Difference Between True And False Pelvis

The human pelvis, a complex structure at the base of the spine, plays a pivotal role in supporting the body, facilitating movement, and protecting vital organs. Understanding its components is crucial in various fields, including medicine, anthropology, and sports science. A fundamental distinction within the pelvis lies between the true pelvis and the false pelvis (also known as the greater and lesser pelvis, respectively). These two regions, while interconnected, serve distinct functions and are defined by specific anatomical boundaries.

Demystifying the Pelvis: An Overview

The pelvis, a basin-shaped structure located between the abdomen and the lower limbs, is formed by several bones:

• The two hip bones (ossa coxae): These are each composed of three fused bones: the ilium, ischium, and pubis.
• The sacrum: A triangular bone formed by five fused vertebrae, located at the base of the spine.
• The coccyx: Commonly known as the tailbone, it is formed by fused vertebrae and articulates with the sacrum.

These bones articulate at several joints, including the sacroiliac joints (between the sacrum and ilium), the pubic symphysis (where the two pubic bones meet), and the hip joints (where the femur articulates with the acetabulum of the hip bone). The bony structure of the pelvis provides a strong and stable base for the trunk, protects the pelvic organs (such as the bladder, rectum, and reproductive organs), and transmits weight from the upper body to the lower limbs. The division into true and false pelvis is based on the pelvic brim (also known as the iliopectineal line).

The False Pelvis: A Supportive Platform

The false pelvis, also known as the greater pelvis or pelvis major, is the region located superior to the pelvic brim. It is essentially the expanded portion of the pelvic bones that provides support for the abdominal organs.

Anatomical Boundaries

The boundaries of the false pelvis are:

• Laterally: The iliac fossae (the broad, concave inner surfaces of the iliac bones).
• Posteriorly: The lumbar vertebrae.
• Anteriorly: The lower part of the anterior abdominal wall.
• Inferiorly: The pelvic brim.

Key Functions

The false pelvis plays several important roles:

• Support for abdominal organs: It provides a broad base of support for the intestines, stomach, and other abdominal organs.
• Attachment for muscles: It serves as an attachment point for several abdominal and trunk muscles, contributing to posture and movement.
• Protection: It offers some degree of protection to the lower abdominal organs.
• During pregnancy: The false pelvis helps to support the growing uterus during pregnancy, accommodating its increasing size.

Clinical Significance

While the false pelvis is not directly involved in childbirth, its dimensions can be relevant in assessing overall body size and skeletal structure. In some cases, abnormalities in the bony structure of the false pelvis may indicate underlying skeletal conditions.

The True Pelvis: The Gateway to Childbirth

The true pelvis, also known as the lesser pelvis or pelvis minor, is the region located inferior to the pelvic brim. This region is of critical importance in obstetrics, as it forms the bony birth canal through which a baby must pass during vaginal delivery.

Anatomical Boundaries

The boundaries of the true pelvis are:

• Superiorly: The pelvic brim (iliopectineal line).
• Anteriorly: The pubic symphysis, pubic crests, and pubic rami.
• Posteriorly: The sacrum and coccyx.
• Laterally: The ischial bones, the obturator foramina, and the sacrotuberous and sacrospinous ligaments.

Key Functions

The true pelvis is primarily responsible for:

• Supporting the pelvic organs: It houses and protects the bladder, rectum, and reproductive organs.
• Forming the birth canal: Its dimensions and shape are crucial for the successful passage of a fetus during childbirth.
• Attachment for muscles: It provides attachment points for muscles of the pelvic floor, which support the pelvic organs and contribute to urinary and fecal continence.

Key Dimensions of the True Pelvis in Obstetrics

The true pelvis is further characterized by specific dimensions that are critical in assessing the suitability of a woman's pelvis for vaginal delivery. These dimensions are measured during prenatal examinations and may influence decisions regarding the mode of delivery. Key measurements include:

• Inlet (superior aperture):

  • Anteroposterior diameter (obstetric conjugate): The distance from the sacral promontory to the pubic symphysis. A measurement of less than 11 cm may indicate cephalopelvic disproportion (CPD), where the baby's head is too large to pass through the pelvic inlet.
  • Transverse diameter: The widest distance across the pelvic inlet.
  • Oblique diameter: The distance from the sacroiliac joint to the iliopectineal eminence on the opposite side.

• Midpelvis:

  • Interspinous diameter: The distance between the ischial spines. This is often the narrowest part of the pelvis and a critical measurement for assessing the likelihood of vaginal delivery.
  • Posterior sagittal diameter: The distance from the tip of the sacrum to the midpoint of the interspinous line.

• Outlet (inferior aperture):

  • Anteroposterior diameter: The distance from the lower border of the pubic symphysis to the tip of the coccyx.
  • Transverse diameter (bituberous diameter): The distance between the ischial tuberosities.

Pelvic Shapes

The shape of the true pelvis also varies among individuals, and these variations are classified into four basic types:

• Gynecoid: The most common type in females (approximately 50%), characterized by a rounded inlet and adequate dimensions for childbirth.
• Android: More typical in males, characterized by a heart-shaped inlet and a narrower pelvic cavity. This shape may present challenges for vaginal delivery.
• Anthropoid: Characterized by an oval-shaped inlet with a long anteroposterior diameter. While vaginal delivery is possible, there may be an increased likelihood of the baby being born in an occiput posterior position.
• Platypelloid: Characterized by a flattened inlet with a wide transverse diameter and a short anteroposterior diameter. This shape is relatively rare and may make vaginal delivery difficult.

