Pelvis and hip joint

The bony pelvis is composed of the two hip bones, the sacrum, and the coccyx, which are firmly connected by the pubic symphysis (between the pubic bodies of the two hip bones), the sacrococcygeal symphysis (between the coccyx and the sacrum), and sacroiliac joints (between the ilium of the hip bones and the sacrum). Each hip bone consists of the ilium, ischium, and pubic bone. The pelvis connects the lower extremity to the trunk, protects abdominal and pelvic organs, and provides attachment to muscles and ligaments. The pelvic cavity is a space located within the pelvic girdle that contains parts of the gastrointestinal tract and urogenital tract. The pelvic joints and the organs are supported by muscles and ligaments (including the urogenital diaphragm). The pelvic cavity contains anatomical spaces, such as the rectouterine pouch (of Douglas) in women and the rectovesical pouch in men. The pelvic floor, which is composed of muscles and fascia, separates the pelvic cavity from the perineum. It has openings that allow for the passage of the rectum, vagina, and urethra. It furthermore helps maintain fecal and urinary continence and prevents pelvic organ prolapse. The female pelvis, which accommodates the birth canal, is larger and wider than the male. The hip joints (acetabulofemoral joint) are joints located between the head of the femur and the acetabulum of the pelvis that connect the trunk to the lower extremities. The hip joint supports dynamic and static body weight. The gluteal region consists of the gluteal muscles that form the buttocks. The gluteal muscles receive vascular supply from the superior and inferior gluteal arteries.

General

• The pelvis (pelvic girdle) is the ring-like structure of the axial skeleton that connects the vertebral column with the lower extremities (e.g., femur).
• The bony pelvis surrounds the pelvic cavity.
• The pelvic cavity allows passage of gastrointestinal and urogenital structures into the pelvis.
• The pelvis is largely immobile (unlike the pectoral girdle), which provides stability and proper transfer of weight from the vertebral column to the lower extremities, especially in the upright position.
• The pelvis is composed of the following bones:
  • The hip bones (os coxae): Ilium, ischium, and pubis
  • Sacrum
  • Coccyx
• In addition, the bony pelvis is divided by the pelvic brim into:
  • The pelvis major (false pelvis)
  • The pelvis minor (true pelvis)

Development of the pelvis

• The pelvis starts to develop during the 3^rd week of gestation.
• Derived from paraxial mesoderm
• Originates from two separate cartilaginous hemipelves
• Events (by weeks) taking place in pelvic development
  • 6^th week of development: The sacroiliac joint starts to develop.
  • 8^th week of development: A fully developed pelvis is present in the embryo.
  • 9^th week of development: The ilium starts to ossify via endochondral ossification.
  • 12^th week of development: The anterior superior iliac spine (ASIS) and the pubis start to ossify.
  • 15^th week of development: The ischium starts to ossify.

References:^[1]

Hip bones

The anterior superior iliac spine helps to determine the course of the inguinal ligament. In addition, it aids in the identification of the McBurney and Lanz points which are important anatomical locations where localized tenderness is indicative of appendicitis.

Pelvic inlet

• Location: superior rim of the pelvic cavity (upper pelvic aperture)
• Boundaries
  • Anterior: pectineal line, pubic crest, and the superior margin of the pubic symphysis
  • Posterior: sacral promontory and anterior border of the sacral ala
  • Lateral: arcuate line (iliopectineal line) of the ilium
• Diameters: transverse, oblique, conjugate (anteroposterior), anatomical conjugate, diagonal, straight, median
• Structures passing through the pelvic inlet: ureter, spermatic cord, round ligament of the uterus, suspensory ligament of the ovary, middle sacral vessels, gonadal vessels, iliolumbar vessels, lumbosacral trunk, sympathetic trunk, obturator nerve

Pelvic outlet

• Location: lower pelvic aperture. It is narrower than the pelvic inlet.
• Boundaries:
  • Anterior: pubic symphysis, ischiopubic ramus, and the arcuate pubic ligament
  • Posterior: sacrum and coccyx
  • Lateral: ischial tuberosities and sacrotuberous ligaments
  • Inferior: pelvic diaphragm and the urogenital diaphragm
• Diameters: sagittal and intertuberous

Joints of the pelvis

Pelvic diameters

See “Birth canal” section for more information on pelvic diameters.

