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Pelvis

The pelvis is a bony structure that can be found in both male and female skeletons. The exception to this compound structure, when compared to all other bones, is that it has differences that are classified by sex, both for functional and general developmental reasons. The rest of the human skeleton differs only in size, which is genetically determined and is usually slightly larger in males than in females.

The structure of the pelvis is designed to give females the ability to undergo pregnancy and childbirth, while males are able to hold larger and heavier muscles upon their frame. Therefore it is heavier in men and has more muscle attachments, a narrower pubic arch, subpubic angle and space between the ischial tuberosities which in turn makes the pelvic outlet smaller. The ilia in women are comparatively more flared than in men which makes their greater pelvis more shallow. The shape of the pelvic inlet and the obturator foramen is oval in women and heart-shaped and round in men respectively. In general, the pelvis is broader in women so that there is ample space for the fetus to exit its mother's body.

Key Facts
Bones Hip bones (ilium, ischium, pubis)
Sacrum (five lower sacral bones fused)
Coccyx
Joints Lumbosacral joints, sacrococcygeal joint, sacroiliac joint, pubic symphysis
Ligaments Sacrotuberous and sacrospinous ligaments
Clinical notes

Multiple fractures within the Paget's disease

Pelvic fractures: anteroposterior compressions, lateral compressions, vertical shears, combined fractures

It is clear that the anatomy of pelvis is complex and consists of the several bones that are connected with mutual joints. Also, a couple of ligaments in the pelvis participate in forming the pelvis cavity. All of these structures, together with the clinical conditions that may affect the pelvis, will be described in this article.

Bones

The pelvis is formed by four bones which include a pair of hip bones otherwise known as innominate bones, the sacrum, which comes with the five lower sacral bones that are fused together and the coccyx which has four fused and a single individual terminal vertebra. The pelvic girdle consists of the hip bones and the sacrum and its function is to transmit the weight from the upper body to the lower limbs, while allowing the body to stay balanced. Meanwhile the ilium, the ischium and the pubis fuse together at puberty to form the innominate bones and are joined by the cartilage found in the acetabulum.

Recommended video: Bones of the pelvis
Overview of the different bones of the pelvis.

Joints

The pelvis as a compound structure contains four different joints, one of which is paired. The lumbosacral joints are compound joints that are stabilised by the iliolumbar ligaments and are made up of two posterior zygapophyseal joints and an intervertebral joint via an intervertebral disc between L4 and S1.

The sacrococcygeal joint is a secondary cartilaginous joint that connects the sacrum to the coccyx. It is reinforced via the anterior and posterior sacrococcygeal ligaments.

The sacroiliac joint is an atypical synovial joint which contains fibrocartilage and has a very limited range of movement. Its articulatory surfaces are between the sacrum and the ilium. It is stabilised by the interosseous ligaments and by the anterior and posterior sacroiliac ligaments.

Lastly, the pubic symphysis is the joint that unites the pubic bones in a secondary cartilaginous articulation. It contains a fibrocartilaginous interpubic disc and is reinforced by the superior and inferior pubic ligaments.

Ligaments

The two main ligaments of the pelvis are the sacrotuberous and sacrospinous ligaments, which enclose the greater and lesser sciatic notches, forming the greater and lesser sciatic foramina. Due to natural forces, when in an orthostatic or upright stance, the weight of the upper body which is relayed via the spine rotates the sacrum and tips it backwards. However, this movement is prevented by the pelvic ligaments.

The sacrotuberous ligament extends from the dorsum of the lateral border of the sacrum as well as the posterior surface of the ilium to the ischial tuberosity and is the larger of the two ligaments. The sacrospinous ligament stretches between the lateral border of the sacrum to the ischial spine.

Sciatic Foramina

These foramina are created by the positioning of bony notches and ligaments. The greater sciatic foramen is made up of the greater sciatic notch and the fibers of the sacrospinous and sacrotuberous ligaments. It contains:

The lesser sciatic foramen is made up of the same ligaments as the greater foramina, however they come into contact with the bony lesser sciatic notch. It contains:

  • the tendon of the obturator internus
  • the nerve of the obturator internus
  • the pudendal nerve
  • the internal pudendal artery

Clinical Notes

Paget's Disease

Paget’s disease or osteitis deformans is a disorder whose etiology is as of yet unknown, however theories point towards the paramyxovirus. The bones are abnormally structured due to the increased activity of both osteoclasts and osteoblasts. It can involve the pelvis among other bones and may result in:

  • multiple fractures
  • high output cardiac failure
  • hearing loss
  • increased risk of osteosarcoma

Pelvic Fractures

Pelvic fractures can be quite debilitating and even life-threatening due to potentially fatal hemorrhages and multi-organ failures. There are several types of pelvic fractures, which are classified according to the mechanism of injury and severity of the fracture itself:

  • Anteroposterior (AP) compressions - the fractures are caused by either direct or indirect forces acting in an anteroposterior direction on the pelvis. The result is diastasis (separation) of the symphysis pubis. There are three grades of AP compressions, distinguished by the degree of diastasis (partially or complete separation, also known as a fracture) and the involvement of the sacroiliac joints and the pelvic ligaments.
  • Lateral compressions - if the force comes from a lateral direction, the pelvic will rotate inwards, resulting in fractures of the sacroiliac region and pubic rami. Similar to the AP compression, there are three grades of severity. The classification depends on the involvement of iliac wing as well or an anteroposterior compression injury on top of a lateral compression.
  • Vertical shear - this type of fracture results if the direction of the force happens in an axial (superoinferior or vice versa) direction. The fracture happens along the sacroiliac joint, resulting in a vertical displacement of the parts in anterior and posterior directions. 
  • Combined injuries - this is the most complex out of all of them. As the name suggests, a combined pelvic fracture results from a combination of at least two different force vectors acting on the pelvis.\

The signs and symptoms associated with pelvic fractures include pelvic displacement, instability on palpation, several neurological and vascular instability, potentially genitourinary injuries associated with the fracture.

Pelvis - want to learn more about it?

Our engaging videos, interactive quizzes, in-depth articles and HD atlas are here to get you top results faster.

Sign up for your free Kenhub account today and join over 852,397 successful anatomy students.

“I would honestly say that Kenhub cut my study time in half.” – Read more. Kim Bengochea Kim Bengochea, Regis University, Denver

Show references

References:

  • Frank H. Netter, MD, Atlas of Human Anatomy, Fifth Edition, Saunders - Elsevier, Chapter 5 Pelvis & Perineum, Subchapter 33. Bones & Ligaments, Guide Pelvis & Perineum: Bones and Ligaments, Page 168 to 170.
  • Arthur S. Schneider and Philip A. Szanto, Board Review Series Pathology, 1st Edition, Wolters Kluwer - Lippincott, Williams and Wilkins, Chapter 22, Musculoskeletal System, Page 346.
  • Guthrie, H.C., R.W. Owens, and M.D. Bircher, Fractures of the pelvis. The Journal of Bone and Joint Surgery. British volume, 2010. 92-B(11): p. 1481-1488.

Author:

  • Dr. Alexandra Sieroslawska

Illustrators:

  • First Illustration Gallery - Liene Znotina
  • Second Illustration Gallery - Yousun Koh, Paul Kim
  • Third Illustration Gallery - Liene Znotina
  • Fourth Illustration Gallery - Liene Znotina
  • Fifth Illustration Gallery - Liene Znotina
© Unless stated otherwise, all content, including illustrations are exclusive property of Kenhub GmbH, and are protected by German and international copyright laws. All rights reserved.

Related Atlas Images

Pelvis

Main bones of the lower extremity

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