Pelvis Anatomy: Understanding the True and False Pelvis

What is the difference between the true pelvis and the false pelvis?

The pelvis, a crucial bony basin connecting the axial skeleton to the lower limbs, is anatomically divided into two distinct regions: the false (or greater) pelvis and the true (or lesser) pelvis, each with unique boundaries, contents, and functional roles.

Introduction to the Pelvis

The pelvis is a robust, ring-like bony structure located at the base of the spine, formed by the two hip bones (ossa coxae), the sacrum, and the coccyx. Its primary functions include transferring weight from the upper body to the lower limbs, providing attachment points for muscles, and protecting the delicate organs housed within its cavity. To better understand its complex anatomy and function, the pelvis is conceptually divided into two parts by an imaginary line.

The False Pelvis (Greater Pelvis)

The false pelvis, also known as the greater pelvis or pelvis major, is the superior and broader portion of the pelvic cavity. It is not considered part of the true pelvic cavity but rather serves as a transitional zone between the abdominal cavity and the true pelvis.

• Boundaries:
  • Superiorly: It is open and continuous with the abdominal cavity, extending upwards to the level of the iliac crests.
  • Anteriorly: Bounded by the anterior abdominal wall.
  • Posteriorly: Formed by the lumbar vertebrae (specifically L5 and S1).
  • Laterally: Defined by the flared wings of the iliac bones (iliac fossae).
• Contents: The false pelvis primarily houses and supports some of the abdominal viscera, such as the inferior parts of the small intestine (ileum) and portions of the large intestine (e.g., sigmoid colon in some individuals, and the cecum and appendix on the right side). It does not contain the true pelvic organs.
• Function: Its main function is to support the abdominal contents and provide a broad base for the attachment of abdominal muscles, which are vital for trunk movement and core stability.

The True Pelvis (Lesser Pelvis)

The true pelvis, also called the lesser pelvis or pelvis minor, is the inferior and narrower portion of the pelvic cavity. It is the anatomical region that truly defines the pelvic cavity and is of significant clinical importance, particularly in obstetrics.

• Boundaries:
  • Superiorly: It is separated from the false pelvis by a distinct anatomical boundary known as the pelvic brim (or pelvic inlet). This imaginary line runs from the sacral promontory posteriorly, along the arcuate line of the ilium, across the pectineal line of the pubis, and anteriorly to the upper border of the pubic symphysis.
  • Inferiorly: It is bounded by the pelvic outlet, which is closed off by the pelvic floor muscles (levator ani and coccygeus muscles) and associated fascia.
  • Anteriorly: Formed by the pubic bones and pubic symphysis.
  • Posteriorly: Composed of the sacrum and coccyx.
  • Laterally: Formed by the ischium and parts of the ilium below the arcuate line.
• Contents: The true pelvis contains the essential pelvic viscera, including the urinary bladder, rectum, and the internal reproductive organs (uterus, ovaries, and vagina in females; prostate gland and seminal vesicles in males). It also houses major blood vessels, nerves, and lymphatic vessels supplying these organs and the lower limbs.
• Function: Its primary functions include protecting the delicate pelvic organs, bearing the weight of the upper body and transferring it to the lower limbs, and in females, forming the bony birth canal through which a baby passes during vaginal delivery. The dimensions of the true pelvis are critical for successful childbirth.

Key Anatomical Distinctions: False vs. True Pelvis

Understanding the differences between these two regions is fundamental for anatomy, kinesiology, and clinical practice.

• Location: The false pelvis is superior and more expansive, while the true pelvis is inferior and more constricted.
• Boundaries: The false pelvis is largely defined by the iliac crests superiorly and opens into the abdominal cavity. The true pelvis is sharply demarcated by the pelvic brim (pelvic inlet) superiorly and the pelvic outlet inferiorly.
• Contents: The false pelvis contains abdominal organs like parts of the small and large intestines. The true pelvis contains the dedicated pelvic viscera such as the bladder, rectum, and reproductive organs.
• Function: The false pelvis primarily supports abdominal contents and provides muscle attachment. The true pelvis protects vital pelvic organs, facilitates weight transmission, and forms the birth canal in females.
• Clinical Significance: The false pelvis has less direct clinical significance in terms of organ protection or passage. The true pelvis is highly relevant in obstetrics (for assessing the birth canal) and in surgical procedures involving pelvic organs.

Functional Significance

The distinct roles of the false and true pelvis highlight the pelvis's multifaceted importance in human anatomy and physiology. The false pelvis acts as a supportive base for the abdominal contents, allowing for their proper positioning and function, and contributes to the overall core strength by providing attachment for large muscle groups. The true pelvis, in contrast, is a robust, protective chamber for critical organs, while also serving as the central conduit for weight transfer during standing, walking, and running. In females, its precise dimensions are a testament to its evolutionary role in childbirth.

Clinical and Practical Considerations

For fitness professionals and kinesiologists, understanding these distinctions is important for appreciating the biomechanics of core stability, pelvic floor function, and the impact of pelvic tilt on posture and movement. In clinical settings, knowledge of the true pelvis's dimensions is crucial for obstetricians during pregnancy and delivery planning, and for surgeons operating on pelvic organs. Furthermore, pathologies like pelvic fractures or pelvic floor dysfunction often involve structures within the true pelvis, necessitating a clear understanding of its boundaries and contents.

Conclusion

The division of the pelvis into the false (greater) and true (lesser) pelvis is a fundamental anatomical concept. While the false pelvis serves as a supportive extension of the abdominal cavity, the true pelvis represents the critical bony basin that houses the essential pelvic organs, bears the body's weight, and plays a pivotal role in childbirth. Recognizing these differences is key to comprehending the complex functions and clinical relevance of this vital skeletal structure.