Clinical Significance

The dimensions and shape of the true pelvis are critical factors in determining the feasibility of vaginal delivery. Cephalopelvic disproportion (CPD) occurs when the baby's head is too large to pass through the mother's pelvis. This condition can lead to prolonged labor, fetal distress, and the need for a Cesarean section. Pelvic measurements are therefore an important part of prenatal care.

Key Differences Summarized

To summarize the key distinctions between the false and true pelvis:

Factors Influencing Pelvic Size and Shape

Several factors can influence the size and shape of the pelvis:

• Genetics: Genetic factors play a significant role in determining overall skeletal structure, including the pelvis.
• Hormones: Hormones, particularly during puberty, influence bone growth and development, shaping the pelvis.
• Nutrition: Adequate nutrition, especially calcium and vitamin D, is essential for healthy bone development.
• Physical Activity: Weight-bearing exercises can promote bone density and strength, potentially influencing pelvic structure.
• Ethnicity: Some studies suggest that there may be ethnic variations in pelvic morphology.
• Age: As individuals age, changes in bone density and joint flexibility can affect the pelvis.

Development of the Pelvis

Understanding the development of the pelvis provides further insight into its complex structure and potential variations.

Embryonic Development

The pelvis begins to develop during the early embryonic period. The hip bones, sacrum, and coccyx originate from mesenchymal cells that differentiate into cartilage models. These cartilage models gradually ossify (turn into bone) through a process called endochondral ossification.

Childhood and Adolescence

During childhood and adolescence, the hip bone remains as three separate bones (ilium, ischium, and pubis) connected by cartilage. These bones eventually fuse together around the time of puberty. Hormonal changes during puberty contribute to the final shaping of the pelvis, particularly in females.

Adult Life

In adulthood, the pelvis reaches its mature size and shape. However, bone remodeling continues throughout life, and the pelvis can be affected by factors such as pregnancy, aging, and disease.

Common Pelvic Conditions

Several conditions can affect the pelvis, causing pain, instability, or other complications. These include:

• Pelvic fractures: Fractures of the pelvic bones can occur due to trauma, such as falls or car accidents.
• Sacroiliac joint dysfunction: This condition involves pain and inflammation in the sacroiliac joint, which connects the sacrum to the ilium.
• Pubic symphysis dysfunction: This condition involves pain and instability in the pubic symphysis, the joint where the two pubic bones meet. It is more common during pregnancy.
• Osteoarthritis: This degenerative joint disease can affect the hip joints and other pelvic joints, causing pain and stiffness.
• Osteoporosis: This condition, characterized by decreased bone density, can increase the risk of pelvic fractures.
• Pelvic floor dysfunction: This condition involves weakening or dysfunction of the pelvic floor muscles, which can lead to urinary or fecal incontinence, pelvic organ prolapse, and sexual dysfunction.
• Piriformis syndrome: This condition involves compression of the sciatic nerve by the piriformis muscle, which can cause pain in the buttock and leg.

Diagnostic Tools and Techniques

Various diagnostic tools and techniques are used to evaluate the pelvis:

• Physical examination: A physical examination can help assess pelvic alignment, range of motion, and areas of tenderness.
• X-rays: X-rays can visualize the bony structures of the pelvis and identify fractures, dislocations, or other abnormalities.
• CT scans: CT scans provide more detailed images of the pelvis than X-rays and can be used to evaluate complex fractures or tumors.
• MRI scans: MRI scans can visualize the soft tissues of the pelvis, including muscles, ligaments, and nerves. They are useful for diagnosing conditions such as sacroiliac joint dysfunction and piriformis syndrome.
• Ultrasound: Ultrasound can be used to evaluate the pelvic organs, such as the bladder, uterus, and ovaries.
• Pelvimetry: Pelvimetry is a technique used to measure the dimensions of the true pelvis. It can be performed using X-rays or CT scans.

Treatment Options

Treatment options for pelvic conditions vary depending on the specific condition and its severity. They may include:

• Pain medication: Over-the-counter or prescription pain medications can help relieve pain and inflammation.
• Physical therapy: Physical therapy can help strengthen the pelvic floor muscles, improve joint mobility, and reduce pain.
• Injections: Corticosteroid injections can be used to reduce inflammation in the sacroiliac joint or other pelvic joints.
• Surgery: Surgery may be necessary to repair pelvic fractures, stabilize unstable joints, or remove tumors.
• Lifestyle modifications: Lifestyle modifications, such as weight loss and exercise, can help manage conditions such as osteoarthritis and osteoporosis.

Conclusion

The distinction between the true and false pelvis is fundamental to understanding the anatomy and function of this critical region of the body. While the false pelvis primarily provides support for abdominal organs, the true pelvis plays a crucial role in childbirth and the support of pelvic organs. Understanding the dimensions and shape of the true pelvis is essential in obstetrics for assessing the feasibility of vaginal delivery. Various conditions can affect the pelvis, and appropriate diagnosis and treatment are crucial for managing pain and restoring function. By appreciating the intricate details of pelvic anatomy, healthcare professionals can provide better care and improve the health and well-being of their patients.