Pelvis is made by the connection of three bones - sacrum and two iliac(hip) bones. Sacrum represents the back wall of pelvis. It connects with the two iliac bones by the SacroIliac joints. The two iliac bones make a curve forward and attach to each other, forming the pubic syndesmosis, thus closing the ring shape of pelvis. Sacrum is made out of five fused vertebraes that make a solid and stable base upon which stands the spine. Sacrum holds up the upper body weight and transfers it to the lower limbs via the Sacroiliac joints. Pelvic surface is rich of bony prominences, pits and rigs, all determined by the multiple functions pelvis has. The inner side of pelvis is divided to greater and lesser pelvis and hosts variety of internal organs and muscles. On the outer front-later iliac side is situated a circular pitted structure called acetabulum. It is a part of the hip joint. Pelvis is a strong and sturdy structure because it is an attachment point of many muscles the majority of which are involved in posture support. The right balancing between the different muscle groups around pelvis determines and provides for the overall and local good health status, good posture and gait. 

Sacroiliac (SI) Joint Pain
Dr. Nikolay Tivchev
M.D., Chief of Othopedics and Traumatology at Serdika Hospital