Pelvis Bone Structure

• The pelvis is a bony structure at the base of the spine, connecting the trunk to the lower limbs
• It has two hip bones, also known as coxal or innominate bones, that join anteriorly at the pubic symphysis
• The hip bones articulate posteriorly with the sacrum
• The pelvis transfers weight from the axial skeleton, to the lower appendicular skeleton
• It encloses and protects pelvic organs like the bladder, rectum, and reproductive organs
• The pelvis provides attachment points for trunk and lower limb muscles
• In females, the pelvis supports and facilitates childbirth
• The ilium, ischium, and pubis fuse during adolescence to form each hip bone
  • The ilium is the largest, most superior part of the hip bone and forms the upper acetabulum and iliac crest
  • The ischium forms the posteroinferior part, featuring the ischial tuberosity, bearing weight when sitting
  • The pubis forms the anteromedial part, joining the opposite pubis at the pubic symphysis

Bone Structure

• Bony landmarks of the pelvis and hip bones:
  • The iliac crest is the superior border of the ilium, palpable through the skin
  • The ASIS (anterior superior iliac spine) is a prominent projection at the anterior iliac crest
  • The AIIS (anterior inferior iliac spine) is inferior to the ASIS and a site for muscle attachment
  • The PSIS (posterior superior iliac spine) is located at the posterior iliac crest
  • The PIIS (posterior inferior iliac spine) is located inferior to the PSIS
  • The ischial tuberosity is a large prominence on the ischium that supports body weight when sitting
  • The ischial spine is a pointed projection posterior to the acetabulum
  • The pubic tubercle is a palpable prominence on the superior pubic ramus
  • The acetabulum is the cup-shaped socket on the lateral hip bone which articulates with the femoral head to form the hip joint
  • The obturator foramen is a large opening in the hip bone formed by the ischium and pubis, largely closed by the obturator membrane
• The sacrum has a triangular shape and is formed by five fused sacral vertebrae
• It articulates with the ilia at the sacroiliac joints
• The coccyx (tailbone) is small, inferior to the sacrum, and composed of fused coccygeal vertebrae

Muscle Attachments

• Numerous muscles attach to the pelvis to contribute to movement and stability
  • Gluteal Muscles:
    • The gluteus maximus attaches to the ilium, sacrum, coccyx, and iliotibial tract to enable hip extension and external rotation
    • The gluteus medius attaches to the ilium and greater trochanter of the femur, responsible for hip abduction and pelvic stabilization during single-leg stance
    • The gluteus minimus attaches to the ilium and greater trochanter of the femur, assisting in hip abduction and internal rotation
  • Iliopsoas:
    • The iliacus arises from the iliac fossa and attaches to the lesser trochanter of the femur, responsible for hip flexion
    • The psoas major arises from the lumbar vertebrae and attaches to the lesser trochanter of the femur; it is responsible for hip and trunk flexion
  • Hamstring Muscles:
    • The biceps femoris attaches to the ischial tuberosity and fibular head and facilitates both hip extension and knee flexion
    • The semitendinosus attaches to the ischial tuberosity and tibia, responsible for hip extension and knee flexion
    • The semimembranosus attaches to the ischial tuberosity and tibia and is responsible for hip extension and knee flexion
  • Quadriceps femoris:
    • The rectus femoris attaches to the AIIS and tibial tuberosity (via the patellar tendon), enabling hip flexion and knee extension
  • Adductor Muscles:
    • The adductor longus attaches to the pubis and linea aspera of the femur and is responsible for hip adduction
    • The adductor brevis attaches to the pubis and linea aspera of the femur and is responsible for hip adduction
    • The adductor magnus attaches to the pubis, ischial tuberosity, and linea aspera of the femur, responsible for hip adduction and hip extension
    • The gracilis attaches to the pubis and tibia and facilitates hip adduction and knee flexion
  • Obturator internus and externus: Attach to the inner and outer surfaces of the obturator foramen, respectively, and insert onto the greater trochanter of the femur to enable hip external rotation
  • The piriformis attaches to the anterior sacrum and inserts on the greater trochanter of the femur, enabling hip external rotation
• Abdominal Muscles:
  • The rectus abdominis attaches to the pubic crest and symphysis and is responsible for trunk flexion
  • The external and internal obliques attach to the iliac crest and contribute to trunk rotation and lateral flexion

