Anatomy of the Pelvis & Perineum 2023 - PDF

Anatomy of the Pelvis & Perineum Author: Dr. Carlos Rocha Block III Spring 2023 Objectives 1. 2. 3. 4. 5. 6. Identify the bones, muscles, ligaments, and organs of the pelvic cavity. Describe the anatomy of the pelvic floor muscles. Explain the structure and function of the perineum and its relations...

Anatomy of the Pelvis & Perineum Author: Dr. Carlos Rocha Block III Spring 2023 Objectives 1. 2. 3. 4. 5. 6. Identify the bones, muscles, ligaments, and organs of the pelvic cavity. Describe the anatomy of the pelvic floor muscles. Explain the structure and function of the perineum and its relationship to the pelvic cavity. Identify and describe the major vessels for to the pelvic and perineal structures. Identify and describe the major nerves of the pelvic and perineal regions. Identify and describe the lymphatic drainage of the pelvic and perineal regions. Pelvis Pelvis The pelvis is the region of the body surrounded by the pelvic bones and the inferior elements of the vertebral column. It is divided into two major regions: the superior region is the false (greater) pelvis and is part of the abdominal cavity the inferior region is the true (lesser) pelvis, which encloses the pelvic cavity Bones and joints of the pelvis The bones of the pelvis consist of: The right and left pelvic (hip) bones, the sacrum, and the coccyx. The joints of the pelvis are: The sacrum articulates superiorly with vertebra LV at the lumbosacral joint. The pelvic bones articulate posteriorly with the sacrum at the sacro-iliac joints and with each other anteriorly at the pubic symphysis. Hip bone Each pelvic (hip) bone is formed by three elements: the ilium, pubis, and ischium. The lateral surface of the pelvic bone has a large articular socket, the acetabulum, which, together with the head of the femur, forms the hip joint. At birth, ilium, ischium and pubis are connected by cartilage in the area of the acetabulum; later, at between 16 and 18 years of age, they fuse into a single bone. Sacrum and coccyx The sacrum is formed by the fusion of the five sacral vertebrae. The base of the sacrum articulates with vertebra LV, and its apex articulates with the coccyx. The small terminal part of the vertebral column is the coccyx, which consists of four fused coccygeal vertebrae. Differences between male and female pelvises The pelvic inlet in women is circular compared with the heart-shaped pelvic inlet in men. The angle formed by the two arms of the pubic arch is larger in women (80°– 85°) than it is in men (50°–60°). Pelvic cavity (true pelvis) The true pelvis is a cylindrical cavity and has: ○ ○ ○ ○ A pelvic inlet and an outlet A pelvic walls Three pelvic apertures A pelvic floor Pelvic inlet and outlet The pelvic inlet is the superior opening of the pelvic cavity and serves as a passway for abdominal and pelvic structures. The pelvic outlet is inferior to the pelvic cavity and serves as the space for the pelvic floor. Pelvic walls The walls of the true pelvis (pelvic cavity) are formed by: Bone: ○ Inferior half of hip bones ○ Sacrum ○ coccyx Ligaments: ○ Sacrospinous ○ Sacrotuberous Muscles: ○ obturator internus ○ piriformis Ligaments of the pelvic wall Stabilize the sacrum on the pelvic bones. Help define the apertures of the pelvic cavity. Muscles of the pelvic wall These muscles originate in the pelvic cavity but attach peripherally to the femur. Therefore, these muscles aid in the mobility of the the inferior limb through the hip joint. Pelvic apertures Each lateral pelvic wall has three major apertures through which structures pass between the pelvic cavity and other regions: 1. 2. 3. Obturator canal Greater sciatic foramen Lesser sciatic foramen Pelvic apertures 1. 