Types of pelvises

See “Birth canal” section for more information on the types of pelvises.

Differences between the male and female pelvis

Urogenital diaphragm

• Triangular muscular sheet located on the anterior part of the pelvic outlet, between the superior and inferior fascia (perineal membrane). It is external and inferior to the pelvic diaphragm.
• Separates the upper pelvis from the deep perineal sac.

Muscle layers of the pelvis

Ligaments of the pelvis

Foramina of the pelvis

Trauma or strain of the piriformis muscle may cause entrapment of the sciatic nerve, leading to buttock pain and paresthesia in the distribution of the sciatic nerve (piriformis syndrome).

References:^[2][3]

Pelvic cavity

• The pelvic cavity is the space located within the pelvic girdle.
• The superior opening is formed by the pelvic inlet, whereas the inferior opening is formed by the pelvic outlet.
• The pelvic outlet is bounded by the pelvic floor, which functions to maintain pelvic organs in place. The division between the pelvic inlet and outlet is demarcated by the pelvic brim.
• The pelvic cavity contains parts of the gastrointestinal tract (e.g., colon and rectum), urogenital tract (e.g., ureters, bladder, uterus), major blood vessels (e.g., iliac arteries and their branches), and nerves (e.g., pudendal nerve). In addition, the pelvic cavity contains muscles that attach to the spine and the lower limbs (e.g., psoas and iliacus muscles)

Pelvic spaces

.

General

• The female pelvis is larger and wider than the male pelvis.
• The female pelvis is divided into:
  • True pelvis: below the linea terminalis (pelvic edge); comprises the bony canal: the ileum (superior-laterally), ischium (inferior-laterally), pubis (anteriorly), sacrum, and coccyx (posteriorly)
  • False pelvis: above the linea terminalis; consists of the abdominal wall (anteriorly), lumbar vertebrae (posteriorly), iliac fossae (laterally)
• The birth canal is the passage, consisting of the mother's bony pelvis and soft tissues (i.e., uterus, cervix, vagina, vulva, and pelvic floor), through which a fetus passes during vaginal delivery. It is described in terms of:
  • Pelvic form
  • 3 pelvic regions
  • 4 pelvic planes
  • Soft tissue structures

Pelvic form, pelvic regions, and pelvic planes

Overview of the pelvic floor

• Composed of muscles and fascia that separate the pelvic cavity superiorly from the perineum inferiorly
• Openings in the pelvic floor allow passage of the rectum, urethra, and the vagina to pass from the pelvic cavity to the perineum
• Contains the perineal body (central tendon of the perineum)
  • Fibromuscular structure
  • Between the anal and urogenital hiatus
• Functions
  • Supports the abdominal and pelvic viscera
  • Prevents prolapse of the pelvic organs
  • Assists in increasing intraabdominal pressure
  • Helps maintain fecal and urinary continence by contraction of muscle fibers
  • Relaxation of muscle fibers facilitate defecation and urination
    • Defecation process
      1. Involuntary relaxation of the internal anal sphincter for anal sampling: prior to defecation, a small amount of rectal content passes into the anal canal to test consistency (gas, liquid, or solid)
      2. Voluntary relaxation of the external anal sphincter and puborectalis muscle and contraction of abdominal muscles or Valsalva maneuver expel stool from the anal canal
      3. Contraction of external anal sphincter to reestablish continence (closing reflex)

Muscles of the pelvic floor ^[4][5]

Kegel exercises involve the contraction of the entire levator ani and can treat both stress and urge incontinence as well as pelvic organ prolapse.

References:^[6]

Arteries

Veins

The veins follow the course of the artery and are named accordingly, and drain the same structures supplied by the arteries mentioned above (e.g., internal iliac artery and internal iliac vein).

