Pelvis

Introduction

The pelvis is a complex bony and muscular structure located at the base of the spine, connecting the vertebral column to the lower limbs. It provides support for abdominal and pelvic organs, facilitates locomotion, and plays a vital role in reproductive and urinary functions. Understanding pelvic anatomy is essential in clinical practice, surgery, and obstetrics.

Anatomy of the Pelvis

Bony Pelvis

The bony pelvis forms a ring-like structure composed of the hip bones, sacrum, and coccyx. It provides attachment points for muscles and ligaments and defines the boundaries of the pelvic cavity.

Hip bones: Each hip bone consists of the ilium, ischium, and pubis, which fuse during adolescence.
Sacrum and coccyx: The sacrum articulates with the ilia at the sacroiliac joints, while the coccyx forms the terminal portion of the vertebral column.
Pelvic brim and inlet: The pelvic brim marks the boundary between the greater and lesser pelvis, forming the pelvic inlet.
Pelvic outlet: Defined by the pubic arch, ischial tuberosities, and coccyx, it represents the inferior opening of the pelvis.

Pelvic Joints and Ligaments

The pelvis contains strong joints and ligaments that provide stability while allowing limited mobility, essential for weight transmission and childbirth.

Sacroiliac joints: Connect the sacrum to the ilia, reinforced by anterior and posterior sacroiliac ligaments.
Pubic symphysis: A fibrocartilaginous joint uniting the pubic bones, providing flexibility and shock absorption.
Sacrospinous and sacrotuberous ligaments: Stabilize the pelvis and form the boundaries of the greater and lesser sciatic foramina.

Muscular Structures

The muscles of the pelvis support the pelvic organs, maintain continence, and assist in movement of the lower limbs.

Pelvic floor muscles: Levator ani and coccygeus form the main support for pelvic viscera.
Obturator internus and piriformis: Lateral rotators of the hip and contributors to pelvic wall stability.
Perineal muscles and sphincters: Control urination, defecation, and sexual function.

Pelvic Compartments and Spaces

The pelvis is divided into compartments that facilitate organization of organs and neurovascular structures.

Greater (false) pelvis: Located above the pelvic brim, supports abdominal organs.
Lesser (true) pelvis: Located below the pelvic brim, contains pelvic organs including bladder, rectum, and reproductive structures.
Pelvic cavity divisions: Anterior, middle, and posterior compartments organize viscera and neurovascular bundles.

Blood Supply and Lymphatics

The pelvis receives a rich blood supply from branches of the internal iliac arteries and has an extensive venous and lymphatic network to support the pelvic organs and surrounding tissues.

Arterial supply: The internal iliac artery and its branches, including the superior and inferior gluteal, obturator, and vesical arteries, supply the pelvic walls, muscles, and organs.
Venous drainage: Pelvic veins form interconnected plexuses, including the vesical, rectal, and uterovaginal plexuses, which drain into the internal iliac veins and ultimately the inferior vena cava.
Lymphatic drainage: Pelvic lymph nodes include external iliac, internal iliac, obturator, and sacral nodes, which drain into the common iliac and para-aortic lymph nodes, playing a key role in immune defense and cancer staging.

Nervous Supply

The pelvis receives both somatic and autonomic innervation, coordinating motor and sensory functions for the pelvic organs and lower limbs.

Somatic nerves: The sacral plexus, including the pudendal nerve, provides motor innervation to pelvic floor muscles and sensory innervation to the perineum.
Autonomic nerves: The hypogastric plexus and pelvic splanchnic nerves regulate bladder, rectal, and reproductive organ function, mediating both sympathetic and parasympathetic activity.

Physiology and Functions

The pelvis serves multiple physiological roles, providing structural support, facilitating locomotion, and enabling reproductive and excretory functions.

Support of abdominal and pelvic organs: The bony and muscular structures of the pelvis maintain the position of the bladder, rectum, and reproductive organs.
Role in locomotion and weight transmission: Transfers the weight of the upper body to the lower limbs and stabilizes the trunk during movement.
Childbirth: Pelvic dimensions and flexibility of ligaments allow passage of the fetus through the birth canal.
Role in continence and reproductive function: Pelvic floor muscles and sphincters maintain urinary and fecal continence and support sexual function.