Joint Movements

• The pelvis is involved in these joint movements:
  • Hip Joint:
    • Formed by the femoral head articulating with the acetabulum of the pelvis
    • It is a ball-and-socket joint allowing a wide range of motion
    • Movements include flexion, extension, abduction, adduction, internal rotation, external rotation, and circumduction
  • Sacroiliac (SI) Joint:
    • Formed via articulation of the sacrum and ilium
    • A strong, weight-bearing joint with limited movement
    • Transfers weight from the upper body to the lower limbs
    • Gliding and rotational movements at the SI joint provide shock absorption and pelvic stability
  • Pubic Symphysis:
    • It is a cartilaginous joint at the anterior midline of the pelvis, where the pubic bones meet
    • It allows minimal movement, primarily during pregnancy to facilitate childbirth
• Movements are closely related to the movements of the lumbar spine and hips
• Anterior pelvic tilt involves forward rotation of the pelvis, increasing lumbar lordosis and hip flexion
• Posterior pelvic tilt involves backward rotation of the pelvis, decreasing lumbar lordosis and hip extension
• Lateral pelvic tilt involves elevation of one side of the pelvis relative to the other, often during walking or running
• Pelvic rotation involves rotation of the pelvis around a vertical axis, occurring during activities such as walking, running, and twisting
• These movements are essential for maintaining balance, transferring weight, and coordinating movements of the trunk and lower limbs

Nerve Supply

• The nerve supply to the pelvis and hips comes from the lumbar and sacral plexuses
• Lumbar Plexus (L1-L4):
  • The femoral nerve innervates the iliacus, pectineus, sartorius, and quadriceps femoris muscles; provides sensory innervation to the anterior thigh and medial leg
  • The obturator nerve innervates the obturator externus, adductor longus, adductor brevis, adductor magnus, and gracilis muscles and provides sensory innervation to the medial thigh
  • The lateral femoral cutaneous nerve provides sensory innervation to the lateral thigh
• Sacral Plexus (L4-S4):
  • The sciatic nerve is the largest; it originates from the sacral plexus and passes through the greater sciatic foramen
    • It divides into the tibial and common fibular nerves in the lower thigh or popliteal fossa
    • The tibial nerve innervates the hamstring muscles (except the short head of biceps femoris) and the posterior compartment muscles of the leg and provides sensory innervation to the posterior leg and plantar surface of the foot
    • The common fibular (peroneal) nerve innervates the short head of the biceps femoris, and the anterior and lateral compartment muscles of the leg and provides sensory innervation to the lateral leg and dorsum of the foot
  • The superior gluteal nerve innervates the gluteus medius, gluteus minimus, and tensor fasciae latae muscles
  • The inferior gluteal nerve innervates the gluteus maximus muscle
  • The pudendal nerve innervates the perineum, including the external genitalia and anal sphincter; also provides sensory innervation to these areas
• These nerves control muscles of the hip, thigh, and lower leg, and provide sensory information from the skin and joints of the lower limb

Blood Circulation

• Blood supply to the pelvis and hips comes primarily from the internal iliac artery and its branches
• Internal Iliac Artery:
  • A major branch of the common iliac artery, supplying the pelvic organs, gluteal region, and medial thigh
  • Branches include:
    • The superior gluteal artery supplies the gluteus medius, gluteus minimus, and tensor fasciae latae muscles
    • The inferior gluteal artery supplies the gluteus maximus muscle and the posterior thigh
    • The obturator artery supplies the adductor muscles of the thigh and the hip joint
    • The internal pudendal artery supplies the perineum and external genitalia
• External Iliac Artery:
  • Continues as the femoral artery after passing under the inguinal ligament
• Femoral Artery:
  • The main artery of the thigh, supplying the anterior thigh muscles and the knee joint
  • Branches include:
    • The deep femoral artery (profunda femoris) supplies the posterior and medial thigh muscles
    • The medial and lateral circumflex femoral arteries supply the hip joint and femoral head
• Venous drainage of the pelvis and hips generally follows the arterial supply
• Veins include:
  • Internal iliac vein
  • External iliac vein
  • Femoral vein
  • Deep femoral vein
  • Gluteal veins
  • Obturator vein
• These veins drain into the common iliac vein, and eventually, into the inferior vena cava
• Adequate blood supply is essential for the health and function of the muscles, bones, and joints of the pelvis and hips