Nerves

For details on the sacral plexus see article on thigh, knee, and popliteal fossa

Lymphatics

Course along the internal iliac vessels and drain into the following lymph nodes:

References:^[7]

• The gluteal region consists of a group of muscles that form the buttocks
• Gluteal muscles arise from the pelvic girdle, are innervated by nerves that leave the pelvis through the greater sciatic foramen, and receive vascular supply from the superior and inferior gluteal arteries.

All superficial gluteal muscles abduct and medially rotate the thigh. All deep gluteal muscles and gluteus maximus laterally rotate the thigh.

Superior gluteal nerve palsy causes paralysis of the gluteus medius and minimus that results in a positive Trendelenburg sign.

Overview

• Definition: The hip joint (acetabulofemoral joint) is a joint between the head of the femur and the acetabulum of the pelvis.
• Function: connects the axial skeleton to the lower extremities, and functions to support static (e.g., standing) and dynamic (e.g., walking, running) weight
• Type of joint: ball-and-socket synovial joint
• Movements: flexion and extension, lateral and medial rotation, abduction and adduction → the combination of these movements results in circumduction
• Articular capsule: fibrous capsule that attaches to the margin of the acetabulum, the transverse acetabular ligament, and the neck of the femur.

For muscles of the hip joint and their blood supply and innervation, see the article on thigh, knee, and popliteal fossa.

Acetabulum

• Cup-like structure on the lateral side of the bony pelvis that articulates with the round femoral head
• Covered by the acetabular labrum
  • Ring of cartilage that provides an articular surface for the femoral head
• Stabilized by capsular ligaments
  • Iliofemoral ligament
  • Pubofemoral ligament
  • Ischiofemoral ligament
• Surrounded by the fibrous capsule
  • Attaches to the margin of the acetabulum and to the transverse acetabular ligament
  • Attaches to the neck of the femur
    • Anterior: intertrochanteric line (anterior) and the greater trochanter
    • Posterior: intertrochanteric crest
  • Encloses the femoral head and the femoral neck
• Receives blood supply from:
  • Medial femoral circumflex artery
  • Lateral femoral circumflex artery
  • Obturator arteries
  • Superior and inferior gluteal arteries
• Innervated by:
  • Femoral nerve
  • Sciatic nerve
  • Obturator nerve
  • Superior gluteal nerve

Ligaments of the hip joint

Movements of the hip joint

• Flexion
  • Iliacus and psoas major
  • Rectus femoris
  • Tensor fasciae latae
  • Pectineus
  • Sartorius
  • Gluteus medius and minimus (anterior fibers)
  • Adductor longus, brevis, and minimus
  • Gracilis
• Extension
  • Gluteus maximus
  • Semitendinosus
  • Semimembranosus
  • Biceps femoris
  • Gluteus medius and minimus (posterior fibers)
  • Adductor magnus (hamstring part)
• Abduction
  • Gluteus medius and minimus
  • Gluteus maximus (upper fibers)
  • Tensor fasciae latae
  • Piriformis
  • Obturator externus
  • Sartorius
• Adduction
  • Adductor magnus
  • Adductor longus
  • Adductor brevis
  • Gluteus maximus (lower fibers)
  • Obturator externus
  • Pectineus
  • Gracilis
• Medial rotation
  • Gluteus medius and minimus (anterior fibers)
  • Tensor fasciae latae
• Lateral rotation
  • Iliacus and psoas major
  • Gluteus maximus
  • Piriformis
  • Obturator externus and internus
  • Gluteus medius and minimus (posterior fibers)
  • Superior and inferior gemellus
  • Quadratus femoris
  • Pectineus
  • Sartorius

• Sacroiliitis (associated with e.g., ankylosing spondylitis, inflammatory bowel disease)
• Uterine prolapse
• Obturator hernia
• Femoral hernia
• Anterior hip dislocation
• Posterior hip dislocation
• Hip replacement
• Coxarthrosis
• Trendelenburg sign
• Piriformis syndrome