than the male sacrum to provide more room for the passage of the fetus through the birth ca**l during childbirth.
Many nerves of the cauda equina at the inferior end of the spinal cord pass through the sacrum. These nerves enter the sacrum from the vertebral foramen of the lumbar vertebrae through the tunnel-like sacral ca**l. From the sacral ca**l these nerves branch out and exit the sacrum through four pairs of holes on the sides of the ca**l called the sacral foramina or through the sacral hiatus at the inferior end of the ca**l.
The nerves that compose the cauda equina innervate the pelvic organs and lower limbs to include motor innervation of the hips, knees, ankles, feet, internal a**l sphincter and external a**l sphincter. In addition, the cauda equina extends to sensory innervation of the perineum and, partially, parasympathetic innervation of the bladder.
The sacrum serves several important functions in the skeletal, muscular, nervous, and female reproductive systems. Acting as the keystone of the pelvis, the sacrum locks the hip bones together on the posterior side and supports the base of the spinal column as it intersects with the pelvis. Several key muscles of the hip joint, including the gluteus maximus, iliacus and piriformis, have their origins on the surface of the sacrum and pull on the sacrum to move the leg.