2. Obturator canal. Greater sciatic foramen. Divided by the piriformis muscle it into two parts: a. b. 3. Foramen above the piriformis. Foramen below the piriformis. Lesser sciatic foramen. Pelvic floor Separates the pelvic cavity, above, from the perineum, below. The pelvic floor is formed by: the pelvic diaphragm the perineal membrane the muscles in the deep perineal pouch Pelvic diaphragm Perineal membrane The perineal membrane is a thick fascial, triangular structure attached to the bony framework of the pubic arch. It is oriented in the horizontal plane and has a free posterior margin. Perineal pouch The perineal membrane is related above to a thin space called the deep perineal pouch (deep perineal space), which contains a layer of skeletal muscle: External urethral sphincter (both genders) Sphincter urethrovaginalis & compressor urethrae (only females) Deep transverse perineal muscle (both genders) Pelvic contents Urinary system: ○ Reproductive system: ○ ○ ureters, bladder and urethra Women: ovaries, uterine tubes, uterus and vagina. Men: prostate, seminal vesicles, ductus deferens, and bulbourethral glands. Gastrointestinal system: ○ rectum and anal canal Peritoneum The peritoneum of the pelvis is continuous at the pelvic inlet with the peritoneum of the abdomen, draping over the pelvic viscera in the midline. Females Males Perineum Perineum The perineum is a diamondshaped region positioned inferiorly to the pelvic floor between the thighs. The perineum is divided into two triangles by an imaginary line between the two ischial tuberosities. an anterior urogenital triangle a posterior anal triangle. Urogenital triangle The urogenital triangle of the perineum is the anterior half of the perineum and is oriented in the horizontal plane. It contains: the roots of the external genitalia the openings of the urogenital system Anal triangle The major muscle in the anal triangle is the external anal sphincter, which surrounds the anal canal, is formed by skeletal muscle and consists of three parts—deep, superficial, and subcutaneous— arranged sequentially along the canal. Nerves, arteries, veins and lymphatics of the Pelvis and Perineum Nerves The innervation to structures in the pelvis and perineum comes from the sacral and coccygeal plexuses. Are formed by the ventral rami of: Sacral plexus: L4-S4 ○ Major nerves: Sciatic, pudendal and gluteal Coccygeal plexus: S4-C0 ○ Major nerve: Anoccygeal Arterial blood supply The major artery of the pelvis and perineum is the internal iliac artery on each side. The internal iliac artery originates from the common iliac artery on each side, approximately at the level of the intervertebral disc between LV and SI Arterial blood supply The internal iliac artery on each side divides into anterior and posterior trunks at the level of the superior border of the greater sciatic foramen. Branches from the posterior trunk supply the lower posterior abdominal wall, the posterior pelvic wall, and the gluteal region. Branches from the anterior trunk supply the pelvic viscera, the perineum, the gluteal region, the adductor region of the thigh, and, in the fetus, the placenta. Venous drainage Pelvic and perineal veins follow the course of all branches of the internal iliac artery. Veins drain into the internal iliac vein, to the common iliac vein, to the inferior vena cava. Lymphatic drainage Lymphatics from most pelvic viscera drain mainly into lymph nodes distributed along the internal iliac and external iliac arteries and their associated branches. Which drain into nodes associated with the common iliac arteries and then into the lateral aortic or lumbar nodes. In turn, these lateral aortic or lumbar nodes drain into the lumbar trunks, which continue to the origin of the thoracic duct at approximately vertebral level TXII. Lymphatic drainage of external genitalia is performed by the inguinal nodes. Clinical case A 36-year-old female patient presents to the clinic with complaints of urinary incontinence and a sensation of pressure in the vaginal area. On physical examination, the pelvic floor muscles are found to be weak, and the uterus is found to be prolapsed. The patient reports a history of multiple vaginal deliveries. What is the name of the muscle that supports the pelvic organs in both men and women, and which muscle is most likely to be affected in this patient's case? A) Psoas major muscle B) Rectus abdominis muscle C) Pelvic diaphragm muscles D) Transversus abdominis muscle Clinical case A 28-year-old male patient presents to the emergency department with a penetrating injury to the perineal region. Upon examination, the patient complains of numbness in the penis and difficulty urinating. Which nerve is most likely to be injured in this patient? A) Femoral nerve B) Sciatic nerve C) Pudendal nerve D) Obturator nerve Reference Drake, R. L., Vogl, W., & Mitchell, A. W. M. (2019). Gray's anatomy for students (4th ed.). Elsevier.