Clinical Significance

Pain Syndromes

Pelvic pain can result from trauma, chronic conditions, or dysfunction of pelvic muscles and organs.

Pelvic fractures: Can cause acute pain, hemorrhage, and instability.
Chronic pelvic pain: May arise from musculoskeletal, urological, gynecological, or neurological causes.
Pelvic floor dysfunction: Leads to urinary or fecal incontinence and discomfort, often requiring physical therapy or surgical intervention.

Obstetric Considerations

Pelvic diameters and fetal passage: Measurements of the pelvic inlet, midpelvis, and outlet are critical in assessing labor progression.
Cephalopelvic disproportion: Occurs when the fetal head is too large to pass through the maternal pelvis, potentially necessitating cesarean delivery.

Trauma and Surgical Access

The pelvis is vulnerable to traumatic injury and serves as a key region for surgical access to pelvic organs.

Pelvic fractures and hemorrhage: High-energy trauma can cause unstable fractures with life-threatening hemorrhage, requiring urgent stabilization.
Surgical approaches to pelvic organs: Anterior, posterior, and lateral approaches are used in urological, gynecological, and colorectal procedures, with careful attention to neurovascular structures.

Pathologies

The pelvis can be affected by hernias, prolapse, and neoplasms, each with distinct clinical implications.

Hernias: Obturator and femoral hernias can occur within the pelvic region, often presenting with pain or bowel obstruction.
Pelvic organ prolapse: Weakness of the pelvic floor allows descent of the bladder, uterus, or rectum, causing urinary, bowel, or sexual dysfunction.
Neoplasms affecting the pelvis: Tumors of the pelvic bones, soft tissue, or organs can present with pain, mass effect, or functional impairment.

Imaging and Diagnostic Techniques

Imaging of the pelvis is essential for evaluating bony structures, soft tissues, and organs, guiding diagnosis and treatment planning.

X-ray: Useful for assessing pelvic fractures, alignment, and gross anatomical landmarks.
CT scan: Provides detailed evaluation of bony anatomy, complex fractures, and associated visceral injuries.
MRI: Ideal for soft tissue assessment, including muscles, ligaments, pelvic floor, and organ pathology.
Ultrasound: Commonly used in obstetric and gynecologic evaluation, assessing fetal position, pelvic organs, and fluid collections.

References

Standring S. Gray’s Anatomy: The Anatomical Basis of Clinical Practice. 42nd edition. London: Elsevier; 2020.
Moore KL, Dalley AF, Agur AMR. Clinically Oriented Anatomy. 8th edition. Philadelphia: Wolters Kluwer; 2021.
Netter FH. Atlas of Human Anatomy. 7th edition. Philadelphia: Elsevier; 2019.
Skandalakis JE, Colborn GL. Surgical Anatomy of the Pelvis. Surg Clin North Am. 1993;73(3):515-529.
Harty RF, Johnston KW. Pelvic Fractures: Imaging and Management. Radiol Clin North Am. 2016;54(5):905-922.
Standring S, Ellis H, Healy JC, Johnson D, Williams A. Pelvic anatomy in obstetrics. Clin Anat. 2019;32(1):72-85.
Chopra S, Bhargava P. Pelvic Floor Dysfunction: Anatomy, Assessment, and Management. Indian J Urol. 2018;34(4):281-290.
Moore KL, Persaud TVN, Torchia MG. The Developing Human: Clinically Oriented Embryology. 11th edition. Philadelphia: Elsevier; 2020.
Rao S, Krishna S. Imaging of the pelvis: Techniques and clinical applications. Indian J Radiol Imaging. 2017;27(2):178-190.
O’Rahilly R, Müller F. Human Embryology and Teratology. 4th edition. Hoboken: Wiley-Blackwell; 2010.

Rate this post