Hip bone (Pelvic bone, Os coxa, Innominate bone, or Coxal bone) : Structure, Functions & Clinical Anatomy

Hip bone (Pelvic bone) : Anatomy, Structure, Parts,  Attachments, Side Determination, Functions, Clinical Anatomy, & Fractures


  • Hip bone or Pelvic bone is a large irregular flat bone made up of three parts – ilium, ischium & pubis.
  • The pelvic bone is irregular in shape and has two major parts separated by an oblique line on the medial surface of the bone :
    – the pelvic bone above this line represents the lateral wall of the false pelvis, which is part of the abdominal cavity;
    – the pelvic bone below this line represents the lateral wall of the true pelvis, which contains the pelvic cavity.


  • Pelvic bone is made up of three parts which are the ilium superiorly, the pubis anteroinferiorly, and the ischium posteroinferiorly.
  • The three parts are joined to each other at a lateral cup-shaped hollow large articular socket, called the acetabulum. The acetabulum articulates with the head of the femur to form the hip joint.
  • The ilium articulates with the sacrum. The pelvic bone is further anchored to the end of the vertebral column (sacrum and coccyx) by the sacrotuberous and sacrospinous ligaments, which attach to a tuberosity and spine on the ischium.
  • The pubis and ischium are separated by a large oval opening called the obturator foramen present inferior to the acetabulum.
  • The pelvic bones articulate posteriorly with the sacrum at the sacro-iliac joints and with each other anteriorly at the pubic symphysis.
  • The pubic parts of the two hip bones meet anteriorly to form the pubic symphysis.
  • The paired hip bones & a sigle sacrum form the pelvic or hip girdle.
  • The bony pelvis is formed by the two hip bones along with the sacrum and coccyx.

Side Determination

  • The acetabulum is directed laterally.
  • The flat, expanded ilium forms the upper part of the bone, that lies above the acetabulum.
  • The obturator foramen lies below the acetabulum. It is bounded anteriorly by the thin pubis, and posteriorly by the thick and strong ischium.

Anatomical Position

  • The pubic symphysis and anterior superior iliac spine lie in the same coronal plane.
  • The pelvic surface of the body of the pubis is directed backwards and upwards.
  • The symphyseal surface of the body of the pubis lies in the median plane.

Clinical Anatomy

Pelvic fractures : There are many ways of classifying pelvic fractures, which enable the surgeon to determine the appropriate treatment and the patient’s prognosis. 

Pelvic fractures are generally of four types.

  • Type 1 injuries occur without disruption of the bony pelvic ring (e.g., a fracture of the iliac crest). These types of injuries are unlikely to represent significant trauma, though in the case of a fracture of the iliac crest, blood loss needs to be assessed.
  • Type 2 injuries occur with a single break in the bony pelvic ring. An example of this would be a single fracture with diastasis (separation) of the symphysis pubis. Again, these injuries are relatively benign in nature, but it may be appropriate to assess for blood loss.
  • Type 3 injuries occur with double breaks in the bony pelvic ring. These include bilateral fractures of the pubic rami, which may produce urethral damage.
  • Type 4 injuries occur at and around the acetabulum
  • Other types of pelvic ring injuries include fractures of the pubic rami and disruption of the sacroiliac joint with or without dislocation. This may involve significant visceral pelvic trauma and hemorrhage. Other general pelvic injuries include stress fractures and insufficiency fractures, as seen in athletes and elderly patients with osteoporosis, respectively.

Pelvic fractures can be associated with appreciable blood loss (concealed exsanguination) and blood transfusion is often required. In addition, this bleeding tends to form a significant pelvic hematoma, which can compress nerves, press on organs, and inhibit pelvic visceral function.

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